Induction of cAMP-dependent protein kinase A activity in human skin fibroblasts and rat osteoblasts by extremely low-frequency electromagnetic fields.

Sinusoidal extremely low-frequency electromagnetic fields (ELF-EMF; 7-8 mT, 20 Hz) have already been shown to inhibit proliferation and to accelerate terminal differentiation of human skin fibroblasts in vitro. In order to elucidate the underlying processes of signal transduction, we analysed the activity of cAMP-dependent protein kinase (PKA). EMF exposure for 60 min resulted in an increased PKA activity in human skin fibroblasts (2-fold) and rat embryonic osteoblasts (1.7-fold). Long-term exposure for up to 7 days with a constant 1 h-on/1 h-off EMF exposure rhythm indicated a transient stimulation of PKA activity during the first two exposure rhythms followed by a decrease to the baseline levels of sham-exposed controls. Based on these results, we postulate that a modulation of proliferation and differentiation processes in cells of mesenchymal origin is triggered by an immediate and transient EMF-induced increase in PKA activity.