Effects of Cys substitutions in the intracellular flanks of S0–S6 and of their reactions with QPD on V₅₀. (A) Mean V₅₀ ± SEM of the V₅₀s from the individual fits of the Boltzmann equation to the currents from each cell. n = 3–5 for each mutant. The dashed red line corresponds to mean V₅₀ of pWT α. (B–D and F–H) Normalized G-V curves of untreated macropatches (control) and after treatment with 40 µM QPD for 5–7 min. The G-V curve of pWT α is shown as a dashed red line. Recordings were from inside-out macropatches with 10 µM Ca²⁺ in the bath solution. (E and I) Bar graph of V₅₀s before and after treatment with QPD for W43C, L175C, and W43C + L175C. Mean ± SEM.