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.