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The Journal of Neuroscience, July 1, 2002, 22(13):5769-5776
µ-Opioid Receptors: Ligand-Dependent Activation of Potassium Conductance, Desensitization, and Internalization
Veronica A. Alvarez1, *, Seksiri Arttamangkul2, *, Vu Dang1, 2, Abdallah Salem1, 3, Jennifer L. Whistler4, Mark von Zastrow5, David K. Grandy2, and John T. Williams1 1 Vollum Institute and 2 Department of Physiology and Pharmacology, Oregon Health and Sciences University, Portland, Oregon 97201, 3 Department of Clinical and Experimental Pharmacology, Adelaide University, Adelaide SA 5005, Australia, 4 Ernest Gallo Clinic and Research Center, Emeryville, California 94608, and 5 Departments of Psychiatry and Cellular and Molecular Pharmacology, University of California, San Francisco, San Francisco, California 94143
ABSTRACT
TOP
ABSTRACT
INTRODUCTION
µ-Opioid receptor (MOR) desensitization and endocytosis have been implicated in tolerance and dependence to opioids. The efficiency of each process is known to be agonist dependent; however, it is not known what determines the relative efficiency of various agonists at either process. In the present study, homologous MOR desensitization in locus ceruleus (LC) neurons and MOR internalization in HEK293 cells were examined using a series of agonists. The results show that the rank order of this series of agonists was different when comparing the magnitude of hyperpolarization and the ability to cause desensitization in LC neurons. Endocytosis of MOR was also examined in HEK293 cells using the same agonists. The relative ability to cause endocytosis in HEK293 cells correlated with the degree of desensitization in LC cells. This strong correlation suggests that the two processes are closely linked. The results also suggest that agonist efficacy is not necessarily a predictor of the ability to cause MOR desensitization or endocytosis. Identification and characterization of the biophysical properties of agonists that favor desensitization and internalization of receptors will lead to a better understanding of opioid signaling.
Key words: opioids; locus ceruleus; homologous desensitization; endocytosis; electrophysiology; imaging
INTRODUCTION
Desensitization and internalization of µ-opioid receptor (MOR) are two regulatory mechanisms thought to contribute to the development of tolerance to opioids (Whistler et al., 1999
; Williams et al., 2001
Like other G-protein-coupled receptors, activation of MOR by an agonist can result in receptor phosphorylation mediated by G-protein receptor kinases (GRKs).
-Arrestins bind to the phosphorylated receptor, and this complex is unable to couple to G-proteins and to activate downstream effectors, resulting in receptor desensitization (Ferguson, 2001
Opioid agonists differ in coupling efficacy to various effectors i.e., G-protein-coupled inwardly rectified potassium channels (GIRK), voltage-gated calcium channels, adenylyl cyclase, as well as GRKs, and these differences appear to depend on the preparation studied. Efficacy was first defined by the ability of an agonist to activate these primary effectors. Desensitization and receptor internalization mediated by GRKs was considered secondary or a follow-on consequence of receptor activation. It has become clear that these regulatory processes may also depend on agonist properties (Kenakin, 2002
In the present study, a series of opioid agonists were examined for their ability to activate potassium currents, cause homologous desensitization, and induce receptor internalization. The results showed that the degree of desensitization of MOR signaling observed in locus ceruleus (LC) neurons correlates well with that of agonist-induced MOR endocytosis assessed in HEK293 cells.
MATERIALS AND METHODS
Electrophysiological recordings. Horizontal slices (225-250 µm) containing the LC were prepared from 6- to 8-week-old male Sprague Dawley rats (Charles River Laboratories, Wilmington, MA) as described previously (Ishimatsu and Williams, 1996
) filled with internal solution containing (in mM): 115 MES potassium salt, 20 KCl, 1.5 MgCl2, 1 BAPTA, 5 HEPES, 4 Mg-ATP, and 0.4 Na-GTP, pH 7.3. For intracellular recordings, pipettes (30-50 M
All of the experiments were performed at 35°C, and, unless otherwise stated, pharmacological agents were applied by bath perfusion. All experiments with [Met]5enkephalin (ME) were done in the presence of the peptidase inhibitors bestatin (10 µM) and thiorphan (1 µM). In some cases, fluorescent agonists were applied at high concentrations using pressure ejection from a patch pipette placed in the slice within 50 µm from the recording site.
