 |
 Previous Article | Next Article 
Volume 17, Number 15,
Issue of August 1, 1997
pp. 5747-5759
Copyright ©1997 Society for Neuroscience
Influence of Subunit Composition on Desensitization of Neuronal
Acetylcholine Receptors at Low Concentrations of Nicotine
Catherine P. Fenster1, 2,
M. Felicia Rains1,
Brett Noerager2,
Michael W. Quick1, 2, and
Robin A. J. Lester1, 2
Departments of 1 Neurobiology and
2 Physiology and Biophysics, University of Alabama at
Birmingham, Birmingham, Alabama 35294
 ABSTRACT
- INTRODUCTION
- MATERIALS AND METHODS
- RESULTS
- DISCUSSION
- FOOTNOTES
- REFERENCES
ABSTRACT 
The influence of  and  subunits on the properties of
nicotine-induced activation and desensitization of neuronal nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus
oocytes was examined. Receptors containing 4 subunits were more
sensitive to activation by nicotine than 3-containing receptors. At
low concentrations of nicotine, nAChRs containing 2 subunits reached near-maximal desensitization more rapidly than 4-containing
receptors. The concentration of nicotine producing half-maximal
desensitization was influenced by the particular subunit expressed;
similar to results for activation, 4-containing receptors were more
sensitive to desensitizing levels of nicotine than 3-containing
receptors. The subunit also influenced the rate of recovery from
desensitization; this rate was approximately inversely proportional to
the apparent nicotine affinity for the desensitized state. The
homomeric 7 receptor showed the lowest sensitivity to nicotine for
both activation and desensitization; 7 nAChRs also demonstrated the
fastest desensitization kinetics. These subunit-dependent properties
remained in the presence of external calcium, although subtle, receptor
subtype-specific effects on both the apparent affinities for activation
and desensitization and the desensitization kinetics were noted. These
data imply that the subunit composition of various nAChRs determines
the degree to which receptors are desensitized and/or activated by tobacco-related levels of nicotine. The subtype-specific balance between receptor activation and desensitization should be considered important when the cellular and behavioral actions of nicotine are
interpreted.
Key words:
nicotinic receptor subtypes;
nicotine addiction;
ion
channel;
CNS;
desensitization;
regulation;
Xenopus oocytes;
calcium ions;
synaptic transmission
INTRODUCTION
Neuronal nicotinic receptors (nAChRs) are a
functionally diverse group of ligand-gated ion channels formed from the
pentameric arrangement of one or more individual subunits (Couturier et
al., 1990 ; Anand et al., 1991; Cooper et al., 1991; Luetje and Patrick, 1991). The existence of multiple subtypes (Role, 1992), their nonuniform distribution within the CNS (Duvoisin et al., 1989; Wada et
al., 1989; Morris et al., 1990; Whiting et al., 1991; Dineley-Miller
and Patrick, 1992; Seguela et al., 1993), and their localization to
both pre- and postsynaptic zones (Clark, 1993; McGehee and Role, 1996;
Role and Berg, 1996; Wonnacott, 1997) imply diverse functions of nAChRs
and suggest that several mechanisms are involved in the behaviorally
important actions of nicotine.
At a minimum, any cellular and molecular theory of nicotine dependency
must take into account that nAChRs can be both activated and
desensitized by nicotine (Katz and Thesleff, 1957). Much evidence supports the idea that each of these receptor states is critical in
addiction (Stolerman and Shoaib, 1991; Dani and Heinemann, 1996).
Because these receptor states vary according to subunit composition
(Cachelin and Jaggi, 1991; Gross et al., 1991; Hsu et al., 1995; Vibat
et al., 1995), subtypes of nAChRs may be involved differentially in the
acute and chronic effects of nicotine and their associated cellular
compensatory events (Balfour, 1994). These include subtype-specific
increases in receptor number within various brain regions (Marks et
al., 1992). Moreover, the extent to which nAChR subtypes are activated
and desensitized by nicotine could determine whether specific receptor
subtypes are functionally up- (Rowell and Wonnacott, 1990;
Gopalakrishnan et al., 1996) or downregulated (Marks et al., 1993)
during chronic agonist exposure (Hsu et al., 1995).
Although the actual subunit composition of native CNS nAChRs is
unknown, many expressed receptor subtypes (Whiting and Lindstrom, 1988;
Flores et al., 1992; Anand et al., 1993) share characteristics of CNS
nAChRs. Thus, understanding the influences of different subunits on
receptor function has value both for determining dominant subunits in
native receptors and for predicting the effects of nicotine on nAChRs
composed of particular subunits. Previous studies have addressed how
subunit composition affects the time course of desensitization and the
agonist potency for activation (Cachelin and Jaggi, 1991; Gross et al.,
1991; Luetje and Patrick, 1991; Cohen et al., 1995; Hsu et al., 1995;
Vibat et al., 1995). However, many of these studies used acetylcholine
as the principal agonist. Because agonists can affect desensitization
differentially, it is not possible to predict accurately how nicotine
will interact with desensitized states of nAChRs. Moreover, except for
one report (Hsu et al., 1995), desensitization has not been
characterized using low, tobacco-related concentrations of nicotine
(Benowitz et al., 1989). In the present study we evaluate the action of low concentrations of nicotine on both activation and desensitization of a number of nAChRs expressed in Xenopus oocytes and
examine the contribution of both and subunits to these
processes.
MATERIALS AND METHODS
Xenopus oocyte preparation and cRNA injection.
Procedures for preparation of oocytes have been described in
detail elsewhere (Quick and Lester, 1994). Briefly, oocytes were
defolliculated and maintained at 18°C in incubation medium containing
ND96 (96 mM NaCl, 2 mM KCl, 1 mM
MgCl2, and 5 mM HEPES, pH 7.4), 1.8 or 3.6 mM CaCl2, 50 µg/ml gentamycin, and
5% horse serum. Subunit cRNAs were synthesized in vitro
(Machine Message; Ambion, Austin, TX) from linearized plasmid templates
of rat cDNA clones. Oocytes were injected with between 5 and 25 ng/subunit per oocyte; and subunit cRNAs were injected in 1:1
ratios, although in some experiments in which 34 receptors were
examined, cRNAs ratios of 10:1 3:4 and 1:10 3:4 were
injected. All salts and drugs were obtained from Sigma (St. Louis,
MO).
Electrophysiology. Whole-cell currents were measured at room
temperature (20-25°C), 24-96 hr postinjection, with a Geneclamp 500 amplifier (Axon Instruments, Foster City, CA) in a standard two-microelectrode voltage-clamp configuration. Electrodes were filled
with 3 M KCl and had resistances of ~0.5-2 M . Oocytes were clamped between  40 and 60 mV and superfused continuously in
calcium-free ND96 (i.e., nominally calcium-free solution) or in the
presence of 3.6 mM calcium (i.e., calcium-containing
solutions). This concentration of calcium is in the middle of the range
for potentiation of nAChRs responses (Mulle et al., 1992b; Vernino et
al., 1992). For comparison, the effects of 1.8 and 3.6 mM
calcium were examined on 7 receptors. All drugs were applied in
these solutions. ()-Nicotine tartrate (nicotine) and acetylcholine chloride (acetylcholine) were prepared from frozen stock solutions (100 mM). Atropine (1 µM) was included in the
superfusion solution to block endogenous muscarinic responses. All
currents were recorded either on a chart recorder and/or on an
80486-based personal computer with AxoScope software (Axon Instruments)
after 50-100 Hz low-pass filtering at a digitization frequency of 200 Hz. For slowly desensitizing responses, peak currents were assessed
on-line from the digital readout of the amplifier and/or off-line with
AxoScope software.
Peak currents at EC50 concentrations were typically in the
range of 100 nA-2 µA. Currents as small as 5 nA could be measured, although for accuracy only currents above 20 nA were included in the
desensitization measurements. Concentration-response curves were fit
with logistic expressions to estimate the EC50 (activation) and IC50 (desensitization). Single and/or double
exponential fits of the data were used to compare the time courses of
desensitization and recovery. Exponential curves were fit either to the
desensitizing phase of the nAChR responses or to the time course of
desensitization development as assessed from the depression of test
pulses applied during incubation with nicotine. In both cases
exponentials were constrained not to fall below zero current. For some
nAChR subtypes, recovery from desensitization could be slow (>1 hr)
and often was incomplete before the recording became unstable. For
these data the exponential fits were constrained to allow full recovery back to control values.
Solutions were gravity-fed via a six-way manual valve (Rainin
Instruments, Woburn, MA) to the oocyte in the recording chamber; some
solution mixing occurred in the dead space between the valve and the
chamber. To estimate the effect of dead space on the agonist application, we calculated the solution exchange rate from the time
course of inhibition of the current induced by nicotine (5 µM) through 4 subunit-containing receptors during a
step from medium containing 96 mM NaCl to one containing 48 mM NaCl (96 mM sucrose was used to restore
osmolality). The time constant for the exchange, obtained from a single
exponential fit, was 1.3 ± 0.3 sec (10 observations from five
different oocytes). Thus, solution exchange was complete within ~5
sec. Because of this noninstantaneous exchange, at high agonist
concentrations and in particular for 7 nAChRs that desensitize very
rapidly, true peak currents are underestimated. This may result in an
overestimation of the EC50 for activation and a smaller
Hill coefficient. Although this is a potential problem in certain types
of analyses, in the present study we were concerned for the most part
with activation and desensitization at relatively low agonist
concentrations in which the influence of exchange rate is less
critical. All data are expressed as the mean ± SEM. For
statistical comparisons of concentration-response curves, t
tests were performed on the regression coefficients, estimated by using
the method of probits (Finney, 1971). For statistical comparisons of
mean data, weighted means t tests were performed for all
unpaired comparisons.
RESULTS
Potency of nicotine for activation of nAChRs
The differential sensitivity of nicotine in activating various
expressed receptors (Luetje and Patrick, 1991) implies that nicotine is
not equipotent at all nAChRs. Nicotine-induced concentration-response relationships for four different expressed nAChRs (34, 32, 44, and 42) confirm this hypothesis (Fig.
