[Localization and function of calcium-sensing mechanism in bone cells]

Elevation of extracellular calcium has been shown to inhibit osteoclastic bone resorption and stimulate proliferation and chemotaxis of osteoblasts. Therefore, calcium released by bone resorption may have important roles in the coupling of bone resorption and bone formation. Although both osteoclasts and osteoblasts have calcium-sensing mechanisms, the responsible molecule in these cells seems to be different. Functional and histological studies show that calcium-sensing mechanism in osteoclasts is a ryanodine receptor-like molecule in plasma membrane. In contrast, calcium-sensing mechanism in osteoblasts has similar functional property to parathyroid calcium-sensing receptor (CaSR), but is a different molecule from CaSR. In addition, several bone marrow cells express CaSR. The elucidation of the identity and the physiological roles of these calcium-sensing mechanisms would give us a more clear view of bone remodeling.