Reciprocal binding properties of 5-hydroxytryptamine type 2C receptor agonists and inverse agonists.
Expression of the 5-hydroxytryptamine type 2C (5-HT 2C) receptor in NIH/3T3 fibroblasts results in agonist-independent 5-HT2C receptor activation. Some 5-HT2c receptor antagonists decrease this activation and are termed inverse agonists. The present study uses this system to evaluate functional and receptor binding properties of other 5-HT2C receptor antagonists. A number of inverse agonists, including clozapine, and a neutral antagonist (methysergide) were identified in a functional assay. Guanine nucleotides increased the affinity of a radiolabeled inverse agonist ([3H]mesulergine), suggesting that inverse agonists bind the G protein-uncoupled form of the 5-HT2C receptor with high affinity. Competition binding was performed using conditions that separately labeled the G protein-coupled and -uncoupled forms of the receptor. These studies demonstrated that inverse agonists bound the uncoupled form of the 5-HT2C receptor with higher affinity, compared with the G protein-coupled form. Agonists, on the other hand, had higher affinity for the coupled form whereas neutral antagonists had equal affinity for both forms of the receptor. Thus, 5-HT2C receptor neutral antagonists exhibited functional and receptor binding properties consistent with those of classical receptor antagonists. However, 5-HT2C receptor inverse agonists displayed functional and receptor binding properties that were opposite those of agonists.
Department of Pharmacology, School of Medicine, Vanderbilt University, Nashville, Tennessee 37232.
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Westphal
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Sanders-Bush
D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine / Q000031:analogs & derivatives / Q000378:metabolism; D016475:3T3 Cells; D000818:Animals; D001667:Binding, Competitive; D002460:Cell Line; D004873:Ergolines / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D006868:Hydrolysis; D051379:Mice; D010716:Phosphatidylinositols / Q000378:metabolism; D011869:Radioligand Assay; D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012702:Serotonin Antagonists / Q000378:metabolism; D017366:Serotonin Receptor Agonists / Q000378:metabolism
D004873:Ergolines; D006150:Guanine Nucleotides; D010716:Phosphatidylinositols; D044405:Receptor, Serotonin, 5-HT2C; D011985:Receptors, Serotonin; D011994:Recombinant Proteins; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D004290:DOM 2,5-Dimethoxy-4-Methylamphetamine; C003943:2,5-dimethoxy-4-bromoamphetamine; C031649:mesulergine