Effect of α-, β-, and γ-178-181 QQQQ or α-, β-, and γ-178-181 QQQQ, K185Q, K189Q, K200Q, and K201Q ENaC mutants on I_Na stimulated by CAP2 and CAP1. (A) CAP2 induced I_Na of WT and 178–181 QQQQ 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. Statistical significance was determined using an unpaired Student's t test. (B) Western blot of surface pool of WT and 178–181 QQQQ γ-ENaC mutant channels. Lane 1, uninjected eggs; lane 2, WT ENaC alone; lane 3, WT ENaC plus CAP2; lane 4, α-, β-, and γ-178-181 QQQQ ENaC alone; lane 5, α-, β-, and γ-178-181 QQQQ ENaC plus CAP2. A representative experiment is shown (n = 3). (C) CAP2 and CAP1 induced I_Na of WT and 178–181 QQQQ, K185Q, K189Q, K200Q, and K201Q 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 **, difference P < 0.05. Statistical significance was determined using ANOVA.