CALCIUM-SENSING RECEPTOR IN MATURE OSTEOCLASTS, WHICH ARE BONE-RESORBING CELLS

Bone metabolism consists of osteoblast-mediated bone formation coupled to osteoclastic resorption of bone. Osteoclastic bone resorption play s an important role in normal skeletal development and the maintenance of its integrity throughout life. Although osteoclastic activity is t hought to be under the control of feedback regulation by extracellular cations, the molecular mechanism of detecting extracellular cations w ithin the bone microenvironment remains to be clarified. In the presen t study we showed by reverse transcription-polymerase chain reaction a nd Northern blot analysis that cultured mature osteoclasts express the calcium-sensing receptor (CaSR) mRNA. The nucleotide sequence of rabb it osteoclast CaSR was approximately 90% identical to that of CaSR cDN A from human, bovine, and rat parathyroid glands. Moreover, the activi ty of osteoclastic bone resorption, as determined by pit formation, wa s regulated by extracellular calcium ion as well as its agonists that are known to act through the CaSR. We conclude that CaSR, homologous t o that identified in parathyroid glands, is present in mature osteocla sts and calcium ion released from bone may directly regulate osteoclas tic bone resorption. (C) 1998 Academic Press.