Figure 6.

Modal classification of K_ACh channel gating in the presence of Gβ₁γ₅. (A) The t _open–f plots were generated from the analysis of the data illustrated in Fig. 5, C and D. In the presence of Gβ₁γ₅, the mean open time of the K_ACh channel was independent of the frequency of channel gating and approached the t _open value estimated for gating mode 1 of receptor-activated channels. (B) Histograms of frequencies of openings are shown for the experiments illustrated in A. The histogram shown at left corresponds to Gβ₁γ₅ concentration of 0.6 nM, whereas the histogram shown at right corresponds to Gβ₁γ₅ concentration of 1.5 nM. Both histograms were fitted by the sum of three geometrics (Colquhoun and Hawkes, 1981): P(f) = a ₁μ₁ ⁻¹(1 − μ₁ ⁻¹)^{f − 1} + a ₂μ₂ ⁻¹(1 − μ₂ ⁻¹)^{f − 1} + a ₃μ₃ ⁻¹(1 − μ₃ ⁻¹)^{f − 1} (continuous line). The mean frequency values and the relative areas of different components are μ₁ = 1.4 Hz (73.2%), μ₂ = 6.9 Hz (23.5%), and μ₃ = 17.6 Hz (3.3%) at 0.6 nM Gβ₁γ₅; and μ₁ = 1.3 Hz (54.9%), μ₂ = 12.6 Hz (35.5%), and μ₃ = 37.0 Hz (9.6%) at 1.5 nM Gβ₁γ₅. The proportion of high frequency data segments consistently increased with Gβ₁γ₅ concentration.