Effect of elevated extracellular calcium on the proliferation of osteoblastic MC3T3-E1 cells:its direct and indirect...

There has been evidence that elevated calcium concentration at the resorptive site of the bone directly regulates osteoclast function. In the present study, in order to clarify the role of elevated calcium concentration at the resorptive site in the regulation of osteoblast function, not only direct but also indirect effect via human monocytes of the increase in extracellular calcium (Cae) on the proliferation of osteoblastic MC3T3-E1 cells have been investigated in serum-free condition. The increase in Cae enormously stimulated osteoblast proliferation at the concentration of 3 to 20 mM. When human monocytes were cultured at the elevated Cae concentration, monocyte-conditioned medium-induced stimulation of osteoblast proliferation was significantly amplified. Present data demonstrate that elevated Cae has pronounced stimulatory effect on osteoblast proliferation not only directly but also indirectly via monocytes. Calcium released from bone matrix at the resorptive sites might be linked to the coupling of osteoclast and osteoblast functions.