Increased basal activity in intact cells expressing KATP (G53D) channels. Relative efflux of 86Rb+ as a function of time in basal conditions (A) or in the presence of metabolic inhibition (B) for reconstituted wild-type (WT) and mutant KATP channels, and untransfected controls (Unt). All transfections were done in parallel. Graphs show compiled data (mean ± sem) from four to six experiments. C, Rate constants for KATP-dependent efflux (k2) in basal conditions relative to metabolic inhibition (MI) for WT, heteromeric, or homomeric KATP channels. Data were fit with a double-exponential equation to obtain rate constants for KATP-dependent efflux, k2 (see Patient and Methods). *, P < 0.05 and **, P < 0.001, compared with wild-type KATP by unpaired Student’s t test.