The calcium-sensing receptor

To maintain divalent ion concentration within the body, a complex sensor has evolved to identify the changes in the extracellular environment and cause the surrounding cells to either secrete or absorb in response to change. An important member of these "sensors" is the calcium-sensing receptor (CaSR), which is constantly monitoring the extracellular environment for changes in salinity, pH, calcium, amino acids and polyamines. The kidney plays a very important role in monitoring both salinity and also water concentration of the presented filtered load. Recent studies have shown that the CaSR is expressed along the nephron and can play an important role in both calcium and salt absorption, and also in the handling of water in the thick ascending limb. This review will outline the basic physiology of the receptor and will then go on to discuss some of the roles that the receptor plays in the various nephron segments. It will conclude with a brief section on future directions and how specific renal receptor-targeted drugs may provide an effective means to regulate both ionic absorption and water balance.