Localization of adenosinetriphosphatase in capillaries of the brain as revealed by electron microscopy

Abstract

The use of formol-calcium as an initial fixative is more suitable than osmium tetroxide for the study of ATPase activity in the brain. Enzyme diffusion complicates the use of tissue blocks for electron histo-chemistry. The length of incubation and type of fixation are factors involved in this phenomenon. Frozen sections appear to be the best available control technic. An electron microscopic examination of cerebral and cerebellar capillaries reveals a localization of ATPase in the basement membrane and endothelial cell. The capillaries of the choroid plexus contain ATPase only in the endothelial cells. This lack of enzyme in the basement membrane is similarly found in the peritubular capillaries of the kidney. The dual localization of ATPase activity in the basement membrane and in the endothelial cell is noted in vascular structures which are singularly characterized by limited permeability to electrolytes and vital dyes (blood-brain barrier). This anatomic fact may have important functional significance. The presence of enzyme activity in the basement membrane indicates that this structure may be important in transfer regulation by cerebral capillaries.