Figure 3.

Dose–response curves for wild-type and SCCMS mutant mouse AChRs. Each symbol represents one or more cell-attached patches containing saline plus agonist. ■ are ACh on wild type (48); all others pertain to choline (●, wild type; ▿, αG153S; ⋄, αN217K; ▵, αS269I; ○, ɛT264P, □, ɛL269F, ⊕, βV266M). (A) Single-channel probability. Choline is a very weak agonist of wild-type AChR and a much more potent agonist of the SCCMS mutants. (B) The effective channel opening rate. The value at limiting high agonist concentration is the intrinsic diliganded channel opening rate constant, which for choline is >10 times faster in the SCCMS mutants compared with the wild-type. The kinetic and equilibrium constants for choline activation of wild-type and SCCMS AChR are given in Table 1.