Cell physiological responses of RAW264 macrophage cells to a 50-Hz magnetic field

Purpose: We previously showed that a 0.5-mT, 50-Hz sinusoidal magnetic field (LFMF) enhanced DNA single-strand breaks (SSB) and necrosis in RAW264 macrophages that had been stimulated by bacterial endotoxin (lipopolysaccharide; LPS). LPS enhances production of nitric oxide (NO) and superoxide anion (O₂⁻) that react with each other to generate peroxynitrite (ONOO⁻). ONOO⁻ causes DNA strand breaks. Hence, we anticipated that 0.5-mT, 50-Hz sinusoidal magnetic field increased production of NO, thereby increasing intracellular ONOO⁻ concentration and promoted DNA strand breaks. However, the NO production was not increased. In this study, we examined if the exposure of the cell to 0.5-mT, 50-Hz magnetic field for 24 h (1) promotes O₂⁻ production, (2) elevated the degree of apoptosis, because apoptosis is an upstream event of necrosis, (3) lowers mitochondrial membrane potential (ΔΦ_m), because it would also promote necrosis. Materials and methods: O₂⁻, was measured with nitroblue tetrazolium and water-soluble tetrazolium salt. Necrosis and apoptosis were quantified with propidium iodide and fluorescence labelling of caspases, respectively. The ΔΦ_m was measured with a fluorescent probe (JC-1) that reflects ΔΦ_m. Results and conclusions: In the LPS-stimulated macrophage, the LFMF did not promote O₂⁻ production. Thus, the LFMF-promoted DNA strand breaks did not result from the increase in the O₂⁻ production. The LFMF did not promote apoptosis, whereas it tended to increase the degree of necrosis, as we showed previously. The ΔΦ_m slightly declined in the LFMF-exposed cell without statistical significance.