Hypokalemia Downregulates Cardiac α1 and Skeletal Muscle α2 Isoforms of Na +,K +-ATPase in Ferrets

Abstract

K + deficiency decreases amount of Na +,K +-ATPase in cardiac and skeletal muscle (SM) and differentially regulates α- and β-subunit isoforms. Expression of the α3 isoform during K + deficiency is unknown, however. In the myocardium of normal adult ferrets, α1 and α3 isoforms are expressed. Therefore, we examined in ferrets the effects of K + deficiency in levels of α- and β-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 α1 in heart and α2 in SM decreased, whereas those of α3 in heart and α1 in SM remained unchanged; β1 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.