Sodium-dependent phosphate transport protein 2A, also known asNa+-Pi cotransporter 2a (NaPi-2a), is aprotein in humans that is encoded by theSLC34A1gene.[5] This gene encodes a member of the type II sodium-phosphate cotransporter family.
The sodium/phosphate cotransporter is a protein found in theproximal tubule of thenephron. It is responsible for reabsorbing approximately 80% of thephosphate that has been filtered out at theglomerulus. 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.[6]
The NaPi channels are regulated byparathyroid hormone (PTH). PTH acts to decrease phosphate reabsorption from the renal filtrate and therefore promote its excretion into the urine. It does this by causing forendocytosis of NaPi transporters on the apical surface of the cell. With less transporter available more phosphate is lost in the urine.[6]
Mutations in this gene are associated with hypophosphatemia nephrolithiasis/osteoporosis 1.[5]
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