Response of osteoblastic clonal cell line (MC3T3-E1) to [Asu]eel calcitonin at a specific cell density or differentiation stage.

Clone MC3T3-E1 cells isolated from newborn mouse calvaria is an osteogenic cell line which retains an ability to differentiate into osteoblastic cell in vitro. The effect of [Asu]eel calcitonin (ECT) on clonal MC3T3-E1 cells was investigated at different stages of differentiation. ECT caused an increase in alkaline phosphatase (ALP) activity. The stimulative effect was demonstrated to be dependent upon cell density or differentiation stage. At a cell density of 1.18 X 10(5)/cm2 cells were incubated with ECT for 2 days. The treatment by ECT caused an increase in ALP activity. A specific response to ECT dependent on the cell density was observed in a narrow range of cell density. Moreover this range of cell density responsible to ECT was found to be a rapid differentiation stage of MC3T3-E1 cells. These results suggest that calcitonin stimulates differentiation of osteoblast. In addition to these results, cellular adenosine-3',5'-cyclic monophosphate (cAMP) level was raised by ECT treatment at a cell density of about 1.4 X 10(5) cell/cm2 and this response was also specific for cell density. At cell density lower or higher than this density no stimulative effect by ECT was observed. On the other hand, N6,O2-dibutyryl adenosine-3',5'-cyclic monophosphate (db-cAMP) and theophylline caused an increase in ALP activity in wide cell density range. These results indicate that an increase in ALP activity by ECT is mediated by intracellular cAMP and that the specific response to ECT dependent on the cell density is regulated in the process of cAMP formation and/or in the preceding process of cAMP formation.