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Developmental change in fast Na channel properties in embryonic chick ventricular heart cells

1995; NRC Research Press; Volume: 73; Issue: 10 Linguagem: Inglês

10.1139/y95-205

1205-7541

Hideaki Sada, Takashi Ban, Takeshi Fujita, Yoshio Ebina, Nicholas Sperelakis,

Neuroscience and Neural Engineering

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.