Regulation of the action potential configuration by taurine in guinea-pig ventricular muscles

1. Effects of taurine on the action potentials in guinea-pig ventricular muscle were examined at different extracellular Ca2+ concentrations ([Ca]o). Experiments were exerted by conventional microelectrode technique at 36 degrees C. 2. At normal Tyrode solution ([Ca]o = 1.8 mM), taurine (10 and 20 mM) had little or no effect on the 50%, 75% and 90% repolarizations of action potential duration (APD). 3. When [Ca]o was 3.6-10.8 mM [Ca]o, the APD shortening was produced [Ca]o-dependently, which was potentiated by addition of taurine. 4. To the contrary, at low [Ca]o (0.9 mM), the APD was prolonged. Taurine (10 and 20 mM) potentiated to prolong the APD. 5. The amplitude of action potential was depressed by taurine. The resting potential was unaffected. The responses to taurine were almost reversible. 6. Under the calcium overload condition ([Ca]o = 10.8 mM) in which a delayed afterdepolarization and spontaneous action potentials occurred, taurine (10 mM) abolished them completely. 7. These results indicate that taurine causes a dual action on the APD dependent on [Ca]o, and simultaneously reduces the cellular Ca2+ level in calcium overloading muscles.