The calcium sensing receptor (CaSR) has been shown to play
a major role in regulating parathyroid hormone secretion and
subsequently influencing the calcium concentration of extracellular
fluids. Based on sequence analysis of cDNA clones
it appears that the CaSR is similar to the 7-transmembranedomain
G-protein-coupled receptor superfamily. Changes in
extracellular calcium are thought to modulate a balance between
proliferation and differentiation in a variety of cell
types. In normal primary keratinocytes and breast epithelial
cells, proliferation is inhibited and elevated extracellular
calcium levels trigger differentiation. Malignant transformations
of these cell types are accompanied by a loss of responsiveness
to the anti-proliferative effects of elevated extracellular
calcium.