UPTAKE AND METABOLISM OF GLUTAMATE IN ASTROCYTES CULTURED FROM DISSOCIATED MOUSE BRAIN HEMISPHERES

Abstract

Abstract— Uptake kinetics of l ‐glutamate in cultured, normal glia cells obtained from the brain hemispheres of newborn mice were measured together with the activities of the glutamate metabolizing enzymes, glutamic‐oxaloacetate‐transaminase, glutamate dehydrogenase and glutamine synthetase. During 3 weeks of culturing, the activities of the enzymes rose from low neonatal values toward the levels in the adult brain (206, 12.3 and 25.9 nmol. min −1 . mg −1 cell protein for the three enzymes, respectively). The uptake kinetics indicated an unsaturable component together with an uptake following Michaelis‐Menten kinetics with a K m of 220 μ m and a V max of 7.9 nmol. min −1 . mg −1 cell protein. The saturable glutamate uptake was inhibited by d ‐glutamate, l ‐aspartate and α‐aminoadipate whereas l ‐glutamine, GABA and glutarate had no effect. The uptake which was Ca 2+ ‐independent had a K m for sodium of 18m m and it was stimulated by an increase in the external potassium concentration from 5 to 10 and 25 m m. The results suggest that glia cells are important for the uptake of glutamate from synaptic clefts and for the subsequent metabolism of glutamate.