title: Characterization of a transient outward K+ current with inward rectification in canine ventricular myocytes.
abstract: 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 microM ryanodine at voltages positive to the K+ equilibrium potential in canine ventricular myocytes. The current was abolished by 200 microM 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.
authors.affiliation: Department of Medicine, Montreal Heart Institute, Quebec, Canada.
authors.forename: G R
authors.initials: GR
authors.lastname: Li
authors.forename: H
authors.initials: H
authors.lastname: Sun
authors.forename: S
authors.initials: S
authors.lastname: Nattel
mesh_terms: D000200:Action Potentials; D000818:Animals; D001464:Barium / Q000378:metabolism; D051668:Delayed Rectifier Potassium Channels; D004285:Dogs; D004594:Electrophysiology; D006352:Heart Ventricles / Q000166:cytology; D066298:In Vitro Techniques; D007700:Kinetics; D008274:Magnesium / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000378:metabolism; D015221:Potassium Channels / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D011743:Pyrimidines / Q000494:pharmacology; D013096:Spermine / Q000378:metabolism
chemical_list: D051668:Delayed Rectifier Potassium Channels; D015221:Potassium Channels; D024661:Potassium Channels, Inwardly Rectifying; D024642:Potassium Channels, Voltage-Gated; D011743:Pyrimidines; D001464:Barium; D013096:Spermine; C034821:4-aminopyrimidine; D008274:Magnesium; D011188:Potassium