Glycine taken up through GLYT1 and GLYT2 heterotransporters into glutamatergic axon terminals of mouse spinal cord elicits release of glutamate by homotransporter reversal and through anion channels.
Glycine concentration-dependently elicited [3H]D-aspartate ([3H]D-ASP) release from superfused mouse spinal cord synaptosomes. Glycine effect was insensitive to strychnine or 5,7-dichlorokynurenic acid, but was prevented by the glycine transporter blocker glycyldodecylamide. Glycine also evoked release of endogenous glutamate, which was sensitive to glycyldodecylamide and abolished in low-Na+ medium. Experiments with purified synaptosomes and gliasomes show that the glycine-evoked [3H]D-ASP release largely originates from glutamatergic nerve terminals. The glycine-evoked [3H]D-ASP release was halved by NFPS, a selective blocker of GLYT1 transporters, or by Org 25543, a selective GLYT2 blocker, and almost abolished by a mixture of the two, suggesting that activation of GLYT1 and GLYT2 present on glutamatergic terminals triggers the release of [3H]D-ASP. Accordingly, confocal microscopy experiments show localization of GLYT1 and GLYT2 in purified synaptosomes immuno-stained for the vesicular glutamate transporter vGLUT1. The glycine effect was independent of extra- and intraterminal Ca2+ ions. It was partly inhibited by the glutamate transporter blocker DL-TBOA and largely prevented by the anion channel blockers niflumic acid and NPPB. To conclude, transporters for glycine (GLYT1 or/and GLYT2) and for glutamate coexist on the same spinal cord glutamatergic terminals. Activation of glycine heterotransporters elicits glutamate release partly by homotransporter reversal and largely through anion channels.
Raiteri
Luca
L
Pharmacology and Toxicology Section, Department of Experimental Medicine, University of Genoa, Viale Cembrano 4, 16148 Genoa, Italy.
Stigliani
Sara
S
Siri
Antonella
A
Passalacqua
Mario
M
Melloni
Edon
E
Raiteri
Maurizio
M
Bonanno
Giambattista
G
D026921:Amino Acid Transport Systems, Neutral / Q000378:metabolism*; D000818:Animals; D017920:Antiporters / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D018698:Glutamic Acid / Q000378:metabolism*; D005998:Glycine / Q000378:metabolism*; D050487:Glycine Plasma Membrane Transport Proteins; D051379:Mice; D017729:Presynaptic Terminals / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism
D026921:Amino Acid Transport Systems, Neutral; D017920:Antiporters; D050487:Glycine Plasma Membrane Transport Proteins; C493270:Slc6a5 protein, mouse; C493267:Slc6a9 protein, mouse; D018698:Glutamic Acid; D005998:Glycine