Desensitization protocols. Three different protocols were used to measure MOR desensitization of the hyperpolarization response in LC neurons (Fig. 1). One method compared the amplitude of the hyperpolarization produced by an EC50 concentration of ME (300 nM) before and after exposure to a high desensitizing concentration of ME (Harris and Williams, 1991
2-adrenoreceptor agonist UK14304 (3 µM) was tested to control for both rundown of the signal pathway during the experiment and heterologous desensitization. This method was used for measuring desensitization induced by agonists that did not wash from the preparation. A third method measured the decline in the amplitude of the hyperpolarization induced by a high agonist concentration (Fig. 1C). This decline was taken as a sign of desensitization. At the end of each experiment, a maximal concentration of the
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Figure 1. Protocols used in recordings from LC neurons to measure desensitization. A, An EC50 concentration of ME (300 nM) was used as a test before (1) and after (2) treating the tissue with a maximal concentration of agonist. The decrease in amplitude of the hyperpolarization immediately after washout was taken as a measure of desensitization. Over time, the amplitude of the hyperpolarization in response to the EC50 test returned toward control values. B, The hyperpolarization induced by a maximal concentration of ME (10 µM) was tested before (1) and during (2) the continuous superfusion with an EC50 concentration of opioid agonists. The decline in the peak hyperpolarization (3) was taken as a sign of desensitization. The hyperpolarization induced by the EC50 concentration of agonist was reversed with naloxone (1 µM). The hyperpolarization induced by a maximal concentration of UK14304 (3 µM) was determined for each experiment. C, A maximal concentration of opioid agonist was applied, and the difference between the peak hyperpolarization (1) and the amplitude of the hyperpolarization after 15 min (2) was taken as a sign of desensitization. In each experiment, naloxone was used to reverse the opioid-induced hyperpolarization, and the hyperpolarization induced by UK14304 was determined.
MOR endocytosis. MOR endocytosis was determined by feeding experiments as described previously (Finn and Whistler, 2001
Image acquisition and analyses. Images were acquired under a confocal microscope equipped with a krypton-argon laser coupled with a Bio-Rad (Hercules, CA) MRC-1000 and an Optiphot II Nikon (Tokyo, Japan) microscope. Cells were visualized under a Plan Apo 60× objective lens (1.4 numerical aperture, oil). The filters used for scanning Alexa488 were 488 nm for excitation and 522 nm for emission and, for Cy5, were 647 nm for excitation and 680 nm for emission. Pictures were taken from four to five fields from each coverslip and analyzed by Scion Image for Windows software (version Beta 4.0.2; Scion, Frederick, MD). The fluorescence intensity of ~50 individual cells (10 cells per field) was determined for each coverslip, and one mean fluorescence intensity value was obtained. For each condition, a duplicate in one experiment and three to five separate experiments were performed.
Statistics and curve fitting. Statistical difference was determined by unpaired t test unless specified, and the two-tailed p values are presented in the text or figure legends. Statistical analysis, curve fits, and correlations were performed with GraphPad Prism (GraphPad Software, San Diego, CA).
Materials. [Met]5enkephalin, dermorphin, bestatin, and yohimbine were obtained from Sigma. Naloxone and UK14304 were obtained from Research Biochemicals (Natick, MA). Thiorphan was from Bachem (Torrance, CA). Dermorphin-BTR and dermorphin-A488 were prepared as described by Arttamangkul et al., 2000
RESULTS
MOR desensitization
The response to an EC50 concentration of ME (300 nM) was significantly reduced after treatment with a high concentration of ME (30 µM) (Figs. 1A, for protocol, 2A, top trace). The amplitude of the EC50 response measured 10 min after washout of the high concentration of ME (MEpost) was approximately half of the initial EC50 response value (MEpost/MEpre = 0.46 ± 0.05; n = 4) (Fig. 2). The amplitude of the MEpost response recovered over a period of 40 min in accordance with previous reports (Harris and Williams, 1991
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Figure 2. Induction of and recovery from desensitization. In this and other figures, the recordings are of membrane potential. In some recordings, the presence of spontaneous oscillations in membrane potential resulted in "noise" in the trace. The oscillations and thus the noise was abolished in the presence of opioid agonists. A, An EC50 concentration of ME (300 nM) was tested every 5 min before and after the application of a maximal concentration of ME (30 µM; top trace) and DERM-A488 (1 µM; bottom trace; applied by pressure ejection). The amplitude of the EC50 MOR response was significantly decreased after the desensitizing treatment with ME (top trace) but only slightly reduced after DERM-A488 (bottom trace). Desensitization recovered over 30-40 min. B, Summarized data from desensitization experiments done with whole-cell (left) and intracellular (right) recordings. The decrease in amplitude of the hyperpolarization after desensitization is presented as a fraction of the amplitude of the initial response to ME (300 nM). Black bars are the ratio obtained after 10 min application, and gray bars are the ratio after 40 min.
