title: 5-Hydroxytryptamine-induced tachyphylaxis of the molluscan heart and concomitant desensitization of adenylate cyclase.
abstract: High concentrations of 5-hydroxytryptamine (5HT) first excite the isolated ventricle of Mercenaria mercenaria and then specifically desensitize it to further additions of the neuropeptide. This 5HT-induced tachyphylaxis is paralleled by a 5HT-specific desensitization of the myocardial adenylate cyclase and a decrease in intracellular cyclic AMP. However, FMRF-NH2, a cardioexcitatory tetrapeptide, can still increase contractility, cyclic AMP, and the adenylate cyclase activity of a tachyphylactic ventricle. These results are consistent with the hypothesis that 5HT augments molluscan myocardial contractility by elevating intracellular cyclic AMP.
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D066298:In Vitro Techniques; D008974:Mollusca / Q000502:physiology*; D009200:Myocardial Contraction / Q000187:drug effects*; D009206:Myocardium / Q000201:enzymology; D012701:Serotonin / Q000494:pharmacology*; D013618:Tachyphylaxis; D013997:Time Factors
chemical_list: D012701:Serotonin; D000262:Adenylyl Cyclases