A rapidly activating delayed rectifier k channel in rabbit sino -atrial node cells. Ito, Hiroyuki, and Kyoichi Ono. Department of Physiology, Faculty of Medicine, Kyushu University, Fukuoka 812-82, Japan
APStracts 2:0073H, 1995.
The single channel current of the delayed rectifier K+ current (IK) was recorded in rabbit sino-atrial node cells. In the cell-attached patch, depolarization from -70 mV to potentials more positive than -50 mV activated the IK channel while repolarization deactivated it. The single channel conductance was 7.8 pS for the outward current and 10.8 pS for the inward current (n = 6). The steady-state open probability (NPo) was maximum at around -30 mV, and markedly decreased at more positive potentials. On repolarization from positive potentials, the channel was initially closed and then rapidly opened. The ensemble average showed an initial rise to a peak followed by the deactivation time course. Since the channel events were completely blocked by E-4031, the drug-sensitive component was examined in the whole-cell current. The steady-state current-voltage relation of the drug-sensitive current showed a marked negative slope at potentials more positive than -10 mV. Upon repolarization, the drug-sensitive current initially increased (removal of inactivation) to the peak of the outward tail current, which was in agreement with the ensemble average of the single channel current. We conclude that IK in the sino-atrial node cells is largely composed of the rapidly activating IK (IK,r) channels, and that the inward rectification of IK,r, which is more marked than had been assumed in previous studies, is due to the decrease in NPo. 

Received 7 July 1994; accepted in final form 23 February 1995.
APS Manuscript Number H592-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 21 March 1995.