Action potential duration-stabilizing action of taurine in guinea pig ventricular myocytes

To examine taurine actions on the rate of repolarization of action potentials (AP), L-type Ca2+ (I-Ca), late outward K+ (I-K) and the inward rectifier currents as affected by the external Ca2+ concentrations ([Ca2+](o)), whole-cell voltage-clamp and current-clamp experiments were conducted in guinea pig ventricular myocytes. At a high (3.6 mM) [Ca2+](o), 10 mM taurine suppressed both I-Ca and I-K, shortened AP duration and decelerated the rate (-dV/dt) of terminal repolarization of AP. In contrast, at a low (0.9 mM) [Ca2+](o), taurine intensified both I-Ca and I-K, lengthened AP duration and accelerated -dV/dt. However, at either [Ca2+](o), the resting membrane potential was slightly hyperpolarized, and the inward rectifier current examined by the ramp-pulse protocol remained unaffected by taurine. Taurine is suggested to maintain a stable AP duration by altering the inward Ca2+ and I-K in the opposite directions, depending on [Ca2+](o). The relevance of the stabilizing action of taurine on the AP duration to its reported antiarrhythmic efficacies is discussed.