Characteristics of L‐type calcium channel blockade by lacidipine in guinea‐pig ventricular myocytes

1 The Ca2+‐antagonistic properties of lacidipine were investigated in patch‐clamp guinea‐pig ventricular myocytes. 2 In basal conditions, 0.1 μm lacidipine reduced the action potential duration, associated with a decrease in the L‐type calcium current (Ica,L) to 66 ± 4% of the control value, without a change in the current‐voltage relationship. Sodium current and background potassium currents were not affected. All the effects reached a steady state within 2 min. 3 The Ca2+‐antagonistic effect of lacidipine was voltage‐dependent: a marked negative shift (about 20 mV) of the steady‐state inactivation curve was observed with long (10 s) conditioning prepulses, but not with short (350 ms) prepulses. 4 The onset of and recovery from the voltage‐dependent effect caused by 0.1 μm lacidipine were significantly slower when compared to those of equiactive concentrations of nimodipine (0.5 μm) and nisoldipine (0.1 μm). ICa,L measured after prepulses at —40 mV lasting 500 ms or less was unchanged (95 ± 5% of maximum current value) while it was reduced to 49±10% by nimodipine and 43 ± 9% by nisoldipine (P