Background potassium current active during the plateau of the action potential in guinea pig ventricular myocytes.
Background outward K+ currents in guinea pig ventricular myocytes were characterized over a broad range of membrane potentials, including those corresponding to the plateau of the action potential. The background current that is blocked by 1 mM Ba2+ (IK,p) activates within 5 msec at positive potentials, does not inactivate, and deactivates very rapidly on repolarization. IK,p is insensitive to Cl- channel blockers, internal or external [Cl-], dihydropyridines, and sulfonylureas. In contrast, the delayed rectifier K+ current (IK) was not completely blocked even by 30 mM Ba2+. Ba(2+)-sensitive current density increased progressively from 0.16 +/- 0.04 pA/pF at 0 mV to 0.52 +/- 0.21 pA/pF at +80 mV (n = 13, mean +/- SEM). The background current remains present when [K+]o is reduced to 0 mM, which suppresses the inward rectifier K+ current (IK1). These and other features suggest that IK,p is generated by K+ channels that are distinct from IK1 or IK. The kinetics and voltage dependence of IK,p render it capable of modulating both the height and duration of the cardiac action potential.
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Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205.
Marban
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D000200:Action Potentials; D000818:Animals; D004553:Electric Conductivity; D005544:Forecasting; D006168:Guinea Pigs; D006321:Heart / Q000502:physiology*; D006352:Heart Ventricles; D009206:Myocardium / Q000166:cytology; D011188:Potassium / Q000502:physiology*; D015221:Potassium Channels / Q000502:physiology
D015221:Potassium Channels; D011188:Potassium