Epithelial Sodium Channel - Location and Function

Location and Function

ENaC is located in the apical membrane of polarized epithelial cells particularly in the kidney (primarily in the collecting tubules), the lung and the colon. It is involved in the transepithelial Na+-ion transport, which it accomplishes together with the Na+/K+-ATPase.

It plays a major role in the Na+- and K+-ion homeostasis of blood, epithelia and extraepithelial fluids by resorption of Na+-ions. The activity of ENaC in colon and kidney is modulated by the mineralcorticoid aldosterone. It can be blocked by either triamterene or amiloride, which are used medically to serve as diuretics. In the kidney it is inhibited by atrial natriuretic peptide, causing natriuresis and diuresis.

ENaC can furthermore be found in taste receptor cells, where it plays an important role in salt taste perception. In rodents virtually the entire salt taste is mediated by ENaC, whereas it seems to play a less significant role in humans: about 20 percent can be accredited to the epithelial sodium channel.

In cells with motile cilia, ENaC is located along the entire length of the cilia indicating that ENaC functions as a regulator of osmolarity of the periciliary fluid. In contrast to ENaC, CFTR is not found on cilia. These findings contradict previous hypothesis that normally ENaC is down regulated by direct interaction with CFTR and that in CF patients, CFTR cannot down regulate ENaC causing hyper-absorption in the lungs and recurrent lung infections.

It has been suggested that it may be a ligand-gated ion channel.