1). Logistic fits to these concentration-response
curves estimate EC50 values that can be divided into two
groups (Table 2): receptors containing 4 subunits have lower
EC50 values than those containing 3 subunits (t = 13.27; p < 0.01), implying that
4 subunits confer a higher apparent nicotine affinity. Because of
the high permeability of various neuronal nAChRs to calcium (Mulle et
al., 1992a; Vernino et al., 1992; Seguela et al., 1993; Rathouz and
Berg, 1994) and the potential contamination of the measured currents
with the activation of oocyte endogenous calcium-dependent
Cl currents (Vernino et al., 1992), the above
series of experiments was conducted in nominally calcium-free media.
Physiologically relevant levels of calcium can, however, regulate nAChR
activation, an effect that may result, in part, from changes in the
affinity of nAChRs for agonist (Mulle et al., 1992b; Vernino et al.,
1992; Galzi et al., 1996). To ascertain that the observed differences in the nAChR concentration-response relationships in calcium-free solutions were physiologically important, we repeated the experiments in calcium-containing media. The addition of calcium produced insignificant changes in EC50 values (t = 0.35; p > 0.05) and did not alter the order of potency
of nicotine for the various nAChR subtypes (Table
1).
Fig. 1.
4 subunits confer high apparent affinity on
nAChRs. A, Concentration-response curves were
constructed by measuring the peak current induced in response to brief
(5-10 sec) applications of nicotine (100 nM-300
µM). The peak responses are plotted with respect to
agonist concentration for four subtypes of nAChRs
(34, 32, 44, and
42). For each subtype all responses were
normalized to a response near the half-maximal concentration
(EC50). Each point represents one to
eight separate measurements. The solid lines are
logistic fits to the data. The calculated EC50 values and
the Hill coefficients were, respectively, 65 µM and 1.5 (34), 75 µM and 0.7 (32), 11 µM and 1.4 (44), and 12 µM and
1.5 (42). B, Representative current
responses for a series of nicotine concentrations applied to two
different oocytes expressing either 34 receptors (top
traces) or 44 receptors (bottom traces). All data shown in this figure were obtained in calcium-free
conditions.
[View Larger Version of this Image (15K GIF file)]
Table 1.
Subunit-specific properties of nAChRs
| Subtype |
EC50a (µM)
|
IC50b (µM) ±Ca |
Desensitization at
500 nM (%) ±Ca |
Desensitization time
coursec ( d;
min)
|
Desensitization
recoveryd (; min) ±Ca
|
| +Ca |
Ca |
+Ca |
Ca
|
|
| 34 |
62 |
65 |
1.15 |
39 |
32.5
± 2.5 (3) |
36.8 ± 4.8 (7) |
42.6 ± 5.5 (4)
|
| 44 |
9 |
11 |
0.042 |
87 |
35.5*
± 3.2 (5) |
16.2 ± 2.8 (3) |
413.8f
± 305.5 (2)
|
| 32 |
123 |
75 |
0.33 |
47 |
 5
(3)e |
3.9 ± 2.1 (4) |
11.7 ± 4.1
(2) |
| 42 |
15 |
12 |
0.061 |
71 |
3.7
± 0.9 (4) |
2.7 ± 0.3 (2) |
86.9 ± 64.7 (4)
|
| 7 |
90* |
234 |
6.2 (Ca) |
1 (Ca) |
0.5
± 0.03 (3) |
1.9 ± 0.5 (4) |
1.9 ± 0.5
(5) |
|
|
|
1.3* (+Ca) |
12 (+Ca) |
|
|
|
|
|
a
EC50 calculated from the
activation concentration-response curve in calcium-containing (+Ca)
and calcium-free (Ca) media.
b
IC50 calculated from the
concentration-response curves constructed from the mean
desensitization produced in both +Ca and Ca media. These combined
data are indicated by ±Ca.
c
The time constant (d)
from a single exponential fit to the time course of desensitization at
near IC50 concentrations of nicotine. These concentrations
were 1 µM (34), 100 nM (44), 300 nM (32), 300 nM (42), 10 µM (Ca, 7), and 3 µM (+Ca, 7). The
number of measurements is indicated in parentheses.
d
The time constant () from a single
exponential fit to the time course of recovery from desensitization at
1 µM nicotine for all subtypes except 7 (10 µM). The number of measurements is indicated in
parentheses. In the majority of experiments, the exponential was fit by
assuming full recovery to control values.
e
The reported values are estimates. It was
difficult to obtain an accurate exponential fit for some of the
32 data sets, because the interpulse interval for the test pulses
was large (5-10 min) and desensitization mainly was complete by the
time of the first test pulse.
f
Two additional oocytes expressing
44 receptors showed no recovery after 20-30 min wash.
*
Indicates significance (p < 0.05), as compared
with data obtained in calcium-free media.
|
|
The much higher apparent nicotine affinity of 4-containing subtypes,
as compared with 3-containing subtypes, is consistent with previous
reports for heterologously expressed nAChRs from both chick (Hussy et
al., 1994) and rat (Vibat et al., 1995). For 3 subunit-containing
receptors, our estimated EC50 values for nicotine were
comparable to previously published data (for review, see Role, 1992;
McGehee and Role, 1995). Little or no comparable data exist for
44 receptors (Role, 1992). Our data for the 42 receptor
predict a lower apparent nicotine affinity (15 µM,
calcium-containing solutions) than reports of heterologously expressed
42 nAChRs from chick (0.8 µM; Bertrand et al.,
1990), rat (0.3 µM; Vibat et al., 1995), and human (1.6 µM; Buisson et al., 1996).
Different time courses of desensitization of nAChR subtypes
Previous data show that nAChRs composed of different subunits
desensitize with different time courses in response to various nicotinic agonists (Cachelin and Jaggi, 1991; Gross et al., 1991, 1995;
Vibat et al., 1995). We have extended these findings, using nicotine as
the agonist. Figure 2A shows
representative responses of oocytes expressing four different nAChR
subtypes to a 3 min application of nicotine at near half-maximal
concentrations (see Fig. 1) in the presence of external calcium.
Receptors containing 4 subunits desensitize slower than those
containing 2 subunits (t = 6.2; p < 0.05). In most experiments the time course of desensitization for
receptors containing 4 subunits was well described by a single exponential decay. In some oocytes, particularly those with larger peak
currents, a faster "desensitizing" component was present in
44-expressing and 34-expressing oocytes (Fig.
2C). The fast component was calcium-dependent because it was
eliminated, for the most part, when the same cells were examined in
calcium-free media (Table 2). In contrast, the slower
component of desensitization was unaffected by calcium
(t = 0.21; p > 0.05; Fig.
2B, Table 2). These data are consistent with previous
reports in which it was argued that a transient calcium-dependent
Cl current could be activated by certain neuronal
nAChRs (Vernino et al., 1992; Seguela et al., 1993). On the other hand,
2-containing receptors generally required the sum of two
exponentials for a good fit to the data in both the presence and
absence of calcium, although the relative amplitude of the fast
component was affected significantly by calcium (t = 76.5; p < 0.01; Fig. 2; Table 2). Thus 2-containing
nAChRs have, in addition to a slow component of desensitization, an
intrinsic fast desensitization process. Differences in the size of the
fast "desensitizing" component of 42 and 32 receptors
in calcium-free and calcium-containing medium potentially could reflect
differences in the extent of activation of the endogenous
Cl current and/or differential modulation of the
fast and slow components by external calcium ions.
Fig. 2.
The time course of desensitization varies with
nAChR subtype. A, Responses to brief (~3 min)
applications of nicotine at near EC50 concentrations in
calcium-containing media for oocytes injected with different subunit
combinations. For comparison, the responses are normalized to their
peaks. The time course of desensitization for responses obtained from
oocytes expressing 4-containing receptors (left two
traces) were well described by a single exponential component.
For 2-containing receptors (right two traces), the decay phase was well described by the sum of two exponentials. B, Responses to 3 min applications of nicotine in
calcium-free (left trace) and calcium-containing
(right trace) media for an oocyte expressing 44
receptors. The traces are normalized to the peak currents. The
solid lines are single exponential functions fit to the
desensitizing phase of the responses, and their associated time
constants (s) are shown. C,
Responses to 3 min applications of nicotine in calcium-free
(left trace) and calcium-containing (right
trace) media for an oocyte expressing 34 receptors. The solid lines are single exponential functions fit to the
desensitizing phase of the responses. In calcium-containing media the
data were fit with two separate single exponentials, designated
f and s. The exponential functions
contained a steady-state component, which was constrained not to fall
below baseline current. The final steady-state values were generally in
the range of 0-20% peak current.
[View Larger Version of this Image (20K GIF file)]
Brief agonist applications do not provide sufficient data to
characterize receptor desensitization fully (Katz and Thesleff, 1957;
Feltz and Trautman, 1982). Moreover, the desensitization resulting from
long applications of nanomolar concentrations of nicotine may reveal
receptor subtype differences that are related more closely to
mechanisms underlying nicotine dependency (Stolerman and Shoaib, 1991;
Dani and Heinemann, 1996). With this in mind, we examined the subunit
dependence of nAChR desensitization induced by low levels of nicotine.
Because it is not possible to measure desensitization directly from the
very small currents produced by such low agonist concentrations,
desensitization was estimated from the nicotine-induced reduction in
the current elicited by a brief (5-10 sec) test pulse of acetylcholine
(ACh) near the half-maximal concentration for each receptor (Feltz and
Trautman, 1982). The ACh test pulses were applied at sufficient time
intervals (2-10 min, based on the particular subunit combination) so
as not to induce any additional desensitization. The data were
expressed as the fractional test current remaining with respect to the
time of nicotine exposure. For those experiments in which nicotine induced some receptor activation, the fractional current remaining was
calculated from the sum of both the nicotine- and ACh-induced currents.
Estimation of desensitization in this manner leads to an
underestimation of the extent of desensitization if the current induced
by nicotine is a significant fraction of the total response. Large
nicotine-induced currents were apparent only at higher agonist concentrations with certain receptor subtypes (e.g., 34; see Fig.
4). In these cases only, both the rate of desensitization development
and the magnitude of desensitization will be underestimated slightly.
Fig. 4.
