BIOPHYSICS LETTER Tim G. St. Pierre á Jon Dobson Theoretical evaluation of cell membrane ion channel activation by applied magnetic ®elds Received: 11 August 1998 / Revised version: 25 October 1998 / Accepted: 11 November 1998 Abstract This letter re-examines a recently published calculation of the forces exerted on a membrane ion channel by a cation passing through in the presence of an externally applied magnetic ®eld. We show here, in contradiction to the originally published calculation, that the forces generated due to the Lorentz force of the magnetic ®eld on the cation are negligible compared with the forces required to activate an ion channel protein conformation change associated with the gating of the channel. Key words Ion channel á Cell membrane á Magnetic ®eld á Lorentz force Introduction During the past two decades a scienti®c controversy has arisen concerning the eects of weak, environmental magnetic ®elds on humans. Many epidemiological and laboratory studies have been undertaken in an eort to resolve this controversy, yet there are credible results supporting both positions: those arguing that there are adverse health eects resulting from exposure and those arguing against these eects Moulder and Foster 1995). Mostofthisworkhasfocusedontheeectsofexposureto extremelylowfrequencyELF:50±60 Hz)magnetic®elds. In order to determine whether there are eects, how- ever, it is necessary to establish a plausible mechanism by which these eects might arise. Several mechanisms have been proposed and, while many have been rejected, a few remain as credible explanations, although their validity has not yet been established experimentally Adair 1992; Kirschvink 1992; Dobson and St Pierre 1996). Recently, a new and straightforward mechanism ex- plaining the eects of weak, ELF magnetic ®elds on biological systems has been proposed Balcavage et al. 1996). This theoretical mechanism is based on the Lorentz force acting on ions as they move through transmembrane ion channels in the presence of a mag- netic ®eld. The force on the ions within the channel, according to the original calculations, is strong enough to activate nearby voltage gated ion channels. It was proposed that this can explain eects on biological sys- tems exposed to ELF magnetic ®elds as weak as 100 lT. We demonstrate here that the calculations presented by Balcavage et al. 1996) were ¯awed and that the Lorentz force exerted on the ions in the channels has a negligible eect even in extremely large magnetic ®elds. The model Balcavage et al. 1996) discuss the passage of cations such as Na + through gated membrane ion channels such as the channel described by Noda et al. 1986). These channels are formed by proteins that span the lipid bilayer membrane of the cell. The structure of the pro- tein results in a channel through the membrane, through which Na + ions may diuse. Gated channels are con- structed from proteins which can change their confor- mation on application of a mechanical force or an electric ®eld such that the new conformation results in an opening or closing of the channel. The magnitude of force required to eect such a change has been estimated to be in the region of 0.2±0.4 pN Howard and Hud- speth 1989). For some channels, this mechanical force can be actuated by application of an electrical potential dierence across the membrane. Charged centres within the protein respond to the electric ®eld within the membrane, thus acting as transducers of the force Conti and StuÈhmer 1989). Such channels are usually described as voltage-gated channels and are typically activated by transmembrane potential dierences in the order of Eur Biophys J 2000) 29: 455±456 Ó Springer-Verlag 2000 T.G. St. Pierre &) á J. Dobson Department of Physics, Biophysics Programme, The University of Western Australia, Nedlands, WA 6907, Australia e-mail: stpierre@physics.uwa.edu.au; Fax: +61-8-93801014