This protocol was also used to examine the desensitization of two other agonists that washed quickly from the tissue, an active metabolite of morphine, morphine 6-glucuronide (M6G) (10 µM), and a fluorescent analog of dermorphin (DERM-A488) (1 µM, applied by pressure ejection). The effect of ME (300 nM) was determined 10 and 40 min after washout of the high concentration of these compounds. The amount of desensitization induced by DERM-A488 (1 µM; n = 6) was present but significantly smaller than that induced by ME, and there was little or no desensitization caused by M6G (10 µM; n = 6) (Fig. 2B).
Desensitization by DERM-A488 and DERM-BTR
When the same experiment was used to examine the desensitization induced by another dermorphin analog, DERM-BTR, the washout was too slow to permit measurements of desensitization. In fact, this protocol was not suitable for testing many agonists. Compounds that washed slowly from the tissue were tested with a protocol that used submaximal concentrations, and desensitization was measured using maximal ME concentration applied at various intervals during the prolonged treatment (Fig. 1B). Using this protocol, DERM-BTR but not DERM-A488 caused significant desensitization (Fig. 3). There was a significant decline in the maximal hyperpolarization induced by ME induced by DERM-BTR (30 nM; 50 ± 7% after 20 min). Neither DERM-A488 (30 nM; 20 min) nor dermorphin (30 nM; 20 min) changed the amplitude of maximal ME hyperpolarization (p > 0.05; one-way ANOVA), indicating that there was no desensitization when applied at this low concentration. Although the EC50 concentration of DERM-A488 did not cause desensitization, a maximal concentration did (Fig. 2), indicating that the desensitization was dependent on the concentration applied. It appears that concentration was not the only factor in causing desensitization, because DERM-BTR (30 nM) induced desensitization, although it caused a hyperpolarization that was smaller than that caused by both DERM-A488 (30 nM) and dermorphin (30 nM) (Fig. 3C). Thus, DERM-BTR was more potent at causing desensitization.
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Figure 3. DERM-BTR induced desensitization in LC. A, Examples of experiments done with the low-dose protocol using DERM-A488 (30 nM; top) and DERM-BTR (30 nM; bottom). The maximum hyperpolarization induced by ME (10 µM) was not changed during treatment with DERM-A488, whereas the maximum hyperpolarization was reduced in the presence of DERM-BTR. B, Summarized data showing the amplitude of the ME-induced hyperpolarization during the treatment of slices with dermorphin, DERM-A488, and DERM-BTR (n = 5 for each experiment). The amplitude is plotted as a fraction of that observed during the first application of ME in the presence of the low concentration of each dermorphin analog. C, A summary of the acute effects of dermorphin, DERM-A488, and DERM-BTR, all applied at 30 nM (left). Right side indicates that the maximal hyperpolarization induced by DERM-A488 (1 µM; applied by pressure ejection) and DERM-BTR (1 µM; applied by pressure ejection) is the same as that induced by ME (10 µM).
MOR endocytosis
Previous work with DERM-A488 and DERM-BTR showed that these agonists differ substantially in their internalization properties, although these agonists had similar binding affinity (Ki ~2.5 nM) and biological activity (EC50 ~30 nM) (Arttamangkul et al., 2000
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Figure 4. Endocytosis of flag-tagged MOR in HEK293 cells by opioid peptide agonists. A, Examples of experiments examining the endocytosis induced by DERM-A488 (top) and DERM-BTR (bottom). The far left images (a, e) show total receptor binding using anti-flag antibodies. In b-d and f-h, the cells were incubated with DERM-A488 and DERM-BTR for the period indicated. At each time point, the anti-flag antibody remaining on the plasma membrane was stripped off so that only internalized label remained. The results show more internalization during treatment with DERM-BTR. B, Summarized data showing the time course of internalization induced by different concentrations of DERM-A488 and DERM-BTR. C, Examples of the maximal internalization caused by DERM-BTR, dermorphin, and DERM-A488 all applied at 30 nM for 30 min. D, Summary of many experiments with the dermorphin analogs and ME after a 30 min incubation period at 37°C. Each of the opioid peptides caused internalization that was dependent on the concentration. Also shown is constitutive internalization, which is the amount of receptor that was internalized in 30 min in the absence of any opioid agonist (No Agonist). *p < 0.05; **p < 0.001; one-way ANOVA; Tukey's multiple comparison test.
