Ion conductance and ion selectivity of potassium channels in snail neurones |
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Authors: | H Reuter C F Stevens |
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Institution: | (1) Department of Physiology, Yale University School of Medicine, 06510 New Haven, Connecticut;(2) Present address: Department of Pharmacology, University of Bern, Friedbuhlstraße 49, 3010 Bern, Switzerland |
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Abstract: | Summary Delayed potassium channels were studied in internally perfused neurone somata from land snails. Relaxation and fluctuation analysis of this class of ion channels revealed Hodgkin-Huxley type K channels with an average single channel conductance (
K) of 2.40±0.15 pS. The conductance of open channels is independent of voltage and virtually all K channels seem to be open at maximum K conductance (g
K) of the membrane. Voltage dependent time constants of activation ofg
K, calculated from K current relaxation and from cut-off frequencies of power spectra, are very similar indicating dominant first-order kinetics. Ion selectivity of K channels was studied by ion substitution in the external medium and exhibited the following sequence: T1+>K+>Rb+>Cs+>NH
4
+
>Li+>Na+. The sequence of the alkali cations does not conform to any of the sequences predicted by Eisenman's theory. However, the data are well accommodated by a new theory assuming a single rate-limiting barrier that governs ion movement through the channel.This paper is dedicated to the memory of Walther Wilbrandt. |
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