Study type: Medical/biological study (experimental study)

Nonthermal effects of radiofrequency-field exposure on calcium dynamics in stem cell-derived neuronal cells: elucidation of calcium pathways. med./bio.

Published in: Radiat Res 2008; 169 (3): 319-329

Aim of study (acc. to author)

This study was performed to examine nonthermal effects of radiofrequency-field exposure on calcium dynamics in murine stem cell-derived neuronal cells.

Background/further details

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).

Endpoint

Exposure

Exposure Parameters
Exposure 1: 700–1,100 MHz
Exposure duration: continuous for 60 min
  • SAR: 0.5 W/kg
Exposure 2: 800 MHz
Exposure duration: continuous for 60 min

Exposure 1

Main characteristics
Frequency 700–1,100 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 60 min
Additional info 700, 750, 800, 850, 900, 1000, and 1100 MHz
Exposure setup
Exposure source
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.
Parameters
Measurand Value Type Method Mass Remarks
SAR 0.5 W/kg - calculated - -

Exposure 2

Main characteristics
Frequency 800 MHz
Type
Charakteristic
  • guided field
Exposure duration continuous for 60 min
Exposure setup
Exposure source
Sham exposure A sham exposure was conducted.
Parameters
Measurand Value Type Method Mass Remarks
SAR 0.5 W/kg - calculated - -
SAR 1.1 W/kg - calculated - -
SAR 5 W/kg - calculated - -
SAR 50 W/kg - calculated - -

Reference articles

  • Pickard WF et al. (2006): Electromagnetic and thermal characterization of an UHF-applicator for concurrent irradiation and high resolution non-perturbing optical microscopy of cells.

Exposed system:

Methods Endpoint/measurement parameters/methodology

Investigated system:
Time of investigation:
  • after exposure

Main outcome of study (acc. to author)

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.

Study character:

Study funded by

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