To study whether a 50 Hz sine wave magnetic field (vertical or horizontal) of various magnetic flux densities can affect cell proliferation and cell cycle kinetics in the human cell line K562 and whether stress responses in the form of changed levels of Hsp70 protein and the superoxide anion radical are consequences of the magnetic field exposure.
Positive controls were peformed with heat treatment (42°C, 1h). Additionally, as positive control for radical production, the phorbol ester PMA was used. Cells were investigated before and at different time points after exposure.
The data showed that magnetic field exposure (0.1 mT (data of other magnetic flux densities not shown)) did not affect either cell cycle kinetics or cell proliferation.
Both vertical and horizontal magnetic field exposures caused significantly and transiently increased Hsp70 levels (>twofold) at several magnetic flux densities, compared to sham exposure and to heat treatment. The strongest effect was found after vertical exposure to 0.025 mT. The twofold increase was observed directly after exposure and persisted until 24 h after exposure, although levels were returning towards base line at 24 h. The highest exposure (0.1 mT) was the weakest inducer of Hsp70 expression.
Exposure to the magnetic field also increased (30-40%) the levels of the superoxide radical anion at all investigated magnetic flux densities, comparable to the positive control PMA.
In conclusion, an early response to extremely low frequency magnetic field in K562 cells seems to be an increased amount of oxygen radicals, leading to Hsp70 induction. Furthermore, the findings suggest that there is a flux density threshold where 50 Hz magnetic field exerts its effects on K562 cells, at or below 0.025 mT. Additionally, it is the magnetic field, and not the induced electric field, which is the active parameter (because Hsp induction occurs both during vertical and horizontal magnetic field exposures).