Effects of a new calcium entry blocking agent, KB-944, on the membrane potential and currents of mammalian ventricular muscle cells.

KB-944 (10(-5)-10(-4) M) decreased the action potential duration measured at 30% repolarization and hyperpolarized the resting membrane potential in ventricular trabeculae of the dog heart. In single ventricular cells of the guinea-pig heart, KB-944 (10(-4) M) abolished the slow inward current and produced an outward shift of the late current measured at the end of 200 msec clamp pulse. From these results it appears that KB-944 selectively blocks the slow inward current and may increase the background potassium conductance.