In the absence of opioid agonists, these cells showed constitutive endocytosis of ~34 ± 3% of the total membrane receptors over a 30 min incubation period at 37°C (Fig. 4B,D). Both dermorphin analogs caused receptor internalization, but the concentrations of agonist required for internalization were very different. Whereas DERM-A488 at an EC50 concentration (30 nM) did not cause endocytosis above constitutive levels (45 ± 3%), a very low concentration of DERM-BTR (3 nM) caused a constant increase of receptor internalization that reached maximal levels over a 60 min incubation (80 ± 8%) (Fig. 4B). Higher concentrations of both fluorescent agonists produced rapid and maximal receptor internalization with a similar time constant (DERM-A488, 1 µM,
of 3.1 ± 1 min, maximum of 78 ± 6%; DERM-BTR, 30 nM,
These results indicate that DERM-BTR itself was not only internalized, as it has been shown previously (Arttamangkul et al., 2000
The internalization of a number of well characterized alkaloid agonists was examined under the same experimental conditions to put the results obtained with the two fluorescent dermorphin analogs into perspective (Fig. 5). In agreement with previous reports, morphine and M6G failed to promote MOR internalization even at very high concentrations. Normorphine at 1 µM did not induce receptor internalization, but, when the concentration was increased to 30 µM, 65 ± 6% of the total membrane receptors were internalized. Methadone and etorphine both caused internalization that was dependent on the concentration of agonist used. No etorphine-induced endocytosis was observed at concentrations up to 100 nM, whereas at 300 nM, a maximum effect was observed (Fig. 5B). Methadone at 1 µM caused some endocytosis, and a maximal response was observed at 30 µM. Thus, the results are completely consistent with the work of others and suggest that the difference in endocytosis induced by DERM-A488 and DERM-BTR results from an agonist-specific property conferred by chemical modification of this opioid peptide.
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Figure 5. Methadone but not morphine caused endocytosis of flag-tagged MOR in HEK293 cells. A, Representative images from endocytosis experiments. Fluorescence stains internalized receptor after 30 min exposure to 30 µM methadone (left), morphine (middle), and M6G (right). B, Summarized data from several endocytosis experiments testing exposure to alkaloid opioids for 30 min at 37°C. Normorphine, methadone, and etorphine caused internalization that was dependent on the concentration. Morphine and M6G did not cause MOR endocytosis above the constitutive level (dotted lines), even at high concentrations. **p < 0.05; one-way ANOVA; Tukey's multiple comparison test.
Desensitization by alkaloid opioid agonists
To correlate the degree of desensitization with the ability of agonists to induced endocytosis, the desensitization measured in LC neurons was determined using the same opioid agonists. Given that the washout of most agonists was slow, a combination of the low-dose (Fig. 1B) and high-dose (Fig. 1C) protocols was used. With the low-dose protocol, morphine (1 µM) and M6G (1 µM) failed to induce changes in the maximal ME response (Fig. 6). The results with M6G are consistent with those obtained with the high-dose protocol (Fig. 2B). These results confirmed that neither morphine nor M6G were capable of inducing desensitization.
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Figure 6. Methadone-induced desensitization using the low-dose protocol. A, Examples of experiments using the low-dose protocol with morphine and methadone. The amplitude of the ME-induced hyperpolarization was not changed during treatment with morphine (3 µM; top trace) but decreased progressively during superfusion with methadone (3 µM; bottom trace). B, Summarized data showing the decline in the ME-induced hyperpolarization in the presence of methadone and the lack of any change in the presence of morphine (3 µM), M6G (3 µM), and UK14304 (100 nM).
Methadone caused both receptor internalization and desensitization. Perfusion with methadone (1 µM) reduced the amplitude of maximal ME response by 50 ± 5% (n = 5) after 20 min (Fig. 6). There was no difference between the mean amplitude of the first ME response (before exposure to methadone) (30 ± 1.5 mV) and the amplitude of first pulse of ME response (32 ± 2 mV) immediately (3 min) after the onset of superfusion with methadone. However, in the continued presence of methadone, a reduction was detected as early as 10 min and declined continuously over 20 min (Fig. 6).
