Rundown of Kir6.2/SUR1 and Kir6.2-G334D/SUR1 channels in macropatches. (A) Macroscopic Kir6.2/SUR1 currents at −60 mV recorded from a giant patch. Patch excision and the start of the perfusion with nucleotide-free intracellular solution are indicated by the arrows. The dotted line represents the zero current level. (B) Macroscopic Kir6.2-G334D/SUR1 currents recorded at −60 mV. Patch excision and the start of the perfusion with nucleotide-free solution are indicated by the arrows. The dotted line represents the zero current level. (C) Mean macroscopic K_ATP current at −60 mV during the first 60 s of rundown, expressed as a fraction of the maximum value reached after excision, is plotted as a function of the time after patch excision for Kir6.2/SUR1 (open circles; n = 10) and Kir6.2-G334D/SUR1 channels (filled circles; n = 10). The lines are the best fit of a double-exponential function to the mean data (solid line, Kir6.2/SUR1; dotted line, Kir6.2-G334D/SUR1).