AJP - Cell Physiology, Vol 266, Issue 1 C37-C41, Copyright © 1994 by American Physiological Society

ARTICLES

Effect of Napip on K0 activation of the Na-K pump in adult rat cardiac myocytes

T. A. Kinard, X. Y. Liu, S. Liu and J. R. Stimers
Department of Pharmacology and Toxicology, University of Arkansas for Medical Sciences, Little Rock 72205.

To determine if environmental factors influence the external K (K0) dependence of Na-K pump current (Ip), we systematically varied internal (pipette) Na (Napip) and Na-K pump activity while measuring the K0 dependence in adult rat cardiac myocytes. For each Napip, reactivation of Ip by K0 was dose dependent. The maximal Ip (Ipmax) and apparent affinity for K0 binding to the Na-K pump (K0.5) increased as Napip increased. The results of making an equimolar substitution of tetramethylammonium for K and Cs, and partial Ip inhibition with ouabain, also showed that Ipmax and K0.5 increased as Napip increased. We simulated pump activity as a function of intracellular Na (Nai) and K0 using a cyclic model of the Na-K pump and found that the model predicts K0.5 for K0 binding increases as Na increases, even when the conditions are adjusted by removing pipette K and partial pump inhibition with ouabain.

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