Characterization of homologous 5-hydroxytryptamine4 receptor desensitization in colliculi neurons.
Exposure of mouse colliculi neurons to selective 5-hydroxytryptamine (5-HT)4 agonists was accompanied by a rapid desensitization of the receptor-stimulated adenylyl cyclase response. Half-maximal desensitization occurred after 2 min. Only exposure of neurons to selective 5-HT4 agonists led to a potent desensitization of the 5-HT4-mediated response. Neurons exposed to other agents, like isoproterenol, vasoactive intestinal peptide, or forskolin, that increase cAMP levels did not undergo any desensitization of 5-HT4 receptors. Activation of protein kinase A with either 8-bromo-cAMP or dibutyryl-cAMP or application of inhibitors of protein kinase A-dependent phosphorylation did not change the rate of 5-HT4-induced desensitization. No shift to lower potency of 5-HT4 agonists in the concentration-response curve was observed. These results suggest that 5-HT4 receptor agonists induced homologous but not cAMP-mediated heterologous desensitization. A good correlation was found between the affinities of nine 5-HT4 agonists and their abilities to desensitize the adenylyl cyclase response. This may indicate that homologous desensitization is a function of the mean occupancy time of the receptors by agonists. When permeabilized neurons were loaded with heparin, an inhibitor of the beta-adrenergic receptor kinase (beta ARK), 5-HT4 receptor desensitization was reduced by 30-40%. Interestingly, Zn2+, an other inhibitor of beta ARK, totally prevented 5-HT4-induced desensitization. Pretreatment of neurons with concanavalin A, reported to inhibit sequestration of beta-adrenergic receptors from the cell surface, reduced the desensitization process by 70%. These data suggest that both sequestration and phosphorylation by beta ARK, or another specific agonist-dependent receptor kinase, are involved in homologous desensitization of 5-HT4 receptors coupled to adenylyl cyclase.
Ansanay
H
H
Centre CNRS-INSERM de Pharmacologie-Endocrinologie, Montpellier, France.
Sebben
M
M
Bockaert
J
J
Dumuis
A
A
D000818:Animals; D002413:Cations, Divalent; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000096:biosynthesis; D006493:Heparin / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D015398:Signal Transduction; D003336:Tectum Mesencephali / Q000166:cytology / Q000187:drug effects / Q000378:metabolism; D015032:Zinc / Q000494:pharmacology
D002413:Cations, Divalent; D047428:Protein Kinase Inhibitors; D011985:Receptors, Serotonin; D006493:Heparin; D000242:Cyclic AMP; D011494:Protein Kinases; D015032:Zinc