The O–S–B Model for the regulation of outward Kir2.1 currents by high-affinity and low-affinity polyamine blocks. (A) The dependence of chord conductance and currents on driving force (Vm–EK). Red line indicates the conductance sensitive to high-affinity block, and blue dash denotes low-affinity block of conductance. The blue-shaded area indicates the voltage range where the slope of I–Vm relationship is positive, and the purple-shaded area indicates the voltage range with negative slope. (B) Cartoons of the channels in C, O, S, and B states and the corresponding single-channel currents. Red dots indicate K ions. (C) Steady-state I–Vm relationships in the presence of only high-affinity block by spermine at the indicated concentrations are shown in the top panel. Currents = G/Gmax × Vm, and G/Gmax values were calculated from Eq. S6, with A1, A2, z1, and Vh1 listed in Table S2. Steady-state I–Vm relationships in the presence of both high- and low-affinity block by spermine are shown in the bottom panel. G/Gmax values were calculated from Eq. S3, with A, A2, z1, z2, Vh1, and Vh2 listed in Table S2.
