The Calcium-sensing receptor (CaSR) is a member of subfamily C of the G-protein-coupled receptor (GPCR) superfamily. As its primary role, the CaSR is a key player in calcium homeostasis and is expressed in tissues involved in calcium metabolism such as parathyroid cells and the kidneys.^1,2

The expression of CaSR was also described in other cell types and tissues, such as neurons, keratinocytes, and the pancreas. However, the role of CaSR in these cells remains to be established.^1,2 Following the identification of functional vitamin D response elements in the CaSR gene, it was suggested that vitamin D might regulate the expression of CaSR.³

CaSR activation is followed by a rapid, transient increase in the cytosolic calcium concentration, resulting from mobilization of calcium from thapsigargin-sensitive intracellular stores, as well as an increased calcium influx through voltage-insensitive calcium channels located at the cell membrane.⁴

CaSR regulates cellular processes such as proliferation, apoptosis, and differentiation under both normal and pathologic conditions.⁵

Recent studies demonstrated the expression in human colon epithelium of CaSR, which regulates proliferation and differentiation. In colon carcinomas, lower levels of expression were found in the cancerous tissue compared to normal colon tissue.