Desensitization was also measured using the decline in the hyperpolarization during a prolonged exposure to a high agonist concentration (Fig. 1C). This protocol can be used for any agonist, regardless of the washout kinetics. The decline in the hyperpolarization was measured at the end of a 15 min application of morphine (30 µM; n = 4), methadone (10 µM; n = 4), etorphine (1 µM; n = 4), and ME (10 µM; n = 5) (Fig. 7). Morphine was the only agonist that did not cause desensitization. The decline in response during the 15 min test was the same for each of the other agonists (~10 mV). Naloxone (1 µM) was used to reverse the effect, and a maximal concentration of the
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Figure 7. Methadone-induced desensitization using the high-dose protocol. A, An example of the desensitization caused by a high concentration of methadone (30 µM). The peak hyperpolarization caused by methadone was approximately the same as the hyperpolarization induced by ME (1 µM) and UK14304 (3 µM). The decline in the hyperpolarization during the 15 min application was taken as a sign of desensitization. B, An example of the same experiment using a high concentration of morphine (30 µM). There is little or no decline in the hyperpolarization induced by morphine. C, Left, Summarized data showing the amplitude of the decline in hyperpolarization during a 15 min application of several agonists. This decline was ~10 mV for methadone, ME, and etorphine but <2 mV for morphine. Middle shows the peak amplitude of the hyperpolarization caused by each agonist. Right shows the amplitude of the hyperpolarization induced by UK14304 (3 µM) before (none) and after treatment with each of the indicated opioid agonists. There is no sign of heterologous desensitization induced by any of the opioid agonists.
Correlation between endocytosis and desensitization
A summary of the results obtained with LC neurons in brain slices and HEK293 cells is illustrated in Figure 8. Desensitization measured in locus ceruleus neurons showed a positive correlation with agonist-induced receptor endocytosis in HEK293 cells. Independent of the assay used to measure desensitization, whether it was a change in EC50 or a change in maximal hyperpolarization, agonists that failed to induce desensitization also failed to produce endocytosis. Furthermore, desensitization was only observed at agonist concentrations that also caused internalization of at least 70% of total membrane receptors.
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Figure 8. A comparison of MOR endocytosis and desensitization. Summarized data from all endocytosis and desensitization experiments. The percentage of the total MOR internalized by a given concentration of agonist (taken from Figs. 4, 5) was plotted as a function of amount of desensitization achieved when tested in LC neurons (expressed as percentage of the maximal opioid hyperpolarization). A significant correlation was found (nonparametric Spearman's test; r = 0.77; two-tailed p = 0.01269). The lowest possible value on the y-axis (35%) is the level of constitutive endocytosis.
DISCUSSION
GIRK activation and desensitization
Striking differences were found among the opioid agonists with respect to the relative ability to activate GIRK-mediated hyperpolarization and to trigger desensitization. The rank of order for desensitization of MOR activation of potassium current in LC neurons was as follows: DERM-BTR > etorphine > methadone
ME > dermorphin
Based on both our experiments and previous literature, the rank of order for receptor activation is as follows: etorphine
The fluorescent opioid peptides were powerful tools for addressing the question of the relationship between agonist efficacy and desensitization and/or internalization of receptors. Created from the same opioid agonist, dermophin, DERM-BTR and DERM-A488 share several characteristics, such as EC50 and binding affinity (Kd of 2.3 and 2.5 nM for DERM-A488 and DERM-BTR, respectively) (Arttamangkul et al., 2000
Conjugation of BTR to dermorphin resulted in a very hydrophobic peptide. Given that this is the primary difference between DERM-BTR and DERM-A488, it is reasonable to propose that the unique desensitization properties of DERM-BTR could be related to its hydrophobicity. At least three possible explanations could account for the results. First, DERM-BTR could accumulate in the proximity of the plasma membrane and create very high local increases in agonist concentration that could saturate receptors, causing desensitization and endocytosis. This explanation, however, should result in the maximal activation of a physiological response. Second, the hydrophobic properties of DERM-BTR could enhance clustering and/or dimerization of receptor, which could facilitate desensitization and endocytosis. Third, DERM-BTR could slow recycling of internalized receptors such that an apparent increase in endocytosis and desensitization could result from failure to recycle.
