Characteristics of (3H)2-Deoxyglucose Uptake by Slices of Rat Cerebral Cortex

Glucose uptake across the brain cell membrane was modelled by the uptake of 3H2-deoxyglucose by rat brain slices. Net 3H2-deoxyglucose uptake was defined as the difference between the uptake of 3H- 2-deoxyglucose total uptake and the uptake of L-3Hglucose diffusional component in parallel samples. L-3HGlucose uptake by slices was a valid approximation of the space available for glucose diffusion because L-3Hglucose is an inactive stereoisomer of glucose and itdistributed to a space essentially equal to total slice water. 3H2-Deoxyglucose uptake was stereospecific, and net uptake was half-maximal at 1.85 mM. Net uptake was inhibited by other hexoses and showed a dependence on incubation temperature. It was not inhibited by phlorizin or by phloretin, two compounds known to inhibit glucose transport by kidney and by erythrocytes, respectively. Net 3H2-deoxyglucose uptake was not affected when various ions were individuallydeleted from the incubation medium. Uptake was inhibited by the oxidative phosphorylation uncoupler 2,4-dinitrophenol which suggested some dependence on mitochondrial energy. The correlation of uptake with adenosine 5-triphosphate levels in the slices was not, however, straightforward. 3H2-Deoxyglucose uptake was increased as much as three-fold after slices were preincubated for up to 60 min in the absence of exogenous D-glucose. It was also Increased after slices werepreincubated in the presence of pyruvate, or 3-0-methylglucose, but was not increased after slices were preincubated with 2-deoxyglucose. These results suggested that uptake was affected in some way at the hexokinase step. The relative amount of phosphorylated hexose accumulated by the slices was also Increased after extended preincubation in the absence of exogenous D-glucose. While these results are consistent with a carrier-mediated process, the phosphorylation reaction was not clearly differentiated from the transport process in these studies.