External signals and internal oscillation dynamics: Biophysical aspects and modelling approaches for Interactions of weak electromagnetic fields at the cellular level

The question of whether or not non-thermal (sub-kT) electromagnetic fields in the non-ionizing frequency range (from extremely low frequency (ELF) to microwave) can influence the function of biological systems is currently of extreme interest and the subject of both ongoing experiments and controversial discussions. In this review, a brief presentation of some of the most prominent experimental results is given, and the principal problems are discussed from both physical and biological points of view. The necessary requirements for modelling approaches are described, including the entire sequence from the primary physical interaction via the secondary biological mechanisms (transductive steps) to the final response. Very smalt changes in the underlying non-linear kinetics caused by very weak coherent signals and noise can lead to strong, but reversible, alterations in the internal non-linear processes and associated biological function. The results of many detailed investigations are given. These include ELF field influences on G-protein activation dynamics, magnetic field influences on radical pair recombination reactions and weak signal amplification by stochastic resonance, All processes are incorporated within Ca2+ signal pathway models. The concept and models presented describe frequency-dependent and frequency-coded influences of very weak fields. The relevance of the results can be shown by sophisticated biological experiments.