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Glial uptake of neurotransmitter glutamate from the extracellular fluid studied in vivo by microdialysis and 13 C NMR
Author(s) -
Kanamori Keiko,
Ross Brian D.,
Kondrat Richard W.
Publication year - 2002
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.2002.01161.x
Subject(s) - microdialysis , neurotransmitter , extracellular , glutamate receptor , extracellular fluid , in vivo , biochemistry , chemistry , exocytosis , biology , secretion , receptor , microbiology and biotechnology
Glial uptake of neurotransmitter glutamate (GLU) from the extracellular fluid was studied in vivo in rat brain by 13 C NMR and microdialysis combined with gas‐chromatography/mass‐spectrometry. Brain GLU C5 was 13 C enriched by intravenous [2,5‐ 13 C]glucose infusion, followed by [ 12 C]glucose infusion to chase 13 C from the small glial GLU pool. This leaves [5‐ 13 C]GLU mainly in the large neuronal metabolic pool and the vesicular neurotransmitter pool. During the chase, the 13 C enrichment of whole‐brain GLU C5 was significantly lower than that of extracellular GLU (GLU ECF ) derived from exocytosis of vesicular GLU. Glial uptake of neurotransmitter [5‐ 13 C]GLU ECF was monitored in vivo through the formation of [5‐ 13 C, 15 N]GLN during 15 NH 4 Ac infusion. From the rate of [5‐ 13 C, 15 N]GLN synthesis (1.7 ± 0.03 µmol/g/h), the mean 13 C enrichment of extracellular GLU (0.304 ± 0.011) and the 15 N enrichment of precursor NH 3 (0.87 ± 0.014), the rate of synthesis of GLN (V′ GLN ), derived from neurotransmitter GLU ECF , was determined to be 6.4 ± 0.44 µmol/g/h. Comparison with V GLN measured previously by an independent method showed that the neurotransmitter provides 80–90% of the substrate GLU pool for GLN synthesis. Hence, under our experimental conditions, the rate of 6.4 ± 0.44 µmol/g/h also represents a reasonable estimate for the rate of glial uptake of GLU ECF , a process that is crucial for protecting the brain from GLU excitotoxicity.