Prostaglandins change cell shape and increase intercellular gap junctions in osteoblasts cultured from rat fetal calvaria.

Mounting experimental evidence indicates that osteoblasts may be cellular intermediaries in the local activation of bone remodeling. To elucidate the role of these cells in activation, we examined the effects of prostaglandins (PGs), known resorption stimulators, on cell shape and intercellular junctional relationships in osteoblasts cultured from rat fetal calvaria. Exposure to PGE2 and PGE1, promoters of bone resorption, rapidly (within 20 min) converted the osteoblasts from a flattened to a stellate shape (shape change), and markedly increased the appearance of intercellular (gap) junctions within 10 min. Both effects were directly related to the prostaglandin concentration, as little as 1 nM being effective. PGE1, but not PGB1, PGF1 alpha, PGD2, and PGF2 alpha, mimicked the substantial effect of PGE2 on shape change. Shape change and gap junction formation appear to arise independently. PTH, an inducer of shape change, did not affect the number of gap junctions appreciably. Colchicine, a microtubule polymerization inhibitor, and trifluoperazine, an inhibitor of calmodulin action, blunted PGE2-mediated shape change but not the effect of PGE2 on gap junctions. Shape change and gap junction formation may be important events in local activation, shape changes in surface osteoblasts serving to expose bone surfaces which are chemotactic for osteoclasts and gap junctions propagating locally initiated activation messages.