[The effect of cell environment on osteoblastic function]

The effect of cell environment on osteoblastic function was described in this review article. Hypocalcemia, hypocalcified dentin and inhibition of bone formation were demonstrated in rats fed a low calcium diet. These phenomena led us to hypothesize that a low-calcium environment must be one of the important factors to induce the inhibition of bone formation. This proposed mechanism was verified in an in vitro experiment. In the rat neonatal femur cultured in a low-calcium medium, the head size of the femur, full longitudinal length of the femur and total hexosamine content increased. Alkaline phosphatase activity, chondroitin sulfate synthesis and DNA synthesis activity increased, but proline synthesis activity decreased. In the calvarial bone cells, the total calcium, IP3 contents and PKC activity decreased, but the sensitivity of the cell membrane to a stimulation was enhanced. In mouse osteoblastic MC3T3-E1 cells, c-fos mRNA expression increased after the treatment with fetal bovine serum (FBS) or epidermal growth factor (EGF), and the degree of increase was highest with the 30-min treatment period in both FBS- and EGF-treated cells. The expression was significantly higher in the low Ca group as compared to the control group (P < 0.01). From these results, it was suggested that tha femur and osteoblasts react to restore the normal cell function against a low-calcium environment, the mediating and intracellular signal transduction system, and a transcriptional activity at the gene level.