期刊
BIOLOGICAL & PHARMACEUTICAL BULLETIN
卷 27, 期 6, 页码 813-816出版社
PHARMACEUTICAL SOC JAPAN
DOI: 10.1248/bpb.27.813
关键词
glutamate transporter; glutamate uptake; glutamate reversed transport; dihydrokainate; DL-threo-beta-hydroxy-aspartate; synaptosome
To establish an assay system for evaluation of the uptake and reversed transport of glutamate, we examined the effects of Na+-concentration and pharmacological agents on the extracellular glutamate concentration ([Glu](o)) in rat cortical synaptosomes in vitro. There was a decrease and increase of the [Glu](o) at high and low Na+ concentrations, respectively, in a Ca2+-free medium. The changes in [Glu](o) in both directions were temperature-sensitive, and reversed at around 30 mm of Na+. Dihydrokainate (DHK), a non-transportable inhibitor selective for glial glutamate transporter GLT-1, suppressed the decrease in [Glul., and the reversal of [Glu](o) change was shifted to about 60 mm Na+. There was no change in the maximum [Glul. at total Na+ substitution. Further pharmacological analysis revealed that D-aspartate and DL-threo-beta-hydroxy-aspartate (THA), transportable substrates of glutamate transporters, increased the [Glu](o) in standard media. In contrast, beta-phenylglutamic acid, a structural analogue of glutamate, suppressed both the decrease in [Glu](o) in standard medium and the increase in [Glu](o) in low Na+ medium. It is, thus, concluded that both the direction and the amount of [Glu](o) changes are determined by a balance of the uptake and reversed transport of glutamate, and that this assay system is suitable for evaluation of the effect of this on glutamate transporters.
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