SUBUNIT STOICHIOMETRY OF THE EPITHELIAL SODIUM-CHANNEL

The epithelial Na+ Channel (ENaC) mediates Na+ reabsorption in a varie ty of epithelial tissues. ENaC is composed of three homologous subunit s, termed alpha, beta, and gamma, All three subunits participate in ch annel formation as the absence of any one subunit results in a signifi cant reduction or complete abrogation of Na+ current expression in Xen opus oocytes. To determine the subunit stoichiometry, a biophysical as say was employed utilizing mutant subunits that display significant di fferences in sensitivity to channel blockers from the wild type channe l. Our results indicate that ENaC is a tetrameric channel with an alph a(2) beta gamma stoichiometry, similar to that reported for other cati on selective channels, such as K-v, K-ir, as well as voltage-gated Na and Ca2+ channels that have 4-fold internal symmetry.