[Ultracytochemical localization on Na(+)-K(+)-ATPase activity in the guinea pig endolymphatic sac]

It is well-known that Na(+)-K(+)-ATPase plays an important role in active transportion of sodium (Na) and potassium (K) ions across the epithelium. This paper reports the ultrastructural localization of the K(+)-NPPase reflecting Na(+)-K(+)-ATPase activity in the guinea pig endolymphatic sac (ES) with the lead citrate one step method. The ultrathin sections viewed in the transmission electron microscope revealed that the reaction product was restricted to the cytoplasmatic side of the basolaterl plasma membranes of the ES epithelial cells. And the reactivity could be traced all the way up to the level of tight junctions close to the luminal aspect of the cells. On the other hand, the luminal plasma membrane of the epithelial cells showed no enzyme activity. Our findings suggest that the rich Na(+)-K(+)-ATPase enzyme activity is preferentially localized on the basolateral plasma of membrane of the ES epithelial cells. Possible physiological mechanism of Na(+)-K(+)-ATPase in the Na(+)-K+ ion transport of ES epithelial cells is discussed.