SCNN1G

The SCNN1G gene encodes for the γ subunit of the epithelial sodium channel ENaC in vertebrates. ENaC is assembled as a heterotrimer composed of three homologous subunits α, β, and γ or δ, β, and γ. The other ENAC subunits are encoded by SCNN1A, SCNN1B, and SCNN1D.

ENaC is expressed in epithelial cells and is different from the voltage-gated sodium channel that is involved in the generation of action potentials in neurons. The abbreviation for the genes encoding for voltage-gated sodium channel starts with three letters: SCN. In contrast to these sodium channels, ENaC is constitutively active and is not voltage-dependent. The second N in the abbreviation (SCNN1) represents that these are NON-voltage-gated channels.

In most vertebrates, sodium ions are the major determinant of the osmolarity of the extracellular fluid. ENaC allows transfer of sodium ions across the epithelial cell membrane in so-called "tight-epithelia" that have low permeability. The flow of sodium ions across epithelia affects osmolarity of the extracellular fluid. Thus, ENaC plays a central role in the regulation of body fluid and electrolyte homeostasis and consequently affects blood pressure.

As ENaC is strongly inhibited by amiloride, it is also referred to as an "amiloride-sensitive sodium channel".

The first cDNA encoding the gamma subunit of ENaC was cloned and sequenced by Canessa et al. from rat mRNA. A year later, two independent groups reported the cDNA sequences of the beta- and gamma-subunits of the human ENaC. The complete coding sequence human γ subunit was reported by Saxena et al.

While the human gene SCNN1A is located in chromosome 12p, the human genes encoding SCNN1B and SCNN1G are located in juxtoposition in the short arm of chromosome 16 (16p12-p13). The structures of the human and rat SCNN1G genes were first reported by Thomas et al. Later studies by Saxena et al. reported the complete coding sequence of the human SCNN1G gene establishing that it has 13 exons The positions of introns are conserved in all three human ENaC genes, SCNN1A, SCNN1B and SCNN1G. The positions of the introns are also highly conserved across vertebrates See: Ensembl GeneTree.

The three ENaC subunits encoded by SCNN1A, SCNN1B, and SCNN1G are commonly expressed in tight epithelia that have low water permeability. The major organs where ENaC is expressed include parts of the kidney tubular epithelia, the respiratory airway, the female reproductive tract, colon, salivary and sweat glands.

ENaC is also expressed in the tongue, where it has been shown to be essential for the perception of salt taste.