Calcium is required for the function of the nervous, muscular, and skeletal systems and must be maintained within a very narrow range in the blood. When blood calcium levels are too low, the parathyroid secretes parathyroid hormone (PTH), triggering increased absorption of dietary calcium in the intestines and removal of calcium from bones.
When calcium levels are too high, calcium-sensing receptors (CaSR) on the parathyroid block the release of PTH and increase uptake of calcium by the kidneys for excretion in urine.
In addition to the parathyroid, CaSR are also found on kidney cells; however, it is unclear what role these calcium sensors play in calcium metabolism.
In the Journal of Clinical Investigation, researchers led by Pascal Houillier at the Hôpital Européen Georges Pompidou in Paris, uncovered a novel function of the CaSR in calcium metabolism. Using parathyroidectomized rats, Houillier and colleagues measured calcium excretion by the kidneys in the presence and absence of CaSR inhibitors.
These studies are the first to show that CaSR can directly determine the level of calcium in the blood by altering calcium transport in the kidneys. Further, these studies suggest that CaSR inhibitors might be useful in treating patients suffering from hypoparathyroid disease.
Reference: Alexandre Loupy, Suresh Krishna Ramakrishnan, Bharath Wootla, Régine Chambrey, Renaud de la Faille, Soline Bourgeois, Patrick Bruneval, Chantal Mandet, Erik Ilso Christensen, Hélène Faure, Lydie Cheval, Kamel Laghmani, Corinne Collet, Dominique Eladari, Robert H. Dodd, Martial Ruat, Pascal Houillier, 'PTH-independent regulation of blood calcium concentration by the calcium-sensing receptor', J Clin Invest. 2012; doi:10.1172/JCI57407 (open access)