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Notes: Abstract: Amino acid release studies were performed by an HPLC procedure using differentiated rat cerebellar granule cell cultures. Kainic acid (KA; 50 μM) caused an increase (about threefold) in the release of endogenous glutamate and a lesser, but statistically significant, increase in the release of glutamine, glycine, threonine, taurine, and alanine. Quisqualic acid (QA) and, to a lesser degree, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) (both 50 μM) enhanced the release of the following amino acids in the order glutamate 〉 aspartate ≥ taurine, whereas the release of other amino acids was either unaffected or affected in a statistically nonsignificant way. The release of glutamate induced by KA was partially (43%) Ca2+ dependent. The other release-inducing effects of KA and QA were not Ca2+ dependent. In all cases, the evoked release could be prevented by the non-N-methyl-D-aspartate (non-NMDA) receptor antagonist 6-cyano-2,3-hydroxy-7-nitroquinoxaline, and thus appeared to be receptor mediated. NMDA (5 and 50 μM) had no releaseinducing activity. The KA-, QA-, and AMPA-evoked release of newly synthesized [3H]glutamate and [3H]aspartate (formed in the cells exposed to [3H]glutamine) was very similar to the evoked release of endogenous glutamate and aspartate. On the other hand, the release of preloaded D-[3H]aspartate (purified by HPLC in the various fractions analyzed, before radioactivity determination) induced by 50 μM KA was twice as high as that of endogenous glutamate. In the case of high [K+] depolarization, in contrast, the release of preloaded D-[3H]aspartate was ∼30% lower than that of endogenous glutamate. The reasons for the above differences in the susceptibility of the various glutamate pools to being released may be the following: Non-NMDA receptor agonists cause essentially a carrier-mediated efflux of glutamate from a cytoplasmic pool that is preferentially labeled by exogenous D-[3H]aspartate, whereas depolarization with high [K+] causes mainly an exocytotic-like release from a vesicular pool to which exogenous D-[3H]aspartate has a more limited access.