Voltage-dependent activation was altered by chloride plus glutamate but not by chloride plus sulfate mixtures. Whole-cell recordings from cells bathed in solution containing [Cl⁻]_e = 140 mM (pH_e = pH_i 7.3) and dialyzed with 60 mM [Cl⁻]_i (A), 60 mM [Cl⁻]_i plus 80 mM [SO²⁻₄]_i (B), and 60 mM [Cl⁻]_i plus 80 mM [Glu]_i (C). (D) Comparison of scaled I_Cl(t) recorded at −140 mV in the presence of Cl⁻ (black), Cl⁻ plus SO²⁻₄ (bluish green), and Cl⁻ plus Glu (reddish purple). (E) V_m dependence of activation obtained from cells dialyzed with 60 mM Cl⁻ (black diamonds), 60 mM Cl⁻ plus 80 mM SO²⁻₄ (bluish green triangles), and 60 mM Cl⁻ plus 80 mM Glu (reddish purple triangles). Continuous lines are Boltzmann fits yielding the following V_0.5 and z values: black diamonds, −116.4 ± 2.0 mV and −0.84 ± 0.01 (n = 7); bluish green triangles, −112.5 ± 1.3 mV and −0.91 ± 0.04 (n = 7); reddish purple triangles, −129.9 ± 1.6 mV and −0.78 ± 0.03 (n = 5). Error bars represent mean ± SEM.