Fig. 5.

Ionic screening reduces ATP inhibitory effects. The relative conductance indicates that ionic screening elicited by the addition of KCl affected the conductance changes induced by ATP addition. The lowest KCl concentration (50 mM) promoted electrostatic interactions, increased binding, and enhanced the ATP-induced inhibition. Increased KCl concentrations (135 and 500 mM, respectively) diminished the ATP-induced inhibition by weakening the electrostatic interactions and the binding affinity. The experimental conductance data (symbols) are presented as mean ± SD from six traces recorded for each of the experiments. The average conductance data fitted to the Hill equation (full lines) yielded the next parameters: (i) 50 mM KCl: IC₅₀ = 3.83 ± 0.05 mM, n = 4.11 ± 0.16; (ii) 135 mM KCl: IC₅₀ = 4.36 ± 0.07 mM, n = 4.14 ± 0.2; and (iii) 500 mM KCl: IC₅₀ = 6.94 ± 0.07 mM, n = 4.1 ± 0.14