title: Constitutive activity of G-protein coupled receptors: emphasis on serotonin receptors.
abstract: Several lines of evidence indicate that G-protein coupled receptors (GPCR) may exist in a state that allows a tonic level of stimulation in vivo (constitutive activity). Several native forms of GPCR, when expressed in recombinant cell lines, display significant signal transduction stimulation in the absence of activating ligand. Many GPCR, including three serotonin receptors, display robust constitutive activation upon the mutation of a single amino acid, indicating mutations producing inappropriate constitutive activation may be etiological factors in diseases. If constitutive activity of GPCR is as common a phenomenon as some researchers suspect, this would suggest significant alterations in the classical model of ligand-receptor interactions. One of the most significant implications of constitutive activity for pharmacologists and medicinal chemists, is the possibility of developing drugs that lower the level of constitutive activity. Such compounds have been termed  inverse agonists . These drugs, in theory, would have different physiological effects, and therefore possibly different therapeutic potential, than classical competitive receptor antagonists ( neutral antagonists ). Theoretical issues concerning constitutive activity in the GPCR family and some of the evidence supporting the existence of constitutive activity in the GPCR family is reviewed. Studies are presented demonstrating the procedures for producing and characterizing constitutive activated forms of serotonin receptors, including the demonstration of inverse agonist activity of drugs on these receptors.
authors.affiliation: Center for Neuroscience and Neuropharmacology, Albany Medical College, 47 New Scotland Avenue, Albany, N.Y. 12208, USA. TeitleM@mail.amc.edu
authors.forename: Milt
authors.initials: M
authors.lastname: Teitler
authors.forename: Katharine
authors.initials: K
authors.lastname: Herrick-Davis
authors.forename: Anil
authors.initials: A
authors.lastname: Purohit
mesh_terms: D000818:Animals; D014150:Antipsychotic Agents / Q000145:classification / Q000494:pharmacology; D001667:Binding, Competitive; D002478:Cells, Cultured; D015195:Drug Design; D019204:GTP-Binding Proteins / Q000378:metabolism / Q000502:physiology; D006801:Humans; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D011485:Protein Binding; D020033:Protein Isoforms; D011985:Receptors, Serotonin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012702:Serotonin Antagonists / Q000737:chemistry / Q000494:pharmacology*; D017366:Serotonin Receptor Agonists / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D014150:Antipsychotic Agents; D020033:Protein Isoforms; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D019204:GTP-Binding Proteins