The time course and extent of desensitization are
concentration-dependent. A, Plot of the peak amplitudes
of the currents induced by ACh test pulses (100 µM) with
respect to time before and during continuous perfusion with 1 µM (open squares), 10 µM (filled circles), or 30 µM
(open circles) nicotine in oocytes expressing 34
receptors. d is the time constant for a single exponential fit to the time course of desensitization. The
arrowheads represent near-equilibrium conditions at
which the magnitude of desensitization was estimated (see Fig. 5).
B, Representative traces of currents induced by ACh test
pulses before (control) and at the indicated
times during incubation with either 1 µM (top
traces) or 10 µM (bottom traces)
nicotine. All data were obtained in calcium-free media.
[View Larger Version of this Image (21K GIF file)]
As shown in Figure 3, incubation of oocytes with
nanomolar concentrations of nicotine (levels that produce little
activation of any of the receptor subtypes; see Fig. 1) induces a
profound desensitization of nAChRs. Differences in the time course of
desensitization for different nAChR subtypes are immediately apparent
and parallel the differences in desensitization observed with brief
pulses (see Fig. 2). In our experiments, receptors with 4 subunits
desensitized more slowly than those containing 2 subunits
(t = 9.7; p < 0.05), irrespective of
the presence or absence of calcium (Fig. 3). For all subunits the time
course of desensitization could be described reasonably well by a
single exponential fit (although see below), which allowed for a more
quantitative comparison of desensitization kinetics. Table 1 shows that
at concentrations of nicotine that produced a half-maximal block (see
Fig. 5) the time constant for the development of desensitization varied
considerably, from 4 min (32) to 45 min (34).
Fig. 3.
The time course of desensitization is slow in
receptors containing 4 subunits. A, Plot of the peak
current amplitudes induced by an ACh test pulse with respect to time
before and during continuous perfusion with either 300 or 100 nM nicotine in oocytes expressing either 42 receptors
(left) or 44 (right) receptors,
respectively, in calcium-containing (top traces) or
calcium-free (bottom traces) media. is the time
constant for a single exponential fit to the desensitization time
course. B, Representative traces of the ACh test pulses
before (control) and at the indicated times after incubation with nicotine for individual 42-expressing
(bottom left) or 44-expressing (bottom
right) oocytes in calcium-free media.
[View Larger Version of this Image (26K GIF file)]
Fig. 5.
4-containing nAChRs are desensitized by
nanomolar concentrations of nicotine. A,
Concentration-response plots of the ACh-induced fractional current
remaining after chronic nicotine incubation in oocytes expressing
32, 34, 42, or 44 receptors. Some of the data
were obtained by extrapolating the exponential fit to 60 min
(34 and 44) or 15-20
min (32 and 42). The
open and filled symbols represent data
obtained in calcium-containing and calcium-free media, respectively.
Each concentration data point represents between 1 and
10 measurements from separate oocytes. Solid lines are
logistic fits to the mean of all the data obtained in calcium-free and
calcium-containing media. Fits were constrained so that the maximal
block could not exceed 100% and so that at infinitely low nicotine
concentrations the block was zero. The half-maximal concentration for
inhibition (IC50) by nicotine is shown for each
nAChR subtype. B, Examples of the inhibition of the ACh
test pulses by different concentrations of nicotine for two receptor
subtypes, 34 (top traces) and 44
(bottom traces). Each pair of traces shows the current
induced before nicotine incubation (con) and the current
remaining after a 60 min incubation, with the concentration of nicotine
indicated.
[View Larger Version of this Image (25K GIF file)]
Potency of nicotine for desensitization of nAChRs
To compare more quantitatively the nicotine-induced
desensitization of nAChR subtypes, we examined desensitization over a range of nicotine concentrations. Because the time course of
desensitization development is concentration-dependent (Fig.
4) and subtype-dependent (see Fig. 3), different periods
of nicotine incubation were required for each nAChR subtype to reach
near-equilibrium conditions. Figure 4A shows that for
the receptor with the slowest desensitization time course, 34, a
60 min exposure was sufficient to produce ~90% desensitization even
at low nicotine concentrations. Longer incubation times typically were
not used to allow time for response recovery and to ensure that
recovery reflected reversal of desensitization rather than de
novo receptor synthesis (Peng et al., 1994; Hsu et al., 1995). In
addition, for receptor subtypes that reached equilibrium faster (e.g.,
32), nicotine exposure was continued in some cases for up to 30 min to ensure that a slower component of desensitization was not
present. Although we cannot exclude completely the possibility that
very slow desensitization components exist, desensitization of these
subunits by nicotine is complete, for the most part, within the first
hour (see also Hsu et al., 1995).
In theory, other mechanisms distinct from desensitization, such as
partial antagonism or channel block by nicotine, could explain the
decrease in ACh-induced currents in the presence of nicotine. Partial
antagonism seems unlikely, especially for 4-containing receptors,
because the block developed and recovered slowly. Even at low
concentrations a purely competitive nicotine effect would be expected
to be instantaneous, for the most part. Because nicotine is not a very
efficacious agonist at chick 32 receptors (Wang et al., 1996) and
given that this receptor subtype shows a relatively fast nicotine
block, partial antagonism remains a possibility; however, nicotine does
not seem to act as a partial antagonist at rat 32 nAChRs (Hussy
et al., 1994). A direct, use-dependent channel block by nicotine,
although reported for neuronal nicotinic receptors, is also unlikely at
such low agonist concentrations (Maconochie and Knight, 1992).
Once the time course of desensitization equilibrium was
established, inhibition dose-response curves were constructed from the
relative depression of an ACh test pulse induced during incubation with
various nicotine concentrations (Fig. 5). The data were
fit to a logistic equation from which the IC50
(half-maximal effective desensitizing concentration) for nicotine was
estimated. In the present study we refer to the IC50 as the
apparent affinity of nicotine for the desensitized state of the
receptor. The receptor subtypes could be divided into two groups, based
on these IC50 values. Similar to activation (see Fig. 1),
nAChRs expressing 4 subunits had a higher apparent affinity for the
desensitized state, as compared with nAChRs containing 3 subunits
(t = 5.6; p < 0.05). There is an
approximately linear relationship between the half-maximal
concentrations of nicotine for activation and desensitization (Table
1). These data indicate that the time course of desensitization is not
a good predictor of nicotine affinity for the desensitized state. For
example, 44 receptors, which have a slow desensitization onset,
demonstrate the highest apparent nicotine affinity for the desensitized
state. On the other hand, 32 receptors, which have a fast onset,
have a relatively low apparent desensitization affinity. At the highest
concentrations of nicotine tested, all nAChR subtypes except 32
receptors were desensitized completely; 32 receptors were
desensitized ~78% (Fig. 5).
Recovery from desensitization
After prolonged exposure to nicotine, the different nAChR subtypes
recovered to pre-nicotine exposure values with different rates (Fig.
6). Differences in the time course of recovery from desensitization among subtypes were compared by fitting single exponentials to the recovery phase of the response after washout of 1 µM nicotine. Receptors containing 4 subunits (i.e.,
nAChRs with a higher-affinity desensitized state) recovered more slowly from desensitization than those containing 3 subunits
(t = 21.2; p < 0.01). This result is
not unexpected, because recovery ultimately involves an unbinding of
agonist and a change in the receptor from desensitized to activatable;
this is likely to be the slowest for the highest affinity receptor.
Indeed, for 44 receptors, recovery often was incomplete even with
2 hr washout (Fig. 6B). On the other hand, 32
receptors recovered within a few minutes (Fig. 6C).
Additionally, receptors containing 4 subunits (i.e., nAChRs in which
the time course of desensitization development is slower) recovered
more slowly than those containing 2 subunits (t = 8.4; p < 0.05; Fig. 6A). Thus,
34 receptors show a rate of recovery intermediate of 32
receptors and 44 receptors.
Fig. 6.
Time course of recovery from nicotine-induced
desensitization is subunit-dependent. A, Histogram of
the mean time constants for a single exponential fit to the time course
of recovery from desensitization induced by 1 µM nicotine
for a number of nAChR subtypes. Data from experiments in calcium-free
and calcium-containing media were combined. The number
of experiments for each subtype is indicated in
parentheses. Recovery was estimated after nicotine incubation of 15-20 min (32 and
42 receptors) and 60 min (34 and 44 receptors). B, Plot of
normalized peak current amplitudes (o o) induced by a repetitively
applied ACh test pulse (5 µM; 5 min intervals) with
respect to time before, during (open bar), and after
continuous perfusion with 300 nM nicotine in
calcium-containing media for an oocyte expressing 44 receptors.
C, Plot of normalized peak amplitudes of currents (oo)
induced by a repetitively applied ACh test pulse (100 µM;
10 min intervals) with respect to time before, during (open
bar), and after continuous perfusion with 3 µM
nicotine in calcium-free media for an oocyte expressing 32 receptors. The time constants () in B and
C result from single exponential fits (solid
line) to the time course of recovery from desensitization. The
exponential fit assumed recovery to control values.
[View Larger Version of this Image (20K GIF file)]
The above analysis assumed a single exponential recovery from
desensitization. This is a reasonable assumption for 4-containing receptors; however, it may be inaccurate for 2-containing receptors. Receptors containing 2 subunits require the sum of two components to
describe the desensitization phase during a brief pulse (see Fig. 2).
These data imply multiple desensitized states for these receptors
(Feltz and Trautman, 1982; Boyd, 1987). Thus, it follows that recovery
from desensitization also may have two components (Feltz and Trautman,
1982; Cachelin and Colquhoun, 1989; Lester and Dani, 1995).
Recovery from desensitization for muscle-type nAChRs has been shown to
be influenced by calcium-dependent mechanisms (Hardwick and Parsons,
1996). Thus, it is possible that similar mechanisms control the
recovery of neuronal nAChRs. Because of the long duration of recordings
necessary to examine the slow recovery from desensitization at low
concentrations of nicotine, we used, instead, a paired-pulse approach
to test the influence of calcium on the recovery from desensitization.
A single 3 min application of nicotine at near EC50
concentrations was followed at a known interval by a second test pulse
of nicotine, and the fractional recovery from desensitization was
estimated in both calcium-free and calcium-containing media (Fig.
7). To reduce variability, often we tested the same
oocyte under both conditions. Our results indicate that calcium has
little effect on recovery from desensitization of nAChRs, although for some subtypes, e.g., 42, the rate of recovery may be enhanced in
the presence of calcium (t = 31.1; p < 0.01).
