Frequency dependence of increased cell proliferation, in vitro, in exposures to a low-amplitude, low-frequency electric field: evidence for dependence on increased mitogen activity released into culture medium.

In order to investigate the mechanism(s) through which an electric field can increase bone cell proliferation, we have developed an in vitro model incorporating a low-amplitude (estimated 10(-7) V/cm in the serum-free culture medium), low-frequency, capacitively coupled electric field. In previous studies with this model, we have shown that electric field exposure can increase bone cell proliferation both in chick tibiae organ cultures and in calvaria-derived monolayer cell cultures. The current in vitro studies demonstrate that skeletal tissue responses to a 30 min electric field exposure are characterized by a) a frequency window for both increased cell proliferation and increased release of mitogen activity into the cell-conditioned medium, with a peak near 16 Hz; b) a dependence on conditioned medium from exposed cells for increased cell proliferation; and c) a correlation between the alkaline phosphatase content of the bone cell cultures and effects of electric field exposure on both cell proliferation and release of mitogen activity into the conditioned medium.