GLUT1 GLUCOSE-TRANSPORTER IN THE PRIMATE CHOROID-PLEXUS ENDOTHELIUM

The objective of the present study was to define the cellular location of the Glut1 glucose transporter in the primate choroid plexus. Immun ogold electron microscopy indicated that Glut1 epitopes were associate d primarily with choroid plexus endothelial cells. Digitized analyses of electron microscopic images provided quantitative estimates of the relative number of Glut1 glucose transporter epitopes on luminal and a bluminal endothelial cell membranes within the choroid plexuses. We re corded a high density of Glut1 in the microvascular endothelium of pri mate choroid plexus, which was consistent in vervet monkeys (5-10 Glut 1 gold particles per micrometer of endothelial cell plasma membrane), as well as in baboons (5-20 Glut1 gold particles per micrometer of cap illary plasma membrane). In the baboon choroid plexus, we observed tha t perivascular cells (presumed to be pericytes) were also Glut1-positi ve, but with substantially reduced activity compared with endothelial cells. Occasional Glut1-immunogold particles were also seen in the bas olateral membranes of the choroid plexus cuboidal cells. Light microsc opic immunocytochemistry confirmed the abundance of Glut1 immunoreacti vity in choroid plexus endothelial cells of vervet monkeys and baboons . A similar pattern was observed in surgically resected human choroid plexus, suggesting differences between primates, including humans and laboratory animals. The only difference was that erythrocytes within t he human choroid plexus exhibited a florid Glut1-positive response, bu t were weakly immunoreactive in nonhuman primates. The observation of high glucose transporter densities in choroid plexus endothelial cells is consistent with the suggestion that choroidal epithelia and capill aries provide a metabolic work capability for maintaining ionic gradie nts and secretory functions across the blood-CSF barriers.