The heterotetrameric architecture of the epithelial sodium channel (ENaC)

Abstract

The epithelial sodium channel (ENaC) is a key element for the maintenance of sodium balance and the regulation of blood pressure. Three homologous ENaC subunits (α, β and γ) assemble to form a highly Na ϩ -selective channel. However, the subunit stoichiometry of ENaC has not yet been solved. Quantitative analysis of cell surface expression of ENaC α, β and γ subunits shows that they assemble according to a fixed stoichiometry, with α ENaC as the most abundant subunit. Functional assays based on differential sensitivities to channel blockers elicited by mutations tagging each α, β and γ subunit are consistent with a four subunit stoichiometry composed of two α, one β and one γ. Expression of concatameric cDNA constructs made of different combinations of ENaC subunits confirmed the four subunit channel stoichiometry and showed that the arrangement of the subunits around the channel pore consists of two α subunits separated by β and γ subunits.

Clinical implication of lung fluid balance in the perinatal period

“…In 1994, it was reported by Canessa et al 27 that ENaC was made of three homologous subunits (a, b, g). ENaC has been proposed to be a heterotetrameric protein (abag), 36 but octameric or nonameric structures have also been suggested. 37,38 The relative importance of these three subunits may vary between species and tissues.…”

Acid-sensing ion channels (ASICs) as pharmacological targets for neurodegenerative diseases

“…Functional ASICs are believed to be tetrameric assemblies of homomeric or heteromeric subunits [19] (Figure 1). However, based on the stoichiometric studies of ENaC, the possibility that ASICs are assembled with four to nine subunits cannot be excluded [20,21].…”

Arachidonic Acid Regulates Surface Expression of Epithelial Sodium Channels

“…Co-expression of iPLA 2 or cPLA 2 Inhibits ENaC-mediated Na ϩ Currents-iPLA 2 and cPLA 2 are implicated in the liberation of arachidonic acid from the sn-2 position of membrane phospholipids under physiological conditions (5,6,9). We performed an [ 3 H]arachidonic acid-release assay to determine whether iPLA 2 is functional when co-expressed with ENaC.…”

“…These data suggest that iPLA 2 is functional when expressed in oocytes. To determine whether co-expression of iPLA 2 and ENaC reproduces the inhibitory effects of arachidonic acid and ETYA on ENaC activity, oocytes were co-injected with ␣␤␥ENaC cRNAs and increasing amounts of iPLA 2 cRNA. After 18 h amiloride-sensitive Na ϩ currents were determined, and currents were normalized to control oocytes expressing ␣␤␥ENaC alone.…”