Distribution of lens sodium-potassium-adenosine triphosphatase.

PURPOSE The specific activity of sodium-potassium-adenosine triphosphatase (Na-K-ATPase) in lens fiber cells is lower than the specific activity in lens epithelium. To test whether there is a reduction in the expression of Na-K-ATPase molecules in lens fibers, a Western blot technique was used. METHODS Membrane material was isolated from different regions of the rabbit lens. Na-K-ATPase (adenosine triphosphate hydrolysis) activity was measured in each membrane sample and Western blots were performed using an antibody to rabbit kidney Na-K-ATPase. RESULTS By immunoblotting, Na-K-ATPase polypeptide was detected in all lens cells. In contrast, adenosine triphosphate hydrolysis by the Na-K-ATPase (Na-K-ATPase activity) was not detectable or was detectable only at very low levels in fiber membranes from the lens nucleus and in cortex. CONCLUSION These findings suggest that plasma membrane adenosine triphosphatase enzyme responsible for sodium-potassium transport is expressed in newly formed lens fibers and the transport molecules are retained 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.