An autoradiographic study of the site of transport of cations in the lens

Abstract Autoradiography of 22 Na and 86 Rb in rabbit lenses cultured in vitro showed that uptake of 22 Na was high in the posterior cortical layer and very low in the anterior cortical layer while that of 86 Rb was high in the anterior cortical layer and low in the posterior cortical layer. The influx of 86 Rb was markedly faster than that of 22 Na. Ouabain and iodoacetate in the incubation medium abolished or obscured the difference of the uptake of 22 Na and 86 Rb at the anterior and posterior cortical layers. In the anterior cortex the accumulation of 22 Na increased and that of 86 Rb decreased while in the posterior cortical layer the changes were not obvious when the lenses were incubated in the presence of the inhibitors. The regional differences in the accumulation of 22 Na and 86 Rb also disappeared in decapsulated lenses and there was a greater influx of both isotopes into the lens, suggesting that lens capsule and epithelium serve as a barrier to the influx of the isotopes. It is concluded that sodium enters the lens from the posterior surface, probably secondary to active extrusion of this ion from the anterior surface, while rubidium enters the lens across the anterior surface by a mechanism involving Na-K ATPase. Thus, the site of active transport for cations in the lens is the epithelium where membrane ATPase is localized, a conclusion also reached on the basis of entirely different techniques by previous investigators.