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Activation of γ‐aminobutyric acid GAT‐1 transporters on glutamatergic terminals of mouse spinal cord mediates glutamate release through anion channels and by transporter reversal
Author(s) -
Raiteri Luca,
Stigliani Sara,
Patti Laura,
Usai Cesare,
Bucci Giovanna,
Diaspro Alberto,
Raiteri Maurizio,
Bonanno Giambattista
Publication year - 2005
Publication title -
journal of neuroscience research
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.72
H-Index - 160
eISSN - 1097-4547
pISSN - 0360-4012
DOI - 10.1002/jnr.20437
Subject(s) - glutamatergic , glutamate receptor , transporter , chemistry , gaba transporter , niflumic acid , gabaergic , gamma aminobutyric acid , glutamate aspartate transporter , channel blocker , pharmacology , nmda receptor , biochemistry , biophysics , biology , metabotropic glutamate receptor , receptor , calcium , organic chemistry , gene
The effects of γ‐aminobutyric acid (GABA) on the release of glutamate from mouse spinal cord nerve endings have been studied using superfused synaptosomes. GABA elicited a concentration‐dependent release of [ 3 H]D‐aspartate ([ 3 H]D‐ASP; EC 50 = 3.76 μM). Neither muscimol nor (–)baclofen mimicked GABA, excluding receptor involvement. The GABA‐evoked release was strictly Na + dependent and was prevented by the GABA transporter inhibitor SKF89976A, suggesting involvement of GAT‐1 transporters located on glutamatergic nerve terminals. GABA also potentiated the spontaneous release of endogenous glutamate; an effect sensitive to SKF89976A and low‐Na + ‐containing medium. Confocal microscopy shows that the GABA transporter GAT‐1 is coexpressed with the vesicular glutamate transporter vGLUT‐1 and with the plasma membrane glutamate transporter EAAT2 in a substantial portion of synaptosomal particles. The GABA effect was external Ca 2+ independent and was not decreased when cytosolic Ca 2+ ions were chelated by BAPTA. The glutamate transporter blocker DL ‐TBOA or dihydrokainate inhibited in part (∼35%) the GABA (10 μM)‐evoked [ 3 H]D‐ASP release; this release was strongly reduced by the anion channel blockers niflumic acid and NPPB. GABA, up to 30 μM, was unable to augment significantly the basal release of [ 3 H]glycine from spinal cord synaptosomes, indicating selectivity for glutamatergic transmission. It is concluded that GABA GAT‐1 transporters and glutamate transporters coexist on the same spinal cord glutamatergic terminals. Activation of these GABA transporters elicits release of glutamate partially by reversal of glutamate transporters present on glutamatergic terminals and largely through anion channels. © 2005 Wiley‐Liss, Inc.