In both the brain slice and HEK293 cell experiments, the onset and recovery from application of DERM-BTR was slower than DERM-A488. Although this observation may be related simply to differences in hydrophobicity, it may also suggest that the receptor binding kinetics are different for the two ligands. A slower dissociation rate might imply that DERM-BTR remains bound to receptors, even after endocytosis, thereby impairing receptor recycling. This notion is supported by the observation that a low concentration of DERM-BTR induced a progressive accumulation of MOR in the intracellular compartment (Fig. 4B). The slow but constant rate of receptor accumulation might suggest a reduced rate of receptor recycling.
Desensitization and internalization
Desensitization was tested using different protocols that included exposure to maximal or submaximal agonist concentrations, all yielding consistent results. In agreement with previous studies, signaling through
The opioid agonists normorphine, methadone, etorphine, dermorphin, DERM-Cys, and DERM-A488 all induced MOR desensitization and internalization in a concentration-dependent manner. Interestingly, supramaximal concentrations of these agonists were often required to cause significant desensitization and endocytosis. An important example is etorphine, which is both potent and efficacious at activating a number of different effectors but required relatively high concentrations to induce both desensitization and endocytosis. This observation suggests that higher receptor occupancy may be required for internalization and desensitization than for activation of other effectors. The exception to this statement is DERM-BTR.
Significance
Acute desensitization and receptor endocytosis have been proposed to be protective mechanisms that come into play during prolonged agonist exposure (Finn and Whistler, 2001
A recent study compared the effect of chronic treatment with morphine (high RAVE value) and etorphine (low RAVE value) on analgesic tolerance and receptor regulation in vivo (Stafford et al., 2001
In summary, acute homologous desensitization and MOR endocytosis were examined using several opioid agonists. A close link between desensitization and endocytosis was found, and both processes were dependent on the individual characteristics and concentration of the agonists used. This study demonstrated that dermorphin, a compound with a relatively high RAVE value was transformed to a compound with a lower RAVE value by the addition of a hydrophobic dye molecule. This observation may lead to a better understanding of the chemical properties of agonists that govern receptor activation, desensitization, and endocytosis.
FOOTNOTES Received Feb. 19, 2002; revised April 17, 2002; accepted April 18, 2002.
* V.A.A. and S.A. contributed equally to this work.
This work was supported by National Institutes of Health Grants DA08163 (J.T.W.), DA07262 (S.A.), DA12864 (M.v.Z.), and DA08562 and DA10703 (D.K.G.). We thank Drs. Amara and Watt for the use of the confocal microscope and Drs. Torrecilla and Morikawa for comments on this work.
Correspondence should be addressed to John T. Williams, Vollum Institute, L474 Oregon Health and Sciences University, 3181 S.W. Sam Jackson Park Road, Portland, OR 97201. E-mail williamj{at}ohsu.edu.
V. A. Alvarez's present address: Department of Neurobiology, Harvard Medical School, Boston, MA 02115.
REFERENCES
- Arttamangkul S, Alvarez-Maubecin V, Thomas G, Williams JT, Grandy DK (2000) Binding and internalization of fluorescent opioid peptide conjugates in living cells. Mol Pharmacol 58:1570-1580
[Abstract/Free Full Text] .- Ferguson SS (2001) Evolving concepts in G protein-coupled receptor endocytosis: the role in receptor desensitization and signaling. Pharmacol Rev 53:1-24
[Abstract/Free Full Text] .- Finn AK, Whistler JL (2001) Endocytosis of the mu opioid receptor reduces tolerance and a cellular hallmark of opiate withdrawal. Neuron 32:829-839[ISI][Medline].
- Fiorillo CD, Williams JT (1996) Opioid desensitization: interactions with G-protein-coupled receptors in the locus coeruleus. J Neurosci 16:1479-1485
[Abstract/Free Full Text] .- Gomes BA, Shen J, Stafford K, Patel M, Yoburn BC (2002) µ-Opioid receptor down-regulation and tolerance are not equally dependent upon G-protein signaling. Pharmacol Biochem Behav 72:273-278[Medline].
- Harris GC, Williams JT (1991) Transient homologous mu-opioid receptor desensitization in rat locus coeruleus neurons. J Neurosci 11:2574-2581[Abstract].
- He L, Fong J, von Zastrow M, Whistler JL (2002) Regulation of opioid receptor trafficking and morphine tolerance by receptor oligomerization. Cell 108:271-282[ISI][Medline].
