Int. J. Environ. Res. Public Health 2010, 7 942 have been detected in cells after exposure to either radio-frequency EMF, extremely low frequency (ELF) and static fields [28,29] (Figure 2). Understanding of mechanisms of these genetic effects attracts much scientific interest. Most intriguing are mechanisms of the bioregulatory effects of weak magnetic and electromagnetic fields. The information conveyed by electromagnetic radiation (rather than heat) appears to cause these biological changes [20]. Thus, the most important and certainly the most universal are non-thermal interactions of electromagnetic fields with cellular systems. Experimental and epidemiological data as well as theoretical considerations suggest that predominantly magnetic, not the electric constituent of the EMFs, is mainly responsible for biological effects of the EMFs, by virtue of its greater ability to penetrate biological tissues [30,31]. Besides, in contrast to EMF, magnetic fields are not attenuated by most common materials. Therefore, we will focus on possible mechanisms of non-thermal bioregulatory effects of weak magnetic fields. Figure 2. Summary of genes regulated as a consequence of cell exposure to radio- frequency (RF) and extremely low frequency (ELF) electromagnetic field*. (From [29], reproduced by the kind permission of Dr. Maercker). * Presented results derived from comparative gene expression studies and are not proven in alternative assays yet. In spite of the large number of works that cover this issue, the primary biological “receiver” of weak electromagnetic radiation, as well as the complete sequence of events—the cause-effect relationships between the physical signal and biochemical or physiological responses—are still controversial questions. However, convincing hypotheses and explanations of pertinent mechanisms have been presented in [19,28,32-34], among others. Theoretically, both electrical and magnetic signals can cause non-thermal biological effects, genuinely: - electrical fields are able to interact with charged molecules, surfaces and electric dipoles of biomolecules, and - magnetic fields can interact with magnetic dipoles of electron spins, whose carriers are paramagnetic molecules, metal ions and ion-radicals [35]. Electrons within atoms and biomolecules clearly play an essential role in mechanisms of bioregulatory effects of weak magnetic fields because electrons directly participate in biochemical reactions as well as being sensitive to magnetic fields because of their magnetic dipole moment [36].