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

Am J Physiol. 1998 Mar;274(3):C577-85. doi: 10.1152/ajpcell.1998.274.3.C577.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Action Potentials
  • Animals
  • Barium / metabolism
  • Delayed Rectifier Potassium Channels
  • Dogs
  • Electrophysiology
  • Heart Ventricles / cytology
  • In Vitro Techniques
  • Kinetics
  • Magnesium / metabolism
  • Myocardium / metabolism*
  • Potassium / metabolism
  • Potassium Channels / drug effects
  • Potassium Channels / metabolism*
  • Potassium Channels / physiology
  • Potassium Channels, Inwardly Rectifying*
  • Potassium Channels, Voltage-Gated*
  • Pyrimidines / pharmacology
  • Spermine / metabolism

Substances

  • Delayed Rectifier Potassium Channels
  • Potassium Channels
  • Potassium Channels, Inwardly Rectifying
  • Potassium Channels, Voltage-Gated
  • Pyrimidines
  • Barium
  • Spermine
  • 4-aminopyrimidine
  • Magnesium
  • Potassium