[Effects of cyproheptadine on the electrophysiological characteristics of the sinus node, ventricular myocytes and papillary muscles of the guinea pig heart].

Cyproheptadine is an antagonist of S1 serotoninergic and H1 histaminergic receptors, with a well known cardiovascular activity, mainly vasodilation and a negative chronotropic effect. It has been suggested that cyproheptadine as other antiserotoninergic drugs act by blocking the calcium channel. In order to explore this possibility the actions of this drug were studied in several cardiac preparations: sinus node, isolated ventricular myocytes and papillary muscle from guinea-pig's heart. The experiments were performed using the conventional recording techniques of intracellular electrical activity and isometric tension. Doses from 0.25 microM to 1.0 microM were studied. The main findings were: in sinus node: a) inhibition of automatic activity, b) a decrease in the upstroke, c) a decrease in the plateau level, and d) a shortening of the action potential. In isolated ventricular myocytes: a) a decrease in the rate of depolarization, b) a decrease in the plateau level and c) a shortening of the action potential. In the papillary muscle: a) a decrease in tension and b) a shortening of the action potential. All the effects observed were dose dependent an agree with a blockade of the calcium channel.