GLUCOSE-TRANSPORT IN DEVELOPING RAT-BRAIN - GLUCOSE-TRANSPORTER PROTEINS, RATE CONSTANTS AND CEREBRAL GLUCOSE-UTILIZATION

Developing rat brain undergoes a series of functional and anatomic cha nges which affect its rate of cerebral glucose utilization (CGU). Thes e changes include increases in the levels of the glucose transporter p roteins, GLUT1 and GLUT3, in the blood-brain barrier as well as in the neurons and glia. 55 kDa GLUT1 is concentrated in endothelial cells o f the blood-brain barrier, whereas GLUT3 is the predominant neuronal t ransporter. 45 kDa GLUT1 is in non-vascular brain, probably glia. Stud ies of glucose utilization with the 2-C-14-deoxyglucose method of Soko loff et al., (1977), rely on glucose transport rate constants, k(1) an d k(2), which have been determined in the adult rat brain. The determi nation of these constants directly in immature brain, in association w ith the measurement of GLUT1, GLUT3 and cerebral glucose utilization s uggests that the observed increases in the rate constants for the tran sport of glucose into (k(1)) and out of (k(2)) brain correspond to the increases in 55 kDa GLUT1 in the blood-brain barrier. The maturationa l increases in cerebral glucose utilization, however, more closely rel ate to the pattern of expression of non-vascular GLUT1 (45 kDa), and m ore specifically GLUT3, suggesting that the cellular expression of the glucose transporter proteins is rate limiting for cerebral glucose ut ilization during early postnatal development in the rat.