Macroscopic properties of connected tetramers. (A) Macroscopic dose–response curves for ATP inhibition of connected K_ATP channels containing different numbers of WT and K185E (M) subunits (◃, 4WT; ▪, 3WT:1M; •, 2WT:2M cis; ▴, 2WT:2M trans; ▾, 1WT:3M; ♦, 4M). n = 5 for all data. The lines are best fit of the data with Eq. 5 with IC₅₀ = 2.6 mM, h = 1.18, P = 0.48 (4M); IC₅₀ = 690 μM, h = 0.84, P = 0.08 (1WT:3M); IC₅₀ = 14 μM, h = 1.36, P = 0 (4WT); IC₅₀ = 31 μM, h = 1.27, P = 0 (3WT:1M); IC₅₀ = 97 μM, h = 0.94, P = 0 (2WT:2M cis); IC₅₀ = 122 μM, h = 0.98, P = 0 (2WT:2M trans). (B) Pedestal amplitude as a function of the number of wild-type subunits in the connected tetramer. Open circles, 2WT:2M trans; filled circles, all other species. The pedestal was estimated from data in A as (a) the fraction of unblocked current at 30mM ATP or (b) from fitting Eq. 5 to the data (4M, 1WT:3M). Solid line, spline function fit through the data; dotted line, prediction of the MWC model (Eq. 15) with P_O = 0.75, F = 0.21, E₀ = 0.12 (Table I) and values K_C,WT/K_O,WT = 51 and K_C,M/K_O,M = 1.9 obtained from the fit of homomeric wild-type and mutant tetramers.