Figure 3.

FLAG-ΔF1388 SUR1_AAA mutant channels have reduced ATP sensitivity and do not respond to MgADP or diazoxide. (A) Dose–response curves of FLAG-SUR1_AAA and FLAG-ΔF1388 SUR1_AAA channels to ATP inhibition. The K_1/2 is estimated by fitting the data points to the Hill equation {I_rel = 1/[1 + ([ATP]/K_1/2)^H]}, with I_rel being the current relative to the current in the absence of ATP. Each data point represents the average of 8–9 patches, with the error bar being the SEM. H = 1.4 and 1.2 for FLAG-SUR1_AAA and FLAG-ΔF1388 SUR1_AAA channels, respectively. (B) Representative current traces recorded from inside-out membrane patches containing FLAG-wild type (WT) SUR1, FLAG-SUR1_AAA, or FLAG-ΔF1388 SUR1_AAA channels. Currents were recorded at −50 mV. Inward currents are shown as upward deflections. Patches were exposed to differing concentrations of ATP and ADP, as indicated by the bars above the records. Free [Mg²⁺] was maintained at 1 mM in all ATP-containing solutions. (C) Representative current traces showing the lack of response to diazoxide of FLAG-ΔF1388 SUR1_AAA channels, in contrast to FLAG-SUR1_AAA channels. Patches were exposed to differing concentrations of ATP and diazoxide, as indicated by the bars above the records. Free [Mg²⁺] was maintained at 1 mM in all ATP-containing solutions.