FIGURE 2.

Glutamate metabolism and transport between the intraparenchymal and blood environments. The concentration of glutamate in the brain ranges from 1 to 10 μM, which is much lower than that in blood (40–60 μM) and astrocytes and neurons (10–100 mM). Under normal conditions, intraparenchymal glutamate is mainly dependent on EAATs on astrocytes and the abluminal membrane of endothelial cells for transport into cells. When the glutamate concentration in an endothelial cell exceeds the blood concentration, glutamate will be transported into the blood via facilitative transport (${\mathit{X}}_{\mathrm{A}\mathrm{G}}^{\mathrm{-}}\mathrm{/}{\mathit{X}}_{\mathrm{G}}^{\mathrm{-}}$); however, it is difficult for blood glutamate to enter the brain via either tight junctions or carriers. EAATs, glutamate transporters.