The Action of Acetylcholine and Epinephrine on the Cellular Membrane Potentials and Contractility of Rat Atrium

Abstract

Acetylcholine diminished the developed tension of contraction in rat atria; simultaneously there was a slight increase in resting potential, no appreciable change in action potential, a decrease in the rate of conduction, only a minor alteration of the form of contraction, and, most strikingly, a decrease in the duration of the action potential or the area enclosed by it. The rate of repolarization subsequent to the action potential was markedly accelerated. Epinephrine, in general, produced the opposite effects and slowed the repolarization rate as it augmented atrial contraction. Cholinesterase does not seem to play a direct role in cardiac membrane potentials or ion transfer since physostigmine had no effect of its own on the electric manifestations. Certain aspects of the mechanisms involved are discussed.