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The Journal of Neuroscience, 2001, 21:RC144:1-5

RAPID COMMUNICATION
Enhancement by T-Type Ca²⁺ Currents of Odor Sensitivity in Olfactory Receptor Cells

Fusao Kawai and Ei-ichi Miyachi

Department of Physiology, School of Medicine, Fujita Health University, Toyoake, Aichi, 470-1192, Japan

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Mechanisms underlying action potential initiation in olfactory receptor cells (ORCs) during odor stimulation were investigated using conventional and dynamic patch-clamp recording techniques. Under current-clamp conditions, action potentials generated by a least effective odor-induced depolarization were almost completely blocked by 0.1 mM Ni²⁺, a T-type Ca²⁺ channel blocker, but not by 0.1 mM Cd²⁺, a high voltage-activated Ca²⁺ channel blocker. Under voltage-clamp conditions, depolarizing voltage steps induced a fast transient inward current, which consisted of Na⁺ (I_Na) and T-type Ca²⁺ (I_Ca,T) currents. The amplitude of I_Ca,T was approximately one-fourth of that of I_Na (0.23 ± 0.03, mean ± SEM). Because both I_Na and I_Ca,T are known to show rapid inactivation, we examined how much I_Na and I_Ca,T are activated during the gradually depolarizing initial phase of receptor potentials. The ratio of I_Ca,T/I_Na during a ramp depolarization at the slope of 0.5 mV/msec was 0.56 ± 0.03. Using the dynamic patch-clamp recording technique, we also recorded I_Ca,T and I_Na during the generation of odor-induced action potentials. This ratio of I_Ca,T/I_Na was 0.54 ± 0.04. These ratios were more than twice as large as that (0.23) obtained from the experiment using voltage steps, suggesting that I_Ca,T carries significant amount of current to generate the action potentials. We conclude that I_Ca,T contributes to enhance odor sensitivity by lowering the threshold of spike generation in ORCs.

Key words: odorant; amyl acetate; odor response; T-type Ca²⁺ channel; newt; action potential; patch clamp

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

The initial step in olfactory sensation involves the binding of odorant molecules to specific receptor proteins on the ciliary surface of olfactory receptor cells (ORCs). Odorant receptors coupled to G-proteins activate adenylyl cyclase leading to the generation of cAMP, which directly gates a cyclic nucleotide-gated cationic channel in the ciliary membrane (Bakalyar and Reed, 1991; Breer and Boekhoff, 1992; Firestein, 1992; Reed, 1992; Ronnett and Snyder, 1992; Kurahashi and Yau, 1994; Restrepo et al., 1996). This initial excitation causes a slow and graded depolarizing voltage change, which is encoded into a train of action potentials that travels to the higher olfactory center (Trotier and MacLeod, 1983; Trotier, 1986; Kurahashi, 1989; Pun and Gesteland, 1991).

Action potentials of ORCs are known to be generated by voltage-gated Na⁺ currents (catfish, Miyamoto et al., 1992; coho salmon, Nevitt and Moody, 1992; Xenopus, Schild, 1989; tiger salamander, Firestein and Werblin, 1987; Dubin and Dionne, 1994; newt, Kawai et al., 1996; rat, Trombley and Westbrook, 1991) and T-type Ca²⁺ currents (newt, Kawai et al., 1996). In this last study, we showed that T-type Ca²⁺ currents (I_Ca,T) lowered the threshold of action potentials induced by injection of current steps into newt ORCs, which have lost their cilia during the dissociation procedure (Kawai et al., 1996). It is unclear, however, whether I_Ca,T lowers the threshold of action potentials induced by odor stimuli in intact ORCs and how I_Ca,T regulates odor sensitivity of ORCs. To test these, we examined the effects of voltage-gated Ca²⁺ channel blockers on action potentials of ORCs induced by puffer application of the odorant amyl acetate using the whole-cell patch-clamp recordings. We found that I_Ca,T lowers the threshold of the odor-induced action potentials in intact ORCs.

