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Department of Medicine, Montreal Heart Institute and University of Montreal, Montreal, Quebec, Canada H1T 1C8
The threshold
potential for the classical depolarization-activated transient outward
K+ current and
Cl
current is positive to
30 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
K+ equilibrium potential in canine
ventricular myocytes. The current was abolished by 200 µM
Ba2+ or omission of external
K+
(K+o) and showed biexponential
inactivation. The current-voltage relation for the peak of the
transient outward component showed moderate inward rectification. The
transient outward current demonstrated voltage-dependent inactivation
(half-inactivation voltage: 43.5 ± 3.2 mV) and rapid,
monoexponential recovery from inactivation (time constant: 13.2 ± 2.5 ms). The reversal potential responded to the changes in
K+o concentration. Action potential clamp
revealed two phases of
Ba2+-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
Ba2+- and
K+o-sensitive, 4-AP-insensitive, transient outward current with inward rectification in canine ventricular myocytes. The properties of this
K+ 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.
cardiac electrophysiology; transient outward potassium current; whole cell patch clamp; excitability; barium- and/or potassium-sensitive transient outward peak current
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