The mitochondrial permeability transition (MPT), which is defined as an increase in the permeability of the mitochondrial membranes for small molecules via opening of so called MPT pores, was examined among other parameters.
Cells were either exposed or sham exposed and some samples were also treated with acetylcysteine (a ROS scavenger), SB216763 (an inhibitor of glycogen synthase kinase (GSK)-3-beta, which might play a role in MPT), and with cyclosporine A (a MPT pore inhibitor).
Exposure duration: continuous for 5, 15, 30, 60 or 120 minutes
|Chamber||two exposure chambers in incubator with 95% air humidity and 5% CO2; the temperature was kept at 37.0 ± 0.2°C|
|Setup||each chamber contained a set of square Helmholtz coils (20 cm Œ 20 cm), which were double-wrapped with two lines of copper wire and encased by µ-metal to shield cells from stray fields; a fan in the wall made air and temperature uniform between chambers and incubator; cell dishes were put in the center of the coils; the magnetic field was perpendicular to the dishes and heterogeneity of MF distribution within the 12 x 12 x 20 cm3 space in the exposure chamber was less than 1%|
|Sham exposure||A sham exposure was conducted.|
|Additional info||one chamber was used for sham exposure with opposite direction currents fed into the coils; exposure and the corresponding sham exposure was conducted simultaneously; the difference of temperature between exposure and sham exposure did not exceed 0.1°C|
|magnetic flux density||4 mT||-||measured||-||-|
Exposure to the magnetic field for 60 min led to a significant increase of MPT compared to sham exposed cells while a simultaneous treatment with cyclosporine A prevented this effect. The mitochondrial membrane potential was not affected by exposure to the magnetic field.
The cytosolic protein expression of cytochrome-c was significantly increased and the whole cell protein expression of Bax was significantly decreased after exposure for 60 minutes compared to sham exposed cells. Protein expression of phosphorylated GSK-3-beta was significantly increased after 15 minutes and significantly decreased after 60 minutes of exposure compared to sham exposed cells. A treatment with the GSK-3-beta inhibitor SB216763 prevented MPT after 60 minutes of exposure. The level of reactive oxygen species was significantly increased after 5, 15 and 30 minutes of exposure compared to sham-exposed cells, with acetylcystein preventing this increase and preventing MPT. Moreover, acetylcystein prevented the changes in protein expression of phosphorylated GSK-3-beta, indicating that magnetic field induced MPT depends on GSK-3-beta activation via reactive oxygen species.
The authors conclude that exposure to a 50 Hz magnetic field might induce mitochondrial permeability transition in human amniotic epithelial cells through the ROS/GSK-3-beta signaling pathway.