Histochemically demonstrable sodium-potassium-activated adenosine triphosphatase (Na-K-ATPase) activity in the rat lens

Abstract

The rat lens epithelium was subjected to histochemical examination in order to demonstrate sodium-potassium-activated adenosine triphosphatase reaction. The histochemical technique was specifically adapted to demonstrate the sodium-potassium activated fraction of the enzyme activity. The precise localization of the enzyme activity in the lens epithelium was demonstrated. It was found that fixation in 2·5% glutaraldehyde for 30 min gave relatively good cytological preservation, but did not unduly inhibit the enzyme activity. The incubation solution contained 3 m m-ATP, lead and magnesium as well as 70 m m-sodium and potassium. When the inhibitory effect of ouabain was to be demonstrated, this treatment had to be carried out prior to fixation. Sodium-potassium-activated adenosine triphosphatase activity was localized on the epithelial cell membranes of the lens. The precipitate was observed on those parts of cell membranes where two adjoining cells were in contact with each other. The cytoplasm of the epithelial cells was negative, whereas the lens fibres seemed to contain some precipitation, which, however, did not fulfill the specifications for the enzyme and was thus considered not to demonstrate the real activity. The results obtained indicated that sodium-potassium activated ATPase, which has been supposed to be responsible at least partly for the ion and water transport of the lens, acts on the epithelial cell mambranes, but what direction this pumping mechanism takes is not yet clear.