Inhibition of glutamate uptake with L-trans-pyrrolidine-2,4-dicarboxylate potentiates glutamate toxicity in primary hippocampal cultures.

Sodium-dependent, high-affinity glutamate transport is generally assumed to limit the toxicity of glutamate in vivo and in vitro, but there is very little direct evidence to support this hypothesis. In the present study, the effects of the specific uptake inhibitor L-trans-pyrrolidine-2,4-dicarboxylate on the toxicity and clearance of glutamate were examined in hippocampal neuronal cultures. At a concentration that was not toxic by itself, L-trans-pyrrolidine-2,4-dicarboxylate increased the toxicity of glutamate approximately fivefold and slowed the clearance of glutamate from the extracellular space. This toxicity was almost completely blocked by the N-methyl-D-aspartate receptor antagonist, D-2-amino-5-phosphonopentanoate. These studies provide direct evidence that sodium-dependent, high-affinity glutamate transport limits glutamate toxicity in vitro.