AN ELECTRON-MICROSCOPIC IMMUNOGOLD ANALYSIS OF DEVELOPMENTAL UP-REGULATION OF THE BLOOD-BRAIN-BARRIER GLUT1 GLUCOSE-TRANSPORTER

Electron microscopy was used to quantitate blood-brain barrier (BBB) g lucose transporters in newborn, 14-day-old suckling, 28-day-old weanli ng, and adult rabbits. A rabbit polyclonal antiserum to a synthetic pe ptide encoding the 13 C-terminal amino acids of the human erythrocyte glucose transporter (GLUT1) was labeled with 10-nm gold particle-secon dary antibody conjugates and localized immunoreactive GLUT1 molecules in rabbit brain capillary endothelia. Three distinct populations of br ain capillary profiles were identified in newborn rabbits: prepatent c apillary buds, partially patent capillaries with highly amplified lumi nal membranes, and patent capillaries. Immunogold analyses indicated t hat the GLUT1 transporter abundance positively correlated with capilla ry developmental status. The mean number of gold particles per capilla ry profile increased at each developmental age examined, suggesting th at developmental up-regulation of the BBB glucose transporter occurred in rabbits. GLUT1 immunoreactivity was three- to fourfold greater on the abluminal than luminal capillary membranes among all ages examined . Changes in the proportions of GLUT1 transporter were also seen, and possible reasons for the postnatal decrease in the percentage of cytop lasmic GLUT1 transporter are discussed. The numbers of cytoplasmic and membrane-associated immunogold particles increased with age. We concl ude that regulatory modulations of BB glucose transport may be charact erized by increases in BBB glucose transporter density with age and st ate of development. In addition, modulation of glucose transporter act ivity may be reflected by minor postnatal shifts of GLUT1 from cytopla smic to membrane compartments, which can be demonstrated with quantita tive immunogold electron microscopy.