Regulation of renal ion transport by the calcium-sensing receptor: an update.

PURPOSE OF REVIEW: Extracellular calcium has profound effects on renal tubular transport, presumably via the calcium-sensing receptor, which is expressed in all nephron segments, but its effects in specific segments and the mechanism of regulation of transport are not fully understood.

RECENT FINDINGS: Recognition that activating calcium-sensing receptor mutations result in a Bartter-like syndrome demonstrate that the transport effects of extracellular calcium are mediated by the calcium-sensing receptor. Its presence in the gills and solute and water-transporting organs of fish coupled with appropriate calcium-sensing receptor kinetics indicate that the calcium-sensing receptor was originally involved in the regulation of sodium chloride, calcium and magnesium transport. Based on its physiological effects on tubular transport and biochemical and genetic data, the calcium-sensing receptor appears to act by mechanisms that distinguish it from other G protein-coupled receptors.

SUMMARY: The calcium-sensing receptor mediates the effects of extracellular calcium on the kidney, is an essential control point in the regulation of calcium balance and possibly the physiological regulation of sodium chloride balance. The thick ascending limb of Henle and distal convoluted tubule appear to be the nephron segments most responsible for the effects of the calcium-sensing receptor, although its mechanisms of action are not fully established.