Effects of the F60Y mutation. ATP sensitivity in the absence (A) and presence (B) of Mg2+. Above: KATP currents recorded at −60 mV in inside-out patches excised from oocytes expressing Kir6.2/SUR1 (wild-type, WT) (left) and homKir6.2-F60Y/SUR1 (homF60Y) (right) channels. The dashed line indicates the zero current level. Below: mean relationship between [ATP] and KATP conductance (G), expressed relative to that in the absence of nucleotide (Gc), for WT (open circles, n = 13), hetF60Y (open squares, n = 7) or homF60Y (filled squares, n = 7) channels in the absence of Mg2+ (A); or for wild-type (open circles, n = 18), hetF60Y (open squares, n = 9) and homF60Y (filled squares, n = 8) channels in the presence of Mg2+ (B). The lines are drawn to Eq. (1), with the following parameters. (A) WT (IC50 = 10 µm, h = 0.99), hetF60Y (IC50 = 76 µm, h = 0.75), homF60Y (IC50 = 328 µm, h = 1.02, a = 0.022). (B) WT (IC50 = 15 µm, h = 0.95), hetF60Y (IC50 = 133 µm, h = 0.81, a = 0.13), homF60Y (IC50 = 1.38 mm, h = 0.8, a = 0.36).