Different Responses of Osteoblasts and Fibroblasts to a Changing Magnetic Field

The purpose of this study was to assess the response of osteoblasts (MC3T3-E1) and fibroblasts (L929) toward an extremely low magnetic field (ELMF) exposure. The strength and frequency of the field were set to 0.4 T and 0.17 Hz, respectively. The cells were exposed to semi-confluent culture plates for 6 hours. Cell proliferation was assessed on days 1, 3, 7 and 10 after the ELMF exposure. To evaluate osteoblastic differentiation, we measured alkaline phosphatase (ALP) activities of MC3T3-E1 cells at 3, 7 and 10 days after the exposure. The effects on mineralized nodule formation was evaluated by Alizarin Red S staining at 21 day culture. The results revealed that proliferation of the MC3T3-E1 cells was stimulated 3 days after ELMF exposure, whereas that of L929 cells was not stimulated in the day 3 culture. This stimulation was not observed at 7 or 10 days in either cell. ALP activities of the MC3T3-E1 cells were significantly increased 7 and 10 days after the exposure, and calcified nodule formation was also promoted as compared to the non exposed control culture on day 21. These results suggest that osteoblasts demonstrate specific response to magnetic fields, and that bone formation can be accelerated through the stimulation of osteoblasts by ELMF.