Single BK channels in CCs from kcnmb2^−/− mice do not inactivate. (A′) Channel openings in a patch from a WT CC were activated with the indicated voltage protocol with 10 µM cytosolic Ca²⁺. Top traces show single channel sweeps before and after (blue trace) brief application of trypsin to remove inactivation. Bottom traces show means of 20 sweeps before and after trypsin, with a single exponential (red) fit to the inactivation time course. (A″) Traces show a single sweep and a mean of 20 for the patch at the top, but with 0 Ca²⁺. Scale bar applies to A′ and A″. (A‴) A G-V curve was generated from BK channel activation (after removal of inactivation) for two cells with mean ensemble inactivation time constants of <35 ms. A fitted Boltzmann yielded the values shown on the figure. Dotted lines correspond to mean G-Vs at 10 µM Ca²⁺ for Slo1 alone and Slo1 + β2, when expressed heterologously in oocytes. (B′) Top traces show channel openings from a patch from another WT CC, before and after removal of inactivation. Bottom traces are means of 20 sweeps before and after removal of inactivation, along with the fitted exponential (red). (B″) Traces correspond to a single sweep (top) and the mean of 20 sweeps with 0 µM Ca²⁺. Scale bar applies to B′ and B″. (B‴) The points reflect an averaged G-V curve for four patches with ensemble inactivation time constants between 42 and 49 ms. Dotted lines are as in A‴. (C′) Traces shows openings elicited with 10 µM Ca²⁺ in a patch from a kcnmb2^−/− CC. (C″) Trace shows ensemble mean of 20 sweeps from the patch at the top. (C‴) A G-V curve for BK channels from three patches from kcnmb2^−/− CCs. Error bars indicate SEM. (D) The frequency distribution of numbers of patches from WT cells having a given inactivation time constant is shown. Bin to the right of the break in the x axis highlights two patches with entirely noninactivating BK channels.