Gating currents of BK-F380 mutants in internal calcium absence. (A–C, insets) I_g of mutants (F380I, F380L, and F380W) was recorded in inside-out macropatches at 0 µM [Ca⁺²]_i. I_g was evoked by 2-ms voltage steps of 10 mV going from −90 to 350 mV. (A–C) Q_c(V) relationships of BK and BK-F380 mutants were obtained by integrating each I_g trace. Boltzmann fitting to the experimental data (mean ± SEM) is indicated by solid lines (V₀ = 182 ± 9 mV, z_Q = 0.56 ± 0.01 e₀ in BK-F380I, n = 5; V₀ = 173 ± 4 mV, z_Q = 0.55 ± 0.01 e₀ in BK-F380L, n = 7; V₀ = 153 ± 6 mV, z_Q = 0.56 ± 0.02 e₀ in BK-F380W, n = 4). Dashed lines represent the Boltzmann fitting to the WT Q_c(V) obtained in the absence of intracellular Ca²⁺ (Fig. 3 E). (D) V₀ of Q_c(V) of mutants (F380I, F380L, and F380W) compared with Q_c(V) of WT and F380A. Mean ± SEM.