In vitro activation of GAT1 transporters expressed in spinal cord gliosomes stimulates glutamate release that is abnormally elevated in the SOD1/G93A(+) mouse model of amyotrophic lateral sclerosis.
The effect of GABA on glutamate release from astrocytes has been studied in healthy mice and in a murine transgenic model of amyotrophic lateral sclerosis (ALS), using mouse spinal cord gliosomes labeled with [(3)H]d-aspartate ([(3)H]d-ASP). GABA concentration-dependently evoked the release of [(3)H]d-ASP. The effect of GABA was not mimicked by GABA(A) or GABA(B) receptor agonists or counteracted by antagonists, excluding receptor involvement. However, it was prevented by the GABA transport inhibitor N-(4,4-phenyl-3-butenyl)-nipecotic acid (SKF 89976A), suggesting participation of GABA transporters type 1 (GAT1) placed on glutamate-releasing astrocyte-derived gliosomes. Accordingly, GAT1 co-expressed with glutamate-aspartate transporter (GLAST) and glutamate transporter type 1 (GLT1) in the majority of glial particles. [(3)H]d-aspartate release was Ca(2+)-independent and not blocked by the glutamate uptake inhibitor dl-threo-b-benzyloxyaspartic acid (dl-TBOA); instead, it was abrogated by the anion channel blockers niflumic acid and 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB). The GAT1-mediated release of [(3)H]d-ASP was significantly enhanced in spinal cord gliosomes from the mouse model of ALS. This excessive [(3)H]d-ASP release was very precocious, largely preceding the onset of the disease symptoms. These data indicate that GAT1, GLAST and GLT1 coexist on the same gliosome in mouse spinal cord and that activation of GAT1 transporters elicits glutamate release by anion channel opening. This phenomenon might have pathological relevance, because [(3)H]d-ASP release is enhanced in experimental ALS.
Milanese
Marco
M
Department of Experimental Medicine, Section of Pharmacology and Toxicology and Center of Excellence for Biomedical Research, University of Genova, 16148 Genova, Italy.
Zappettini
Simona
S
Jacchetti
Emanuela
E
Bonifacino
Tiziana
T
Cervetto
Chiara
C
Usai
Cesare
C
Bonanno
Giambattista
G
D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002614:Chelating Agents / Q000494:pharmacology; D004195:Disease Models, Animal; D004305:Dose-Response Relationship, Drug; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D018682:GABA Agents / Q000494:pharmacology; D050485:GABA Plasma Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology*; D005911:Gliosis / Q000139:chemically induced / Q000473:pathology; D018698:Glutamic Acid / Q000494:pharmacology*; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D009557:Nipecotic Acids / Q000494:pharmacology; D013116:Spinal Cord / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D013482:Superoxide Dismutase / Q000235:genetics*; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D002614:Chelating Agents; D018682:GABA Agents; D050485:GABA Plasma Membrane Transport Proteins; D009419:Nerve Tissue Proteins; D009557:Nipecotic Acids; D018698:Glutamic Acid; D004533:Egtazic Acid; D005680:gamma-Aminobutyric Acid; C045598:N-(4,4-diphenyl-3-butenyl)nipecotic acid; D007770:L-Lactate Dehydrogenase; C109415:SOD1 G93A protein; D013482:Superoxide Dismutase; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium