FIGURE 4.

Mutations at sites in the late finger and top of the thumb of α ENaC affect P8 inhibition. A, summary of the effects of mutations on P8 inhibition and Na⁺ self-inhibition. Each point represents the mean values of P8 and Na⁺ self-inhibition for an individual mutation. The fitted curve for wild-type ENaC (see Fig. 3B) is overlaid for comparison. Statistical analyses using NLMR were performed to determine whether mutants bound P8 with weaker affinity (red and blue) or 10-fold weaker affinity (blue) than wild-type. B, effect of Trp mutation at individual sites on P8 inhibition. Mutations in the latter half of the finger domain and the top of the thumb reduced P8 inhibition (10 μm P8). Two Cys (C) residues in the thumb that may be functionally important and three endogenous Trp (W) residues were not mutated. Values are mean ± S.D. (n = 5–12). Dashed line indicates wild-type value (77 ± 6%). Red and blue bars are as defined for A. p values were determined by nonlinear mixed regression model analyses (see Fig. 3) and are indicated here and in supplemental Table S1. Values of p < 0.0001 were considered significant.