Ultracytochemical studies of capillary endothelial cells in the rat central nervous system

The ultracytochemical localization of eight hydrolytic enzymes (TMPase, 5'-NPase, TPPase, TTPase, Mg++-ATPase, Ca++-ATPase, ALPase and K+-NPPase) and one oxidative enzyme (MAO) was determined in rat brain capillary endothelial cells. In the somal plasma membrane, the enzymatic activity was mainly located in the antiluminal plasma membrane. This finding was appropriate for enzymes possessing the optimal pH at alkaline ranges, except for alkaline phosphatase. Most enzymes investigated showed a positive reaction on the pinocytotic vesicles of capillary endothelial cells. Differences in the intensity of the enzyme activities of the luminal and antiluminal plasma membranes may reflect the polarity in the capillary endothelial cells and relate to blood-brain barrier mechanisms.