Activities of transport enzymes located in the plasma membranes of corneal endothelial cells.

Plasma membranes from bovine corneal endothelial cells have been prepared for assay of ion transport enzymes (ATPase, EC 3.6.1.8). The membrane were judged to be highly purified by protein recovery, electron microscopy, and assay of enzyme markers. Sodium-potassium-stimulated ATPase was more than six times more active in the membranes (6.7 mumoles phosphate released/mg protein/30 min) than the whole homogenates (1.1 mumoles phosphate released). However, no increase in activity was seen with anionic ATPase of membranes (2.5 mumoles phosphate released with bicarbonate stimulation) vs. whole homogenates (3.0 mumoles phosphate released; insignificant difference). In contrast, the bicarbonate-stimulated ATPase activity of a mitochondrial preparation from the same cells was 10.6 mumoles phosphate released (p less than 0.001). It is suggested that anionic ATPase has no direct role in deturgescence as part of and endothelial cell "pump."