Inhibition of the fast Na+ current by taurine in guinea pig ventricular myocytes.

1. Effects of taurine on the fast Na+ current (INa) in isolated guinea pig ventricular cardiomyocytes were examined by using the whole-cell voltage-clamp method. Experiments were performed at room temperature (22 degrees C). 2. Test pulses were applied from -60 to +40 mV from a holding potential of -90 mV. Addition of taurine to the bath solution markedly inhibited the INa in a concentration-dependent manner; at -30 mV, by 39.0 +/- 4.1% (n = 8, P < 0.01) at 10 mM and by 56.1 +/- 4.7% (n = 9, P < 0.001) at 20 mM. 3. Simultaneously, the time constant of inactivation phase for INa decreased to 0.95 +/- 0.4 ms (n = 8, P < 0.05) at 10 mM and to 1.02 +/- 0.3 ms (n = 9, P < 0.05) at 20 mM, from 1.29 +/- 0.3 ms in normal Tyrode solution. 4. These results indicate that taurine inhibits the INa current, which would play an important role in the cell functions.