FURTHER EVIDENCE FOR NEGATIVE INOTROPIC ACTION OF ACETYLCHOLINE

Abstract

Physiological significance of shortened action potential on the negative inotropic action of acetylcholine was studied in isolated atria of guinea pigs from the aspect of drug-antagonism at the configuration of the transmembrane action potential. A series of agents which cause prolongation of duration in action potential and without marked effects on the contractility such as o-benzoyl thiamine, E-10, quinidine and diphenhydramine were used as antagonists to observe the effect of acetylcholine in shortening the duration of action potential. Additional applications of these antagonists to the atria during exposure to acetylcholine recovered to the normal state, both the shortened action potential as well as the suppressed contractility. The results herein clearly indicate that the negative inotropic action of acetylcholine is dependent on the shorter duration of depolarization.