Hypokalemia downregulates cardiac alpha 1 and skeletal muscle alpha 2 isoforms of Na+,K(+)-ATPase in ferrets.

K+ deficiency decreases amount of Na+,K(+)-ATPase in cardiac and skeletal muscle (SM) and differentially regulates alpha- and beta-subunit isoforms. Expression of the alpha 3 isoform during K+ deficiency is unknown, however. In the myocardium of normal adult ferrets, alpha 1 and alpha 3 isoforms are expressed. Therefore, we examined in ferrets the effects of K+ deficiency in levels of alpha- and beta-subunit isoforms. A K+ deficient diet greatly reduced plasma K+ concentrations. Tissue K+ content in myocardium remained unchanged, whereas that of SM decreased markedly. Corresponding to these changes, Na+,K(+)-ATPase enzyme activity decreased in SM but not in heart. Levels of alpha 1 in heart and alpha 2 in SM decreased, whereas those of alpha 3 in heart and alpha 1 in SM remained unchanged; beta 1 remained unchanged in both tissues. Thus, in ferrets, K+ deficiency differentially regulated the levels of Na+,K(+)-ATPase isoforms in an isoform- and tissue-dependent manner.