Carrier Mediated Glucose Transport in Capillaries Isolated From Rat Brain1

Uptake of 2‐deoxy‐d‐glucose (2‐DG) was investigated in capillaries isolated from rat brain. A high affinity, carrier‐mediated transport system was defined with an apparent Km for 2‐DG of 93 μM. Uptake was temperature‐dependent and markedly inhibited by phloretin and selected hexose isomers. The apparent Ki for d‐glucose inhibition of 2‐DG uptake was 98 μM. Essentially all of the 2‐DG retained by the capillary preparation could be released by sonication and 95% was recovered as free unphosphorylated 2‐DG. Uptake was not sodium‐dependent and not altered by insulin. These results suggest that movement of glucose across the blood‐brain barrier through endothelial cells probably is not rate‐limiting unless blood glucose levels are extremely low.