Enhanced serotonin-stimulated adenylate cyclase activity in membranes from adult guinea pig hippocampus.
We have developed an assay for serotonin (5-HT) stimulation of adenylate cyclase activity in membranes from adult guinea pig hippocampus. The response to 5-HT is concentration-dependent, with an EC50 of 0.01 microM, a shallow slope, and mean maximal stimulation of 90% over basal activity. The response to 5-HT is GTP-dependent and additive to the maximal stimulation by histamine. Micromolar concentrations of the known 5-HT receptor agonists, tryptamine and 5-methoxytryptamine, also stimulate cAMP production in this system, and their effect is not additive to that elicited by a maximal concentration of 5-HT. These results are consistent with the hypothesis that the response to 5-HT is elicited through a distinct receptor coupled to adenylate cyclase; the magnitude and the reproducibility of the 5-HT response in this system should make it useful for receptor classification. To examine the effect of prior exposure to endogenous 5-HT on the responsiveness of the system, we assayed 5-HT stimulation of enzyme activity in membranes prepared from animals 25-27 hrs after treatment with a single injection of reserpine (5 mg/kg, i.p.). The mean maximal stimulation of adenylate cyclase by 5-HT was increased to 150% over basal activity with no effect on the EC50 or slope of the 5-HT concentration-response curve. Reserpine pretreatment did not affect basal activity or histamine-stimulated adenylate cyclase activity. These results are discussed in the context of a hypothesis that endogenous 5-HT normally exerts a desensitizing effect on its receptors in situ.
D008735:5-Methoxytryptamine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D006168:Guinea Pigs; D006624:Hippocampus / Q000201:enzymology*; D006632:Histamine / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008566:Membranes / Q000201:enzymology; D012110:Reserpine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology*; D014363:Tryptamines / Q000494:pharmacology
D014363:Tryptamines; D012701:Serotonin; D008735:5-Methoxytryptamine; C030820:tryptamine; D006632:Histamine; D012110:Reserpine; D000262:Adenylyl Cyclases