ROLE OF THE STEADY-STATE NA+ CHANNEL CURRENT IN PACEMAKER DEPOLARIZATIONS IN YOUNG EMBRYONIC CHICK VENTRICULAR MYOCYTES

To assess the age-related changes in kinetic properties of the cardiac Na+ channel, whole-cell voltage-clamp (v-c) experiments were conducte d using 3-, 10- and 17-day-old embryonic chick ventricular heart cells . In line with the first-order kinetic model, kinetic parameters for t he activation and inactivation of the channel were determined from the v-c results. Simulation studies using kinetic parameters so determine d have reproduced the current-voltage relations and the steady-state i nactivation characteristics observed in cells in the three age groups. The rate of depolarization of the simulated action potentials was als o comparable to that experimentally recorded. In conclusion, the stead y-state Na+ conductance can play a significant role in the automatic d epolarizations observed in young embryonic ventricular cells.