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

IN RECENT STUDIES of cerebral fluid imbalance,],? swelling and loosening of endothelial cells was a constant morphologic change. This cellular alteration did not correlate with the presence or absence of a blood-brain barrier, the preservation of which was determined by the use of colloidal dyes. Therefore, it was logical to believe that a functional mechanism, which could not be visualized by routine technics, may be involved in the regulation of capillary permeability in the brain. I'he development of enzyme histochemistry in recent years has enabled investigators to study more adequately the function of normal and altered cells. Some of these technics utilize heavy metals in the capture of the reaction product. Since heavy metals are visible in the electron microscope, these methods of study were combined with electron microscopy.3-5 The distribution of adenosinetriphosphatase ( ATPase) and adenosinediphosphatase (ADPase$ activity has been described in normal rat brain using frozen sections which were prepared from tissue blocks that were fixed in formol-cal~ium.~ ATPase activity was localized on the cell membranes of many neurons, on the neuroglia, and in both smooth muscle and endothelium of the blood vessels. The substitution of adenosinediphosphate ( ADP) for adenosinetriphosphate ( ATP) in the incubation medium resulted in a similar localization except that no neuronal activity was present. In the frozen sections, only diffuse capillary staining was noted. These thick sections did not permit accurate visualization of the capillary basement membrane. Therefore, we hoped that the application of the electron microscope to the study of these vascular structures would reveal more accurate localization of ATPase activity.