Role of the steady-state Na+ channel current in pacemaker depolarizations in young embryonic chick ventricular...

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