Q52K-Kir6.2//WT(E203)-SUR1 channels do not have extremely increased ATP sensitivity. (A) Representative traces of inside-out patch voltage-clamp recordings from COSm6 cell transfected with Q52K-Kir6.2//WT-SUR1 or WT channels. Patches were exposed to various concentrations of ATP or nucleotide-free Kint/EDTA control solution. Dashed lines represent zero current. (B) Dose–response data illustrating the mean currents in several ATP concentrations relative to maximum in nucleotide-free solution. Best fit curves (solid lines) were generated using the Hill equation for WT and Q52K-Kir6.2 (IC₅₀: 29 ± 1 µM and 12 ± 0 µM, respectively). Note because only three ATP concentrations were tested, the IC₅₀ values differ from data presented using more thorough analysis. Q52R dose–response data were fit manually (dashed line), with an estimated IC₅₀ of ∼1 mM. n = 3–8 for each data point. Error bars represent SEM, and some are smaller than the symbols.