The sodium–hydrogen antiporter or sodium–proton exchanger (Na+/H+ exchanger) 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).

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 structure ...

of the

kidney The kidneys are two reddish-brown bean-shaped organs found in vertebrates. They are located on the left and right in the retroperitoneal space, and in adult humans are about in length. They receive blood from the paired renal arteries; blo ...

, 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 system is the last part of nephron and participates in elect ...

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 pole of the Bowman's capsule to the beginning of loop of Henle. It can be further classified into the proximal convoluted tubule (PCT) and the proximal straig ...

. The membrane pump is primarily responsible for maintaining

homeostasis In biology, homeostasis (British also homoeostasis) (/hɒmɪə(ʊ)ˈsteɪsɪs/) is the state of steady internal, physical, and chemical conditions maintained by living systems. This is the condition of optimal functioning for the organism and ...

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