DIGITALIS-LIKE COMPOUNDS AND NA-ATPASE ACTIVITY IN BOVINE LENS(, K+)

Digitalis-like compounds in bovine lens capsule, cortex and nucleus we re determined quantitatively, following extraction, by their ability t o inhibit [H-3]ouabain binding to red blood cells. These compounds wer e found to be highly concentrated in the epithelium cap sule and were significantly diminished in the cortex and nucleus. Na+, K+-ATPase den sity in the different regions was determined by [H-3]ouabain binding t o membranes and by autoradiography of lens slices. The highest concent ration of [H-3]ouabain-binding sites was observed to occur in membrane s prepared from the epithelial cells of the capsule, and was almost 10 0- and 200-fold higher than the concentrations observed in membranes p repared from fiber cells of the cortex and nucleus, respectively. In t he autoradiography studies, strong labeling of [H-3]ouabain appeared i n the epithelial cell zone. and only weak specific labeling appeared i n the lens cortex and nucleus. Almost all (99%) of the Na+,K+-ATPase s pecific 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 nucl eus. These results indicate that the digitalis-like compounds and Na+, K+-ATPase are concentrated in the lens capsule epithelium and are pre sent only at low levels in the cortex and nucleus, thus implying that the lens capsular epithelial layer is the major region of the lens res ponsible for the homeostasis of ions and water in this tissue.