Fig. 7.
Subunit-specific differences in the recovery
from desensitization. A, Paired-pulses of nicotine (10 µM) applied to an oocyte expressing 42 receptors at
an interpulse interval of 20 min. To account for differences in the
relative amount of desensitization in calcium-containing and
calcium-free media, we quantified recovery by measuring the fractional
increase in the amplitude of the second pulse
(I2) with respect to the amount of
desensitization (I1) induced by a 3 min application of nicotine. B, Plot of the fractional recovery from desensitization at various interpulse intervals in the
presence (open circles) or absence (filled
circles) of added calcium. C, Histogram of the
relative recovery from desensitization for each nAChR subtype in the
presence or absence of calcium. The number of
experiments for each subtype is indicated in
parentheses. The interpulse intervals were 10 min for
both 44 receptors and 42 receptors, 5 min for 34
receptors, and 3 min for 32 receptors. Individual oocytes
expressing 42 and 32 receptors were measured in both
calcium-free and calcium-containing media. Significant differences
(p < 0.05) between the results obtained in
the two conditions are indicated by the asterisk.
[View Larger Version of this Image (19K GIF file)]
The outcome of prolonged exposure to nicotine is determined initially
by the balance between receptor activation and desensitization at a
particular nicotine concentration. To illustrate how this balance
varies for different nAChR subtypes, we have replotted the activation
and desensitization curves (Figs. 1A, 5) on the same
axes (Fig. 8). The concentration range in which the
activation and desensitization curves overlap indicates a "window
current" (Steinbach, 1990), a region over which nicotine always
produces some nAChR channel activation, because desensitization will be incomplete. At tobacco-related concentrations (60-300 nM;
Benowitz et al., 1989) the main effect of nicotine will be to
desensitize nAChRs (see Table 1), thus reducing the population of
receptors available for potential stimulation by endogenously released
ACh (see Lester and Dani, 1995). However, for the higher affinity 4
subunit-containing nAChRs, nicotine at these concentrations will
produce some channel activation.
Fig. 8.
Receptor activation and desensitization have
subtype-specific overlapping concentration ranges. Shown are summary
concentration-response plots for activation in calcium-containing
media (filled symbols; solid
lines) and for desensitization (open symbols) of
four nAChR subtypes. For comparison, the logistic fits to the
activation concentration-response curves obtained in calcium-free
media are indicated with dashed lines.
[View Larger Version of this Image (27K GIF file)]
7 receptor desensitization and activation by nicotine
Although the above data demonstrate that and subunits
differentially influence the desensitization process, not all expressed nAChRs require subunits for channel formation or, indeed, for desensitization (e.g., 7 receptors; Couturier et al., 1990). For
these receptors, desensitization characteristics must be determined solely by the subunit (see Revah et al., 1991). The demonstration that 7-containing receptors mediate a presynaptic release of transmitter in the continuous presence of low concentrations of nicotine (McGehee et al., 1995; Gray et al., 1996) demands a detailed investigation of this subtype with respect to desensitization.
Figure 9 characterizes activation and desensitization
for 7 receptors. As described by others (Couturier et al., 1990;
Revah et al., 1991; Seguela et al., 1993), 7 nAChRs activate and
desensitize rapidly to brief applications of high agonist
concentrations (Fig. 9A). The dose-response relationship
for nicotine reveals a relatively high EC50 (234 µM, calcium-free solutions), implying that 7 receptors have a very low apparent affinity for nicotine. There was an
approximately twofold shift in the EC50 to lower values in
the presence of extracellular calcium ions (t = 9.4;
p < 0.05) with little effect on maximal activation
(Fig. 9B). Our EC50 values of 79 µM (3.6 mM calcium) and 90 µM
(1.8 mM calcium) are slightly higher than those reported previously for human 7 (49 µM; Gopalakrishnan et al.,
1995), rat 7 (~30 µM; Seguela et al., 1993), and
chick 7 (24 µM; Amar et al., 1993). Accounting for the
decrease in single-channel conductance because of calcium (Mulle et
al., 1992b; Amador and Dani, 1995), these data imply that calcium may
increase both the affinity and efficacy of 7 nAChRs (Galzi et al.,
1996). Desensitization of 7 receptors (and subsequent recovery from
desensitization) at low concentrations of nicotine was rapid (Fig.
9C,D). However, in the absence of added calcium,
desensitization was observed only for concentrations of nicotine above
~1 µM, setting it apart from the various -paired
nAChRs. In calcium-free media, the half-maximal concentration of
nicotine for desensitization was 6 µM, the highest of all
receptors tested (Fig. 9F). The addition of calcium
significantly increased the effectiveness of nicotine to desensitize
7-expressing receptors (IC50 = 1 µM;
t = 18.5; p < 0.01), with little
observable effect on the time course of desensitization
(t = 2.7; p > 0.05; Fig.
9E,F). Thus, although 7 receptors exhibit
pronounced and rapid desensitization, much higher concentrations of
nicotine are required.
Fig. 9.
Homomeric 7 receptors have low affinity for
nicotine and rapid desensitization kinetics. A, Example
of rapid desensitization induced by 200 µM nicotine in
calcium-free media in an oocyte expressing 7 receptors. The mean
time constant (decay) resulting from a single
exponential fit to the decay phase is indicated; the steady-state/peak
current ratio was 0.023 ± 0.003 (10 observations from four
cells). B, Concentration-response curves for
nicotine-induced activation. The solid lines are
logistic fits to the data sets. The EC50 values were 90 µM (n = 4) and 234 µM
(n = 10) in the presence (open
circles) or absence (closed circles) of calcium, respectively. The Hill coefficients for each were 1.1. C, Example of the currents induced by test pulses of ACh
(100 µM) before (control), during
continuous exposure, and after washout of 30 µM nicotine
in calcium-free media. D, Plot of the peak test pulse amplitude (ACh, 100 µM) in two different oocytes
expressing 7 receptors before, during, and after incubation with 1 µM (open symbols) or 30 µM
(closed symbols) nicotine in calcium-free media. E, Plot of the peak test pulse amplitude induced by ACh
before, during, and after incubation of an 7-expressing oocyte with
a 10 min application of 5 µM nicotine in the presence
(open circles) or absence (closed
circles) of calcium. F, Concentration-response curve for nicotine-induced inhibition of the ACh test pulse in 7
receptor-expressing oocytes. The solid lines are
logistic fits, and the half-maximal concentrations for inhibition
(IC50) by nicotine were 1.3 and 6.2 µM
in the presence (open circles) or absence (closed
circles) of calcium, respectively. The activation
concentration-response curves obtained in the same conditions are
shown (dashed lines) for comparison.
[View Larger Version of this Image (31K GIF file)]
DISCUSSION
Examination of a number of expressed nAChRs reveals patterns of
functional contributions of particular and subunits to the
process of activation and desensitization. For heteromeric nAChRs we
find that the subunit makes a significant contribution in
determining the apparent nicotine affinity of the active and desensitized states of an nAChR; the subunit makes a significant contribution in determining the overall time course of the
desensitization development of an nAChR. In addition, we have
demonstrated that external calcium ions, while producing subtle effects
on the kinetics and apparent affinities of nicotine for activation and
desensitization of the nAChRs, do not alter the pattern of
contributions of these various subunits. In contrast, for the homomeric
7 nAChR, which displays faster kinetics and generally lower
affinities for nicotine than the pairs, we find that calcium
increases the apparent affinity of nicotine for both the active and
desensitized states.
Contribution of the subunit to activation of nAChRs
by nicotine
Activation of various nAChR subtypes by nicotine produced
straightforward results: 4-containing receptors have higher apparent affinities for nicotine than 3-containing receptors. Vibat et al.
(1995) have observed a similar leftward shift in nicotine-induced dose-response curves on switching an 4 subunit for an 3 subunit in receptors containing rat 4 subunits. Chick and human 42 receptors (Bertrand et al., 1990; Peng et al., 1994; Buisson et al.,
1996) also are activated more potently by nicotine than are 34
receptors (Hussy et al., 1994). If the subunit is the principal agonist-binding subunit, these results could indicate differences in
agonist-binding affinity between these two subunits. However, this
is likely an oversimplification. First, subunits, as noted above,
also affect the apparent affinity for some nAChR subtypes (Cachelin and
Jaggi, 1991; Gross et al., 1991; Luetje and Patrick, 1991; Cohen et
al., 1995), and, second, apparent affinity reflects both agonist
binding and channel gating, so the observed subtype differences in
concentration-response curves could represent differences in either
affinity and/or efficacy. By examining the contribution of subunits
to the concentration-response relationship, Cohen et al. (1995) have
argued that affinity differences cannot be explained by a change in
efficacy and that, by analogy with muscle nAChRs, the binding site is
likely to form between both and subunits. This argument is
supported by observations that antagonist sensitivity also is
determined by both and subunits (Cachelin and Rust, 1995;
Harvey and Luetje, 1996). It is possible, therefore, that our
activation results are attributable to the fortuitous selection of
particular nAChRs.
and subunits contribute to
nicotine-induced desensitization
The desensitization time course for nAChR subtypes, measured
either directly from the current decay during brief nicotine applications or from the decrease in response to ACh test pulses in the
presence low concentrations of nicotine, is influenced for the most
part by the subunit: fast for 2-containing nAChRs and slow for
4-containing nAChRs. These data extend previous findings for rat
nAChRs (Cachelin and Jaggi, 1991; Hsu et al., 1995). Because homomeric
7 receptors also desensitize, it is likely that the subunit
plays a modulatory, rather than a permissive role, in
desensitization.