Furthermore, to investigate mechanisms underlying action potentials evoked by odor stimuli, first we recorded voltage-gated Na⁺ currents (I_Na) and I_Ca,T activated by depolarizing voltage steps under voltage-clamp conditions. Because it is known that both I_Na and I_Ca,T show inactivation during graded depolarizations (Hodgkin and Huxley, 1952; Nowycky et al., 1985; Tsien et al., 1988; Kaneko et al., 1989), we examined how much I_Na and I_Ca,T are activated during a ramp depolarization, of which the slope is similar to that of the odor-induced depolarization. In addition, using the dynamic patch-clamp recording techniques, we also recorded I_Ca,T and I_Na during the generation of odor-induced action potentials and compared their ratio. We found that I_Ca,T carries a significant amount of current to generate action potentials in ORCs during odor stimuli.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Preparation and recording procedures. ORCs were dissociated enzymatically from the olfactory epithelium of the newt Cynops pyrrhogaster, as reported (Kawai et al., 1996). Isolated cells were viewed on an Olympus upright microscope with differential interference contrast optics (40× water-immersion objective). Membrane voltages and currents were recorded in the whole-cell configuration (Hamill et al., 1981) using a patch-clamp amplifier (Axopatch 200B; Axon Instruments, Foster City, CA) linked to a computer. Recording procedures were controlled by pClamp software (Axon Instruments). Data were low-pass-filtered (four-pole Bessel type) with a cutoff frequency of 5 kHz and then digitized at 10 kHz by an analog-to-digital interface. All experiments were done at room temperature (23-25°C).

Solutions and odorant stimuli. The recording pipette was filled with pseudointracellular (K⁺) solution (in mM): 119 KCl, 1 CaCl₂, 5 EGTA, and 10 HEPES (pH adjusted to 7.4 with KOH) or Cs⁺ solution: 119 CsCl, 1 CaCl₂, 5 EGTA, and 10 HEPES (pH adjusted to 7.4 with CsOH). The resistance of the pipette was ~6 M. The control bath solution used to record voltage responses and the odorant-induced currents contained (in mM): 110 NaCl, 3.7 KCl, 3 CaCl₂, 2 HEPES, and 15 glucose, the solution used to record I_Na contained 110 NaCl, 3.7 KCl, 3 CoCl₂, 2 HEPES, and 15 glucose, and the solution for I_Ca,T contained 110 choline-Cl, 3.7 KCl, 3 CaCl₂, 0.1 CdCl₂, 2 HEPES, and 15 glucose. CdCl₂ (0.1 mM) was added to the bath to block L-type Ca²⁺ currents selectively. For odorant stimuli, amyl acetate (100 µ mM) was dissolved in the control bath solution, included into a puffer pipette, and applied from a pressure ejection system.

	RESULTS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

I_Ca,T enhances odor sensitivity by lowering the threshold of spike generation in ORCs

We examined whether I_Ca,T lowers the threshold of action potentials induced by odor stimuli in intact ORCs with cilia attached. To test this, we recorded action potentials generated by a least effective odor-induced depolarization. An example is shown in Figure 1. Isolated newt ORCs had a resting potential of 73 ± 3 mV (mean ± SEM; n = 34). When 0.1 mM amyl acetate was applied to an ORC for 50 msec from a puffer pipette in control Ringer's solution, a single action potential was generated (Fig. 1A, thin line). Addition of 0.1 mM Ni²⁺, a T-type Ca²⁺ channel blocker, to the bath blocked the action potential (Fig. 1A, thick line), and this effect was reversible (Fig. 1B), suggesting that I_Ca,T may be involved in spike generation. If 0.1 mM amyl acetate was applied for longer (75 msec) under this condition, an action potential reappeared (Fig. 1C,D). Similar results were obtained in nine cells. These suggest that I_Ca,T may enhance odor sensitivity by lowering the threshold of spike generation in ORCs. In contrast, addition of 0.1 mM Cd²⁺, a high voltage-activated (HVA) Ca²⁺ channel blocker, failed to block the action potential (data not shown), indicating that HVA Ca²⁺ currents are not involved in spike generation.

