Ultrastructural localization of calcium-activated adenosine triphosphatase (Ca2+-ATPase) in cerebral endothelium

There is increasing interest in the role of calcium in a variety of biological processes. One of the mechanisms that regulate intracellular calcium concentrations is the calcium-activated adenosine triphosphatases (Ca2+-ATPase). The availability of an histochemical method for ultrastructural localization of Ca2+-ATPase has led to a number of studies attempting to localize this enzyme in a variety of cell types. This ultrastructural study was undertaken to localize Ca2+-ATPase in walls of intracerebral cortical vessels of rats. Both capillary and arteriolar endothelium showed discontinuous deposits of Ca2+-ATPase along the outer plasma membrane including the junctional plasma membranes. Patchy distribution of Ca2+-ATPase was also observed on the outer plasma membranes of smooth muscle and adventitial cells. Focal deposits of reaction product were associated with the actin filaments in endothelium. Invaginating pinocytotic vesicles at the outer plasma membrane of endothelium and smooth muscle cells showed Ca2+-ATPase. Intracytoplasmic vesicles showed the enzyme along the inner plasma membrane. Localization of Ca2+-ATPase on endothelial plasma membranes suggests that Ca2+ may be involved in many endothelial reactions. Further studies are required to determine the role of this enzyme and Ca2+ in endothelial reactions in normal and abnormal states.