Cytochemical and immunocytochemical localization of Na,K-ATPase α subunit isoenzymes in the rat heart

In order to understand the functional significance of Na,K-ATPase subunits as well as their isoenzymes, a precise subcellular localization of these in the myocyte is a crucial prerequisite. Cytochemical, immunofluorescence, preembedding immunogold and horse radish peroxidasediaminobenzidine methods, demonstrated α1 isoenzyme immunoreactivity on the sarcolemma, T-tubules and the subsarcolemmal cisterns of the adult cardiac myocytes. Cytochemically, ouabain resistant Na,K-ATPase precipitate was localized only in the subsarcolemmal cisterns and junctional sarcoplasmic reticulum. For α2 isoenzyme, immunoreactivity was demonstrated on the sarcolemma as well as in all areas of the myocytes in particularly a close proximation to the sarcoplasmic reticulum and microsomes. For α3 isoenzyme, only a weak insignificant signal was noted on the sarcolemma, intercalated disc and sarcoplasm. It is suggested that cytochemical ouabain resistant precipitate present in subsarcolemmal cisterns and junctional sarcoplasmic reticulum represent α1 isoenzyme of Na,K-ATPase. A differential as well as unique localization of α subunit isoenzymes of Na,K-ATPase in specific structures of cardiac myocytes may suggest importance in physiological function at these sites.