GLUCOSE-TRANSPORT IN IMMORTALIZED RAT-BRAIN CAPILLARY ENDOTHELIAL-CELLS IN-VITRO - TRANSPORT ACTIVITY AND GLUT1 EXPRESSION

RBE4 cells, an immortalized cell line derived from primary cultures of rat brain capillary endothelial cells, transport 3-O-methylglucose by a mechanism which is saturable with an apparent K-m of 14.3 mM. The 3 -O-MG uptake can be inhibited by other potential substrates and by non -competitive inhibitors, but not by L-glucose or sucrose, The transpor t is unaffected by removal or disruption of the sodium gradient. Under conditions of glucose deprivation the V-max is increased by 100% with no significant change in K-m. GLUT1 protein expression in glucose-dep rived cells is also increased by 116%. This increase in V-max can be b locked by the protein synthesis inhibitor, cycloheximide. Uptake was a lso increased in preconfluent cells and this increase was associated w ith increases in GLUT1 protein expression. This suggests that the chan ges in uptake are due to a de novo synthesis of transporters and not t o insertion of transporters from an intracellular pool. This study wou ld support the conclusion that the GLUT1 isoform is responsible for gl ucose transport in RBE4 cells and that these immortalized brain capill ary endothelial cells may be used as an in vitro model for analysis of glucose transport regulation at the blood-brain barrier.