Inotropic and electrophysiological effects of AB--2, a new antiarrhythmic agent, on isolated cardiac preparations

Abstract

Effects of AB--2, a compound structurally related to quinidine, on the force of contraction and intracellular potentials were studied in isolated cardiac preparations obtained from guinea pigs, rabbits, cats and dogs. AB--2 in concentrations of 3 and 6 microM increased the force of contraction of both ventricular and atrial muscle. This effect was absent in reserpinized preparations. In concentrations of 24-96 microM, AB--2 induced a concentration-dependent depression of contraction (ED50 approximately equal to 55 microM). Electrophysiological effects consisted of: 1) concentration-dependent reduction of maximum rate of depolarization (Km for guinea pig ventricular and atrial muscles was 72 and 111 microM, resp.) with no change in the resting membrane potential; 2) shortening of action potential duration in ventricular and Purkinje fibers while prolongation in atrial muscle; 3) reduction of pacemaker activity in Purkinje fibers. It is concluded that electrophysiological effects of AB--2 are similar to those of Class I antiarrhythmic agents.