Figure 2.

(A) In neuronal cells, glutamine is required for the production of both the excitatory neurotransmitter gamma-aminobutyric acid (GABA) and the inhibitory neurotransmitter glutamate. Glial cells take up both GABA and glutamate and convert them back to glutamine, which can then be either pumped out of the cell to replenish glutamine stores in the extracellular space or utilized to meet the metabolic requirements of the glial cells. (B) Uridine transport across membranes is mediated by the SLC29A family of equilibrative nucleoside transporters and the SLC28A family of concentrative nucleoside transporters.