D117A modifies unitary conductance and absolute open probability of EAAT4 anion channels. A and B, power density spectra of WT (A) and D117A EAAT4 (B) from current recordings at −125 mV (WT) and +125 mV (D117A) with 100 μm l-glutamate. Fits with double Lorentzian functions are given as solid lines, and background power density spectra of untransfected tsA201 cells are given as filled circles. C and D, representative stationary noise analyses for WT EAAT4 (C) and D117A EAAT4 (D). E and F, voltage dependence of unitary anion currents of WT (E) and D117A EAAT4 (F) derived from stationary noise analysis (n = 9/9). G and H, absolute open probabilities for WT (G) and D117A EAAT4 (H). The open symbols give values determined in the presence of 100 μm glutamate, and the filled symbols give values determined in its absence.