[Effects of static magnetic field with different exposure time on the maturation of rat osteoblasts in vitro and the expression of the estrogen receptor gene].

Objective: To investigate the effects of static magnetic fields (SMFs) with different exposure time on the maturation of rat osteoblasts in vitro and the expression of the estrogen receptor (ER) gene.

Methods: The calvarial osteoblasts were isolated from newborn rats by enzyme digestion and randomly divided into 9 groups after one passage based on the exposure time of the SMFs[0 (control), 0.5 h, 1.0 h, 1.5 h, 2.0 h, 2.5 h, 3.0 h, 3.5 h, and 4.0 h]. The intensity was 3.9 mT in all SMFs. Those without SMFs exposure were used as the controls. The oeteoblasts were observed under the contrast phase microscope on a daily basis. After 48 h, cell proliferation was assayed by MTT method. The osteocalcin contents were measured after exposure to SMFs for 3 d, 6 d, 9 d, and 12 d. ERΑ and ERΒ mRNA expressions were measured by real-time PCR after SMFs treatment for 0 h, 24 h, 48 h, and 72 h.

Results: Compared with the controls, the cell proliferation was significantly enhanced in the 2.0-h, 2.5-h, and 3.0-h groups (P<0.05). After SMFs treatment for 6 d, 9 d and 12 d, the 2.5-h group had significantly higher osteocalcin content than the control group did (P<0.05). After SMFs treatment for 0 h and 72 h, elevated ERΑ mRNA expression and reduced ERΒ mRNA expression were observed.

Conclusion: Exposure to SMFs, regardless of exposure time, is associated with enhanced cell proliferation, increased osteocalcin contents, and altered ERΑ and ERΒ mRNA expressions in opposite directions.