| Research Abstract |
It has been reported that the administration of strontium salt to animal induced abnormal dentinogenesis and bone formation, what's called, "Sr rickets", and hypocalcemia, the inhibition of PTH secretion, and 1alpha, 25(OH)_2D_3 synthesis, and acceleration of calcitonin secretion. These factors seemed to induce the low-calcium environment for the cells and organs. We conjectured that this low-calcium environment must be one of factors to make the disturbance of calcification and resorption in hard tissue. Recently, it has been reported that intracellular signal transduction system (A kinase, G kinase, C kinase and PI turnover) were related to the response of cells.
We tried to examine the movements of the intracellular free calcium, inositol-1, 4, 5-triphosphate (IP_3) and protein kinase C (PKC) in osteoblast-like cells in a low calcium environment. Bone cells in the calvaria of Wistar strain-rat embryos were isolated by collagenase digestion method. Their bone cells were cultured in BG
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J. Culture medium whose calcium concentration was 1.87mM in control medium and O.30mM in low calcium medium, exchanging culture medium every other day for 7 to 8 days.
[Ca^2^+]i concentration was significantly lower in low Ca group than in control group (P<0.01). [Ca^2^+]i in the bone cells stimulated by Con. A in calibration solution with 1mM CaCl_2 did not almost change in control group and increased in low Ca group. [Ca^2^+]i increased rapidly in low Ca group after the addition of 1mM CaCl_2. In calcium free calibration solution, the extent of results described above was higher in both groups respectively. The content of IP_3 in low Ca group decreased, compared with that in control group. In the bone cells stimulated by phospholipase C (2mug/ml), the content of IP_3 showed to increase in both groups and the extent of increase was higher in low Ca group than in control group. Protein Kinase C activity is lower in low Ca groupthan in control group. Particularly this activity was lower in cytosole than in membrane. From these results, it was shown that in the bone cells placed in the low Ca environmental condition, the enhancement of cell membrane permeability as compensation mechanism to maintain normal calaium homeostasis occurred and on the other hand, intracellular signal transduction system. Which play an important role to keep normal cell response was inhibited. It was suggested that this inhibition of intracellular signal transduction system is related to one of the factors to disturb the hard tissue metabolism. Less
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