Electrophysiological study of cibenzoline in voltage-clamped rabbit sinoatrial node preparations

Effects of cibenzoline (0.1-30 microM) on membrane potentials and currents were investigated in rabbit sinoatrial node cells using conventional microelectrode and double microelectrode voltage clamp methods. Cibenzoline reduced the heart rate, the maximum rate of rise and the action potential amplitude in a dose-dependent manner. At the same time, the action potential duration at half-amplitude was prolonged, and the slope of phase 4 depolarization was decelerated. The voltage clamp experiment revealed that cibenzoline (7-30 microM) depressed the slow inward current, the time-dependent potassium outward current and the hyperpolarization activated current. Neither the kinetic variable of the time-dependent potassium outward current nor the decay time of the outward current tail was altered by the drug perfusion. The results suggest that cibenzoline exerts a depressant effect on the electrical activity of sinoatrial node cells and that the depression of the currents induced by cibenzoline is due to a reduction in conductances of the current systems.