Effect of high extracellular K+ on Na-K-ATPase in cultured canine kidney cells.
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.
Manuli
M A
MA
Department of Biochemistry and Molecular Biophysics, College of Physicians and Surgeons, Columbia University, New York, New York 10032.
Edelman
I S
IS
D000818:Animals; D015152:Blotting, Northern; D002460:Cell Line; D004285:Dogs; D005110:Extracellular Space / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology / Q000378:metabolism*; D009994:Osmolar Concentration; D011188:Potassium / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D012967:Sodium Dodecyl Sulfate / Q000494:pharmacology; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism*
D012333:RNA, Messenger; D012967:Sodium Dodecyl Sulfate; D000254:Sodium-Potassium-Exchanging ATPase; D011188:Potassium