ENaC, short for epithelial sodium channel, is a protein channel embedded in the surface of cells that lines your kidneys, lungs, colon, and other organs. It works like a tiny gate that lets sodium ions pass into cells, and by controlling sodium movement, it plays a central role in regulating your blood pressure, fluid balance, and even how well your lungs clear mucus.
How ENaC Is Built
A functional ENaC channel is made from three different protein subunits called alpha, beta, and gamma, arranged in a 1:1:1 ratio. These subunits are encoded by genes in the SCNN1 family: SCNN1A, SCNN1B, SCNN1G, and SCNN1D. A fourth subunit, delta, exists but is expressed in different tissues and has been studied far less. The channel sits at the outer (apical) surface of epithelial cells, the layer of cells that line organs and body cavities, positioned to catch sodium from whatever fluid passes over them.
ENaC belongs to a broader family of channels that share a key trait: they are not triggered by electrical voltage the way many nerve channels are. Instead, they are always ready to conduct sodium and are switched on or off by other signals, including enzymes called proteases that clip parts of the alpha and gamma subunits to open the channel wider.
What ENaC Does in the Kidneys
The kidneys filter an enormous volume of fluid every day, and most of the sodium in that fluid gets reabsorbed before it reaches the urine. ENaC handles the final stretch. Located in the last segments of the kidney’s tiny tubules, it reabsorbs less than 10% of the total filtered sodium. That number sounds small, but this final adjustment is what allows your body to fine-tune how much sodium actually leaves in urine. Without it, you would lose the ability to respond to changes in salt intake or blood volume.
When sodium moves through ENaC into kidney cells, water follows passively. That increases blood volume and, in turn, blood pressure. At the same time, potassium is pushed out into the urine. This sodium-in, potassium-out exchange is why diseases that affect ENaC can cause both blood pressure problems and abnormal potassium levels.
Aldosterone: The Hormone That Controls ENaC
The hormone aldosterone is the main dial that turns ENaC activity up or down. When your blood pressure drops or sodium levels fall, your adrenal glands release aldosterone. It enters kidney cells, binds to a receptor, and switches on specific genes. One of the most important is SGK1, which produces a protein that protects ENaC from being pulled off the cell surface and broken down.
Normally, a cleanup protein tags ENaC subunits for destruction when they are no longer needed. SGK1 blocks that cleanup protein, so more ENaC channels stay active on the cell surface, more sodium gets reabsorbed, and blood pressure rises. When aldosterone levels drop, the cleanup process resumes, channels are removed, and sodium passes through to the urine instead. This feedback loop is one of the body’s most important tools for keeping blood pressure stable.
ENaC in the Lungs
Your airways are lined with a thin layer of liquid called airway surface liquid. Its depth matters: too much and the lungs flood, too little and mucus becomes thick and sticky. ENaC absorbs sodium (and with it, water) from this liquid, working alongside another channel called CFTR, which secretes chloride and water outward. The balance between the two keeps the airway surface liquid at the right depth for tiny hair-like structures called cilia to sweep mucus and trapped bacteria out of the lungs.
In cystic fibrosis, CFTR is defective. That creates what researchers describe as a “double hit.” Chloride and water secretion drops, while ENaC activity increases, pulling even more water out of the airway surface. The result is dehydrated, sticky mucus that cilia cannot move efficiently. Bacteria settle into the stagnant mucus, causing the chronic lung infections that define much of cystic fibrosis. Because of this, ENaC remains an important therapeutic target: inhibiting it could restore some hydration to the airway even when CFTR is not working.
Genetic Diseases Linked to ENaC
Liddle Syndrome (Overactive ENaC)
Liddle syndrome is a rare inherited form of high blood pressure caused by mutations in the SCNN1B or SCNN1G genes (the beta or gamma subunits). These mutations alter the part of the subunit that signals the cell to pull the channel off the surface and break it down. Because that signal is disrupted, too many ENaC channels accumulate on kidney cells, sodium reabsorption goes into overdrive, and blood volume climbs. The result is hypertension that begins early in life, often paired with low potassium levels because the excess sodium reabsorption forces extra potassium out into the urine.
Pseudohypoaldosteronism Type 1 (Underactive ENaC)
The mirror image of Liddle syndrome is pseudohypoaldosteronism type 1 (PHA1), caused by loss-of-function mutations in SCNN1A, SCNN1B, or SCNN1G. With reduced or nonfunctioning ENaC channels, the kidneys cannot hold onto sodium properly. Infants with the condition lose excessive sodium in their urine, leading to dangerously low blood sodium, high potassium, and dehydration. Early signs include failure to gain weight and grow at the expected rate. In the more severe autosomal recessive form, multiple organs are affected, and children can experience abnormal heart rhythms, recurrent lung infections, and skin lesions. Adults with this form may still have episodes of salt wasting but generally have fewer symptoms.
ENaC and Salt Taste
In rodents, ENaC functions as the primary receptor for detecting salty taste at low to moderate concentrations. Whether it plays the same role in humans is still an open question. Studies of human taste buds show that the delta subunit of ENaC appears in the taste pore region where saliva contacts taste cells, while the alpha, beta, and gamma subunits sit lower on the cells, away from the initial point of contact. This unusual arrangement suggests ENaC may be involved in processing the sodium signal after detection rather than being the first sensor that recognizes salt on the tongue. Psychophysical studies in humans have produced mixed results, with some showing that blocking ENaC reduces salty taste perception and others showing no clear effect.
Drugs That Block ENaC
Two well-known diuretics work by plugging the ENaC pore directly. Amiloride blocks the channel at very low concentrations (an IC50 of 100 to 200 nanomolar), and triamterene does the same at slightly higher concentrations. Both are classified as “potassium-sparing” diuretics because, by stopping sodium from entering through ENaC, they also stop the linked potassium loss that other diuretics cause. These drugs are commonly used to treat fluid retention and high blood pressure, particularly when preserving potassium levels is important. Amiloride’s ability to block ENaC was, in fact, the tool researchers used to first isolate the channel’s alpha subunit in the early 1990s.