Role of the rapidly activating delayed rectifier k+ current in
sino-atrial node pacemaker activity.
Ono, Kyoichi, and Hiroyuki Ito.
Department of Physiology, Faculty of Medicine, Kyushu University,
Fukuoka 812-82, Japan
APStracts 2:0074H, 1995.
A rapidly activating component of delayed rectifier K+ current (IK,r)
was dissected using a selective blocker, E-4031, during the action
potential clamp (AP clamp) in rabbit sino-atrial node cells.
Application of E-4031 induced a large compensation current, of which
amplitude was similar to or larger than the net current during
repolarization and was maximum (2.2 +/- 0.2 pA/pF) at -46.0 +/- 1.8
mV (n = 13). During the slow diastolic depolarization, the
compensation current gradually decayed, and then abruptly decreased
at the peak of action potential. The time-dependent change of IK,r
was calculated using a mathematical model, in which independent gates
of activation and inactivation were assumed based on the whole-cell
voltage clamp experiments. The reconstructed IK,r corresponded well
with the E-4031-sensitive current measured by the AP clamp method.
Partial block of IK,r by E-4031 in spontaneously beating cells
decreased the action potential amplitude, maximum rate of rise and
maximum rate of repolarization and induced a positive shift of the
maximum diastolic potential. Complete block of IK,r terminated the
spontaneous action potential at -37.4 +/- 2.9 mV (n = 3). It is
concluded that IK,r plays an essential role in determining the
maximum diastolic potential and ensures the firing of the following
action potential in sino-atrial node cells.
Received 7 July 1994; accepted in final form 23 February 1995.
APS Manuscript Number H593-4.
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.