Sodium-dependent phosphate transport protein 2A, also known as Na⁺-P_i cotransporter 2a (NaPi-2a), is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respon ...

in humans that is encoded by the ''SLC34A1''

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

. This gene encodes a member of the type II sodium-phosphate cotransporter family.

Function

The sodium/phosphate cotransporter is a protein found in the

proximal 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 ...

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 ...

. It is responsible for reabsorbing approximately 80% of the

phosphate In chemistry, a phosphate is an anion, salt, functional group or ester derived from a phosphoric acid. It most commonly means orthophosphate, a derivative of orthophosphoric acid . The phosphate or orthophosphate ion is derived from phosph ...

that has been filtered out at the

glomerulus ''Glomerulus'' () is a common term used in anatomy to describe globular structures of entwined vessels, fibers, or neurons. ''Glomerulus'' is the diminutive of the Latin ''glomus'', meaning "ball of yarn". ''Glomerulus'' may refer to: * the filter ...

. The transporter moves hydrogen phosphate (HPO₄²⁻) into the cell along with 3 sodium ions. Alternatively it can move dihydrogen phosphate (H₂PO₄⁻ along with 2 sodium ions. For both movements the net charge is +1. Once inside the cell hydrogen phosphate and dihydrogen phosphate may react with water to form each other. Transport of these chemicals out of the cell at the basolateral surface is not understood currently. The NaPi channels are regulated by

parathyroid hormone Parathyroid hormone (PTH), also called parathormone or parathyrin, is a peptide hormone secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine. PTH influences bone r ...

(PTH). PTH acts to decrease phosphate reabsorption from the renal filtrate and therefore promote its excretion into the urine. It does this by causing for

endocytosis Endocytosis is a cellular process in which substances are brought into the cell. The material to be internalized is surrounded by an area of cell membrane, which then buds off inside the cell to form a vesicle containing the ingested material. E ...

of NaPi transporters on the apical surface of the cell. With less transporter available more phosphate is lost in the urine.

Clinical significance

Mutations in this gene are associated with hypophosphatemia nephrolithiasis/osteoporosis 1.

References

External links

* Solute carrier family {{membrane-protein-stub

Function

Clinical significance

See also

References

Further reading

External links