Demonstration of ouabain-sensitive, potassium-dependent p-nitrophenylphosphatase activity in the rat cardiac muscle by cobalt-based cytochemistry.

We have utilized cobalt-reaction technique for histochemical and cytochemical demonstration of ouabain-sensitive, K(+)-dependent p-NPPase (Na(+)-K(+)-ATPase). The incubation medium consisted of: cobalt chloride, tricine buffer, p-nitrophenylphosphate, KCl, and phenylalanine. Final pH 7.4. Ultracytochemically, reaction products were localized along the internal side of sarcolemma and its vesicles, T-tubule membrane, and capillary endothelial cells. These results suggest that the method is reliable and can be used to investigate the localization of Na(+)-K(+)-ATPase activity.