View larger version (18K): [in this window] [in a new window]   Figure 1.   Contribution of ICa,T to action potentials of an isolated ORC evoked by the odorant amyl acetate. A, Response to near threshold depolarization induced by puffer application of 0.1 mM amyl acetate for 50 msec in control (thin line) and after addition of 0.1 mM Ni2+, a T-type Ca2+ channel blocker (thick line). Recording pipette was filled with K+ solution. Timing of odorant stimulation is indicated by the upward deflection shown below the voltage traces. B, Response to near threshold depolarization induced by 50 msec amyl acetate puff after washout of Ni2+. C, Response of the same ORC as in A to depolarization induced by puffer application of 0.1 mM amyl acetate for 75 msec in control (thin line) and after addition of 0.1 mM Ni2+ (thick line). D, Response to 75 msec amyl acetate puff after washout of Ni2+.

To elucidate mechanisms underlying spike generation in ORCs, we examined the effects of 0.1 mM Ni²⁺ on I_Ca,T and I_Na under voltage-clamp conditions. In control conditions, membrane depolarization to 40 mV from a holding potential (V_h) of 100 mV induced I_Ca,T of approximately 60 pA (Fig. 2A). Addition of 0.1 mM Ni²⁺ to the bath decreased the peak amplitude of I_Ca,T by 71 ± 6% (n = 7; Fig. 2A, thick line). The reduction of the I_Ca,T amplitude was observed over the entire voltage range tested (Fig. 2B). In contrast, 0.1 mM Ni²⁺ did not change I_Na significantly (Fig. 2C). To exclude the possibility that Ni²⁺ may affect directly cyclic nucleotide-gated (CNG) cationic channels in olfactory cilia, we also tested the effects of Ni²⁺ on the odorant-induced currents. However, 0.1 mM Ni²⁺ did not change significantly the current induced by puffer application of 0.1 mM amyl acetate (Fig. 2D). These results suggest that the inhibition by Ni²⁺ of spike generation shown in Figure 1A is caused by blockage of I_Ca,T rather than blockage of I_Na or the CNG currents.

View larger version (20K): [in this window] [in a new window]   Figure 2.   Blockage by Ni2+ of ICa,T in ORCs. A, ICa,T induced by a depolarizing voltage step to 40 mV from a Vh of 100 mV in a control solution (thin line) and the solution containing 0.1 mM Ni2+, a T-type Ca2+ channel blocker (thick line). Currents were recorded using pipettes filled with the Cs+ solution. The bath solution contained (in mM): 110 choline-Cl, 3.7 KCl, 3 CaCl2, 0.1 CdCl2, 2 HEPES, and 15 glucose. CdCl2 (0.1 mM) was added to the bath to block L-type Ca2+ currents selectively. B, I-V relation of the cell shown in A in the control solution (filled circles) and the solution containing 0.1 mM Ni2+ (filled triangles). C, INa induced by depolarization to 40 mV from a Vh of 100 mV in a control solution (thin line) and the solution containing 0.1 mM Ni2+ (thick line). Recording pipette was filled with Cs+ solution. The bath solution contained (in mM): 110 NaCl, 3.7 KCl, 3 CoCl2, 2 HEPES, and 15 glucose. CoCl2 (3 mM) was added to the bath to block voltage-gated Ca2+ currents. D, Odorant-induced currents recorded from an ORC at a Vh of 70 mV in a control Ringer's solution (thin line) and the solution containing 0.1 mM Ni2+ (thick line). Timing of 0.1 M amyl acetate puff for 50 msec is indicated by the upward deflection shown below the current traces.

A ratio of I_Ca,T amplitude to I_Na amplitude during the generation of action potentials

Under voltage-clamp conditions, the peak amplitude of I_Ca,T induced by a depolarizing voltage step to 30 mV from a V_h of 70 mV, which is near the resting potential of ORCs, was approximately one-fourth of I_Na (0.23 ± 0.03; n = 8; Fig. 3A). I_Ca,T began to be activated at 60 mV and was maximal at 40 mV, whereas I_Na began at 50 mV and was maximal at 30 mV (Fig. 3B). Figure 3C shows activation curves of I_Ca,T and I_Na. The relation between I_Ca,T (filled squares) and membrane voltage was fitted by a single Boltzmann function. The half-activation voltage of I_Ca,T was 45 mV. The activation curve of I_Na (filled circles) was also fitted by a single Boltzmann function with a half-activation voltage of 35 mV. This value is 10 mV more positive than that of I_Ca,T.

