Two types of outward K+ channel currents in early embryonic chick ventricular myocytes.
Outward K+ currents were recorded from 3-day-old embryonic chick ventricular myocytes using the patch clamp method. Two types of macroscopic outward currents were observed, one with rapid activation and de-activation time courses, and the other displaying a slower activation and long-duration tail currents. A time-dependent inactivation at positive potentials was a feature of the rapidly-activating current, allowing resolution of an early outward current. Single K+ channel currents were recorded using the outside-out patch technique. Two classes of K+ channels, which may contribute to the macroscopic currents, were differentiated on the basis of their conductances and kinetics. One class (ca 20 pS conductance) showed a rapid activation upon depolarization, and the other class (ca 60 pS) had a more delayed activation. A time-dependent inactivation of the rapid-activating, single-channel K+ current was also recorded. The two types of K+ channels contribute outward current during the plateau and promote the repolarization of the action potential, and the slowly de-activating K+ current may also be involved in the electrogenesis of automaticity observed in some of these cells.
Josephson
I R
IR
Department of Physiology and Biophysics, University of Cincinnati, College of Medicine.
Sperelakis
N
N
D000200:Action Potentials; D000818:Animals; D001693:Biological Transport, Active; D002478:Cells, Cultured; D002642:Chick Embryo; D006352:Heart Ventricles; D066298:In Vitro Techniques; D015640:Ion Channel Gating / Q000502:physiology; D009206:Myocardium / Q000378:metabolism*; D011188:Potassium / Q000493:pharmacokinetics*; D015221:Potassium Channels / Q000502:physiology*
D015221:Potassium Channels; D011188:Potassium