Figure 12. γR138A mutation prevents the gain-of-function phenotype of the γK181A mutation.

The experiments were essentially performed as described in Fig. 10 using oocytes expressing the C-terminal V5 tag constructs for wild-type γ-ENaC (wt), γK181A, γR138A or γR138R/K181A mutant subunits (γ_K181A, γ_R138A, γ_R138A/K181A, respectively). A, average ΔI_ami values are shown for wt, γ_K181A, γ_R138A and γ_R138A/K181A expressing oocytes before (open columns; trypsin –) and after (filled columns, trypsin +) exposure to trypsin (2 μg ml⁻¹) for 2 min. ΔI_ami values were normalized to the average ΔI_ami measured in wt-expressing oocytes from the same batch prior to the application of trypsin (for each column: n= 24; N= 3). B, the lanes of the representative Western blot correspond to the experimental conditions of the current data shown in A. C, summary of Western blot results for γ_R138A- and γ_R138A/K181A-expressing oocytes from similar experiments (n= 3; N= 3) as shown in B. Average ΔI_ami values shown in D were obtained from oocytes expressing either wt-αβγ-ENaC (wt) or channels with one or two mutated subunits as indicated below the columns: γ_K181A, α_Fmut (αR205A/R231A), γ_Fmut (γR138A) or γ_Fmut/K181A (n= 18; N= 3 for each group).