Ultracytochemical studies on blood-retinal barriers: enzymatic polarity in retinal capillaries.

The ultracytochemical localization of Mg2(+)-ATPase and Ca2(+)-ATPase activities was determined in rat retinal capillary endothelial cells. The predominant localization of both enzymatic activities was on the antiluminal cell membranes in all retinal capillaries. The two enzymes investigated showed a positive reaction on the pinocytic vesicles of capillary endothelial cells. Differences in the intensity of enzyme activities of the luminal and antiluminal plasma membranes may reflect the polarity in the capillary endothelial cells and relate to blood-retinal barrier mechanisms.