Drug sensitivity is increased for 3R. (A) Structure of PiMA, here in the uncharged form with the carboxylic acid group protonated. (B) G(V) shifts induced by 70 µM PiMA at pH 7.4 and 9.0 for WT and 3R. Mean ± SEM (n = 12, 6, 4, and 6; one-way ANOVA together with Bonferroni’s pairwise comparison test: **, P < 0.01; ***, P < 0.001). (C) Representative current traces at pH 9.0 for WT in control solution (black) and in 70 µM PiMA (red) for a voltage corresponding to 10% of G_max in control solution (i.e., −35 mV). The current amplitude is increased fourfold. (D) Representative G(V) curves. Same cell as in C (control, black symbols; PiMA, red symbols). ΔG(V)_PiMA = −9.0 mV in this example. (E) Representative current traces at pH 9.0 for 3R in control solution (black) and in 70 µM PiMA (red) for a voltage corresponding to 10% of G_max in control solution (i.e., 5 mV). The current amplitude is increased >10 times. (F) Representative G(V) curves. Same cell as in F (control, black symbols; PiMA, red symbols). ΔG(V)_PiMA = −28.5 mV in this example.