ALP induction by beta-glycerophosphate during the non-mineralization phase in vitro.

beta-GP influences on rat osteoblast development at the early period of culture i.e., the non-mineralization phase, and changes with the different cell passages were investigated. Alkaline phosphatase (ALP) was chosen as a main object. Northern blot analysis revealed up to two-fold increase in the steady state level of ALP mRNA after stimulation of rat osteoblast with 10 mM beta-GP. Likewise, 10 mM beta-GP induced a 10-30% increase in ALP activity (P < 0.01) of early passages (1 to 4), but not of later passages (5 to 6). The beta-GP induced increase in ALP activity was totally inhibited by the protein synthesis inhibitor, cycloheximide (50 microM). beta-GP stimulation was found to be without effect on cell proliferation measured as 3H-thymidine incorporation. It is concluded that beta-GP has no effect on proliferation but induces an increase in both mRNA level and activity of ALP in the non-mineralization phase of cultures of fetal rat calvarial cells, which lasts for several passages but will disappear in older cultures.