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Novel Loss‐of‐function Variants in the Epithelial Na+ Channel Extracellular Domain

Mutations in epithelial Na+ channel (ENaC) subunits cause hypertensive or hypotensive human diseases. Several genetic variants in ENaC genes are associated with high blood pressure or salt sensitivity. Certain ENaC variants reportedly serve as modifiers to diseases such as cystic fibrosis. In this study, we sought to identify loss‐of‐function human ENaC variants in a heterologous expression system. A total of 48 variants in extracellular domains of α and γ ENaC subunits were selected. Mutant α subunits were co‐expressed with wild type β and γ subunits whereas mutant γ subunits were co‐expressed with wild type α and β subunits in Xenopus oocytes. Amiloride‐sensitive currents measured by two‐electrode voltage clamp in cells expressing wild type and mutant ENaCs were compared to identify functional variants. Among the tested 24 αENaC variants, four (αH255R, αT274M, αG454V and αΔF528) showed significantly less currents than wild type channels (p< 0.001, n=16~26). Four out of 24 γENaC variants (γS134F, γN282S, γE314K and γW486X) also had significantly less currents than wild type channels (p < 0.05, n=16~30). To explore the underlying mechanisms for the loss‐of function phenotype, we examined Na+ self‐inhibition responses of the mutant channels. All four α (H255R, T274M, G454V and ΔF528) and one γ (E314K) mutants displayed significantly greater Na+ self‐inhibition responses than wild type channels, corresponding to lower open probabilities. Our results identify eight novel loss‐of‐function ENaC variants in the extracellular domain and suggest that five variants are ENaC gating modifiers.