metabolism. However, EAAC1 protein was detected in SH-SY5Y and C6 cell mitochondria where, as in brain, DL-TBOA inhibited glutamate-stimulated ATP synthesis, whereas GLAST mRNA and protein were barely detectable and GLT1 mRNA was virtually absent. To establish whether EAAC1 was the transporter subtype mediating stimulation of glutamate-induced metabolism, we investigated the effect of selective EAAC1 knockdown with antisense oligonucleotides on ATP responsiveness to glutamate in SH-SY5Y and C6 cells. Treatment with EAAC1 AsODN completely abolished glutamate-induced ATP synthesis in both systems. Since selective knock-down of EAAC1 abrogated glutamate-stimulated ATP synthesis, this ruled out an involvement of GLAST, suggesting that the process relies solely on EAAC1. The ” latter observation Mitochondrial NCX1/EAAC1 Sustain Brain Metabolism 3 Mitochondrial NCX1/EAAC1 Sustain Brain Metabolism mitochondria from rat hippocampus and cortex after 1 h incubation with glutamate or vehicle with or without oligomycin. ATP production by mitochondria from rat hippocampus and cortex after 1 h incubation with glutamate or vehicle or different glucose concentrations. ATP production in rat hippocampal or cortical mitochondria exposed for 1 h to DL-TBOA in the 518303-20-3 site presence of glutamate or vehicle. GLAST, GLT1, and EAAC1 glutamate transporters in mitochondrial protein extracts from rat hippocampus or cortex. Plasma membrane proteins were used as a positive control. The same panel shows EAAC1 immunoreactivity in different rat tissues. Rat testis were used as negative control. ATP production in rat hippocampal or cortical mitochondria exposed for 1 h to TFBTBOA 50 nM in the presence of 
glutamate or vehicle. Each bar in panels B, C, D, F represents the mean 6 SEM of 18 different determinations. p,0.01 vs control; p,0.001 “7851504 vs control; p,0.01 vs 1 mM glutamate; p,0.001 vs 1 mM glutamate. In addition, in isolated SH-SY5Y and C6 mitochondria, glutamate stimulated ATP production in a Na- dependent manner. Finally, we explored the possible involvement of AGCs. Real time experiments disclosed that SHSY5Y and C6 cells expressed only Citrin/AGC2; we therefore used these cell lines in experiments where we knocked down Citrin/AGC2 by transfecting human and rat specific ODNs, respectively. These experiments failed to document an involvement of the AGC pathway in glutamatedependent ATP production in our model. Additional support for the mitochondrial localization of EAAC1 came from immunoelectron microscopy, showing the presence of specific staining in neuronal and glial mitochondria in rat cerebral cortex and hippocampus. Notably, the specificity of EAAC1 antibody was verified by looking for reactivity in different rat tissues by western blot. As previously described EAAC1 was not detected in rat testis . Moreover, the lack of immunoreactivity demonstrated no cross-reaction with GLAST and GLT-1, known to be expressed in the same tissue. 6 Mitochondrial NCX1/EAAC1 Sustain Brain Metabolism Glutamate induces inner mitochondrial membrane depolarization treated with DL-TBOA, the glutamate-dependent drop in DYmit was significantly prevented in agreement with the TMRE data previously obtained in non permeabilized cells. Role played by sodium and calcium ions in glutamatestimulated ATP synthesis. Involvement of NCX Since EAATs cotransport Na/glutamate using the favorable Na gradient to carry glutamate, their activity is expected to diminish as Na accumulates, and eventually to sto
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