Heterogeneity of sodium‐dependent excitatory amino uptake mechanisms in rat brain

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Abstract
The pharmacologic and kinetic characteristics of sodium-dependent uptake of [3H] L-glutamate, [3H] D-aspartate, and [3H] L-aspartate into crude synaptosomal preparations of rat corpus striatum and ecrebellum have been examined in vitro. In cerebellum the apparent Kt s and Vmax for the three excitatory amino acids were identical whereas in striatal synaptosomes, the Vmax for [3H] L-glutamate was 30% greater (P≤.001) than for [3H] D-aspartate and 50% greater (P ≤.001) than for [3H] L-aspartate. L-Amino adipic acid inhibited the uptake of the three amino acids in both regions of brain but was 15- to 20-fold more potent in cerebellum than in striatum. In contrast, dihydrokainic acid inhibited transport processes in the corpus straitum but was without activity in cerebellar preparations. The neurotoxin kainic acid blocked only a portion (60%) of [3H] L-glutamate and [3H] D-aspartate uptake in cerebellum while completeley inhibiting amino acid trasport in corpus striatum. Three days post kainic acid lesion, [3H] D-aspartate uptake was attenuated more than [3H] L-glutamate uptake in the corpus straitum; destruction of corticostriatal afferents reduced [3H] L-glutamate to a greater extent than [3H] D-aspartate. Various lesions of the cerebellum affected excitatory amino acid transport processes to a similar extent. These results suggest that excitatory amino acid transport systems are pharmacologically distinct in different brain regions and may be heterogeneous within a single region.