Re-perfusion (reconstitution of the blood perfusion) of the heart after ischemia leads to severe cardiomyocyte injury (see Ma et al. 2013).
Cells were preconditioned with magnetic fields for 0, 2, 4, 6, or 8 hours. Afterwards, they were submitted to a hypoxia/reoxygenation treatment which simulates the ischemia and the re-perfusion.
To test whether the expression level of Hsp25 and the enzyme activities of caspases 3, 8, and 9 are dependent on the activity of the p38 mitogen activated protein kinase, an inhibitor (SB203580) was partially added to the culture medium.
Exposure duration: continuous for 2, 4, 6, 8 h
|Exposure duration||continuous for 2, 4, 6, 8 h|
|Setup||Helmholtz coils with a diameter of 38.1 cm (15 inch) vertically oriented and housed inside a water-jacketed cell culture incubator with a constant temperature of 37°C and 5% of CO2; depth of culture medium over the cells maintained at 5 mm|
|Sham exposure||A sham exposure was conducted.|
|magnetic flux density||1 µT||minimum||measured||-||-|
|magnetic flux density||3 µT||-||measured||-||-|
|magnetic flux density||7.5 µT||-||measured||-||-|
|magnetic flux density||15 µT||-||measured||-||-|
|magnetic flux density||30 µT||-||measured||-||-|
|magnetic flux density||60 µT||-||measured||-||-|
|magnetic flux density||120 µT||-||measured||-||-|
|magnetic flux density||240 µT||maximum||measured||-||-|
In magnetic field preconditioned cells (4-8 hours), the cell viability was significantly increased compared to cells submitted to hypoxia/reoxygenation treatment without preconditioning. A magnetic flux density of 120 µT resulted in the highest cell viability and therefore further experiments were performed with this intensity.
The protein expression level of Bcl-2 was significantly increased after preconditioning with 4 and 6 hours exposure and the enzyme activities of the caspases 3, 8, and 9 were significantly decreased (4-8 hours exposure) in comparison to cells without preconditioning. No mentionable effect of magnetic field exposure on the expression of the heat shock proteins Hsp25, Hsp32 and Hsp72 was observed (no data are given for Hsp27). However, preconditioning with magnetic fields (4-8 hours) led to a significant decrease (77%) in the hypoxia/reoxygenation induced translocation of phosphorylated Hsp25 from the cytosolic to the nuclear-cytoskeletal fraction. An addition of the p38 mitogen activated protein kinase-inhibitor SB203580 (blocks the phosphorylation of Hsp25) to the magnetic field preconditioned cells resulted in a significant increase in the enzyme activity of caspase 3 compared to the magnetic field preconditioned cells without inhibitor. Hence, the magnetic field induced reduction of the activity of the caspase 3 was diminished by the inhibitor SB203580.
The authors conclude that preconditioning with extremely low frequency magnetic fields could protect heart cells from damage by simulated ischemia and re-perfusion.