Identification of ionic currents underlying the repolarization process in the frog auricle.

Voltage clamp experiments were performed to analyse the voltage and time dependence of the secondary inward current in frog atrial preparations. The fibers were treated with tetrodotoxin and tetraethylammonium or cesium to suppress the fast inward current and reduce the outward current; Cl- was replaced by CH3SO-4 to reduce the background current. Evidence is obtained suggesting that the inactivation process of the calcium dependent inward current is relatively rapid in the frog atrium. The current-voltage relationship of this current system appears to be nonlinear. The calcium dependent inward current transient is followed by a subsidiary net inward current which is presumably mainly Na+ dependent and underlies the depolarization tail of the action potential.