Physiology and pathophysiology of the calcium-sensing receptor.

The near constancy of extracellular calcium concentration is required for t he numerous physiological functions of extra- and intracellular calcium. Th is implies that any change in extracellular calcium concentration must be d etected in order to allow the appropriate correction by the homeostatic sys tems. The identification and cloning of a calcium-sensing receptor (CaR), w hich is expressed in the plasma membrane of parathyroid cells as well as ma ny other cell types, has been a major advance in the understanding of the m echanisms involved in the control of extracellular calcium concentration. I n addition, it demonstrated that extracellular calcium concentration itself is the first informative hormonelike messenger in this system. CaR belongs to the C subfamily of seven transmembrane-spanning G protein-coupled recep tors. Several inherited disorders in extracellular calcium homeostasis are due to both activating or inactivating mutations in CaR gene, strenghthenin g the essential role of CaR in the control of calcium metabolism. (C) 2001 Editions scientifiques et medicales Elsevier SAS.