Connexin-selective inhibition of hemichannel currents by BQ⁺. (A) Membrane currents in a Cx50-expressing oocyte voltage clamped at −70 mV. Reduction of Ca²⁺ from 1.8 to 0.2 mM in a KCl solution promoted robust opening of Cx50 hemichannels, evident by the development of a large inward current. The application of 500 µM and 1 mM BQ⁺ in the continued presence of 0.2 mM Ca²⁺ caused a rapid and concentration-dependent reduction in current at −70 mV, an effect that was reversible upon washout. (B and C) Cx46 hemichannels were only moderately affected by 500 µM and 1 mM BQ⁺. Bar graph shows a comparison of the decrease in Cx46 (black bars) and Cx50 (gray bars) hemichannel currents caused by 500 µM and 1 mM BQ⁺. Because Cx46 activates only at positive voltages, tail current amplitudes were measured at −70 mV after 5-s depolarizing voltage steps to +50 mV. Each bar represents the mean ± SEM of six oocytes. (C) Selective inhibition by BQ⁺ of GJ channels formed by Cx50 but not Cx46. Bars represent the mean ± SEM of the decrease in junctional currents caused by the addition of BQ⁺ to patch pipettes (n ranged from 4 to 15). The decrease caused by BQ⁺ was measured after 12 min of achieving whole cell configuration.