Effects of Electromagnetic Fields On K⁺(Rb⁺) Uptake by HeLa Cells

Conclusions

Exposure to strong homogeneous magnetic fields with various magnetic flux densities ofless than 1.6 T had no significant effect on either active or passive Rb⁺ influxes into HeLa cells at normal or high temperatures. Exposure to a similar magnetic field of 2 T at different temperatures of 10 to 45°C did not cause any change in active or passive Rb⁺ influx, and no evidence was obtained for the presence of a phase transition point of the cell membrane between 10 and 37°C.

In contrast, exposure to a strong, time-varying magnetic field of quasi-rectangular wave form caused significant inhibition of active Rb⁺ influx when the frequency of change in the magnetic field was more than 1/20 Hz. Conversely, K⁺ efflux was stimulated, but passive Rb⁺ influx was unaffected. Analyses of the amplitudes of the frequency components of the time-varying magnetic field B and its differential dB/dt revealed that B mainly consisted of components with the lowest angular frequencies, whereas dB/dt contained components of various frequencies. The inhibition of active Rb⁺ influx was not due to change in the cellular ATP content.

Results obtained by micro-fluorometry with fluorescent probes of the membrane potential (diS-C3-(5)) and pH (4-heptadecyl-7-hydroxy-coumarin) showed change in the electrical properties of the cell surface on exposure to the time-varying magnetic field. Results suggested an uneven distribution of electrical charge and an increase in negative charge on the cell surface. The inhibition of active Rb⁺ influx and the change in electrical properties of the cell membrane were reversible. Further studies are needed to determine whether change in electrical properties is the direct cause of inhibition of the Na⁺-pump.