Concentration and voltage dependence of the inhibition of single Cx50 hemichannels by BQ⁺ applied to the extracellular side. (A) Plots of fractional inhibition (F_BQ) versus V_m at BQ⁺ concentrations of 300 µM, 500 µM, and 1 mM demonstrate the voltage dependence of inhibition. Solid lines are fits to a Boltzmann equation. The mean V_1/2 values from Boltzmann analysis are −86, −53, and −30 mV, with slope factors of 26, 25, and 23 mV⁻¹ for 300 µM, 500 µM, and 1 mM BQ⁺, respectively. (B) Plots of fractional inhibition (F_BQ) versus BQ⁺ concentrations of −30, −50, −70, and −90 mV. The solid lines are fits to the Hill equation, with K_d values of 1.14, 0.556, 0.38, and 0.24 mM and Hill slopes of 1.6, 1.7, 1.9, and 1.7 at −30, −50, −70, and −90 mV, respectively.