Age-related changes in activation and inactivation kinetics of the Na channels in cultured heart muscle from chick embryo

To investigate age-related changes in Na^+ channel kinetics, ventricular cells obtained from chick embryos of various developmental stages were voltage-clamped with patch pipettes, and the Na^+ current (I_<Na>) together with the membrane potential (V_m) were recorded (16℃). The data stored in VTR as PCM signal was A/D converted and analyzed in terms of Hodgkin-Huxley model. I_<Na> underwent the activation/inactivation sequence in response to change in V_m. While the activation kinetics little changed throughout embryogenesis, the inactivation kinetics was altered with embryonic development. Yet, the density of Na^+ channel per unit membrane area also was drastically increased with development. We discuss the present voltage-clamp data in comparison with those obtained from different tissues and/or animal species.