Figure 3. Dilution of ionic strength by 90% with isotonic sucrose shifted V_rev positively, indicating that most Asp¹¹² mutants are anion selective.

a Measurement of V_rev by tail currents in a cell transfected with D112H at pH 5.5//5.5 and (b) after sucrose. c, V_rev in the same cell in pH 5.5 Cl⁻ solution, and (d) after sucrose. Arrows indicate zero current. V_hold = −40 mV, V_pre = +60 mV. e, Mean shifts of V_rev with decreasing ionic strength in CH₃SO₃⁻ solutions or (f) in Cl⁻ solutions. Each value was determined in 3–6 cells. X = not done. g, Shifts of V_rev when CH₃SO₃⁻ was replaced by Cl⁻. Values for WT and D112E do not differ significantly from 0 mV. For all anion selective mutants except D112N, the difference between shifts at pH 5.5 and 7.0 was significant (p<0.001, one-way ANOVA followed by Tukey’s test; n = 3–8). Error bars in e–g are s.e.