GLUT-1 GLUCOSE TRANSPORTER IS PRESENT WITHIN APICAL AND BASOLATERAL MEMBRANES OF BRAIN EPITHELIAL INTERFACES AND IN MICROVASCULAR ENDOTHELIA WITH AND WITHOUT TIGHT JUNCTIONS

We investigated the diversity of cellular localization of the GLUT-1 glucose transporter protein at epithelial and endothelial barriers either possessing or lacking occluding junctions. The avidin-biotin immunoperoxidase and the immunogold-silver staining (IGSS) techniques were used. A rabbit polyclonal antiserum prepared against a synthetic peptide encoding the 13 amino acids at the carboxyl terminus of the GLUT-1 glucose transporter protein was used. Both techniques were found to have comparable sensitivity in detecting immunoreactive GLUT-1. The IGSS experiments employed a light-insensitive stabilizer, and no immunoreactive GLUT-1 was found in brain cells (neurons, glial cells), but abundant immunoreactive GLUT-1 was found in brain capillary endothelium, which is composed of cells with occluding junctions. However, immunoreactive GLUT-1 was also found in endothelium known not to contain occluding junctions, such as testicular microvascular endothelium and endothelium on the fetal side of the syncytiotrophoblast of the placenta. In epithelial barriers, GLUT-1 was also found in the basolateral membrane of renal collecting duct epithelium, choroid plexus, and the placental syncytiotrophoblast layer. However, immunoreactive GLUT-1 was found in the apical membrane of ependymal epithelium near the lower portion of the third ventricle. In conclusion, there is diversity underlying the expression of the GLUT-1 glucose transporter protein in different cell types, and the transporter protein can be found in endothelium with and without occluding junctions, and in both apical and basolateral membranes of epithelial barriers.