DHA sensitivity of the single arginine mutants. (A–C) Representative current traces for voltages corresponding to 10% of Gmax in control solution at pH 7.4. Black traces indicate control, and red traces indicate 70 µM DHA. The increments in current amplitudes are R362R (WT), 2.2 times (A); for L361R/R362Q, 0.9 times (B); and A359R/R362Q, 2.7 times (C). (D) DHA-induced G(V) shifts for the single-charge mutants (70 µM DHA at pH 7.4). The black line equals the DHA-induced shift for R362Q. Mean ± SEM (n = 8, 8, 6, 9, 10, 14, 9, and 9). DHA-induced shifts compared with R362Q (one-way ANOVA together with Dunnett’s multiple comparison test: **, P < 0.01; ***, P < 0.001). Green bars denote significantly larger DHA-induced shifts relative to the neutral 356–362 segment (open bar), the red bars denote significantly smaller shifts, and the yellow bars denote no significant differences. (E) Mutated residues are marked on one VSD of the Shaker K channel in states C3 and O. Same color coding as in D. (F) Correlations between the V1/2 values and the DHA-induced shifts for the channels described in D. Slope is significantly different from zero (Pearson correlation test, and linear regression: P < 0.01 for both). The symbols denote mean ± SEM, the continuous line is the linear regression, and the dashed lines denote the 95% confidence interval.
