EVIDENCE FOR 2 SODIUM PUMPS IN CRYSTALLINE LENS OF RABBIT EYE

The effect of ouabain on the ATPase activity, the electrical potential, 86Rb uptake, and sodium content in the crystalline lens of the rabbit were studied. The ouabain-sensitive ATPase activity of the lens epithelium was compared to that of segments of lens cortex. The lens fibres were found to possess one-third of the total ouabain-sensitive ATPase activity of the lens. Dose-response studies of ATPase inhibition by ouabain gave a KI of about 1·4 × 10-6 m for the epithelium and about 3·3 × 10-5 m for the anterior cortex. Although ouabain sensitive ATPase was present in the posterior cortex, ouabain had no effect on 86Rb uptake across the posterior lens surface. Application of ouabain to the anterior surface of the lens resulted in an 8 mV decrease in the absolute value of the lens potential, a reduction of 86Rb uptake to about one-third of its value in unpoisoned lenses, and a significant increase in sodium content after 2 hr of incubation. Dose-response studies of these effects suggested that the Na K ATPase of the anterior cortex, but not that of the epithelium, makes an electrogenic contribution to the measured lens potential. On the other hand, inhibition of the epithelial ATPase effects a greater reduction in 86Rb uptake than inhibition of the cortical ATPase. The maintenance of lens sodium content cannot be ascribed solely to the activity of the sodium pump in the lens epithelium. The results of these studies suggest that two types of Na K ATPase with different anatomical localizations contribute to the maintenance of cation balance in the rabbit lens. © 1978.