CARDIAC ELECTROPHYSIOLOGICAL EFFECTS OF LEVOSIMENDAN, A NEW CALCIUM SENSITIZER

1. The conventional microelectrode and the patch clamp techniques were used to study the electrophysiological effects of levosimendan, a new calcium sensitizing cardiotonic drug, in cardiac ventricular muscle. 2. Levosimendan (5 mu M) did not change the main repolarizing currents , such as the inward rectifier potassium, transient outward and the de layed rectifier outward potassium current, in rabbit ventricular myocy tes. 3. In rabbit ventricular muscle, levosimendan, at relatively low concentrations (0.1-1 mu M), did not change significantly the amplitud e of the inward calcium current but increased the amplitude of the twi tch tension. 4. In guinea pig ventricular muscle, levosimendan, at hig her concentrations (1-5 mu M), significantly increased the amplitude o f the inward calcium current and the slow response action potential pa rameters. 5. It is concluded that levosimendan, in addition to its cal cium sensitizing properties characterized by ''silent electrophysiolog y,'' exhibits cardiac electrophysiological effects similar to those of phosphodiesterase inhibitors.