“Extra” shut and open components in unliganded gating. In all panels, there was no agonist present in the pipette or bath. (A; top) Continuous trace of clustered unliganded openings from AChRs having only the αA96H mutation (in both α subunits). This single mutation increases substantially E₀ and, hence, constitutive activity. (Bottom) Interval duration histograms of events within clusters and an example cluster (underlined, above). Two components are apparent in both the shut and open histograms. E₀^obs was estimated from the predominant components. (B) Adding the β-subunit M4 mutation βT456I increases E₀^obs but does not eliminate the extra components. (C) Adding the binding site mutation αW149M eliminates the long openings but has little effect on E₀^obs. (D) Another example of extra components in both the shut- and open-interval duration histograms. (E) These extra components disappear with the addition of the binding site mutation αW149F. After correcting for the backgrounds, the E₀ values were the same with or without the extra components.