AJP - Renal Physiology, Vol 259, Issue 2 227-F232, Copyright © 1990 by American Physiological Society

ARTICLES

Effect of high extracellular K+ on Na-K-ATPase in cultured canine kidney cells

M. A. Manuli and I. S. Edelman
Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.

The Madin-Darby canine kidney (MDCK) cell line was used to evaluate the influence of high extracellular K+, independent of hormonal effects, on renal Na-K-adenosinetriphosphatase (ATPase) activity and abundance. Confluent cell monolayers were incubated in control (5 mM) or high K+ (7.5 mM) medium for 24 h. Exposure to high K+ elicited a 46% rise in Na-K-ATPase activity and a 55% increase in ouabain-sensitive 86Rb uptake. Na-K-ATPase abundance, estimated from the number of ouabain-binding sites, also increased 63% over control in cells exposed to 7.5 mM K+, and as a consequence there was no statistically significant change in the catalytic turnover number. Northern blot analysis using rat cDNA probes for the alpha 1- and beta-subunits showed no corresponding changes in subunit-specific mRNA abundances at 24 h. We conclude that chronic exposure to high extracellular K+ produces a rise in renal epithelial Na-K-ATPase activity and active K+ transport, independent of changes in aldosterone, renal blood flow, or extracellular Na+ concentration. This effect is due to an increase in enzyme abundance rather than a change in catalytic turnover rate. The results of Northern analysis suggest that regulation of Na-K-ATPase activity and abundance by high K+ may involve translational or posttranslational mechanisms, but further study with cDNA probes of canine origin is needed to resolve this issue.

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