Allosteric modulation of the human 5-HT(7A) receptor by lipidic amphipathic compounds.
Human 5-HT7A receptors positively modulated adenylyl cyclases via Gs subtypes of G proteins in human embryonic kidney 293 cells, and bound 5-hydroxytryptamine (HT) with high and low affinity (K(I) values of 1.5 +/- 0.3 and 93 +/- 4 nM). More than 60% of 5-HT7A receptors, however, displayed the high-affinity 5-HT binding with no sensitivity to 5'-guanylylimidodiphosphate. In this study, we found that select amphipathic agents affected the high-affinity 5-HT binding to 5-HT7A. Oleic acid at low concentrations (<15 microM), but not palmitic, stearic, and arachidonic acids, increased maximal [3H]5-HT binding without affecting its K(D) value and [3H]mesulergine (antagonist) binding. Fatty acid-free bovine serum albumin (FF-BSA), a scavenger of fatty acids and lipid metabolites, substantially reduced maximal [3H]5-HT binding (no change in K(D) value and antagonist binding) but lost its action upon treatment with inactive stearic acid. FF-BSA and oleic acid produced no appreciable effects on [3H]5-HT binding to analogous 5-HT receptors 5-HT1D and 5-HT2C. Among various lysophospholipids, lysophosphatidyl choline (50 microM) decreased maximal [3H]5-HT binding, and a similar zwitterion, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate (CHAPS; 0.1%), increased it (no change in K(D)). Functionally, 5-HT-induced guanosine-5'-O-(3-[35S]thio)triphosphate (GTPgamma35S) binding was enhanced by oleic acid and CHAPS, but reduced by FF-BSA and lysophosphatidyl choline; the amphipathic agents and FF-BSA did not affect dopamine-induced GTPgamma35S binding at D1, a prototypic Gs-coupled receptor. At 5-HT7A, oleic acid, FF-BSA, CHAPS, and lysophosphatidyl choline also brought about corresponding changes in the half-maximal 5-HT concentration for cAMP production, without affecting the maximal and basal levels. We propose that endogenous, amphipathic lipid metabolites may modulate 5-HT7A receptors allosterically to promote high-affinity 5-HT binding and to enable receptors to couple more efficiently to Gs subtypes of G proteins.
Alberts
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GL
Department of Biology II/Neurobiology, Pharmacia & Upjohn, Kalamazoo, Michigan.
Chio
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D000494:Allosteric Regulation; D002478:Cells, Cultured; D004873:Ergolines / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D019301:Oleic Acid / Q000378:metabolism*; D009829:Oleic Acids / Q000378:metabolism; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology; D014316:Tritium
D004873:Ergolines; D009829:Oleic Acids; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; C104425:serotonin 7 receptor; D014316:Tritium; D019301:Oleic Acid; D012701:Serotonin; C029407:oleylamide; C031649:mesulergine