Probing for an α7 C-loop mutation with selective and nonselective agonists. (A) Mutation of the α7 tyrosine 188 to phenylalanine reduces sensitivity to low concentrations of ACh, with little impact on sensitivity to the responses to the α7-selective agonist 4OH-GTS-21 (Horenstein et al., 2007). The upper traces are representative responses of oocytes expressing wild-type α7, for which 300 µM 4OH-GTS-21 evoked responses that are 57 ± 4% the magnitude of the responses evoked by 300 µM ACh, in net charge. In contrast, for oocytes expressing α7Y188F, 300-µM 4OH-GTS-21–evoked net charge responses that are 405 ± 55% of the magnitude of the responses evoked by 300 µM ACh. (B) Oocytes were injected with RNA for α7Y188F and wild-type α7 at (mutant/wild-type) 1:0, 5:1, 3:1, 1:1, and 0:1 ratios and then tested for their relative responses to 300 µM ACh and 300 µM 4OH-GTS-21. The values are plotted in relation to the fraction of α7Y188F RNA injected at each ratio and are the means ± SEM of at least four oocytes for every condition.