Ultracytochemical demonstration of alkaline phosphatase activity in astrocytes and subependymal cells in the rat brain.

Ultrastructural localization of alkaline phosphatase activity was studied in astrocytes of the cerebral cortex and corpus callosum, and in the ependymal and subependymal cells of the lateral ventricle of normal rat brain by means of electron microscopic histochemistry employing the lead citrate method. Astrocytes exhibited alkaline phosphatase activity on the plasma membrane of the endfeet facing the vascular basement membrane and at the gap junctions, but not on other parts of the plasma membrane or in the cytoplasm. Immature astrocytes containing small bundles of filaments, a few glycogen granules and other cell organelles, exhibited alkaline phosphatase activity on the inner and outer nuclear membranes, the outer mitochondrial membrane and on portions of the plasma membrane. Thus, it was concluded that the distribution of alkaline phosphatase in astrocytes shifts from the cytoplasm and plasma membrane to the endfeet and gap junctions with cell maturation. Alkaline phosphatase activity was detected on the plasma membrane of the subependymal cells and surrounding processes, but not on the ependymal cells.