Continuous exposure to 60 Hz extremely low frequency electromagnetic field at 10 to 16 mT promotes various human cell proliferation by activating extracellular-signal-regulated kinase

Abstract

We previously showed that continuous exposure to 60 Hz extremely low-frequency electromagnetic fields (ELF-EMF) at 6 mT promotes cell proliferation. Here, we investigated the cellular effect of 60 Hz ELF-EMF at over 10 mT. We revised the ELF-EMF-generating device to increase the magnetic flux density of the ELF-EMF stably without thermal effect. We investigated the cellular effect of 10-16 mT ELF-EMF on various mammalian cells including human cervical carcinoma HeLa, rat neuroblastoma B103, liver cancer stem cells Huh7 and Hep3B, immortalized normal hepatic cell MIHA, and normal fibroblast IMR-90. Cell proliferation was promoted around 20% or more in all cells through continuous ELF-EMF exposure at 10 and 14 mT for 72 h, compared with the sham exposure group. In the cells whose proliferation was activated by 14 mT ELF-EMF, the MEK-ERK pathway and NF-{kappa}B were activated but not Akt. These cells showed a slight increase in the S phase population in BrdU incorporation and Ki-67 expression. In these cells, intracellular and mitochondrial ROS levels were not changed, and the proliferation-activating cellular effects of ELF-EMF were maintained even when oxidative phosphorylation was interrupted by CCCP. Additionally, no changes in intracellular calcium levels were observed in ELF-EMF-exposed cells and the proliferation-activating cellular effects of ELF-EMF were maintained in the presence of a calcium chelator, BAPTA-AM. These observations suggested that ROS and intracellular calcium do not mediate ELF-EMFs proliferation-activating physiological effect. Altogether, we demonstrated that 60 Hz ELF-EMF at 10 to 14 mT promotes cell proliferation by activating ERK1/2 and does not affect intracellular ROS and calcium levels.