- Ishimatsu M, Williams JT (1996) Synchronous activity in locus coeruleus results from dendritic interactions in pericoerulear regions. J Neurosci 16:5196-5204
[Abstract/Free Full Text] .- Keith DE, Murray SR, Zaki PA, Chu PC, Lissin DV, Kang L, Evans CJ, von Zastrow M (1996) Morphine activates opioid receptors without causing their rapid internalization. J Biol Chem 271:19021-19024
[Abstract/Free Full Text] .- Keith DE, Anton B, Murray SR, Zaki PA, Chu PC, Lissin DV, Monteillet-Agius G, Stewart PL, Evans CJ, von Zastrow M (1998) mu-Opioid receptor internalization: opiate drugs have differential effects on a conserved endocytic mechanism in vitro and in the mammalian brain. Mol Pharmacol 53:377-384
[Abstract/Free Full Text] .- Kenakin T (2002) Efficacy and G-protein-coupled receptors. Nature Rev 1:103-110.
- Koch T, Schulz S, Schroder H, Wolf R, Raulf E, Hollt V (1998) Carboxyl-terminal splicing of the rat mu opioid receptor modulates agonist-mediated internalization and receptor resensitization. J Biol Chem 273:13652-13657
[Abstract/Free Full Text] .- Kovoor A, Celver JP, Wu A, Chavkin C (1998) Agonist induced homologous desensitization of mu-opioid receptors mediated by G protein-coupled receptor kinases is dependent on agonist efficacy. Mol Pharmacol 54:704-711
[Abstract/Free Full Text] .- Law PY, Erickson LJ, El-Kouhen R, Dicker L, Solberg J, Wang W, Miller E, Burd AL, Loh HH (2000) Receptor density and recycling affect the rate of agonist-induced desensitization of mu-opioid receptor. Mol Pharmacol 58:388-398
[Abstract/Free Full Text] .- Lefkowitz RJ (1998) G protein-coupled receptors. III. New roles for receptor kinases and beta-arrestins in receptor signaling and desensitization J Biol Chem 273:18677-18680
[Free Full Text] .- Osborne PB, Williams JT (1995) Characterization of acute homologous desensitization of mu-opioid receptor-induced currents in locus coeruleus neurones. Br J Pharmacol 115:925-932[ISI][Medline].
- Stafford K, Gomes AB, Shen J, Yoburn BC (2001) mu-Opioid receptor downregulation contributes to opioid tolerance in vivo. Pharmacol Biochem Behav 69:233-237[Medline].
- Sternini C, Spann M, Anton B, Keith Jr DE, Bunnett NW, von Zastrow M, Evans C, Brecha NC (1996) Agonist-selective endocytosis of mu opioid receptor by neurons in vivo. Proc Natl Acad Sci USA 93:9241-9246
[Abstract/Free Full Text] .- Sternini C, Brecha NC, Minnis J, D'Agostino G, Balestra B, Fiori E, Tonini M (2000) Role of agonist-dependent receptor internalization in the regulation of mu opioid receptors. Neuroscience 98:233-241[ISI][Medline].
- Trafton JA, Abbadie C, Marek K, Basbaum AI (2000) Postsynaptic signaling via the µ-opioid receptor: responses of dorsal horn neurons to exogenous opioids and noxious stimulation. J Neurosci 20:8578-8584
[Abstract/Free Full Text] .- Whistler JL, von Zastrow M (1998) Morphine-activated opioid receptors elude desensitization by beta-arrestin. Proc Natl Acad Sci USA 95:9914-9919
[Abstract/Free Full Text] .- Whistler JL, Chuang HH, Chu P, Jan LY, von Zastrow M (1999) Functional dissociation of mu opioid receptor signaling and endocytosis: implications for the biology of opiate tolerance and addiction. Neuron 23:737-746[ISI][Medline].
- Williams JT, Christie MJ, Manzoni O (2001) Cellular and synaptic adaptations mediating opioid dependence. Physiol Rev 81:299-343
[Abstract/Free Full Text] .- Zhang J, Ferguson SS, Barak LS, Bodduluri SR, Laporte SA, Law PY, Caron MG (1998) Role for G protein-coupled receptor kinase in agonist-specific regulation of mu-opioid receptor responsiveness. Proc Natl Acad Sci USA 95:7157-7162
[Abstract/Free Full Text] .
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Mol. Pharmacol., October 1, 2008; 74(4): 972 - 979.
