MAGNETIC-FIELD EFFECTS ON BIOMOLECULES, CELLS, AND LIVING ORGANISMS

This article surveys three major areas of biomagnetic research: (a) th e magneto-orientation effect; (b) the role of the geomagnetic field in bird orientation and navigation; and (c) the biological effects of ex tremely low-frequency magnetic fields. The magneto-orientation effect is caused by diamagnetic anisotropy of highly ordered biological struc tures, such as visual photoreceptor and chloroplast membranes, in a ho mogeneous magnetic field of about 10 kG. While it is not possible to o rient the individual constituent molecules with such a field because o f thermal fluctuation, these ordered structures can be oriented as a w hole by virtue of summing the anisotropy over a large number of mutual ly oriented molecules. While the magneto-orientation effect seems to r equire the use of unphysiologically strong magnetic fields, certain bi rds apparently have highly sensitive sensors to detect the geomagnetic field for the purpose of orientation and navigation. However, the adv ances in this latter field were made mainly in the behavioral studies; the magneto-sensors and the neural mechanisms remain elusive. A numbe r of candidates of the sensors are evaluated. We suggest that pecten o culi, which is unique to avian eyes, should not be overlooked for its possible role as a magneto-sensor based on the magneto-orientation eff ect. Birds primarily use a static (DC) magnetic field for orientation, but recent investigations indicate that weak alternating (AC) magneti c fields with extremely low frequency (ELF) may have hazardous health effects. Such reports are often received with skepticism, because the effects usually involve magnetic energies that are less than the kT en ergy. However, some of the in vitro studies yield experimental results that are too significant to be ignored. Here, we propose an argument to explain why low-level magnetic fields can be detected without being overshadowed by thermal noises. Relevance of biomagnetic research to the development of biosensors and novel computational paradigms is als o discussed.