Estimating the partial charge associated with the opening and closing transitions for BK_B channels gating in saturating Ca²⁺_i. (A) Plot of Po versus voltage. Circles plot data obtained for BK_B channels expressed in oocytes for patches with a single channel (open circles) and from two to six channels per patch (closed circles). Squares plot data obtained from macro currents from BK_B channels expressed in HEK cells. (B) Voltage dependence of mean open times at negative potentials. The line is a linear fit to open times negative to −100 mV. Projecting to 0 mV gives an intrinsic channel closing rate (K in Schemes III, IV, and V) of 6,420 ± 680 s⁻¹ with a partial charge of −0.099 ± 0.015 e_o (257 mV/e-fold change). (C) Voltage dependence of mean closed times. The line is a linear fit to closed times negative to −100 mV. Projecting to 0 mV gives an estimate of the intrinsic opening rate (H in Schemes III, IV, and V) of 3.87 ± 1.88 s⁻¹ with a partial charge of 0.237 ± 0.06 e_o (108 mV/e-fold change). Data in B and C are a mean of the data obtained with single-channel recording.