Stoichiometry of astroglial solute carrier (SLC) neurotransmitter transporters. EAAT1,2 , excitatory amino acid transporters 1 and 2; Sxc, cystine-glutamate exchanger; GAT1,3, GABA transporters 1 and 3; GlyT1, glycine transporter; ENT, equilibrative nucleotide transporters; CNT, concentrative nucleotide transporters; NET, norepinephrine transporter.