Role of slow inward current on premature excitation in ventricular muscle.

Action potential durations in premature excitations showed paradoxical prolongation at the shorter coupling intervals; this was abolished by manganous ions. Voltage-clamp experiments also disclosed a transient increase of slow inward current in premature excitations. These results indicate that prolongation of action potential durations was mainly brought about by changes in slow inward current, especially in its characteristics of recovery from inactivation.