FIGURE 2.

Relationship of gating and desensitization. A, normalized and averaged dose-response relationships for four mutants with significant shift of the dose-response relationship when compared with the wild type receptor. EC₅₀ values for these mutants, along with other mutants, are listed in Table 1. Error bars are smaller than the symbols. Note that compared with the wild type receptor, all four M2 mutants exhibited higher sensitivity to ACh. B, spontaneous currents were evident when they were blocked by nAChR antagonist mecamylamine (MCA). The maximal activatable currents were determined by a saturation concentration of ACh. C, the rate of desensitization was slower in four gating mutants when compared with that for the wild type receptor. D, the desensitization rate and fraction of spontaneous (spont.) opening (spontaneous current/total current (spontaneous + activatable)) were highly correlated (p = 0.001; r² = 0.9818).