Extracellular calcium sensing and signalling

Ca2+ is well established as an intracellular second messenger. However, the molecular identification of a detector for extracellular Ca2+ - the extracellular Ca2+-sensing receptor - has opened up the possibility that Ca2+ might also function as a messenger outside cells. Information about the local extracellular Ca2+ concentration is conveyed to the interior of many cell types through this unique G-protein-coupled receptor. Here, we describe new emerging concepts concerning the signalling function of extracellular Ca2+, with particular emphasis on the extracellular Ca2+-sensing receptor.