View larger version (23K): [in this window] [in a new window]   Figure 3.   Comparison of ICa,T and INa. A, ICa,T (thick line) and INa (thin line) induced by depolarization to 30 mV from a Vh of 70 mV. Each current-response was recorded from the same ORC. Recording pipette was filled with Cs+ solution. The bath solution used to record INa contained (in mM): 110 NaCl, 3.7 KCl, 3 CoCl2, 2 HEPES, and 15 glucose, and the solution for ICa,T contained 110 choline-Cl, 3.7 KCl, 3 CaCl2, 0.1 CdCl2, 2 HEPES, and 15 glucose. B, I-V relation of the cell shown in A. Peak amplitude of ICa,T (filled squares) and INa (filled circles) was plotted against the voltage. C, Activation curves of ICa,T (filled squares) and INa (filled circles) recorded at a Vh of 100 mV. Symbols represent mean of eight cells, and vertical bars represent SEM. Lines represent a single Boltzmann function obtained by the least-squares nonlinear fit to the data. D, ICa,T (thick line) and INa (thin line) induced by ramp depolarization to 20 mV from a Vh of 70 mV at the rate of 0.5 mV/msec. Each current-response was recorded from the same ORC.

As shown in Figure 1, puffer application of amyl acetate to ORCs induces a gradually depolarizing receptor potential. Because it is known that both I_Na and I_Ca,T show inactivation during graded depolarizations (Hodgkin and Huxley, 1952; Nowycky et al., 1985; Tsien et al., 1988; Kaneko et al., 1989), next we examined how much I_Na and I_Ca,T are activated during a ramp depolarization, of which the slope is similar to that of the odor-induced graded depolarization. Depolarizing voltage ramp at the slope of 0.5 mV/msec activated I_Ca,T (Fig. 3D, thick line) earlier than I_Na (thin line); I_Ca,T started at ~35 msec (arrow in the figure), whereas I_Na started at ~45 msec. This result suggests that I_Ca,T contributes to membrane depolarization initially. The peak amplitude of I_Ca,T was 33 pA and that of I_Na was 58 pA (I_Ca,T/I_Na ratio, 0.57). A similar ratio (0.56 ± 0.03, mean ± SEM) was obtained in six cells. This ratio was more than twice as large as the ratio (0.23) obtained by depolarizing voltage steps. The difference was caused by significantly smaller I_Na during the ramp depolarization than the step depolarization (Fig. 3A,D).

Furthermore, using the dynamic patch-clamp recording techniques, we also recorded I_Ca,T and I_Na during the action potentials induced by puffer application of amyl acetate and compared the I_Ca,T/I_Na ratio. The waveform of the action potential, which was shown in Figure 1A (thin line), was used as a command voltage for the voltage-clamp recordings. This command voltage also activated I_Ca,T (Fig. 4, thick line) earlier than I_Na (thin line). The peak amplitude of I_Ca,T was 46 pA, and that of I_Na was 84 pA (I_Ca,T/I_Na ratio, 0.55). A similar ratio (0.54 ± 0.04, mean ± SEM) was obtained in six cells. This ratio was also significantly larger than the ratio (0.23 ± 0.03) obtained by depolarizing voltage steps. These results suggest that I_Ca,T carries a significant amount of charge to depolarize the membrane potential during odor stimuli.

View larger version (18K): [in this window] [in a new window]   Figure 4.   ICa,T and INa induced by depolarization using a waveform of the odorant-induced action potentials under voltage-clamp conditions. The waveform of the action potential shown in Figure 1A (thin line) was used as a command voltage. ICa,T (thick line) and INa (thin line) were recorded from the same ORC at a Vh of 70 mV and are shown at the faster time scale. The waveform of the command voltage was shown below the current traces.

	DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

Effects of I_Ca,T on action potentials induced by odor stimuli

In various preparations, I_Ca,T is known to be involved in the generation of action potentials. Hagiwara et al. (1988) reported that Ni²⁺ prolonged the pacemaker depolarization of rabbit sinoatrial node cells by blocking I_Ca,T. A similar contribution of I_Ca,T to spike generation is also reported in inferior olivary neurons (Llinas and Yarom, 1981). In this last study, we showed that I_Ca,T lowered the threshold of action potentials induced by injection of current steps into ORCs (Kawai et al., 1996). It was not clear, however, whether I_Ca,T lowers the threshold of action potentials induced by odor stimuli.

