Gr. Li et al., CHARACTERIZATION OF A TRANSIENT OUTWARD K+ CURRENT WITH INWARD RECTIFICATION IN CANINE VENTRICULAR MYOCYTES, American journal of physiology. Cell physiology, 43(3), 1998, pp. 577-585
The threshold potential for the classical depolarization-activated tra
nsient outward K+ current and Cl- current is positive to -30 mV. With
the whole cell patch technique, a transient outward current was elicit
ed in the presence of 5 mM 4-aminopyridine (4-AP) and 5 mu M ryanodine
at voltages positive to the K+ equilibrium potential in canine ventri
cular myocytes. The current was abolished by 200 mu M Ba2+ or omission
of external K+ (K-o(+)) and showed biexponential inactivation. The cu
rrent-voltage relation for the peak of the transient outward component
showed moderate inward rectification. The transient outward current d
emonstrated voltage-dependent inactivation (half-inactivation voltage:
-43.5 +/- 3.2 mV) and rapid, monoexponential recovery from inactivati
on (time constant: 13.2 +/- 2.5 ms). The reversal potential responded
to the changes in K-o(+) concentration. Action potential clamp reveale
d two phases of Ba2+-sensitive current during the action potential, in
cluding a large early transient component after the upstroke and a lat
er outward component during phase 3 repolarization. The present study
demonstrates that depolarization may elicit a Ba2+- and K-o(+)-sensiti
ve, 4-AP-insensitive, transient outward current with inward rectificat
ion in canine ventricular myocytes. The properties of this K+ current
suggest that it may carry a significant early outward current upon dep
olarization that may play a role in determining membrane excitability
and action potential morphology.