Electronmicroscopical, histochemical and biochemical findings on the Na-K-ATPase activity in the epithelium of the rat lens

Abstract

The sodium-potassium activated adenosine triphosphatase (Na-K-ATPase) activity in the epithelium of the rat lens was investigated histochemically using light and electron microscopy and biochemistry. The histochemical demonstration of Na-K-ATPase activity in the lens epithelium was modified to be highly specific and to give a precise localization. The enzyme reaction was localized on the epithelial cell membranes that are adjacent to neighbouring epithelial cell membranes, whereas the apical and basal cell membranes were negative. The reaction product was almost totally absent in the presence of the specific enzyme inhibitor (ouabain). The reaction was strongly decreased also in the absence of the specific enzyme activators (sodium and potassium). The lens capsule as well as the lens fibres were negative. Biochemical studies of the kinetic properties of the lens epithelium were characterized by studying the effect of various chemicals on Na-K-ATPase activity. The enzyme activity was increased by the Na +, K + and Mg 2+ and inhibited by ouabain. Enzyme activity was optimal when Mg 2+ ATP ratio was approximately 1·4 and the pH at 7·7. Optimal activity was also obtained by using 85·0 m m-sodium and 1·0 m m-potassium in the solution. The results in this study indicate that the adjoining cell membranes of the lens epithelium contain the Na-K-ATPase activity and that these are probably responsible for the exchange of water and ions across the lens epithelium.