Electromagnetic field absorption in stochastic cellular systems: enhanced signal detection in ion channels and calcium oscillators

The basic problem in understanding the mechanisms of low frequency electromagnetic field interactions with biological systems arises because of the small strength of the signal compared to the thermal noise in the irradiated system. We have investigated, experimentally and theoretically, the possibilities for signal amplification relative to noise in those parts of the cellular calcium signalling pathway which constitute stochastic and chaotic processes. In many types of cells the signal tranduction from plasmalemma to intracellular targets is linked to the oscillatory behavior of intracellular Ca2+. The pattern of calcium fluctuations in a cell line of T lymphocytes (Jurkat), studied by us, consists of a repeated sequence of randomly occurring spikes. The spectral power densities of these spikes were diminished by applied 50 Hz electromagnetic fields. A source of enhancing the detection of weak electromagnetic signals in this system is the interaction with channel gating, where signal amplification is shown to follow from the theory of periodically driven stochastic processes. We have also investigated the sensitivity of intracellular calcium oscillators in detecting the modulated channel currents. This was done by numerical simulations on theoretical models, two-variable model of Goldbeter et al., 1990 [Goldbeter A, Dupont G, Berridge M. Proc Natl Acad Sci USA 1990;87: 1461–5] and the three-variable model with chaos by Shen and Larter, 1995 [Shen P, Larter R, Cell Calcium 1995;17:225–32]. Both models reproduced the experimental results with the chaotic model showing an irregularity in the pattern consistent with the experimental results. The models were also able to reproduce the effects of electromagnetic fields and the simulations revealed that the most sensitive part in the chain of reactions involved in Ca2+ oscillations was the Ca2+ release from internal stores by calcium-induced calcium release (CICR). Simulations on the three-variable model revealed the extreme sensitivity of a chaotic state to periodic forcing, suggesting a possible role of chaotic processes in detection of weak signals within cells.