High extracellular calcium inhibits osteoclast-like cell formation by directly acting on the calcium-sensing receptor existing in osteoclast precursor cells

Although it has recently been suggested that high extracellular calcium ([C a2+](e)) inhibits osteoclast function via a calcium-sensing receptor (CaSR) in mature osteoclasts, the role of CaSR in the regulation of osteoclast fo rmation remains unknown. The present study was performed to investigate whe ther osteoclast precursor cells possess CaSR and to clarify the possible ro le of CaSR in the regulation of osteoclast formation. Immunocytochemistry d etected CaSR in osteoclast precursor cells derived from spleen cells as wel l. as in osteoblastic MC3T3-E1 cells. The use of reverse-transcription poly merase chain reaction (RT-PCR) with CaSR-specific primers, followed by nucl eotide sequencing of the amplified products, also identified CaSR transcrip ts in osteoclast precursor cells derived from spleen cells as well as in MC 3T3-E1 cells. High [Ca2+](e) (3 to 5 mM) concentration dependently inhibite d 1,25(OH)2D3- or human parathyroid hormone (hPTH) (1-34)-induced osteoclas t-like cell (Ocl) formation from osteoclast precursor cells derived from sp leen cells. Further, the CaSR agonist neomycin also concentration dependent ly inhibited 1,25(OH)2D3- or hPTH(1-34)-induced Ocl formation. Moreover, a calcimimetic which mimics or potentiates the effects of [Ca2+](e) at the Ca SR NPS R-467 (1-100 mu M) concentration dependently inhibited Ocl formation stimulated by 1,25(OH)2D3 or hPTH(1-34). These findings first demonstrated that osteoclast precursor cells possess CaSR very similar, if not identica l, to those in the parathyroid and kidney. Furthermore, the CaSR in osteocl ast precursor cells could play a key role in regulating Ocl formation by se nsing local changes in [Ca2+](e) at the resorptive sites, (C) 1999 Academic Press.