To study the effects of extremely low frequency magnetic fields on voltage-gated sodium ion channels activity in rat cerebellar granule cells (and the related pathway).
Cerebellar granule cells are used as a model for neuronal cell development and apoptosis. The authors have shown previously that the sodium current densities of cerebellar granule cells are modulated by arachidonic acid: elevation of intracellular arachidonic acid levels increases the sodium current of cerebellar granule cells through the prostaglandin E2-mediated activation of the cAMP/protein kinase A pathway. Arachidonic acid can be converted to prostaglandin E2, e.g. by cyclooxygenases. Phospholipase A2 plays an important role in producing intracellular arachidonic acid.
| Exposure | Parameters |
|---|---|
|
Exposure 1:
50 Hz
Exposure duration:
10, 30, 60 or 90 min
|
|
|
Exposure 2:
50 Hz
Exposure duration:
6 h or 12 h
|
|
Maximum temperature increase in exposed cultures was 0.4±0.1°C; temperature controls were performed at 37°C and 37.4°C.
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 10, 30, 60 or 90 min |
| Exposure source | |
|---|---|
| Chamber | a pair of Helmholtz coils placed opposite to each other; surfaces of the culture plates were parallel to the force lines of the magnetic field |
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 1 mT | - | measured | - | - |
| Frequency | 50 Hz |
|---|---|
| Type | |
| Exposure duration | 6 h or 12 h |
| Exposure source |
|
|---|---|
| Sham exposure | A sham exposure was conducted. |
| Measurand | Value | Type | Method | Mass | Remarks |
|---|---|---|---|---|---|
| magnetic flux density | 0.4 mT | - | - | - | - |
The data revealed that exposure of cerebellar granule cells to extremely low frequency magnetic fields significantly increased sodium currents of voltage-gated sodium ion channels in a time- and intensity-dependent manner. The voltage gated sodium channel steady-state activation curve, but not the steady-state inactivation curve, was significantly shifted towards hyperpolarization by the magnetic field exposure.
Increases in intracellular arachidonic acid, prostaglandin E2 and phosphorylated protein kinase A levels in cerebellar granule cells were observed following magnetic field exposure. In addition, the magnetic field exposure significantly enhanced the enzyme activity of phospholipase A2 but not of COX-1 or COX-2.
The voltage gated sodium channel 1.2 subunit protein on the granular cell membrane was increased, but the total expression levels of 1.2 subunit protein were not affected after the magnetic field exposure indicating an insertion of new sodium ion channels into the membrane.
Cyclooxygenase inhibitors and prostaglandin E2 receptor antagonists were able to eliminate the magnetic field-induced increase in phosphorylated protein kinase A and sodium current. A protein kinase A antagonist significantly attenuated the magnetic field-induced increase in sodium current. Administration of db-cAMP (a cAMP analog) produced a significant increase of sodium current. Thus, these data support the hypothesis that cAMP/protein kinase A pathway is involved in the effect of magnetic field exposure on sodium current.
These findings demonstrated that the neuronal sodium current was significantly increased by extremely low frequency magnetic field exposure via a "phospholipase A2-arachidonic acid-prostaglandin E2- prostaglandin E2 receptor-protein kinase A" signaling pathway.
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