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Speed of voltage threshold shift after step-changes of (Na) 0 and (Ca) 0 at the outer surface of frog skin

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Summary

The voltage thresholdV s of the N-shaped I–V curve of in vitro frog skin was studied with respect to its dependence on the Na- and Ca-concentration of the outer bathing solution. Step changes of (Na)0 and (Ca)0 were repeatedly produced in a fast flow chamber, and the time course of the resulting threshold change was determined stroboscopically under voltage clamp conditions. In response to an increasing step of (Na)0 (complete in 20 ms),V s increased rather slowly with a halftime of about 200 ms, while the short circuit current increased 4 times faster. This increase in short circuit current can have raised the cellular Na-concentration (Na) c by no more than 0.1 mM within 200ms. Therefore, the change ofV s -although slow—will hardly have been caused by an increase of (Na) c . We explain the change ofV s by a direct influence of (Na)0 on the apical membrane of the Str. granulosum. In response to a step increase of (Ca)0,V s decreased with a halftime of 50 ms. This fast response and the low Ca-permeability of the apical membrane again make a causal role of cellular concentration changes unlikely. Apparently, (Na)0 and (Ca)0 affectV s directly—from the outside of the membrane—and not by mediation of more time consuming changes of intracellular concentrations.

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Authors and Affiliations

  1. Abteilung für Membranforschung an Epithelien, II. Physiologisches Institut, D-6650, Homburg (Saar), Germany

    U. Gebhardt & B. Lindemann

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  1. U. Gebhardt
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  2. B. Lindemann
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Supported by the DFG through Sonderforschungsbereich 38, project C1.

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Gebhardt, U., Lindemann, B. Speed of voltage threshold shift after step-changes of (Na) 0 and (Ca) 0 at the outer surface of frog skin. Pflugers Arch. 347, 9–18 (1974). https://doi.org/10.1007/BF00587050

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  • DOI: https://doi.org/10.1007/BF00587050

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