Changes in intrinsic P_o do not fully account for high Q52E-Kir6.2//E203K-SUR1 ATP sensitivity. (A) Representative traces from inside-out patch voltage-clamp recordings from COSm6 cell transfected with WT or mutant K_ATP channels exposed to 5 µM PIP₂ twice for 30 s. Dashed lines represent zero current. (B) Mean fold increase in current after one or two 30-s treatments with PIP₂ for WT or single or double mutant channels. The key to bar graph is indicated by the patterns shown below each condition in A. Number of patches tested is given below each condition. Error bars represent SEM. (C) Intrinsic P_o was calculated by two indirect means (see Materials and methods), stationary noise analysis (NA) and PIP₂ response method. Number in each dataset for PIP₂ method is given in B (right); n for NA method is 19, 18, 17, and 19 for WT, E203K-SUR1, Q52E-Kir6.2, and Q52E-Kir6.2//E203K-SUR1, respectively. Error bars represent SEM, and some are smaller than the symbols. ***, P < 0.001 using one-way ANOVA with Tukey post-hoc test for NA and PIP₂ methods.