Role of Na‐K ATPase in regulation of resting membrane potential of cultured rat skeletal myotubes

Chaya Brodie, Asia Bak, A. Shainberg, S. R. Sampson

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The role of Na‐K ATPase in the determination of resting membrane potential (Em) as a function of extracellular K ion concentration was investigated in cultured rat myotubes. The Em of control myotubes at 37°C varied as a function of (K+)0 with a slope of about 58–60 mV per ten‐fold change in (K+)0. Inhibition of the Na‐K pump with ouabain or by reduced temperature revealed that this relation consists of two components. One, between (K+)0 of 10 and 100 mM, remains unchanged by alterations in enzyme activity; The second, between (K+)0 of 1 and 10 mM, is related to the amount of Na‐K pump activity, the slope decreasing as pump activity decreases. Indeed, with complete inhibition of the Na‐K pump, Em does not change over the range of (K+)0 1 to 10 mM. Measurements of 86Rb efflux and input resistance of individual myotubes showed that membrane permeability does not change as (K+)0 increases from 1 to 10 mM but increases as (K+)0 increases further. Monensin, which increases Na ion permeability, increases Em at values of external K+ below 10 mM, and is without effect at higher values of K+ concentration. The effect of monensin is blocked by ouabain. Tetrodotoxin, which blocks voltage‐dependent Na+ channels, decreases Em at low (2–10 mM) K+. We conclude that changes in Em as a function of extracellular K+ concentration in the physiological range are not adequately explained by the diffusion potential hypothesis of Em, and that other theories (electrogenic pump, surface‐absorption) must be considered.

Original languageEnglish
Pages (from-to)191-198
Number of pages8
JournalJournal of Cellular Physiology
Issue number2
StatePublished - Feb 1987


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