Figure 3.

Gating of loop C proline mutants in the absence of agonists is homogeneous. (A; left) Single-channel clusters from unliganded AChRs (adult type, −100 mV; background mutation were added to increase constitutive activity; see Materials and methods). (Right) Intra-cluster interval duration histograms and an example cluster. WT, αP194A, and αP197A show both brief and long (arrow) unliganded openings. The briefer, main component of each distribution represents C-O gating; the longer open component(s) is characteristic of unliganded activity but is distinct from C-O and of unknown origin (Purohit and Auerbach, 2009). (B) Adding the agonist site mutation αY93F eliminates long unliganded openings but does not affect the gating open interval time constant (Purohit and Auerbach, 2010).