Effects of Internal Divalent Cations on Voltage-Clamped Squid Axons |
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| Authors: | Ted Begenisich and Carl Lynch |
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| Affiliation: | From the Department of Biophysics, University of Maryland School of Medicine, Baltimore, Maryland 21201, the Department of Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York 14620, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02546 |
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| Abstract: | We have studied the effects of internally applied divalent cations on the ionic currents of voltage-clamped squid giant axons. Internal concentrations of calcium up to 10 mM have little, if any, effect on the time-course, voltage dependence, or magnitude of the ionic currents. This is inconsistent with the notion that an increase in the internal calcium concentration produced by an inward calcium movement with the action potential triggers sodium inactivation or potassium activation. Low internal zinc concentrations (~1 mM) selectively and reversibly slow the kinetics of the potassium current and reduce peak sodium current by about 40% with little effect on the voltage dependence of the ionic currents. Higher concentrations (~10 mM) produce a considerable (ca. 90%) nonspecific reversible reduction of the ionic currents. Large hyperpolarizing conditioning pulses reduce the zinc effect. Internal zinc also reversibly depolarizes the axon by 20–30 mV. The effects of internal cobalt, cadmium, and nickel are qualitatively similar to those of zinc: only calcium among the cations tested is without effect. |
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