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Studies on the release of exogenous and endogenous GABA and glutamate from rat brain synaptosomes

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Abstract

The aim of the present study was to determine whether exogenous radioactive GABA and glutamate previously taken up by rat brain synaptosomes are released preferentially with respect to the endogenous unlabeled amino acids. Preferential release was monitored by comparing the specific radioactivity of the amino acids released to that present in synaptosomes at the beginning and at the end of the release period. The GABA released spontaneously or by depolarizing the synaptosomes with high K+ in the presence of Ca2+ had the same specific radio-activity as that present in synaptosomes before or after superfusion. Depolarization with veratridine or superfusion with OH-GABA caused a moderate increase (15–20%) in the specific radioactivity of the GABA released and a corresponding slight decrease in that of superfused synaptosomes. In conditions causing a ‘supraadditive” release of exogenous and endogenous GABA (see ref. 13), the specific radioactivity of the GABA released was increased 20–30%. The GABA with higher-than-average specific radioactivity is probably representative of the cytoplasmic pool of this amino acid. The glutamate released spontaneously had a specific radioactivity lower than that present in synaptosomes at the start of superfusion, and also the specific radioactivity in superfused synaptosomes was lower than at the start of superfusion. The glutamate released by aspartate (by heteroexchange), by veratridine, or by high K+ had a specific radioactivity higher than that of the amino acid released spontaneously, similar to that present in synaptosomes at the start of superfusion, and higher than that found in superfused synaptosomes. These findings suggest that exogenous radioactive glutamate is released preferentially with respect to the endogenous amino acid and to the glutamate synthesized from glucose during the superfusion period.

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Authors and Affiliations

  1. Laboratorio di Biologia Cellulare, CNR, Via Romagnosi 18/A, 00196, Rome, Italy

    Giulio Levi

  2. Center for Neurochemistry, Rockland Research Institute, Ward's Island, 10035, New York

    Miriam Banay-Schwartz

  3. Istituto di Farmacologia e Farmacognosia Facoltà di Farmacia, Università di Genova, Genova, Italy

    Maurizio Raiteri

Authors
  1. Giulio Levi
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  2. Miriam Banay-Schwartz
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  3. Maurizio Raiteri
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Levi, G., Banay-Schwartz, M. & Raiteri, M. Studies on the release of exogenous and endogenous GABA and glutamate from rat brain synaptosomes. Neurochem Res 6, 275–285 (1981). https://doi.org/10.1007/BF00964043

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