Localization of Na-K-ATPase in guinea-pig myocardium

The cytochemical distribution of Na-K-ATPase was demonstrated in the guinea-pig myocardium. The hearts were fixed with paraformaldehyde glutaraldehyde mixture, sections were incubated at room temperature in modified Ernst medium employing p-nitrophenyl phosphate as substrate and the tissue was processed for electron microscopy. The ATPase activity was localized in the subsarcolemmal cisterns, inner side of plasma membrane, T-tubules, free and junctional sarcoplasmic reticulum and capillary endothelium. The reaction product on the plasma membrane and T-tubules was inhibited by ouabain or by potassium deletion. However, the amount of precipitation in mitochondria, sarcoplasmic reticulum (free and junctional) and subsarcolemmal cisterns remained unaffected by ouabain or by potassium deletion. The enzyme reaction in the myocardium represents ouabain-sensitive, potassium-dependent ATPase.