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Edition No. 2/E December 1995
The Influence of High-Frequency Electromagnetic Fields on the Intracellular Calcium Concentration of Excitable and Non-Excitable Cells

Dr. rer. nat. Rainer Meyer, Dr. rer. nat. Frank Gollnick,
Dr. rer. nat. Stephan Wolke, Institute of Physiology,
Rheinische-Friedrich-Wilhelms-Universität Bonn

All cells contain an ionic solution, in which all the other cellular components are embedded, the cytoplasm. The concentration of calcium ions in the cytoplasm is kept extremely low by the cells. Thus, small changes in the number of calcium ions result in relatively big changes in the cytoplasmic calcium. This allows the cells to generate signals of a good signal-to-noise ratio by small numbers of calcium ions. The cells make use of this feature, therefore the intracellular calcium concentration is one of the main factors for the control of cell metabolism. Cellular reactions like muscle contraction, contraction of the heart cells, ameboid movement of cells, cell division, activation of immune cells or synaptic transmission are controlled by the calcium concentration in the cytoplasm. As many cellular reactions lead to changes in the cytoplasmic calcium concentration, the calcium concentration will reflect, whether cellular processes are occurring normally or not. Therefore, the cytoplasmic calcium concentration is a useful indicator for external influences that disturb cell metabolism.

We examined the influence of high-frequency electromagnetic fields on the intracellular calcium concentration of excitable and nonexcitable cells. Various carrier frequencies and pulsation patterns were tested, among those the ones utilized in mobile communication with cellular phones. As representative for the excitable cells we investigated isolated heart muscle cells of the guinea pig and as nonexcitable cell cultured T-lymphoctes of the cell line Jurkat were studied. T-Jurkat were chosen, because they have been shown to react with oscillations of the cytoplasmic calcium concentration onto the influence of 50 Hz magnetic fields. Possibly, these cells are extraordinary sensitive to magnetic fields.

For the application of the high-frequency fields a transversal electromagnetic cell (TEM- cell) was developed which allows microscopic observation of the cells during simultaneous exposure to the field. The cells were kept in a temperature controlled, permanently perfused experimental chamber inside the TEM-cell. Intracellular calcium concentrations were measured by means of the fluorescent indicator fura-2. The fluorescence of this dye changes in proportion to the calcium concentration and depending on the excitation wavelength. At an excitation wavelength of 340 nm the emitted fluorescence intensity increases with increasing calcium concentration, while at an excitation wavelength of 380 nm the fluorescence intensity decreases with increasing calcium concentration. Measuring the fluorescence at both wavelengths and dividing the measured values by each other allows to get a good estimation of the calcium concentration. To do so, the setup was equipped with an epifluorescence illumination with a step motor driven filter wheel for automatic change of the excitation wavelength. Images were recorded by an image analysis system based on an intensified CCD-camera and a frame grabber with appropriate software.

Both cell types were subjected to an extensive measurement programme with various carrier frequencies (between 900 and 1900 MHz) and pulsation patterns (0, 16, 50, 217 Hz, and 30 kHz) among those were the frequencies and pulsation patterns utilized in mobile communication (GSM-Standard). The specific absorption rate gained dependend on the combination of carrier frequency and pulsation pattern, it varied between 9 and 59 mV/kg. An experiment was usually divided into three parts each of these lasting 500 s. During the first phase the cells were monitored without any field present (sham exposure). During the second phase the cells were usually exposed to the field, as control some runs with sham exposure instead of field exposure were also performed. During the third phase a chemical stimulation was carried out, in order to raise the calcium concentration in the cytoplasm of the cells. As chemical stimulation the membrane potential of the heart cells was depolarised from -80 mV resting potential to 0 mV by increasing the external potassium concentration. In the case of the T-Jurkat cells the external sodium concentration was lowered, to block the sodium/calcium exchanger and thereby disable the cells from pumping out calcium. With the heart cells additional experiments were performed, long term exposures (120 min) and exposures of depolarized cells (depolarization from -80 mV to -50, -30, and 0 mV).

In the experiments with the heart cells the chemical stimulation lead always to an increase and a subsequent decrease in the cytoplasmic calcium concentration indicating that the calcium transport mechanisms were working properly in these cells. In contrast, the field exposure did not influence the calcium concentration in any case. There was no difference between the sham exposed and the cells exposed in the high-frequency field. Likewise in the case of the T-Jurkat cells, the cytoplasmic calcium concentration could not be influenced by the high-frequency field. However, in these cells the cytoplasmic calcium concentration did neither change during the chemical stimulation. Although the T-cells were definitely alive these experiments do not prove the failure of an effect definitely, because the T-cells may have been to insensitive to answer to any stimulation.

The experiments performed in this investigation did not give any sign for an influence of weak (athermal) high-frequency electromagnetic fields on the intracellular calcium concentration of cells independently of the carrier frequency and the pulsation pattern.

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