An undifferentiated neuronal stem cell of the mouse was selected as it can be easily differentiated into neuronal cells using a known combination of biochemical factors. Furthermore some ion channels are not expressed on the stem cells in undifferentiated state until they undergo neurodifferentiation (e.g. N-type Ca2+ channel, a voltage-dependent calcium channel of the cell membrane). To elucidate the possible Ca2+ influx/efflux pathways the cells were treated with pharmacological inhibitors (amongst others nifedipine, ω-conotoxin: N-type Ca2+ channel blocker, thapsigargin: Ca2+ ATPase inhibitor).
|Chamber||The applicator was constructed of brass with four pairs of "windows" allowing real-time optical imaging when placed on a microscope stage. An insulating well provided a buffer solution for the seeded cells.|
|Sham exposure||A sham exposure was conducted.|
|Additional info||The differentiated cells were plated on to 24 x 30 mm glass cover slips and cultured with serum-free neurobasal medium for 48 to 60 h before experiments. All experiments were conducted at room temperature of 24-26°C.|
|Exposure duration||continuous for 60 min|
The exposure to radiofrequency irradiation was found to significantly increase the number of Ca2+ spikes, especially in differentiated neuronal cells (maximal number of Ca2+ spikes at a frequency of about 800 MHz). The increase in the Ca2+ spiking activities was dependent on the frequency but not on the specific absortpion rate between 0.5 to 5 W/kg. A statistical significant reduction in the number of Ca2+ spikes was observed at the 50 W/kg specific absorption rate.
No Ca2+ spikes were observed either in control cells or in the exposed cells in the absence of extracelllular Ca2+. This indicates a critical role of Ca2+ influx across the cell membrane. Using pharmacological inhibitors, it was found that both the N-type Ca2+ channels and phospholipase C enzymes appear to be involved in mediating increased Ca2+ spiking.