The calcium-sensing receptor (CaSR) is a Class C G-protein coupled receptor which senses extracellular levels of calcium ion. In the parathyroid gland, the calcium-sensing receptor controls calcium homeostasis by regulating the release of parathyroid hormone (PTH).[1]
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The release of PTH is inhibited in response to elevations in plasma calcium concentrations and activation of the calcium receptor. Decreased calcium binding on the extracellular side gives a conformation change in the receptor, which, on the intracellular side, initiates the phospholipase C pathway,[2][3] presumably through a Gqα type of G protein, which ultimately increases intracellular concentration of calcium, which triggers vesicle fusion and exocytosis of parathyroid hormone. It also inhibits (not stimulates, as some[4] sources state) the cAMP dependent pathway.[3]
Mutations that inactivate a CaSR gene cause Familial hypocalciuric hypercalcemia (FHH) (also known as Familial Benign Hypercalcemia because it is generally asymptomatic and does not require treatment),[5] when present in heterozygotes. Patients who are homozygous for CaSR inactivating mutations have more severe hypercalcemia.[6] Other mutations that activate CASR are the cause of autosomal dominant hypocalcemia[7] or Type 5 Bartter syndrome. An alternatively spliced transcript variant encoding 1088 aa has been found for this gene, but its full-length nature has not been defined.[8]
The drug cinacalcet is an allosteric modifier of the calcium-sensing receptor.[9] It is classified as a calcimimetic, which binds to the calcium-sensing receptor and decreases parathyroid hormone release.
Calcium-sensing receptor has been shown to interact with Filamin.[10][11]
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