Potentiation of the 5-hydroxytryptamine-induced increases in myocardial contractility in Mercenaria mercenaria ventricle by forskolin.

Forskolin (10(-5) M), an activator of adenylate cyclase in many mammalian cell types, potentiated the positive inotropic effects of 5-hydroxytryptamine (5-HT) on the bivalve, Mercenaria mercenaria, myocardium. Forskolin (10(-5) M) also significantly increased intracellular cyclic AMP concentrations when compared to 5-HT controls. Ro 20-1724 (10(-5) M), a putative inhibitor of cyclic AMP phosphodiesterase, had no effect on myocardial contractility or cyclic AMP concentration. A positive correlation between intracellular cyclic AMP concentration and the efficacy of 5-HT was obtained.