CAP2 stimulated α-R205A/R231A, β-, and γ-138K or α-, β-, and γ-138K plus 178–181 QQQQ but not α-R205A/R231A, β-, and γ-138A or α-, β-, and γ-138A plus 178–181 QQQQ mutant channels. (A) CAP2 induced I_Na of WT and α-R205A/R231A, β-, γ-, or α-R205A/R231A, β-, and γ-R138A or α-R205A/R231A, β-, and γ-R138K ENaC mutant channels (n = 12). (B) CAP2 induced I_Na of α-, β-, and γ-R138A, R178Q, K179Q, R180Q, and K181Q or α-, β-, and γ-R138K, R178Q, K179Q, R180Q, and K181Q ENaC mutant channels. Amiloride-sensitive currents were measured as described in Fig. 1. Batches of oocytes were extracted from three different frogs (n = 12). Results are expressed as the means ± SE. * and **, P < 0.0001.