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Uptake and metabolism ofl-[3H]glutamate andl-[3H]glutamine in adult rat cerebellar slices

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Abstract

Using very low concentrations (1 μmol range) ofl-2-3-[3H]glutamate, (3H-Glu) orl-2-3-[3H]glutamine (3H-Gln), we have previously shown by autoradiography that these amino acids were preferentially taken up in the molecular layer of the cerebellar cortex. Furthermore, the accumulation of3H-Glu was essentially glial in these conditions. We report here experiments in which uptake and metabolism of either (3H-Glu) or (3H-Gln) were studied in adult rat cerebellar slices. Both amino acids were rapidly converted into other metabolic compounds: after seven minutes of incubation in the presence of exogenous3H-Glu, 70% of the tissue accumulated radioactivity was found to be in compounds other than glutamate. The main metabolites were Gln (42%), α-ketoglutarate (25%) and GABA (1,4%). In the presence of exogenous3H-Gln the rate of metabolism was slightly slower (50% after seven minutes of incubation) and the metabolites were also Glu (29%), α-ketoglutarate (15%) and GABA (5%). Using depolarizing conditions (56 mM KCl) with either exogenous3H-Glu or3H-Gln, the radioactivity was preferentially accumulated in glutamate compared to control. From these results we conclude: i) there are two cellular compartments for the neurotransmission-glutamate-glutamine cycle; one is glial, the other neuronal; ii) these two cellular compartments contain both Gln and Glu; iii) transmitter glutamate is always in equilibrium with the so-called “metabolic” pool of glutamate; iv) the regulation of the glutamate-glutamine cycle occurs at least at two different levels: the uptake of glutamate and the enzymatic activity of the neuronal glutaminase.

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Authors and Affiliations

  1. Unité 44 INSERM and Centre de Neurochimie du CNRS, 5, rue Blaise Pascal, 67000, Strasbourg, France

    J. de Barry (respectively Chargé de Recherche INSERM and Maître de Recherche CNRS), G. Vincendon & G. Gombos (respectively Chargé de Recherche INSERM and Maître de Recherche CNRS)

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  1. J. de Barry
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  2. G. Vincendon
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  3. G. Gombos
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de Barry, J., Vincendon, G. & Gombos, G. Uptake and metabolism ofl-[3H]glutamate andl-[3H]glutamine in adult rat cerebellar slices. Neurochem Res 8, 1321–1335 (1983). https://doi.org/10.1007/BF00964001

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