Characterization of a ttx-sensitive sodium current in pacemaker
cells isolated from the rabbit sinoatrial node.
Muramatsu, Hikaru, An-Ruo Zou, Gerald A. Berkowitz, and Richard D.
Nathan.
Department of Physiology, Texas Tech University Health Sciences
Center, Lubbock, TX 79430, USA
APStracts 2:0495H, 1995.
A tetrodotoxin (TTX)-sensitive Na+ current (iNa) was investigated in
single pacemaker cells after 1-4 days in culture. Ruptured-patch and
perforated-patch whole-cell recording techniques were used to record
iNa and spontaneous electrical activity, respectively. For 7 cells
exposed to 20 mM Na+ (22-24 oC) and held at -98 mV (25% of the
channels inactivated), the uncorrected maximum iNa was -39 +/- 10
pA/pF at -29.1 +/- 3.4 mV (mean +/- SEM), and maximum conductance was
0.9 +/- 0.2 nS/pF (1.6 +/- 0.2 mS/cm2). Half-activation and
inactivation potentials were -41.4 +/- 2.0 mV and -90.6 +/- 2.5 mV,
and the corresponding slope factors were 6.0 +/- 0.4 mV and 6.4 +/-
0.6 mV. Both inactivation and recovery from inactivation were best
fit by sums of two exponentials. During action potential clamp, a
TTX-sensitive compensation current accounted for 55% of the upstroke
velocity. The results suggest that iNa contributes significantly to
the action potential in some nodal pacemaker cells, and the
characteristics of iNa are similar to those of atrial and ventricular
myocytes.
Received 2 June 1995; accepted in final form 18 October 1995.
APS Manuscript Number H508-5.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 November 95