REGULATORY SITES AND EFFECTORS OF D-[H-3]ASPARTATE RELEASE FROM RAT CEREBRAL-CORTEX

To study the effect of agents interfering with the biosynthesis and/or the K+-evoked Ca2+-dependent release of neurotransmitter glutamate, r at cerebral slices were preincubated with Krebs-Ringer-HEPES-glucose-g lutamine buffer (KRH buffer), loaded with D-[H-3]aspartate and superfu sed with the preincubation medium in the presence or in the absence of Ca2+. The difference in radioactivity release divided by the basal re lease per min under the two conditions represented the K+-evoked Ca2+- dependent release. The agents used were: 1) Aminooxyacetic acid (AOAA) , the inhibitor of transaminases, 2) Leucine (Leu), the inhibitor of p hosphate activated glutaminase (PAG), 3) NH4+, the inhibitor of PAG, 4 ) Phenylsuccinic acid (Phs), the inhibitor of the mitochondrial ketodi carboxylate carrier, 5) ketone bodies, the inhibitors of glycolysis, 6 ) the absence of glutamine, the substrate of PAG. The results show tha t Leu, NH4+, Phs and the absence of Gln significantly increase the K+- evoked Ca2+ -dependent release of radioactivity by 64%, 200%, 95% and 147% respectively, indicating that these agents are inhibitors of the K+-evoked Ca2+-dependent release of glutamate. Ketone bodies and AOAA had no effect. These results indicate that the major if not the exclus ive biosynthetic pathway of neurotransmitter glutamate in rat cerebral cortex is through the PAG reaction and support a model for the pathwa y followed by neurotransmitter glutamate i.e. glutamate formed outside the inner mitochondrial membrane has to enter the mitochondrial matri x or is formed within it from where it can be extruded to supply the t ransmitter pool in exchange of GABA.