OBJECTIVETo investigate the effect of the extremely low frequency pulsed electromagnetic field (PEMF) on the proliferation and differentiation of osteoblast-like cells.

METHODSThe MC3T3-E1 cell and the primary osteoblast cell derived from 2-day-old Sprague Dawley (SD) rat calvaria were exposed to PEMF with a magnetic flux density of 1.55 mT at 48 Hz for 24 or 48 h. MTS was applied to analyze cell proliferation and flow cytometry to detect cell cycle. The intracellular alkaline phosphatase (ALP) activity was measured by colorimetry.

RESULTSPEMF of 1.55 mT at 48 Hz decreased significantly the cell percentage of S or G(2)M phase (P < 0.05), but did not affect cell number of MC3T3-E1 cells. Although the number of the primary osteoblast cells did not alter by MTS assay after exposure to PEMF for 24 h continuously, the cell percentage of G(2)M phase increased significantly (P < 0.01). When the culture time extended to 48 h, the cell number increased greatly (P < 0.01) and the cell percentage of G(2)M phase decreased significantly despite of the exposure type (P < 0.01). After the primary osteoblast cells were exposed to PEMF for 24 h continuously, the ALP activity decreased significantly (P < 0.05), whereas it increased significantly after exposure to PEMF for 48 h continuously (P < 0.05).

CONCLUSIONPEMF of 1.55 mT at 48 Hz does not affect proliferation and differentiation of MC3T3-E1 cell, but it promotes proliferation of primary osteoblast cell, inhibits differentiation at proliferation stage and promotes differentiation at differentiation stage of primary osteoblast cell.