Studies investigating ACh desensitization of both chick and rat nAChRs,
in which the subunit was not varied, imply that the subunit
also can influence the time course of desensitization (Gross et al.,
1991; Vibat et al., 1995). Aside from agonist-dependent differences in
desensitization, the contribution of subunits may be explained if
one considers how desensitization was measured. For example, although
short applications of nicotine demonstrate that 32 receptors
desensitize faster than 42 receptors (Gross et al., 1991; Vibat
et al., 1995), the reverse is true when the desensitization time course
is followed by repetitive pulses (Vibat et al., 1995). Such differences
may be explained if one considers a cyclical model for
desensitization (Katz and Thesleff, 1957). In the continued presence of
agonist, the time course of desensitization reflects the rates
governing equilibration between the active/open and the desensitized
states. These rates would be expected to be faster for 32
receptors than 42 receptors; hence 32 receptors would
desensitize faster in the continued presence of agonist. However, on
removal of agonist, recovery can occur by the unbinding of agonist from
the desensitized state (Dilger and Lui, 1993). Thus, if recovery in the
absence of agonist is slow for 42 receptors as compared with
32 receptors, as we have observed, then desensitization measured
by repetitive pulses (the agonist is absent in the interpulse interval)
over a longer period of time would show a greater accumulation of
42 receptors in the desensitized state (Vibat et al., 1995).
Relationship between nAChR channel properties and
receptor regulation
Prolonged nicotine exposure leads to subtype-specific modulation
(Schwartz and Kellar, 1985; Stolerman and Shoaib, 1991; Marks et al.,
1993; Hsu et al., 1995; Dani and Heinemann, 1996). Because these
changes arise at low nicotine concentrations, one must consider individual differences in nAChR behavior at these concentrations. A
complete understanding of the cellular effects resulting from prolonged
exposure to nicotine requires knowledge of the balance between
activated and desensitized states of receptor subtypes (Steinbach,
1990; Balfour, 1994). All nAChRs studied desensitize at lower
concentrations than they activate (Katz and Thesleff, 1957); however,
for each receptor there is a concentration range over which
desensitization is incomplete and activation has begun. Particularly
for 42 receptors, this window approximately corresponds to the
estimated levels of nicotine found in the brain after tobacco smoke
inhalation (Benowitz et al., 1989).
For certain nAChR subtypes, e.g., 42 receptors, chronic nicotine
exposure results in pronounced upregulation of receptor number (Flores
et al., 1992; Peng et al., 1994; Gopalakrishnan et al., 1996). Because
the desensitized state of 42 receptors has high nicotine affinity
(it is desensitized for the most part by 1 µM nicotine),
this state may be the trigger for the increase in receptor number
(Ochoa et al., 1990; Peng et al., 1994; Gopalakrishnan et al., 1996).
This idea is supported by evidence that exposure to nAChR antagonists
also induces an increase in receptor number; i.e., a nonactive state of
the receptor is a sufficient stimulus (Collins et al., 1994; Peng et
al., 1994; Gopalakrishnan et al., 1996). An accompanying increase in
receptor sensitivity then could be a direct consequence of increased
receptor number (Rowell and Wonnacott, 1990; Gopalakrishnan et al.,
1996). However, others have observed a downregulation in receptor
function (Marks et al., 1993; Collins et al., 1994; Peng et al., 1994).
The relatively high activation affinity of 42 receptors means
that, although most receptors are desensitized by tobacco-related
levels of nicotine, a continuous low level of activity remains.
Prolonged low rates of synaptic activity have been associated with an
NMDA-mediated calcium-dependent long-term depression of glutamatergic
responses (Dudek and Bear, 1992; Mulkey and Malenka, 1992). An
intriguing possibility is that functional downregulation of nAChRs is
related to their high calcium permeability. The concept of an
overlapping agonist concentration window for activation and
desensitization could account for the dual up- and downregulation of
42 receptor function (Peng et al., 1994; Gopalakrishnan et al.,
1996); the precise agonist concentration would control the relative
balance between active and desensitized receptor states.
Differences in regulation among nAChRs could be explained by
subtype-specific nicotine sensitivities of both the desensitized and
active receptor states. Studies on the homomeric 7 receptor provide
some support for this notion. The finding that nanomolar concentrations
of nicotine can, via 7-like presynaptic nAChRs, cause a continuous
release of glutamate from synaptic terminals (McGehee et al., 1995;
Gray et al., 1996) is consistent with the present observation that
these concentrations of nicotine would cause little desensitization of
7 receptors. The desensitization hypothesis for increases in nAChR
number would predict that 7 receptors should not be upregulated as
readily as 42 receptors. In fact, the number of -bungarotoxin
(-BTX) binding sites, putatively formed from 7 subunits
(Couturier et al., 1990), can be upregulated by chronic nicotine
treatment. However, relatively high concentrations of nicotine are
required (Marks et al., 1983). At lower concentrations of nicotine
(that result in increased 42 receptor number), 7/-BTX receptors are unaffected (Marks et al., 1985; Collins et al., 1994).
It should be noted that some CNS nAChRs, including 7, may contain
more than a single type of or subunit (Conroy et al., 1992;
Anand et al., 1993; Ramirez-Latorre et al., 1996; Wang et al., 1996).
Also, there may be some differences between nAChRs expressed in oocytes
and mammalian cells (Peng et al., 1994; Wong et al., 1995; Buisson et
al., 1996). Such differences may result in shifts in
concentration-response curves and/or desensitization properties
(Ramirez-Latorre et al., 1996; Wang et al., 1996). Regardless,
knowledge of the subunit contribution to activation and desensitization
is important for accurate predictions of the differential effects of
tobacco-related levels of nicotine on CNS nAChRs.
FOOTNOTES
Received Dec. 30, 1996; revised April 18, 1997; accepted May 19, 1997.
This work was supported by United States Public Health Service (USPHS)
National Institute of Neurological Disorders and Stroke Grant R29
NS31669 (R.A.J.L.), USPHS National Cancer Institute Grant CA13148
(M.W.Q.), and W. M. Keck Foundation Grant 931360. We thank Dr. David S. Weiss for helpful discussions and comments on this manuscript.
Correspondence should be addressed to Dr. Robin A. J. Lester,
Department of Neurobiology, CIRC Room 560, University of Alabama at
Birmingham, 1719 Sixth Avenue South, Birmingham, AL 35294-0021.
REFERENCES
-
Amador M,
Dani JA
(1995)
Mechanism for modulation of nicotinic acetylcholine receptors that can influence synaptic transmission.
J Neurosci
15:4525-4532[Abstract].
-
Amar M,
Thomas P,
Johnson C,
Lunt GG,
Wonnacott S
(1993)
Agonist pharmacology of the neuronal alpha 7 nicotinic receptor expressed in Xenopus oocytes.
FEBS Lett
327:284-288[Web of Science][Medline].
-
Anand R,
Conroy WG,
Schoepfer R,
Whiting P,
Lindstrom J
(1991)
Neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes have a pentameric quaternary structure.
J Biol Chem
266:11192-11198[Abstract/Free Full Text].
-
Anand R,
Peng X,
Lindstrom J
(1993)
Homomeric and native alpha 7 acetylcholine receptors exhibit remarkably similar but non-identical pharmacological properties, suggesting that the native receptor is a heteromeric protein complex.
FEBS Lett
327:241-246[Web of Science][Medline].
-
Balfour DJK
(1994)
Neural mechanisms underlying nicotine dependence.
Addiction
89:1419-1423[Web of Science][Medline].
-
Benowitz NL,
Porchet H,
Jacob III P
(1989)
Nicotinic dependence and tolerance in man: pharmacokinetic and pharmacodynamic investigations.
Prog Brain Res
79:279-287[Web of Science][Medline].
-
Bertrand D,
Ballivet M,
Rungger D
(1990)
Activation and blocking of neuronal nicotinic acetylcholine receptor reconstituted in Xenopus oocytes.
Proc Natl Acad Sci USA
87:1993-1997[Abstract/Free Full Text].
-
Boyd ND
(1987)
Two distinct kinetic phases of desensitization of acetylcholine receptors of clonal rat PC12 cells.
J Physiol (Lond)
389:45-67[Abstract/Free Full Text].
-
Buisson B,
Gopalakrishnan M,
Arneric SP,
Sullivan JP,
Bertrand D
(1996)
Human 42 neuronal nicotinic acetylcholine receptor in HEK 293 cells: a patch-clamp study.
J Neurosci
16:7880-7891[Abstract/Free Full Text].
-
Cachelin AB,
Colquhoun D
(1989)
Desensitization of the acetylcholine receptor of frog end-plates measured in a Vaseline-gap voltage clamp.
J Physiol (Lond)
415:159-188[Abstract/Free Full Text].
-
Cachelin AB,
Jaggi R
(1991)
subunits determine the time course of desensitization in rat 3 neuronal nicotinic acetylcholine receptors.
Pflügers Arch
419:579-582[Web of Science][Medline].
-
Cachelin AB,
Rust G
(1995)
subunits codetermine the sensitivity of rat neuronal nicotinic receptors to antagonists.
Pflügers Arch
429:449-451[Web of Science][Medline].
-
Clark PBS
(1993)
Nicotinic receptors in mammalian brain: localization and relation to cholinergic innervation.
Prog Brain Res
98:77-83[Web of Science][Medline].
-
Cohen BN,
Figl A,
Quick MW,
Labarca C,
Davidson N,
Lester HA
(1995)
Regions of 2 and 4 responsible for differences between the steady-state dose-response relationships of the 32 and 34 neuronal nicotinic receptors.
J Gen Physiol
105:745-764[Abstract/Free Full Text].
-
Collins AC,
Luo Y,
Selvaag S,
Marks MJ
(1994)
Sensitivity to nicotine and brain nicotinic receptors are altered by chronic nicotine and mecamylamine infusion.
J Pharmacol Exp Ther
271:125-133[Abstract/Free Full Text].
-
Conroy WG,
Vernallis AB,
Berg DK
(1992)
The 5 gene product assembles with multiple acetylcholine receptor subunits to form distinctive receptor subtypes in brain.
Neuron
9:679-691[Web of Science][Medline].
-
Cooper C,
Courturier S,
Ballivet M
(1991)
Pentameric structure and subunit stoichiometry of a neuronal nicotinic acetylcholine receptor.
Nature
350:235-238[Medline].
-
Couturier S,
Bertrand D,
Matter JM,
Hernandez MC,
Bertrand S,
Millar N,
Valera S,
Barkas T,
Ballivet M
(1990)
A neuronal nicotinic acetylcholine receptor subunit (alpha 7) is developmentally regulated and forms a homo-oligomeric channel blocked by alpha-BTX.
Neuron
5:847-856[Web of Science][Medline].