All the data we obtained in the present study suggest that I_Ca,T has a role of enhancing the sensitivity to odorants by lowering the threshold of action potentials. (1) Under voltage-clamp conditions, addition of 0.1 mM Ni²⁺ to the bath decreased the peak amplitude of I_Ca,T by 71 ± 6% but did not change significantly I_Na or the odorant-induced current. These suggest that the inhibition by Ni²⁺ of action potentials evoked by a least effective odor stimulation (Fig. 1A) is caused by blockage of I_Ca,T rather than blockage of I_Na or the CNG currents. Divalent cations in the bath are known to decrease the CNG currents in ORCs (Zufall and Firestein, 1993; Frings et al., 1995; Kleene, 1999; Gavazzo et al., 2000). In the present experiment, however, 0.1 mM Ni²⁺ did not change significantly the CNG currents, probably because 3 mM Ca²⁺ was always added to the bath, when the CNG currents were recorded. (2) The half-activation voltage of I_Ca,T is 10 mV more negative than that of I_Na, indicating that I_Ca,T is more important for spike generation than I_Na near threshold. Indeed, an action potential generated by a least effective odor-induced depolarization was blocked by 0.1 mM Ni²⁺. In contrast, when the odorant was applied for a longer time in the bath containing 0.1 mM Ni²⁺, an action potential reappeared (Fig. 1C). This is probably caused by I_Na activated directly by a more depolarizing odorant-induced receptor potential. From these observations we conclude that I_Ca,T contributes to enhance odor sensitivity by lowering the threshold of spike generation in ORCs

In addition, I_Ca,T in newt ORCs may also contribute to make the olfactory sensation robust. Regardless of changes in the external environment, ionic concentrations of the mammalian extracellular solution are known to be fairly invariable. In contrast, it is known that ionic concentrations of the fish and amphibian extracellular solution change as the external environment changes. A decrease in the extracellular Na⁺ concentration would reduce the inward current to generate action potentials in ORCs, if Na⁺ was the sole current carrier. When a Ca²⁺ component through T-type Ca²⁺ channels is present, however, such a reduction in I_Na would be compensated by I_Ca,T, thus maintaining the effectiveness of the mechanism to generate action potentials. Another mechanism of compensation for environmental changes is reported in olfactory cilia (Kurahashi and Yau, 1994). They showed that a Ca²⁺-activated Cl current in olfactory cilia would compensate changes in inward currents through CNG cationic channels.

Comparison of I_Ca,T and I_Na for the role of spike generation

In a voltage-clamp experiment using depolarizing voltage steps, the maximum I_Ca,T was 45 pA, whereas that of I_Na was 190 pA, giving an I_Ca,T/I_Na ratio of 0.24. By contrast, the amplitude of I_Ca,T during the ramp depolarization was 33 pA, and that of I_Na was 58 pA, giving an I_Ca,T/I_Na ratio of 0.57. A similar ratio (0.54 ± 0.04) was also obtained by the voltage-clamp experiments using the waveform of the odorant-induced action potentials. These results indicate that I_Ca,T contributes to spike generation more than we expected based on data obtained by the experiments using voltage steps. One of the reasons for this difference is that I_Na is more rapidly inactivated by the membrane depolarization than I_Ca,T. In fact, the inactivation kinetics of I_Na in ORCs (time constant = 1-1.5 msec; Trotier, 1986; Firestein and Werblin, 1987; Schild, 1989; Trombley and Westbrook, 1991; Miyamoto et al., 1992; Kawai et al., 1996) is much faster than that of I_Ca,T (time constant = 10-20 msec; Kawai et al., 1996).

I_Ca,T started to flow earlier than I_Na during the ramp depolarization (Fig. 3D), and the odorant-induced depolarization (Fig. 4). These observations are interpreted by a lower activation voltage for I_Ca,T than I_Na. Lower activation voltage and slower inactivation of I_Ca,T than I_Na support that I_Ca,T carries a significant amount of charge to generate action potentials in ORCs.

