Developmental changes of action potential configuration and the transient
outward potassium current in canine epicardium.
Gilmour, Linda M. Pacioretty and Robert F., Jr.
Department of Physiology, College of Veterinary Medicine, Cornell
University, Ithaca, NY
APStracts 2:0013H, 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 12 August 1994; accepted in final form 5 January 1995.
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 24 February 1995.