FIGURE 4.

A nonfunctional loop 7 mutant (V132I/R133Y/W134N) could be rescued by a gating mutation with altered desensitization kinetics compared with the gating mutant alone. A, the V132I/R133Y/W134N mutant was not functional. However, addition of V252S mutation to the mutant rescued the function of the receptor. B, the ACh dose-response relationships of the rescued receptor (V132I/R133Y/W134N/V252S) exhibited rightward shift (EC₅₀ = 0.56 ± 0.02 μm) when compared with V252S alone. Error bars are smaller than the symbols. C, the rescued receptor had faster desensitization kinetics when compared with the gating mutant alone (fraction of remaining current relative to the peak after 10-s ACh application was 0.75 ± 0.01 for the rescued receptor (V132I/R133Y/W134N/V252S) and 0.98 ± 0.01 for V252S mutant alone; p < 0.001). Note that due to limited desensitization of the 10 μm ACh-induced current in V252S, exponential fitting for time constant was not successful.