Ionophore A23187 promotes osteoclast formation in bone organ culture.

Morphologic effects of the ionophore A23187 were compared with those of PTH and 1,25(OH)2 vitamin D3 on fetal rat limb bone cultures. All three treatments resulted in loss of bone and the appearance of multinucleate osteoclasts. Only PTH caused proliferation of fibroblast-like cells within the marrow cavity. Cleanly dissected ("stripped") bones were unresponsive to A23187 and exhibited many dead and dying cells after 48 h in culture with this agent; in contrast, stripped bones were responsive to PTH. All three treatments showed a similar time course of appearance of osteoclasts. The results indicate that all three agents promote osteoclast formation. There are several possible explanations for the differential effects of A23187 and PTH in stripped bones, including the possibility that the cells of the periosteum are required for the action of A23187 but not of PTH.