The sodium–hydrogen antiporter or sodium–proton exchanger (Na+/H+ exchanger or NHX) is a

membrane protein Membrane proteins are common proteins that are part of, or interact with, biological membranes. Membrane proteins fall into several broad categories depending on their location. Integral membrane proteins are a permanent part of a cell membrane ...

that transports Na⁺ into the cell, and H⁺ out of the cell (

antiport An antiporter (also called exchanger or counter-transporter) is an integral membrane protein that uses secondary active transport to move two or more molecules in opposite directions across a phospholipid membrane. It is a type of cotransporter, ...

Function

They are found in the membranes of many cells, and especially in those of the

nephron The nephron is the minute or microscopic structural and functional unit of the kidney. It is composed of a renal corpuscle and a renal tubule. The renal corpuscle consists of a tuft of capillaries called a glomerulus and a cup-shaped structu ...

of the

kidney In humans, the kidneys are two reddish-brown bean-shaped blood-filtering organ (anatomy), organs that are a multilobar, multipapillary form of mammalian kidneys, usually without signs of external lobulation. They are located on the left and rig ...

, specifically in the intercalary cells of the

collecting duct The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct participates in electrolyte and fluid balance through rea ...

and in the epithelial cells of the

proximal convoluted tubule The proximal tubule is the segment of the nephron in kidneys which begins from the renal (tubular) pole of the Bowman's capsule to the beginning of loop of Henle. At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s ...

. The membrane pump is primarily responsible for maintaining

homeostasis In biology, homeostasis (British English, British also homoeostasis; ) is the state of steady internal physics, physical and chemistry, chemical conditions maintained by organism, living systems. This is the condition of optimal functioning fo ...

of pH and sodium. Defects in Na+/H+ antiporters may result in heart or kidney failure.

Angiotensin II Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the ...

upregulates this antiporter in the proximal convoluted tubule in order to promote Na⁺ reabsorption and H⁺ secretion. Na+/H+ exchangers are thought to be implicated in other disorders such as hypertension. In one study, transgenic mice over expressing this membrane protein were shown to have increased reabsorption and retention of sodium after increased salt intake. In dopamine receptor signalling, the widely expressed Na+/H+ exchanger NHE-1 is activated downstream of the D2, D3, and D4 receptors.

Isoforms

There are several isoforms of the antiporter: * Sodium–hydrogen antiporter 1 * Sodium–hydrogen antiporter 2 *

Sodium–hydrogen antiporter 3 Sodium–hydrogen antiporter 3 also known as sodium–hydrogen exchanger 3 (NHE3) or solute carrier family 9 member 3 (SLC9A3) is a protein that in humans is encoded by the ''SLC9A3'' gene. SLC9A3 is a sodium–hydrogen antiporter. It is found ...

* Sodium–hydrogen antiporter 4 * Sodium–hydrogen antiporter 5 * Sodium–hydrogen antiporter 6 * Sodium–hydrogen antiporter 7 * Sodium–hydrogen antiporter 8 * Sodium–hydrogen antiporter 9

Families

There are several families of sodium/proton antiporters that facilitate the exchange of sodium ions with protons across the lipid membrane. Some of them include:
TC# 2.A.33
- Na⁺:H⁺ Antiporter (NhaA) Family
TC# 2.A.34
- Na⁺:H⁺ Antiporter (NhaB) Family
TC# 2.A.35
- Na⁺:H⁺ Antiporter (NhaC) Family
TC# 2.A.36
- Monovalent Cation:Proton Antiporter-1 (CPA1) Family
TC# 2.A.37
- Monovalent Cation:Proton Antiporter-2 (CPA2) Family
TC# 2.A.62
- Na⁺:H⁺ Antiporter (NhaD) Family
TC# 2.A.63
- Monovalent Cation (K⁺ or Na⁺):Proton Antiporter-3 (CPA3) Family
TC# 2.A.111
- Na⁺:H⁺ Antiporter (NhaE) Family

References

External links

* Transport proteins Transmembrane proteins {{membrane-protein-stub