- Epithelial sodium channel
The epithelial sodium channel (short: ENaC, also: sodium channel non-neuronal 1 (SCNN1) or amiloride sensitive sodium channel (ASSC)) is a membrane-bound ion-channel that is permeable for Li+-ions,
protons and especially Na+-ions. It is a constitutively active ion-channel. It is arguably the most selective ion channel.
ENaC consists of three different subunits: α, β, γ.cite journal |author=Loffing J, Schild L |title=Functional domains of the epithelial sodium channel |journal=J. Am. Soc. Nephrol. |volume=16 |issue=11 |pages=3175–81 |year=2005 |month=November |pmid=16192417 |doi=10.1681/ASN.2005050456 |url=http://jasn.asnjournals.org/cgi/pmidlookup?view=long&pmid=16192417] The stoichometry of these subunits is still to be verified, but ENaC is very likely to be a heterotrimeric
proteinlike the recently analyzed acid-sensing ion channel 1 (ASIC1), which belongs to the same family. [cite journal| journal=Nature| author=Jasti J, Furukawa H, Gonzales EB, Gouaux E| title=Structure of acid-sensing ion channel 1 at 1.9 Å resolution and low pH| year=2007| volume=449| pages=316–322| doi=10.1038/nature06163] Each of the subunits consists of two transmembrane helices and an extracellular loop. The amino- and carboxy-termini of all polypeptides are located in the cytosol.
Location and function
ENaC is located in the apical membrane of polarized epithelial cells particularly in the
kidney, the lungand 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
homeostasisof blood, epitheliaand 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 triamtereneor amiloride, which are used medically to serve as diuretics.
ENaC can furthermore be found in
taste receptor cells, where it plays an important role in salttaste 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.
It has been suggested that it may be a
ligand-gated ion channel.cite journal |author=Horisberger JD, Chraïbi A |title=Epithelial sodium channel: a ligand-gated channel? |journal=Nephron Physiol |volume=96 |issue=2 |pages=p37–41 |year=2004 |pmid=14988660 |doi=10.1159/000076406 |url=http://content.karger.com/produktedb/produkte.asp?typ=pdf&file=NEP2004096002037]
In addition there is a fourth, so-called δ-subunit, that shares considerable sequence similarity with the α-subunit and can form a functional ion-channel together with the β- and γ-subunits. Such δ, β, γ-ENaC appears in
pancreas, testes and ovaries. Their function is yet unknown.
Units β and γ are associated with
Liddle's syndrome. [ [http://www.neuro.wustl.edu/neuromuscular/mother/chan.html#nachnvg Ion Channel Diseases ] ] Amilorideand triamtereneare potassium-sparing diuretics which act upon the Epithelial sodium channel.
SCNN1A, SCNN1B, SCNN1G, SCNN1D
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