Inhibitions of the E166A and E166Q mutants by fatty acids. (A and B) Inhibitions of E166A by 300 μM octanoate (OA) and butyrate (BA). (C) Dose-dependent inhibition curves of the E166A mutant by various fatty acids at −140 mV. The color-coded symbols are as follows: black, proprionate (PA); red, butyrate (BA); green, hexanoate (HA); blue, octanoate (OA); cyan, decanoate (DeA); magenta, dodecanoate (DoA). (D) Dose-dependent inhibition curves of the E166Q mutant by various fatty acids. The color representations are the same as in C. (E and F) Voltage dependence of the K_1/2 of the E166A and E166Q mutants by various amphiphilic blockers. Data points are connected by straight lines. The color representations are the same as those in C and D. For comparison, yellow symbols represent the apparent K_1/2 of CPA. The slopes of the fitted straight lines (not shown) are as follows: E166A: PA, 0.56; BA, 0.61; HA, 0.74; OA, 0.90; DeA, 0.67; DoA, 0.51; CPA, 0.88; and E166Q: PA, 0.57; BA, 0.42; HA, 0.61; OA, 0.61; DeA, 0.41; DoA, 0.36; CPA, 0.45.