The effect of calcium and 3',5' cAMP on the induction of ornithine decarboxylase activity in bone and bone cells.

The interrelationship between mediators of hormone action (cAMP and calcium) and induction of ornithine decarboxylase (ODC) activity was investigated in bone and bone cells. Stimuli that enhanced the cAMP level in both osteoblastlike (BL) and osteoclastlike (CL) cells and in intact calvaria only induced ODC activity in the isolated cell populations. Moreover, addition of fresh medium induced ODC activity in BL cells and not in calvaria, without an effect on the cAMP level. The tumor-promoting agent 12-O-tetradecanoyl-phorbol-13-acetate (TPA), however, induced in both systems ODC activity, without an effect on the cAMP concentration. From these data it was concluded that induction of ODC activity may not be mediated by cAMP. The role of Ca in ODC induction was also investigated. Experiments with BL cells, incubated in media with various Ca concentrations, as well as experiments with the Ca blocker D600 showed that basal and hormone-induced ODC activity was dependent on the intracellular Ca concentration. A regulatory role of cAMP, however, in concert with Ca, cannot be excluded.