I_Ca,T in ORCs

In the past, it has been believed that the transient inward current of ORCs contributing to action potential generation is solely carried by Na⁺ (catfish, Miyamoto et al., 1992; coho salmon, Nevitt and Moody, 1992; Xenopus, Schild, 1989; tiger salamander, Firestein and Werblin, 1987; Dubin and Dionne, 1994; rat, Trombley and Westbrook, 1991; Rajendra et al., 1992). The reason why I_Ca,T was not identified in ORCs of other animal species is still obscure, but there are several possibilities. (1) The presence of I_Ca,T may depend on the development or regeneration of ORCs. It is known that the olfactory epithelia undergo regeneration continuously (Firestein, 1992; Reed, 1992; Ronnett and Snyder, 1992; Restrepo et al., 1996). The different observations concerning I_Ca,T may be attributable to different populations of cells under the experimental conditions. In cultured ORCs Ca²⁺-activated K⁺ channel is absent (Trombley and Westbrook, 1991), whereas it has shown to be ubiquitous in adult ORCs (Maue and Dionne, 1987; Kurahashi, 1989; Schild, 1989; Miyamoto et al., 1992). Expression of Ca²⁺-activated K⁺ channel has been shown to be developmentally related in cultured spinal neurons of Xenopus (Blair and Dionne, 1985). (2) Another possibility may be just a simple species difference. However, it is interesting to note that Liman and Corey (1996) have reported that I_Ca,T is expressed in the chemosensory neurons from the mouse vomeronasal organ. Because there are so many identities between principal and accessory ORCs in terms of the expression of ionic channels, this observation raises a possibility that I_Ca,T might be expressed not only in newt ORCs but also in ORCs of other species. Further study would be required to reexamine the presence of I_Ca,T in ORCs from other species.

	FOOTNOTES

Received Jan. 12, 2001; revised Feb. 23, 2001; accepted Feb. 28, 2001.

This work was supported by the Promotion and Mutual Aid Corporation for Private Schools of Japan, Japan Society of the Promotion of Science (Grants 12780620 to F.K. and 11680794 to E.M.), and Takeda Science Foundation. We thank Drs. A. Kaneko and T. Kurahashi for their advice.

Correspondence should be addressed to Dr. Fusao Kawai, Department of Physiology, School of Medicine, Fujita Health University, 1-98 Dengakugakubo, Kutsukakechou, Toyoake, Aichi, 470-1192, Japan. E-mail: fkawai{at}fujita-hu.ac.jp.

This article is published in The Journal of Neuroscience, Rapid Communications Section, which publishes brief, peer-reviewed papers online, not in print. Rapid Communications are posted online approximately one month earlier than they would appear if printed. They are listed in the Table of Contents of the next open issue of JNeurosci. Cite this article as: JNeurosci, 2001, 21:RC144 (1-5). The publication date is the date of posting online at www.jneurosci.org.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS DISCUSSION REFERENCES

