Sodium dependences of WT and mutant EAAT4. A and D, representative current recordings of WT (A) and D117A (D) EAAT4 in the absence of l-glutamate and sodium (left panel), in the presence of sodium (middle panel), and in the presence of sodium and l-glutamate (right panel). B, C, E, and F, sodium dependence of late WT (B and C) and D117A EAAT4 anion currents (E and F), in the absence (B and E), or in the presence of external glutamate (C and F).