Figure 4.

ADP and GDP sensitivities in the presence and absence of Mg²⁺ A, Kir6.2-F333I/SUR1, Kir6.2-F333I/SUR2A and Kir6.2-F333I/SUR2B currents elicited by voltage ramps from −110 to +100 mV. MgADP (1 mm) was applied as indicated. B, mean relationship between [MgADP] and K_ATP conductance (G), expressed relative to the conductance in the absence of nucleotide (G₀) for F333I plus SUR1 (○), SUR2A (□) and SUR2B (▴). The line is the best fit of eqn (2) (EC₅₀ = 52 μm, A = 4.4). C, mean relationship between [ADP] and K_ATP conductance (G), expressed relative to the conductance in the absence of nucleotide (G₀), in Mg²⁺-free solution. Kir6.2/SUR2A (⋄, n = 4) or Kir6.2-F333I/SUR2A (⋄, n = 6). The lines are the best fit of eqn (1) (IC₅₀ = 80 μm, h = 1.2 for Kir6.2/SUR2A; IC₅₀ = 1.7 mm, h = 1.0 for Kir6.2-F333I/SUR2A). D, mean conductance recorded in the presence of 100 μm MgGDP expressed relative to the mean of that recorded in the absence of the nucleotide, for the channels indicated. The number of patches was 4–7 in each case.