-
Dani JA,
Heinemann S
(1996)
Molecular and cellular aspects of nicotine abuse.
Neuron
16:905-908[Web of Science][Medline].
-
Dilger JP,
Lui Y
(1993)
Desensitization of acetylcholine receptors in BC3H-1 cells.
Pflügers Arch
420:479-485.
-
Dineley-Miller K,
Patrick J
(1992)
Gene transcripts for the nicotinic acetylcholine receptor subunit, beta 4, are distributed in multiple areas of the rat central nervous system.
Mol Brain Res
16:339-344[Medline].
-
Dudek SM,
Bear MF
(1992)
Homosynaptic long-term depression in area CA1 of hippocampus and effects of N-methyl-D-aspartate receptor blockade.
Proc Natl Acad Sci USA
89:4363-4367[Abstract/Free Full Text].
-
Duvoisin RM,
Deneris ES,
Patrick J,
Heinemann S
(1989)
The functional diversity of the neuronal nicotinic acetylcholine receptor is increased by a novel subunit 4.
Neuron
3:487-496[Web of Science][Medline].
-
Feltz A,
Trautmann A
(1982)
Desensitization at the frog neuromuscular junction: a biphasic process.
J Physiol (Lond)
322:257-272[Abstract/Free Full Text].
-
Finney D
(1971)
In: Probit analysis, 3rd Ed. New York: Cambridge UP.
-
Flores CM,
Rogers SW,
Pabreza LA,
Wolfe BB,
Kellar KJ
(1992)
A subtype of nicotinic cholinergic receptor in rat brain is composed of 4 and 2 subunits and is up-regulated by chronic nicotine treatment.
J Pharmacol Exp Ther
41:31-37.
-
Galzi JL,
Bertrand S,
Corringer PJ,
Changeux JP,
Bertrand D
(1996)
Identification of calcium binding sites that regulate potentiation of a neuronal nicotinic acetylcholine receptor.
EMBO J
15:5824-5832[Web of Science][Medline].
-
Gopalakrishnan M,
Buisson B,
Touma E,
Giordano T,
Campbell JE,
Hu IC,
Donnelly-Roberts D,
Arneric SP,
Bertrand D,
Sullivan JP
(1995)
Stable expression and pharmacological properties of the human alpha 7 nicotinic acetylcholine receptor.
Eur J Pharmacol
290:237-246[Web of Science][Medline].
-
Gopalakrishnan M,
Monteggia LM,
Anderson DJ,
Molinari EJ,
Piattoni-Kaplan M,
Donnelly-Roberts D,
Arneric SP,
Sullivan JP
(1996)
Stable expression, pharmacologic properties, and regulation of the human neuronal nicotinic acetylcholine alpha 4 beta 2 receptor.
J Pharmacol Exp Ther
276:289-297[Abstract/Free Full Text].
-
Gray R,
Rajan A,
Radcliffe KA,
Yakehiro M,
Dani JA
(1996)
Hippocampal synaptic transmission enhanced by low concentrations of nicotine.
Nature
383:713-716[Medline].
-
Gross B,
Ballivet M,
Rungger D,
Bertrand D
(1991)
Neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes: role of the alpha subunit in agonist sensitivity and desensitization.
Pflügers Arch
419:545-551[Web of Science][Medline].
-
Hardwick JC,
Parsons RL
(1996)
Activation of the protein phosphatase calcineurin during carbachol exposure decreases the extent of recovery from end-plate desensitization.
J Neurophysiol
76:3609-3616[Abstract/Free Full Text].
-
Harvey SC,
Luetje CW
(1996)
Determinants of competitive antagonist sensitivity on neuronal nicotinic receptor subunits.
J Neurosci
16:3798-3806[Abstract/Free Full Text].
-
Hussy N,
Ballivet M,
Bertrand D
(1994)
Agonist and antagonist effects of nicotine on chick neuronal receptors are defined by and subunits.
J Neurophysiol
72:1317-1326[Abstract/Free Full Text].
-
Hsu Y-N,
Amin J,
Weiss DS,
Wecker L
(1995)
Sustained nicotine exposure differentially affects 32 and 42 neuronal nicotinic receptors expressed in Xenopus oocytes.
J Neurochem
66:667-675[Web of Science][Medline].
-
Katz B,
Thesleff S
(1957)
A study of the desensitization produced by acetylcholine at the motor end-plate.
J Physiol (Lond)
138:63-80.
-
Lester RAJ,
Dani JA
(1995)
Acetylcholine receptor desensitization induced by nicotine in rat medial habenula neurons.
J Neurophysiol
74:195-206[Abstract/Free Full Text].
-
Luetje CW,
Patrick JP
(1991)
Both and subunits contribute to the agonist sensitivity of neuronal nicotinic acetylcholine receptors.
J Neurosci
11:837-845[Abstract].
-
Maconochie DJ,
Knight DE
(1992)
A study of the bovine adrenal chromaffin nicotinic receptor using patch-clamp and concentration-jump techniques.
J Physiol (Lond)
454:129-153[Abstract/Free Full Text].
-
Marks MJ,
Burch JB,
Collins AC
(1983)
Effects of chronic nicotine infusion on tolerance development and nicotinic receptors.
J Pharmacol Exp Ther
226:817-825[Free Full Text].
-
Marks MJ,
Stitzel JA,
Collins AC
(1985)
Time course study of the effects of chronic nicotine infusion on drug response and brain receptors.
J Pharmacol Exp Ther
235:619-628[Abstract/Free Full Text].
-
Marks MJ,
Pauly JR,
Gross SD,
Deneris ES,
Hermana-Borgmeyer I,
Heinemann SF,
Collins AC
(1992)
Nicotine binding and nicotinic receptor subunit RNA after chronic nicotine treatment.
J Neurosci
12:2765-2784[Abstract].
-
Marks MJ,
Grady SR,
Collins AC
(1993)
Downregulation of nicotinic receptor function after chronic nicotine infusion.
J Pharmacol Exp Ther
266:1268-1276[Abstract/Free Full Text].
-
McGehee DS,
Role LW
(1995)
Physiological diversity of nicotinic acetylcholine receptors expressed by vertebrate neurons.
Annu Rev Physiol
57:521-546[Web of Science][Medline].
-
McGehee DS,
Role LW
(1996)
Presynaptic ionotropic receptors.
Curr Opin Neurobiol
6:342-349[Web of Science][Medline].
-
McGehee DS,
Heath MJ,
Gelber S,
Devay P,
Role LW
(1995)
Nicotine enhancement of fast excitatory synaptic transmission in CNS by presynaptic receptors.
Science
269:1692-1696[Abstract/Free Full Text].
-
Morris BJ,
Hicks AA,
Wisden W,
Darlison MG,
Hunt SP,
Barnard EA
(1990)
Distinct regional expression of nicotinic acetylcholine receptor genes in chick brain.
Mol Brain Res
7:305-315[Medline].
-
Mulkey RM,
Malenka RC
(1992)
Mechanisms underlying induction of homosynaptic long-term depression in area CA1 of the hippocampus.
Neuron
9:967-975[Web of Science][Medline].
-
Mulle C,
Choquet D,
Korn H,
Changeux JP
(1992a)
Calcium influx through nicotinic receptor in rat central neurons: its relevance to cellular regulation.
Neuron
8:135-143[Web of Science][Medline].
-
Mulle C,
Lena C,
Changeux JP
(1992b)
Potentiation of nicotinic receptor response by external calcium in rat central neurons.
Neuron
8:937-945[Web of Science][Medline].
-
Ochoa ELM,
Li L,
McNamee MG
(1990)
Desensitization of central cholinergic mechanisms and neuroadaptation to nicotine.
Mol Neurobiol
4:251-287[Medline].
-
Peng X,
Gerzanich V,
Annad R,
Whiting PJ,
Lindstrom J
(1994)
Nicotine-induced increase in neuronal nicotinic receptors results from a decrease in the rate of receptor turnover.
Mol Pharmacol
46:523-530[Abstract].
-
Quick MW,
Lester HA
(1994)
Methods for expression of excitability proteins in Xenopus oocytes.
In: Methods in neurosciences (Conn PM,
ed), pp 261-279. San Diego: Academic.
-
Ramirez-Latorre J,
Yu CR,
Qu X,
Perin F,
Karlin A,
Role L
(1996)
Functional contributions of 5 subunit to neuronal acetylcholine receptor channels.
Nature
380:347-351[Medline].
-
Rathouz MM,
Berg DK
(1994)
Synaptic-type acetylcholine receptors raise intracellular calcium levels in neurons by two mechanisms.
J Neurosci
14:6935-6945[Abstract].
-
Revah F,
Bertrand D,
Galzi JL,
Devillers-Thiery A,
Mulle C,
Hussy N,
Bertrand S,
Ballivet M,
Changeux JP
(1991)
Mutations in the channel domain alter desensitization of a neuronal nicotinic receptor.
Nature
353:846-849[Medline].
-
Role LW
(1992)
Diversity in primary structure and function of neuronal nicotinic acetylcholine receptor channels.
Curr Opin Neurobiol
2:254-262[Medline].
-
Role LW,
Berg DK
(1996)
Nicotinic receptors in the development and modulation of CNS synapses.
Neuron
16:1077-1085[Web of Science][Medline].
-
Rowell PP,
Wonnacott S
(1990)
Evidence for functional activity of up-regulated nicotine binding sites in rat striatal synaptosomes.
J Neurochem
55:2105-2110[Web of Science][Medline].
-
Schwartz RD,
Kellar KJ
(1985)
In vivo regulation of [3H]acetylcholine recognition sites in brain by nicotinic cholinergic drugs.
J Neurochem
45:427-433[Web of Science][Medline].
-
Seguela P,
Wadiche J,
Dineley-Miller K,
Dani JA,
Patrick JW
(1993)
Molecular cloning, functional properties, and distribution of rat brain alpha 7: a nicotinic cation channel highly permeable to calcium.
J Neurosci
13:596-604[Abstract].
-
Steinbach JH
(1990)
Mechanism of action of the nicotinic acetylcholine receptor.
Ciba Found Symp
152:53-67[Medline].
-
Stolerman IP,
Shoaib M
(1991)
The neurobiology of tobacco addiction.
