Different cell densities were used and exposed (from 1x106 cells/ml through 0.5, 0.25, 0.125 to 0.062 x106 cells/ml). To induce cell death a high dose of puromycin 100 µg/ml (a antitumor drug) was added to the cell culture at a cell density of 0.25 x106 cells/ml (simultaneously during the first PEMF exposure cycle or during all three PEMF exposures). Cells were investigated four days after the exposures.
Exposure duration: three times 3 hr with 24 hr intervals
|Setup||plate with cells placed in the generator pocket|
|magnetic flux density||45 mT||-||-||-||+/- 5 mT|
The data showed that higher initial cell densities increased cell death in cultures of U937 cells. The PEMF exposure further decreased the amount of cells only at higher cell densities and induced apoptosis (i.e. increased the amount of annexin V positive cells). The PEMF exposure potentiated the cell density-induced cell death through both apoptosis and necrosis. The strongest influence of PEMF exposure was found for cell densities of 1 x 106 cells/ml and 0.5 x 106 cells/ml.
To eliminate the cell density effect on cell death, for the subsequent experiments with puromycin a cell density of 0.25 x 106 cells/ml was used. Co-exposure of three doses of puromycin and PEMF resulted in a decrease of apoptosis by 24.7% and necrosis by 13%.
In conclusion, PEMF exposure protected U937 cells against puromycin-induced cell death. The effects of PEMF exposure on the U937 cell line depend on cell density.