Identifying the types of assembled BK channels expressed following a 1:1 injection of G375R mutant and WT cRNA. (A) Representative single-channel recordings from three different single BK channels: WT channel (top row) following injection of WT cRNA; an assembled channel following 1:1 injection of G375R mutant and WT cRNA, (second row); and a G375R homotetrameric mutant channel following injection of G375R mutant cRNA (third row). Recordings are shown at three different voltages for each channel type. Depolarization activates each channel type with a markedly different V_h of 140 mV for the WT channel, 6 mV for the assembled channel, and −100 mV for the G375R homotetrameric mutant channel. Arrows indicate closed channel current levels. (B) Plots of Po-V for 33 individual assembled channels following a 1:1 injection of mutant and WT cRNA (red diamonds with Boltzmann fits). (C) Plots of Po-V for 12 single G375R homotetrameric mutant channels following injection of G375R mutant cRNA (blue squares with Boltzmann fits), and for nine WT channels following injection of WT cRNA (black circles and Boltzmann fits). (D) Identifying the types of assembled channels. Blue and gray areas indicate the range of observed V_h values for G375R homotetrameric mutant channels and WT channels, respectively, from C. One of the assembled channels (rightmost red Po-V curve) overlaps with the WT channels (gray shading), indicating that this assembled channel is likely a WT channel with four WT subunits. Four of the assembled channels (four leftmost red Po-V curves) overlap with the G375R homotetrameric mutant channels (blue shading) suggesting that these four assembled channels are G375R homotetrameric mutant channels assembled from four mutant subunits. The remaining 28 assembled channels would be hybrid channels with mixed subunits (Fig. 1), as their V_h values do not overlap with those of either homotetrameric mutant or WT channels.