Ultracytochemical localisation of Na+, K(+)-ATPase in cerebral endothelium in acute hypertension.

This ultracytochemical study was undertaken to determine whether increased arteriolar permeability in acute hypertension is accompanied by altered localisation of the ouabain-sensitive, K(+)-dependent p-nitrophenyl-phosphatase (K(+)-NPPase), a component of the Na+, K(+)-ATPase system. Rats were injected with horseradish peroxidase (HRP) intravenously and acute hypertension was induced by a 2-min infusion of angiotensin amide. Rats were killed at 3 and 15 min, following which brains were sliced and reacted for demonstration of K(+)-NPPase and HRP reaction product. Vessels of normotensive and hypertensive rats that were nonpermeable to HRP showed discontinuous distribution of K(+)-NPPase on the outer plasma membranes of endothelial and adventitial cells of arterioles and endothelial cells and pericytes of capillaries. Arterioles of the hypertensive rats which were permeable to HRP showed marked reduction of K(+)-NPPase localisation in their walls at 3 min while at 15 min when the blood pressure had returned to resting levels the enzyme localisation was similar to controls. This study demonstrates transient alteration of the NA+, K(+)-ATPase system during increased endothelial permeability in acute hypertension. The implication of this finding and our previous observation of reduced Ca2(+)-ATPase localisation in endothelial plasma membranes in acute hypertension has been discussed.