Abstract
The electrophysiological and antiarrhythmic effects of LB-46 on the membrane potentials of Purkinje fibers and ventricular muscle fibers of the dog were studied by means of the microelectrode technique in comparison with those of propranolol. The effects of LB-46 on the membrane potential of Purkinje fibers consisted of a reduction in amplitude of the action potential due to a diminution or loss of overshoot and unchanged resting potential, an acceleration of repolarization, a prolongation of latency, and a decrease in mean rate of rise. Nearly the same electrophysiological effects were produced by propranolol at a lower concentration. LB-46, as well as propranolol, prevented the isoproterenol-induced arrhythmia by blocking the increase in diastolic depolarization. The antiarrhythmic action of LB-46 may be due considerably to direct action on the cardiac cell membrane and partly to a beta-receptor blockade. It is very probable that LB-46 is more specific in beta-receptor blocking and little weaker in antiarrhythmic activity than propranolol.
