Effects of electromagnetic fields on the bioactivities of an osteoblast-like cell line (UMR-106)

In the present study, we first investigated the effects of various types of low-energy, low-frequency electromagnetic fields (EMFs) on DNA synthesis i n UMR-106 osteoblast-like cells. The experimental groups were exposed to EM Fs for 2 days (twice/day, 30 min/time), and DNA synthesis was measured. The results showed that the cells responded most sensitively to EMFs of some s pecific combinations of the parameters by an increase in DNA synthesis, imp lying that EMFs with a specific waveform rather than a complex one can be u sed in clinical electrotherapy. The parameters were as follows: pulsed elec tric field (PEF) with pulse width 0.2 ms, field strength 10 V/cm, frequency 125 Hz; sinusoidal electric field (SEF) with field strength 1 V/cm, freque ncy 10 Hz; and alternating magnetic field (AMF) with field density 0.5 mT, frequency 5 Hz. In addition to frequency, the field strength or field densi ty within a suitable intensity scale played a dominant role in causing the DNA synthesis response. We then compared the effects of two kinds of fields , PEF and AMF, with the optimum parameters identified by the experiments, o n alkaline phosphatase (ALP) activity, protein and collagen synthesis, and intracellular levels of cyclic adenosine monophosphate (cAMP). The results indicated that both fields could not only affect UMR-106 cells proliferatio n but could particularly affect a series of characteristic bioactivities of UMR-106 such as ALP activity and collagen synthesis. The intracellular cAM P levels were increased rapidly and greatly with exposure to both PEF and A MF, implying that the action of low-frequency EMFs proceeds via second mess enger-dependent processes originating from signals at the cell membrane. Th e difference in action between PEF and AMF suggests that they may couple to the cell membrane in a partially different way.