The calcium-sensing receptor as a nutrient sensor

Critical to cell fate in many cell types is the ability to sense and respond to acute changes in free ionized extracellular calcium concentration ([Ca²⁺]_o). Such tight control is mediated by the activation of a protein known as the extracellular-calcium-sensing receptor (CaR). CaR belongs to the ‘family C’ of G-protein-coupled receptors and was the first G-protein-coupled receptor to be identified to have an inorganic cation, calcium, as its ligand. While calcium is the physiological agonist of the receptor, several other polyvalent cations and polycations can also modulate CaR function as do certain L-aromatic amino acids, polyamines, salinity and pH. This feature renders the CaR uniquely capable of generating cell- and tissue-specific responses, and of integrating inputs deriving from changes in the Ca²⁺_o concentration with signals deriving from the local metabolic environment. Here we address the role of the CaR in physiology and disease, the range of CaR modulators and the potential roles of the CaR as a metabolic sensor in a variety of physiological (and pathological) scenarios.