Na,K-ATPase and phospholipid degradation in bovine and human lenses

Na,K-ATPase, an enzyme intrinsic to the membrane of most cells, is inhibited in cataract. Na,K-ATPase, activity in clear non-cataractous lenses is found predominantly in the lens epithelium. The lens fiber cells would appear to be unique, among mammalian cells in that Na,K-ATPase activity is low if not absent. The study presented here indicates that Na,K-ATPase is present, often in high concentration, but progressively more functionally compromised as the fiber cells mature. The membrane lipid environment as causative agent in the loss of normal function of Na,K-ATPase, is considered in this study. The data indicate a correlation between increasing cholesterol/phospholipid ratio, increasing phospholipase A2 activity and decreasing Na,K-ATPase activity in normal clear lenses. The phospholipase A2 activity is higher in cortex and nucleus than in the epithelium of normal bovine and human lenses. The phospholipase A2 is Ca2+ dependent and may be membrane associated.