Sodium epithelial channel

The epithelial sodium channel is a membrane-bound ion channel, which is permeable to Li+ ions and protons, but above all to Na+ ions. This type of channel is open in its basic state (so-called constitutively active channel). The epithelial sodium channel is composed of three subunits (α, β, γ), which are probably built up to a heterotrimer. Each of the three subunits has two transmembrane helices and an extracellular loop. The amino and carboxy termini of the polypeptide chains are each located in the cytosol.

Occurrence of ENaCs: ENaCs are located in the apical membranes of polar epithelial cells, mainly in the kidney, lung and colon. They are responsible for the transepithelial transport of Na+ ions and thus play an important role in maintaining Na+ and K+ concentrations in blood, epithelia and intercellular space. ENaC activity and expression in kidney and colon is modulated by the mineralocorticoid aldosterone. The ENaC channel type can be blocked by amiloride (use of amiloride as diuretic).

Furthermore, the ENaC channel type is found in gustatory cells and plays an important role in the perception of salt taste.

There is another so-called δ subunit which has great homology with the α subunit and can replace it by forming a functional channel. Such δ, β, γ tetramers occur for example in pancreas, testicles or ovaries, but their function is still unclear.

Mutations in genes coding for the ENaC subunits can cause the following diseases:

• Pseudohypoaldosteronism type 1 (α, β)
• Liddle syndrome (β, γ).

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