The Journal of General Physiology
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The Journal of General Physiology, Vol 53, 685-703, Copyright © 1969 by The Rockefeller University Press

ARTICLE

The Influence of External Potassium on the Inactivation of Sodium Currents in the Giant Axon of the Squid, Loligo pealei

William J. Adelman Jr. 1 and Yoram Palti 1

1 From the Department of Physiology, The University of Maryland School of Medicine, Baltimore, Maryland 21201, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543.

Dr. Palti's permanent address is the Department of Physiology, The Hebrew University, Hadassah Medical School, Jerusalem, Israel

Isolated giant axons were voltage-clamped in seawater solutions having constant sodium concentrations of 230 mM and variable potassium concentrations of from zero to 210 mM. The inactivation of the initial transient membrane current normally carried by Na+ was studied by measuring the Hodgkin-Huxley h parameter as a function of time. It was found that h reaches a steady-state value within 30 msec in all solutions. The values of hinfin, tauh, alphah,and ßh as functions of membrane potential were determined for various [Ko]. The steady-state values of the h parameter were found to be inversely related, while the time constant, tauh, was directly related to external K+ concentration. While the absolute magnitude as well as the slopes of the hinfin vs. membrane potential curves were altered by varying external K+, only the magnitude and not the shape of the corresponding tauh curves was altered. Values of the two rate constants, alphah and ßh, were calculated from hinfin and tauh values. alphah is inversely related to [Ko] while ßh is directly related to [Ko] for hyperpolarizing membrane potentials and is independent of [Ko] for depolarizing membrane potentials. Hodgkin-Huxley equations relating alphah and ßh to Em were rewritten so as to account for the observed effects of [Ko]. It is concluded that external potassium ions have an inactivating effect on the initial transient membrane conductance which cannot be explained solely on the basis of potassium membrane depolarization.

Submitted on December 16, 1968


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