Trends Pharmacol Sci
12:467-473[Medline].
-
Vernino S,
Amador M,
Luetje CW,
Patrick J,
Dani JA
(1992)
Calcium modulation and high calcium permeability of neuronal nicotinic acetylcholine receptors.
Neuron
8:127-134[Web of Science][Medline].
-
Vibat CRT,
Lasalde JA,
McNamee MG,
Ochoa ELM
(1995)
Differential desensitization properties of rat neuronal nicotinic acetylcholine receptor subunit combinations expressed in Xenopus oocytes.
Cell Mol Neurobiol
15:411-425[Web of Science][Medline].
-
Wada E,
Wada K,
Boulter J,
Deneris E,
Heinemann S,
Patrick J,
Swanson LW
(1989)
Distribution of alpha 2, alpha 3, alpha 4, and beta 2 neuronal nicotinic receptor subunit mRNAs in the central nervous system: a hybridization histochemical study in the rat.
J Comp Neurol
284:314-355[Web of Science][Medline].
-
Wang F,
Gerzanich V,
Wells GB,
Anand R,
Peng X,
Keyser K,
Lindstrom J
(1996)
Assembly of human neuronal nicotinic receptor alpha 5 subunits with alpha 3, beta 2, and beta 4 subunits.
J Biol Chem
271:17656-17665[Abstract/Free Full Text].
-
Whiting P,
Lindstrom J
(1988)
Characterization of bovine and human neuronal nicotinic acetylcholine receptors using monoclonal antibodies.
J Neurosci
8:3395-3404[Abstract].
-
Whiting PJ,
Schoepfer R,
Conroy WG,
Gore MJ,
Keyser KT,
Shimasaki S,
Esch F,
Lindstrom JM
(1991)
Expression of nicotinic acetylcholine receptor subtypes in brain and retina.
Mol Brain Res
10:61-70[Medline].
-
Wong ET,
Holstad SG,
Mennerick SJ,
Hong SE,
Zorumski CF,
Isenberg KE
(1995)
Pharmacological and physiological properties of a putative ganglionic nicotinic receptor, alpha 3 beta 4, expressed in transfected eucaryotic cells.
Mol Brain Res
28:101-109[Medline].
-
Wonnacott S
(1997)
Presynaptic nicotinic ACh receptors.
Trends Neurosci
20:92-98[Web of Science][Medline].
This article has been cited by other articles:
|
|
|
|
 
T.-Y. Wu, C. M. Smith, S. M. Sine, and M. M. Levandoski
Morantel Allosterically Enhances Channel Gating of Neuronal Nicotinic Acetylcholine {alpha}3{beta}2 Receptors
Mol. Pharmacol.,
August 1, 2008;
74(2):
466 - 475.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Mamede, K. Ishizu, M. Ueda, T. Mukai, Y. Iida, H. Kawashima, H. Fukuyama, K. Togashi, and H. Saji
Temporal Change in Human Nicotinic Acetylcholine Receptor After Smoking Cessation: 5IA SPECT Study
J. Nucl. Med.,
November 1, 2007;
48(11):
1829 - 1835.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Xu, W. Yang, G. Zhang, Q. Gu, and L.-Y. Lee
Calcium transient evoked by nicotine in isolated rat vagal pulmonary sensory neurons
Am J Physiol Lung Cell Mol Physiol,
January 1, 2007;
292(1):
L54 - L61.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Wu, Q. Liu, K. Yu, J. Hu, Y.-P. Kuo, M. Segerberg, P. A. St John, and R. J. Lukas
Roles of nicotinic acetylcholine receptor {beta} subunits in function of human {alpha}4-containing nicotinic receptors
J. Physiol.,
October 1, 2006;
576(1):
103 - 118.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Xiao, H. Fan, J. L. Musachio, Z.-L. Wei, S. K. Chellappan, A. P. Kozikowski, and K. J. Kellar
Sazetidine-A, A Novel Ligand That Desensitizes {alpha}4beta2 Nicotinic Acetylcholine Receptors without Activating Them
Mol. Pharmacol.,
October 1, 2006;
70(4):
1454 - 1460.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Hu, K. Lindenberger, G. Hu, H. Wang, R. J. Lukas, and J. Wu
Iptakalim as a Human Nicotinic Acetylcholine Receptor Antagonist
J. Pharmacol. Exp. Ther.,
February 1, 2006;
316(2):
914 - 925.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. S. Gutkin, S. Dehaene, and J.-P. Changeux
A neurocomputational hypothesis for nicotine addiction
PNAS,
January 24, 2006;
103(4):
1106 - 1111.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Fonck, B. N. Cohen, R. Nashmi, P. Whiteaker, D. A. Wagenaar, N. Rodrigues-Pinguet, P. Deshpande, S. McKinney, S. Kwoh, J. Munoz, et al.
Novel Seizure Phenotype and Sleep Disruptions in Knock-In Mice with Hypersensitive {alpha}4* Nicotinic Receptors
J. Neurosci.,
December 7, 2005;
25(49):
11396 - 11411.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. C Klein and J. L Yakel
Paired-pulse potentiation of {alpha}7-containing nAChRs in rat hippocampal CA1 stratum radiatum interneurones
J. Physiol.,
November 1, 2005;
568(3):
881 - 889.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. A. Davis, J. R. James, S. J. Siegel, and T. J. Gould
Withdrawal from Chronic Nicotine Administration Impairs Contextual Fear Conditioning in C57BL/6 Mice
J. Neurosci.,
September 21, 2005;
25(38):
8708 - 8713.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y.-P. Kuo, L. Xu, J. B. Eaton, L. Zhao, J. Wu, and R. J. Lukas
Roles for Nicotinic Acetylcholine Receptor Subunit Large Cytoplasmic Loop Sequences in Receptor Expression and Function
J. Pharmacol. Exp. Ther.,
July 1, 2005;
314(1):
455 - 466.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. E. Gomez-Casati, P. A Fuchs, A. B. Elgoyhen, and E. Katz
Biophysical and pharmacological characterization of nicotinic cholinergic receptors in rat cochlear inner hair cells
J. Physiol.,
July 1, 2005;
566(1):
103 - 118.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Alkondon and E. X. Albuquerque
Nicotinic Receptor Subtypes in Rat Hippocampal Slices Are Differentially Sensitive to Desensitization and Early in Vivo Functional Up-Regulation by Nicotine and to Block by Bupropion
J. Pharmacol. Exp. Ther.,
May 1, 2005;
313(2):
740 - 750.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C.-H. Cho, W. Song, K. Leitzell, E. Teo, A. D. Meleth, M. W. Quick, and R. A. J. Lester
Rapid Upregulation of {alpha}7 Nicotinic Acetylcholine Receptors by Tyrosine Dephosphorylation
J. Neurosci.,
April 6, 2005;
25(14):
3712 - 3723.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Tsuneki, Y. You, N. Toyooka, S. Kagawa, S. Kobayashi, T. Sasaoka, H. Nemoto, I. Kimura, and J. A. Dani
Alkaloids Indolizidine 235B', Quinolizidine 1-epi-207I, and the Tricyclic 205B are Potent and Selective Noncompetitive Inhibitors of Nicotinic Acetylcholine Receptors
Mol. Pharmacol.,
October 1, 2004;
66(4):
1061 - 1069.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Y. Lopez-Hernandez, J. Sanchez-Padilla, A. Ortiz-Acevedo, J. Lizardi-Ortiz, J. Salas-Vincenty, L. V. Rojas, and J. A. Lasalde-Dominicci
Nicotine-induced Up-regulation and Desensitization of {alpha}4{beta}2 Neuronal Nicotinic Receptors Depend on Subunit Ratio
J. Biol. Chem.,
September 3, 2004;
279(36):
38007 - 38015.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Abdrakhmanova, L. Cleemann, J. Lindstrom, and M. Morad
Differential Modulation of {beta}2 and {beta}4 Subunits of Human Neuronal Nicotinic Acetylcholine Receptors by Acidification
Mol. Pharmacol.,
August 1, 2004;
66(2):
347 - 355.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. L. Parker, Y. Fu, K. McAllen, J. Luo, J. M. McIntosh, J. M. Lindstrom, and B. M. Sharp
Up-Regulation of Brain Nicotinic Acetylcholine Receptors in the Rat during Long-Term Self-Administration of Nicotine: Disproportionate Increase of the {alpha}6 Subunit
Mol. Pharmacol.,
March 1, 2004;
65(3):
611 - 622.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Metherate
Nicotinic Acetylcholine Receptors in Sensory Cortex
Learn. Mem.,
January 1, 2004;
11(1):
50 - 59.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. I. Pidoplichko, J. Noguchi, O. O. Areola, Y. Liang, J. Peterson, T. Zhang, and J. A. Dani
Nicotinic Cholinergic Synaptic Mechanisms in the Ventral Tegmental Area Contribute to Nicotine Addiction
Learn. Mem.,
January 1, 2004;
11(1):
60 - 69.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K G Paradiso and J. H. Steinbach
Nicotine is highly effective at producing desensitization of rat {alpha}4{beta}2 neuronal nicotinic receptors
J. Physiol.,
December 15, 2003;
553(3):
857 - 871.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. B. Eaton, J.-H. Peng, K. M. Schroeder, A. A. George, J. D. Fryer, C. Krishnan, L. Buhlman, Y.-P. Kuo, O. Steinlein, and R. J. Lukas
Characterization of Human {alpha}4{beta}2-Nicotinic Acetylcholine Receptors Stably and Heterologously Expressed in Native Nicotinic Receptor-Null SH-EP1 Human Epithelial Cells
Mol. Pharmacol.,
December 1, 2003;
64(6):
1283 - 1294.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. Khiroug, R. Giniatullin, R. C. Klein, D. Fayuk, and J. L. Yakel
Functional Mapping and Ca2+ Regulation of Nicotinic Acetylcholine Receptor Channels in Rat Hippocampal CA1 Neurons
J. Neurosci.,
October 8, 2003;
23(27):
9024 - 9031.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. R. A. Wooltorton, V. I. Pidoplichko, R. S. Broide, and J. A. Dani
Differential Desensitization and Distribution of Nicotinic Acetylcholine Receptor Subtypes in Midbrain Dopamine Areas
J. Neurosci.,
April 15, 2003;
23(8):
3176 - 3185.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. W. Fitch, Y. Xiao, K. J. Kellar, and J. W. Daly
Membrane potential fluorescence: A rapid and highly sensitive assay for nicotinic receptor channel function
