Figure 7.

Modal equilibrium of Gβ₁γ₅-activated K_ACh channels. For each individual Gβ₁γ₅ experiment, the relative occupancy of different gating modes was estimated from the fraction of the f histogram fit by the corresponding geometric component. In some f histograms, the components representing gating modes 3 and 4 were too small to be accurately distinguished from each other and, therefore, the sojourns of the channel to these modes are jointly represented. In each experiment, the probability of Gβ₁γ₅-binding, P, was calculated from the relative occupancy of mode 1, 𝔉₁, according to the equation 𝔉₁ = 4P(1 − P)³/[1 − (1 − P)⁴], as a standardization procedure. The solid lines represent the predicted occupancy of the different gating modes for a model assuming independent and equivalent binding of a different number of Gβγ subunits to four binding sites in the channel structure. The symbols and error bars are the mean values ± SEM of two to four separate experiments.