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Am J Physiol Cell Physiol 277: C891-C898, 1999;
0363-6143/99 $5.00
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Vol. 277, Issue 5, C891-C898, November 1999

K+/Na+ antagonism at cytoplasmic sites of Na+-K+-ATPase: a tissue-specific mechanism of sodium pump regulation

Alex G. Therien and Rhoda Blostein

Department of Biochemistry, McGill University, Montreal, Canada H3G 1A4

Tissue-distinct interactions of the Na+-K+-ATPase with Na+ and K+, independent of isoform-specific properties, were reported previously (A. G. Therien, N. B. Nestor, W. J. Ball, and R. Blostein. J. Biol. Chem. 271: 7104-7112, 1996). In this paper, we describe a detailed analysis of tissue-specific kinetics particularly relevant to regulation of pump activity by intracellular K+, namely K+ inhibition at cytoplasmic Na+ sites. Our results show that the order of susceptibilities of alpha 1 pumps of various rat tissues to K+/Na+ antagonism, represented by the ratio of the apparent affinity for Na+ binding at cytoplasmic activation sites in the absence of K+ to the affinity constant for K+ as a competitive inhibitor of Na+ binding at cytoplasmic sites, is red blood cell < axolemma approx  rat alpha 1-transfected HeLa cells < small intestine < kidney < heart. In addition, we have carried out an extensive analysis of the kinetics of K+ binding and occlusion to the cytoplasmic cation binding site and find that, for most tissues, there is a relationship between the rate of K+ binding/occlusion and the apparent affinity for K+ as a competitive inhibitor of Na+ activation, the order for both parameters being heart >=  kidney > small intestine approx  rat alpha 1-transfected HeLa cells. The notion that modulations in cytoplasmic K+/Na+ antagonism are a potential mode of pump regulation is underscored by evidence of its reversibility. Thus the relatively high K+/Na+ antagonism characteristic of kidney pumps was reduced when rat kidney microsomal membranes were fused into the dog red blood cell.

alpha 1-isoform; heart; kidney


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