DISTRIBUTION OF LENS SODIUM-POTASSIUM-ADENOSINE TRIPHOSPHATASE

Purpose. The specific activity of sodium-potassium-adenosine triphosph atase (Na-K-ATPase) in lens fiber cells is lower than the specific act ivity in lens epithelium. To test whether there is a reduction in the expression of Na-K-ATPase molecules in lens fibers, a Western blot tec hnique was used. Methods. Membrane material was isolated from differen t regions of the rabbit lens. Na-K-ATPase (adenosine triphosphate hydr olysis) activity was measured in each membrane sample and Western blot s were performed using an antibody to rabbit kidney Na-K-ATPase. Resul ts. By immunoblotting, Na-K-ATPase polypeptide was detected in all len s cells. In contrast, adenosine triphosphate hydrolysis by the Na-K-AT Pase (Na-K-ATPase activity) was not detectable or was detectable only at very low levels in fiber membranes from the lens nucleus and in cor tex. Conclusion. These findings suggest that plasma membrane adenosine triphosphatase enzyme responsible for sodium-potassium transport is e xpressed in newly formed lens fibers and the transport molecules are r etained as the fibers age and are compressed toward the center of the lens. However, with fiber aging there is a loss of functional ability of the Na-K-ATPase to hydrolyze adenosine triphosphate.