Developmental change in fast Na channel properties in embryonic chick ventricular heart cells.
To assess development changes in kinetic properties of the cardiac sodium current, whole-cell voltage-clamp experiments were conducted using 3-, 10-, and 17-day-old embryonic chick ventricular heart cells. Experimental data were quantified according to the Hodgkin-Huxley model. While the Na current density, as examined by the maximal conductance, drastically increased (six- to seven-fold) with development, other current - voltage parameters remained unchanged. Whereas the activation time constant and the steady-state activation characteristics were comparable among the three age groups, the voltage dependence of the inactivation time constant and the steady-state inactivation underwent a shift in the voltage dependence toward negative potentials during embryonic development. Consequently, the steady-state (window current) conductance, which was sufficient to induce automatic activity in the young embryos, was progressively reduced with age.
Sada
H
H
Department of Pharmacology, School of Medicine, Yamaguchi University, Ube, Japan.
Ban
T
T
Fujita
T
T
Ebina
Y
Y
Sperelakis
N
N
D000818:Animals; D002642:Chick Embryo; D004594:Electrophysiology; D006321:Heart / Q000196:embryology; D008564:Membrane Potentials; D018408:Patch-Clamp Techniques; D015222:Sodium Channels / Q000502:physiology*
D015222:Sodium Channels