• Bakalyar HA, Reed RR (1991) The second messenger cascade in olfactory receptor neurons. Curr Biol 1:204-208.
• Blair LAC, Dionne VD (1985) Development acquisition of Ca²⁺-sensitivity by K⁺ channels in spinal neurons. Nature 315:329-331.
• Breer H, Boekhoff I (1992) Second messenger signalling in olfaction. Curr Biol 2:439-443.
• Dubin AE, Dionne VE (1994) Action potentials and chemosensitive conductances in the dendrites of olfactory neurons suggest new features for odor transduction. J Gen Physiol 103:181-201.
• Firestein S (1992) Electrical signals in olfactory transduction. Curr Biol 2:444-448.
• Firestein S, Werblin FS (1987) Gating currents in isolated olfactory receptor neurons of the larval tiger salamander. Proc Natl Acad Sci USA 88:6292-6296.
• Frings S, Seifert R, Godde M, Kaupp UB (1995) Profoundly different calcium permeation and blockage determine the specific function of distinct cyclic nucleotide-gated channels. Neuron 15:169-179.
• Gavazzo P, Picco C, Eismann E, Kaupp UB, Menini A (2000) A point mutation in the pore region alters gating, Ca²⁺ blockage, and permeation of olfactory cyclic nucleotide-gated channels. J Gen Physiol 116:311-326.
• Hagiwara N, Irisawa H, Kameyama M (1988) Contribution of two types of calcium currents to the pacemaker potentials of rabbit sino-atrial node cells. J Physiol (Lond) 395:233-253.
• Hamill OP, Marty A, Neher E, Sakmann B, Sigworth FJ (1981) Improved patch-clamp techniques for high resolution current recording from cells and cell-free membrane patches. Pflügers Arch 391:85-100.
• Hodgkin AL, Huxley AF (1952) A quantitative description of membrane current and its application to conduction and excitation in nerve. J Physiol (Lond) 117:500-544.
• Kaneko A, Pinto LH, Tachibana M (1989) Transient calcium current of retinal bipolar cells of the mouse. J Physiol (Lond) 410:613-629.
• Kawai F, Kurahashi T, Kaneko A (1996) T-type Ca²⁺ channel lowers the threshold of spike generation in the newt olfactory receptor cell. J Gen Physiol 108:525-535.
• Kleene SJ (1999) Both external and internal calcium reduce the sensitivity of the olfactory cyclic-nucleotide-gated channel to cAMP. J Neurophysiol 81:2675-2682.
• Kurahashi T (1989) Activation by odorants of cation-selective conductance in the olfactory receptor cells isolated from the newt. J Physiol (Lond) 419:177-192.
• Kurahashi T, Yau K-W (1994) Tale of an unusual chloride current. Curr Biol 4:256-258.
• Liman ER, Corey DP (1996) Electrophysiological characterization of chemosensory neurons from the mouse vomeronasal organ. J Neurosci 16:4625-4637.
• Llinas R, Yarom Y (1981) Electrophysiological of mammalian inferior olivary neurons in vitro. different types of voltage-dependent ionic conductances. J Physiol (Lond) 315:549-567.
• Maue RA, Dionne VE (1987) Patch-clamp studies of isolated mouse olfactory receptor neurons. J Gen Physiol 90:95-125.
• Miyamoto T, Restrepo D, Teeter JH (1992) Voltage-dependent and odorant-regulated currents in isolated olfactory receptor neurons of the channel catfish. J Gen Physiol 99:505-530.
• Nevitt GA, Moody WJ (1992) An electrophysiological characterization of ciliated olfactory receptor cells of the coho salmon Oncorhynchus kisutch. J Exp Biol 166:1-17.
• Nowycky MC, Fox AP, Tsien RW (1985) Three types of neuronal calcium channel with different calcium agonist sensitivity. Nature 316:440-443.
• Pun RYK, Gesteland RC (1991) Somatic sodium channels of frog olfactory receptor neurons are inactivated at rest. Pflügers Arch 418:504-511.
• Rajendra S, Lynch JW, Barry PH (1992) An analysis of Na⁺ currents in rat olfactory receptor neurons. Pflügers Arch 420:342-346.
• Reed RR (1992) Signaling pathways in odorant detection. Neuron 8:205-209.
• Restrepo D, Teeter JH, Schild D (1996) Second messenger signaling in olfactory transduction. J Neurobiol 30:37-48.
• Ronnett GV, Snyder SH (1992) Molecular messengers of olfaction. Trends Neurosci 15:508-513.
• Schild D (1989) Whole-cell currents in olfactory receptor cells of Xenopus laevis. Brain Res 78:223-232.
• Trombley PQ, Westbrook GL (1991) Voltage-gated currents in identified rat olfactory receptor neurons. J Neurosci 11:435-444.
• Trotier D (1986) A patch-clamp analysis of membrane currents in salamander olfactory receptor cells. Pflügers Arch 407:589-595.
• Trotier D, MacLeod P (1983) Intracellular recording from salamander olfactory receptor cells. Brain Res 268:225-237.
• Tsien RW, Lipscombe D, Madison DV, Bley KR, Fox AP (1988) Multiple types of neural calcium channels and their selective modulation. Trends Neurosci 11:431-438.
• Zufall F, Firestein S (1993) Divalent cations block the cyclic nucleotide-gated channel of olfactory receptor neurons. J Neurophysiol 69:1758-1768.

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