Effects of Flunarizine on Impulse Initiation in Canine Purkinje Fibers

Effects of Flunarizine on Impulse Initiation. Introduction: The calcium channel blocker, flunarizine, selectively blocks accumulation of intracellular calcium during conditions of calcium overload. It has been reported to selectively terminate delayed after depolarization‐induced arrhythmias in intact dogs. Methods and Results: Using standard microelectrode techniques, we studied the effects of flunarizine on the transmembrane action potential and various arrhythmogenic mechanisms in canine Purkinje fibers. Flunarizine significantly decreased the fast response action potential duration at 50% repolarization in a concentration‐dependent manner (10‐ 8 to 10‐ 5 M), but had no effect on maximum diastolic potential, overshoot, maximum upstroke velocity (V max ), or APD at 90% repolarization. For Ca 2+ ‐induced slow response action potentials, flunarizine decreased the overshoot, and prolonged action potential duration at both 50% and 90% repolarization. It had no effect on automaticity of Purkinje fibers exposed to solutions containing either low K + or barium chloride. Flunarizine, 10‐ 5 M, inhibited the development of both ouabain‐induced and calcium‐ and catecholamine‐induced delayed after depolarizations. It did not inhibit the development of cesium‐induced early afterdepolarizations. Conclusions: Thus, in vitro, flunarizine selectively suppresses delayed after depolarizations and has no effects on early afterdepolarizations or normal or abnormal automaticity. Hence, its utility in intact animal models of triggered arrythmias is borne out mechanistically in these isolated tissue studies. ( J Cardiovasc Electrophysiol, Vol. 3, pp. 306–314, August 1992 )