Subunit stoichiometry of the epithelial sodium channel

The epithelial Na⁺ ChAnnel (ENaC) mediates Na⁺ reabsorption in a variety of epithelial tissues. ENaC is composed of three homologous subunits, termed α, β, and γ. All three subunits participate in channel formation as the absence of any one subunit results in a significant reduction or complete abrogation of Na⁺ current expression in Xenopus oocytes. To determine the subunit stoichiometry, a biophysical assay was employed utilizing mutant subunits that display significant differences in sensitivity to channel blockers from the wild type channel. Our results indicate that ENaC is a tetrameric channel with an α₂βγ stoichiometry, similar to that reported for other cation selective channels, such as K(r), K(ir), as well as voltage- gated Na⁺ and Ca²⁺ channels that have 4-fold internal symmetry.