Biochemical Characteristics of Cerebral Capillaries
The endothelial cells of the cerebral vessels differ histochemically from those of other organs (1). Cerebral capillaries had been found to be rich in γ glutamyl transpeptidase (γ-GTP) and alkaline phosphatase, enzymes found in the endothelial cells of the gut and renal cells, but not in the capillaries of other organs (2). On the basis of these kinds of observations, it was thought that enzymes found in endothelial cells of the brain may play a role in the function of the blood-brain barrier (BBB) (3). More recently, enzymatic studies of these cells have been facilitated by the simplicity of isolation of cerebral capillaries (4–8), Using this approach, the specific activities of many enzymes in brain capillaries were found to differ from those in brain parenchyma (6,8,9). Studies of hexokinase, lactate dehydrogenase (LDH), adenosine triphosphatase (ATPase) and guanosine triphosphatase (GTPase) in the brain capillaries and parenchyma have shown this difference and indicate that there may be a difference in enzyme function dependent on location (10,11). We tentatively propose that the enzymatic organization of the brain microvasculature functions in the maintenance of the BBB and participates in the transport of substances between blood and brain.
KeywordsGTPase Activity Adenosine Triphosphatase Brain Capillary Brain Microvessels Pinocytotic Vesicle
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