Developmental changes of action potential configuration and the
transient outward potassium current in canine epicardium.
Pacioretty, Linda M., and Robert F. Gilmour, Jr.
Department of Physiology, College of Veterinary Medicine, Cornell
University, Ithaca, NY
APStracts 2:0131H, 1995.
Developmental changes of the transient outward current (Ito) and
action potential configuration were determined in canine epicardium
ranging in age from fetal to 60 weeks. The contributions of Ito to
rapid initial repolarization and to terminal repolarization were
estimated by measuring the amplitude of phase 1 of the action
potential and action potential duration, respectively. Phase 1
amplitude decreased progressively from fetal to 40 weeks, and
remained constant thereafter. Action potential duration decreased
from fetal to 2 weeks, increased to 20 weeks and tended to decrease
thereafter. Peak Ito at +40 mV increased progressively from 2 to 60
weeks. However, Ito density was less at 2 to 10 weeks than at 20 to
60 weeks. The time constant of decay of Ito increased with age from 2
to 60 weeks, whereas the steady-state voltage dependence of
inactivation did not vary with age. The time constant for the initial
rapid phase of recovery from inactivation decreased from 2 to 10
weeks, and remained constant thereafter. The time constant for the
more slowly evolving phase did not vary with age. The observation
that the age-dependent reduction in phase 1 amplitude did not
necessarily coincide with significant increases in Ito density
suggests that maturation of other ionic currents or transport
mechanisms may contribute to developmental alterations of phase 1
repolarization.
Received 5 January 1995; accepted in final form 12 August 1994.
APS Manuscript Number H724-4.
Article publication pending Am. J. Physiol. (Heart Circ. Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 19 April 1995.