Sodium currents in the membrane of isolated cardiomyocytes

In the experiments on ventricular myocytes which were enzymatically isolated from hearts of 4 weeks old rats and were internally perfused in voltage clamp conditions the existence of two sodium currents was demonstrated. The data obtained suggest that the so called fast sodium current in the membrane of ventricular myocytes is in fact a sum of two currents with different kinetics and potential dependent properties, sensitivity to tetrodotoxin and external pH which are supposed to be passed through separate membrane channel populations. Due to about four fold difference in their time courses of inactivation the currents were called fast sodium current (IfNa) and slow sodium current (IsNa).