ATP dependence of burst ratio. Relationship between burst ratio and ATP concentration measured experimentally for connected K_ATP channel tetramers containing different numbers of wild-type and mutant subunits (as indicated to the right of each trace). Each data point is the average of three to five experiments. (A) Linear scale. The lines were generated by fitting Eq. 14 to the data for each tetramer separately. The best fit of Eq. 11 to the data for 4M channels gave values of K_O,M = 3.3 mM⁻¹ and m_M = 1.13, and these were used for the mutant subunits in all other fits. The best fit of Eq. 14 to K_ATP channels containing one to four WT subunits was obtained with the following values of K_O,WT and m_WT: K_O,WT = 5.0 mM⁻¹; m_WT = 2.7 (1WT:3M); K_O,WT = 4.2 mM⁻¹; m_WT = 2.7 (2WT:2M cis); K_O,WT = 5.3 mM⁻¹; m_WT = 2.7 (2WT:2M trans); K_O,WT = 2.9 mM⁻¹; m_WT = 2.7 (3WT:1M); K_O,WT = 3.1 mM⁻¹; m_WT = 2.8 (4WT). Log scale. The lines were generated with Eq. 14 using K_O,WT = 3.1 mM⁻¹; m_WT = 2.8 for wild-type subunits and K_O,M = 3.3mM⁻¹; m_M = 1.13 for K185E subunits (see text for details).