Studies on the alteration of calcium ions in osteoblastic cell line using a fluorescence dye

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In mouse osteoblastic clone MC3T3-E1 cells, influx and intracellular alteration of Ca^<2+>ions were investigated with the fluorescence-spectrophotometer and fluorrescence-microscopic measurement system using a fluorescence reagent for intracellular Ca^<2+>ions. One passing influx of Ca^<2+>ions responsive to epidermal growth factor (EGF) was observed in human epidermoid carcinoma cell line : A431, but not in the osteoblastic cell line : MC3T3-E1 with both the fluorescence measurements. However, the increase of intracellular concentration of free Ca^<2+>ions responsive to fetal calf serum (FCS) was detected in both cell lines. With the manner of one passage, futhermore, influx of Ca^<2+>ions responsive to EGF appeared in the osteblastic MC3T3-E1 cells after the FCS-treatment, suggesting that a slight influx of Ca^<2+>ions into the MC3T3-E1 cells is induced with the synergistic function of EGF and any factor (s) in FCS.These results indicate that a very silght signal transduing due to the EGF-EGF receptor system is functioning by the synergistic effect during the initial growth phase of MC3T3-E1 cells. On the other hand, we also found that neurotrophin-3 (NT-3 : one of nerve growth factors) and its receptor (TRKC) is expressed in the osteoblastic MC3T3-E1 cells and the influx of Ca^<2+>ions responsive to NT-3 occurs in the osteoblastic cells. This implies that the signal transdicing sytem due to the interaction between NT-3 and TRKC is acting during the initial growth of MC3T3-E1.Moreover, photomapping data on the alteration of intracellular Ca^<2+>concentration detected with a fluorescence-microscopic measurement system indicated that the intracellular Ca^<2+>accumulation in MC3T3-E1 cells is higher than that in A431 cells. This suggests that an osteoblast-specific mechanism of intracellular Ca^<2+> accumulation plays in the osteoblastic cell system with the different manner from other cells such as epidermal cells.