Physical-chemical approach to the transient change in Na ion conductivity of excitable membranes

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Abstract
A new method is proposed for analyzing the rapid transient current component (Na+) in voltage clamp experiments on excitable membranes. The method is based on only 2 general assumptions: Na+ conductivity of an excitable membrane is determined by some general membrane parameter, the kinetic behavior of which is consistently described by the sum of 2 simple exponential terms. A least square computer analysis for the data by Goldman et Schauf (1973) on Myxicola axons is described. The method gives (as a result) the relationship between conductivity and membrane parameter. A physically plausible chemical model (cycle of 3 states) is proposed for a dissipative control of the Na+ conductivity. The rate constants for the specific model are calculated from kinetic parameters derived only from the general analysis. These rate constants reproduce the original voltage clamp data in every feature which includes peak current ratios (H.infin.-shift with test potential. By allowing for differences in the experimental conditions, essentially the same rate constants as in the voltage clamp data of A.L. Hodgkin and A.F. Huxley on squid giant axons are derived.