[Abstract] [Full Text] [PDF]
A. Gupta, R. Rozenfeld, I. Gomes, K. M. Raehal, F. M. Decaillot, L. M. Bohn, and L. A. Devi
Post-activation-mediated Changes in Opioid Receptors Detected by N-terminal Antibodies
J. Biol. Chem., April 18, 2008; 283(16): 10735 - 10744.
[Abstract] [Full Text] [PDF]
M. S. Virk and J. T. Williams
Agonist-Specific Regulation of {micro}-Opioid Receptor Desensitization and Recovery from Desensitization
Mol. Pharmacol., April 1, 2008; 73(4): 1301 - 1308.
[Abstract] [Full Text] [PDF]
D. Thompson, M. Pusch, and J. L. Whistler
Changes in G Protein-coupled Receptor Sorting Protein Affinity Regulate Postendocytic Targeting of G Protein-coupled Receptors
J. Biol. Chem., October 5, 2007; 282(40): 29178 - 29185.
[Abstract] [Full Text] [PDF]
W. Walwyn, C. J. Evans, and T. G. Hales
{beta}-Arrestin2 and c-Src Regulate the Constitutive Activity and Recycling of {micro} Opioid Receptors in Dorsal Root Ganglion Neurons
J. Neurosci., May 9, 2007; 27(19): 5092 - 5104.
[Abstract] [Full Text] [PDF]
D. Liao, O. O. Grigoriants, H. H. Loh, and P.-Y. Law
Agonist-Dependent Postsynaptic Effects of Opioids on Miniature Excitatory Postsynaptic Currents in Cultured Hippocampal Neurons
J Neurophysiol, February 1, 2007; 97(2): 1485 - 1494.
[Abstract] [Full Text] [PDF]
J. D. Urban, W. P. Clarke, M. von Zastrow, D. E. Nichols, B. Kobilka, H. Weinstein, J. A. Javitch, B. L. Roth, A. Christopoulos, P. M. Sexton, et al.
Functional Selectivity and Classical Concepts of Quantitative Pharmacology
J. Pharmacol. Exp. Ther., January 1, 2007; 320(1): 1 - 13.
[Abstract] [Full Text] [PDF]
S. Arttamangkul, M. Torrecilla, K. Kobayashi, H. Okano, and J. T. Williams
Separation of {micro}-Opioid Receptor Desensitization and Internalization: Endogenous Receptors in Primary Neuronal Cultures
J. Neurosci., April 12, 2006; 26(15): 4118 - 4125.
[Abstract] [Full Text] [PDF]
V. C. Dang and J. T. Williams
Morphine-Induced {micro}-Opioid Receptor Desensitization
Mol. Pharmacol., October 1, 2005; 68(4): 1127 - 1132.
[Abstract] [Full Text] [PDF]
Z. Zuo
The Role of Opioid Receptor Internalization and {beta}-Arrestins in the Development of Opioid Tolerance
Anesth. Analg., September 1, 2005; 101(3): 728 - 734.
[Abstract] [Full Text] [PDF]
H. Haberstock-Debic, K.-A. Kim, Y. J. Yu, and M. von Zastrow
Morphine Promotes Rapid, Arrestin-Dependent Endocytosis of {micro}-Opioid Receptors in Striatal Neurons
J. Neurosci., August 24, 2005; 25(34): 7847 - 7857.
[Abstract] [Full Text] [PDF]
S. E. Bartlett, J. Enquist, F. W. Hopf, J. H. Lee, F. Gladher, V. Kharazia, M. Waldhoer, W. S. Mailliard, R. Armstrong, A. Bonci, et al.
Dopamine responsiveness is regulated by targeted sorting of D2 receptors
PNAS, August 9, 2005; 102(32): 11521 - 11526.
[Abstract] [Full Text] [PDF]
C. A. McClung, E. J. Nestler, and V. Zachariou
Regulation of Gene Expression by Chronic Morphine and Morphine Withdrawal in the Locus Ceruleus and Ventral Tegmental Area
J. Neurosci., June 22, 2005; 25(25): 6005 - 6015.
[Abstract] [Full Text] [PDF]
M. A. Simmons
Functional Selectivity, Ligand-Directed Trafficking, Conformation-Specific Agonism: What's In A Name?
Mol. Interv., June 1, 2005; 5(3): 154 - 157.
[Abstract] [Full Text] [PDF]
