Characterization of a transient outward K1 current with inward rectification in canine ventricular myocytes

Li, Gui-Rong, Haiying Sun, and Stanley Nattel. Characterization of a transient outward K1 current with inward rectification in canine ventricular myocytes. Am. J. Physiol. 274 (Cell Physiol. 43): C577–C585, 1998.—The threshold potential for the classical depolarization-activated transient outward K1 current and Cl2 current is positive to 230 mV. With the whole cell patch technique, a transient outward current was elicited in the presence of 5 mM 4-aminopyridine (4-AP) and 5 μM ryanodine at voltages positive to the K1 equilibrium potential in canine ventricular myocytes. The current was abolished by 200 μM Ba21 or omission of external K1 (Ko ) and showed biexponential inactivation. The currentvoltage relation for the peak of the transient outward component showed moderate inward rectification. The transient outward current demonstrated voltage-dependent inactivation (half-inactivation voltage: 243.5 6 3.2 mV) and rapid, monoexponential recovery from inactivation (time constant: 13.2 6 2.5 ms). The reversal potential responded to the changes in Ko 1 concentration. Action potential clamp revealed two phases of Ba21-sensitive current during the action potential, including a large early transient component after the upstroke and a later outward component during phase 3 repolarization. The present study demonstrates that depolarization may elicit a Ba21and Ko -sensitive, 4-AP-insensitive, transient outward current with inward rectification in canine ventricular myocytes. The properties of this K1 current suggest that it may carry a significant early outward current upon depolarization that may play a role in determining membrane excitability and action potential morphology.