PNAS,
April 15, 2003;
100(8):
4909 - 4914.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. L. Gentry, L. H. Wilkins Jr., and R. J. Lukas
Effects of Prolonged Nicotinic Ligand Exposure on Function of Heterologously Expressed, Human alpha 4beta 2- and alpha 4beta 4-Nicotinic Acetylcholine Receptors
J. Pharmacol. Exp. Ther.,
January 1, 2003;
304(1):
206 - 216.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. J. Middlebrook, C. Martina, Y. Chang, R. J. Lukas, and D. DeLuca
Effects of Nicotine Exposure on T Cell Development in Fetal Thymus Organ Culture: Arrest of T Cell Maturation
J. Immunol.,
September 15, 2002;
169(6):
2915 - 2924.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Rush, A. Kuryatov, M. E. Nelson, and J. Lindstrom
First and Second Transmembrane Segments of alpha 3, alpha 4, beta 2, and beta 4 Nicotinic Acetylcholine Receptor Subunits Influence the Efficacy and Potency of Nicotine
Mol. Pharmacol.,
June 1, 2002;
61(6):
1416 - 1422.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. S. Broide, R. Salas, D. Ji, R. Paylor, J. W. Patrick, J. A. Dani, and M. De Biasi
Increased Sensitivity to Nicotine-Induced Seizures in Mice Expressing the L250T alpha 7 Nicotinic Acetylcholine Receptor Mutation
Mol. Pharmacol.,
March 1, 2002;
61(3):
695 - 705.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Abdrakhmanova, J. Dorfman, Y. Xiao, and M. Morad
Protons Enhance the Gating Kinetics of the alpha 3/beta 4 Neuronal Nicotinic Acetylcholine Receptor by Increasing Its Apparent Affinity to Agonists
Mol. Pharmacol.,
February 1, 2002;
61(2):
369 - 378.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Fabian-Fine, P. Skehel, M. L. Errington, H. A. Davies, E. Sher, M. G. Stewart, and A. Fine
Ultrastructural Distribution of the {alpha}7 Nicotinic Acetylcholine Receptor Subunit in Rat Hippocampus
J. Neurosci.,
October 15, 2001;
21(20):
7993 - 8003.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. R. Genzen, W. Van Cleve, and D. S. McGehee
Dorsal Root Ganglion Neurons Express Multiple Nicotinic Acetylcholine Receptor Subtypes
J Neurophysiol,
October 1, 2001;
86(4):
1773 - 1782.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. L. Meyer, Y. Xiao, and K. J. Kellar
Agonist Regulation of Rat alpha 3beta 4 Nicotinic Acetylcholine Receptors Stably Expressed in Human Embryonic Kidney 293 Cells
Mol. Pharmacol.,
September 1, 2001;
60(3):
568 - 576.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. Buisson and D. Bertrand
Chronic Exposure to Nicotine Upregulates the Human {alpha}4{beta}2 Nicotinic Acetylcholine Receptor Function
J. Neurosci.,
March 15, 2001;
21(6):
1819 - 1829.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Narahashi, C. P. Fenster, M. W. Quick, R. A. J. Lester, W. Marszalec, G. L. Aistrup, D. B. Sattelle, B. R. Martin, and E. D. Levin
Symposium Overview: Mechanism of Action of Nicotine on Neuronal Acetylcholine Receptors, from Molecule to Behavior
Toxicol. Sci.,
October 1, 2000;
57(2):
193 - 202.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. A. Ross, J. Y. F. Wong, J. J. Clifford, A. Kinsella, J. S. Massalas, M. K. Horne, I. E. Scheffer, I. Kola, J. L. Waddington, S. F. Berkovic, et al.
Phenotypic Characterization of an alpha 4 Neuronal Nicotinic Acetylcholine Receptor Subunit Knock-Out Mouse
J. Neurosci.,
September 1, 2000;
20(17):
6431 - 6441.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. B. Aramakis, C. Y. Hsieh, F. M. Leslie, and R. Metherate
A Critical Period for Nicotine-Induced Disruption of Synaptic Development in Rat Auditory Cortex
J. Neurosci.,
August 15, 2000;
20(16):
6106 - 6116.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Narahashi
Neuroreceptors and Ion Channels as the Basis for Drug Action: Past, Present, and Future
J. Pharmacol. Exp. Ther.,
July 1, 2000;
294(1):
1 - 26.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
M. M. Francis, R. W. Vazquez, R. L. Papke, and R. E. Oswald
Subtype-Selective Inhibition of Neuronal Nicotinic Acetylcholine Receptors by Cocaine Is Determined by the alpha 4 and beta 4 Subunits
Mol. Pharmacol.,
July 1, 2000;
58(1):
109 - 119.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
S. Zia, A. Ndoye, T. X. Lee, R. J. Webber, and S. A. Grando
Receptor-Mediated Inhibition of Keratinocyte Migration by Nicotine Involves Modulations of Calcium Influx and Intracellular Concentration
J. Pharmacol. Exp. Ther.,
June 1, 2000;
293(3):
973 - 981.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
Y. Lu, M. J. Marks, and A. C. Collins
Desensitization of Nicotinic Agonist-Induced [3H]gamma -Aminobutyric Acid Release from Mouse Brain Synaptosomes Is Produced by Subactivating Concentrations of Agonists
J. Pharmacol. Exp. Ther.,
December 1, 1999;
291(3):
1127 - 1134.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
O. Salminen, T. Seppa, H. Gaddnas, and L. Ahtee
The Effects of Acute Nicotine on the Metabolism of Dopamine and the Expression of Fos Protein in Striatal and Limbic Brain Areas of Rats during Chronic Nicotine Infusion and Its Withdrawal
J. Neurosci.,
September 15, 1999;
19(18):
8145 - 8151.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Q.-S. Liu and D. K. Berg
Extracellular Calcium Regulates Responses of Both alpha 3- and alpha 7-Containing Nicotinic Receptors on Chick Ciliary Ganglion Neurons
J Neurophysiol,
September 1, 1999;
82(3):
1124 - 1132.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. P. Fenster, T. L. Whitworth, E. B. Sheffield, M. W. Quick, and R. A. J. Lester
Upregulation of Surface alpha 4beta 2 Nicotinic Receptors Is Initiated by Receptor Desensitization after Chronic Exposure to Nicotine
J. Neurosci.,
June 15, 1999;
19(12):
4804 - 4814.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. C. Perry, M. I. Dávila-García, C. A. Stockmeier, and K. J. Kellar
Increased Nicotinic Receptors in Brains from Smokers: Membrane Binding and Autoradiography Studies
J. Pharmacol. Exp. Ther.,
June 1, 1999;
289(3):
1545 - 1552.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
J. Zhang, Y. Xiao, G. Abdrakhmanova, W. Wang, L. Cleemann, K.J. Kellar, and M. Morad
Activation and Ca2+ Permeation of Stably Transfected alpha 3/beta 4 Neuronal Nicotinic Acetylcholine Receptor
Mol. Pharmacol.,
June 1, 1999;
55(6):
970 - 981.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
A. R. McQuiston and D. V. Madison
Nicotinic Receptor Activation Excites Distinct Subtypes of Interneurons in the Rat Hippocampus
J. Neurosci.,
April 15, 1999;
19(8):
2887 - 2896.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. D. Milner and L. T. Landmesser
Cholinergic and GABAergic Inputs Drive Patterned Spontaneous Motoneuron Activity before Target Contact
J. Neurosci.,
April 15, 1999;
19(8):
3007 - 3022.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. P. Fenster, M. L. Beckman, J. C. Parker, E. B. Sheffield, T. L. Whitworth, M. W. Quick, and R. A. J. Lester
Regulation of alpha 4beta 2 Nicotinic Receptor Desensitization by Calcium and Protein Kinase C
Mol. Pharmacol.,
March 1, 1999;
55(3):
432 - 443.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
A. M. Aragay and M. W. Quick
Functional Regulation of Galpha 16 by Protein Kinase C
J. Biol. Chem.,
February 19, 1999;
274(8):
4807 - 4815.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. K. Mahata, M. Mahata, R. J. Parmer, and D. T. O'Connor
Desensitization of Catecholamine Release. THE NOVEL CATECHOLAMINE RELEASE-INHIBITORY PEPTIDE CATESTATIN (CHROMOGRANIN A344-364) ACTS AT THE RECEPTOR TO PREVENT NICOTINIC CHOLINERGIC TOLERANCE
J. Biol. Chem.,
January 29, 1999;
274(5):
2920 - 2928.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. L. Aistrup, W. Marszalec, and T. Narahashi
Ethanol Modulation of Nicotinic Acetylcholine Receptor Currents in Cultured Cortical Neurons
Mol. Pharmacol.,
January 1, 1999;
55(1):
39 - 49.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
K. Sabey, K. Paradiso, J. Zhang, and J. H. Steinbach
Ligand Binding and Activation of Rat Nicotinic alpha 4beta 2 Receptors Stably Expressed in HEK293 Cells
Mol. Pharmacol.,
January 1, 1999;
55(1):
58 - 66.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
V. Gerzanich, F. Wang, A. Kuryatov, and J. Lindstrom
alpha 5 Subunit Alters Desensitization, Pharmacology, Ca++ Permeability and Ca++ Modulation of Human Neuronal alpha 3 Nicotinic Receptors
J. Pharmacol. Exp. Ther.,
July 1, 1998;
286(1):
311 - 320.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
M. Zoli, C. Lena, M. R. Picciotto, and J.-P. Changeux
Identification of Four Classes of Brain Nicotinic Receptors Using beta 2 Mutant Mice
J. Neurosci.,
June 15, 1998;
18(12):
4461 - 4472.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Eddins, L. K. Lyford, J. W. Lee, S. A. Desai, and R. L. Rosenberg
Permeant but not impermeant divalent cations enhance activation of nondesensitizing alpha 7 nicotinic receptors
Am J Physiol Cell Physiol,
April 1, 2002;
282(4):
C796 - C804.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
