Digitalis-like compounds and Na⁺, K⁺-ATPase activity in bovine lens

Digitalis-like compounds in bovine lens capsule, cortex and nucleus were determined quantitatively, following extraction, by their ability to inhibit [³H]ouabain binding to red blood cells. These compounds were found to be highly concentrated in the epithelium capsule and were significantly diminished in the cortex and nucleus. Na⁺, K⁺-ATPase density in the different regions was determined by [³H]ouabain binding to membranes and by autoradiography of lens slices. The highest concentration of [³H]ouabain-binding sites was observed to occur in membranes prepared from the epithelial cells of the capsule, and was almost 100- and 200-fold higher than the concentrations observed in membranes prepared from fiber cells of the cortex and nucleus, respectively. In the autoradiography studies, strong labeling of [³H]ouabain appeared in the epithelial cell zone, and only weak specific labeling appeared in the lens cortex and nucleus. Almost all (99%) of the Na⁺,K⁺-ATPase specific activity was found to be in the capsule epithelium and only 0.5% was measured in the cortex and no activity was detected in the nucleus. These results indicate that the digitalis-like compounds and Na⁺, K⁺-ATPase are concentrated in the lens capsule epithelium and are present only at low levels in the cortex and nucleus, thus implying that the lens capsular epithelial layer is the major region of the lens responsible for the homeostasis of ions and water in this tissue.