Weaver J C, Vaughan T E, Adair R K, Astumian R D
Harvard-M.I.T. Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Biophys J. 1998 Nov;75(5):2251-4. doi: 10.1016/S0006-3495(98)77669-6.
Understanding exposure thresholds for the response of biological systems to extremely low frequency (ELF) electric and magnetic fields is a fundamental problem of long-standing interest. We consider a two-state model for voltage-gated channels in the membrane of an isolated elongated cell (Lcell = 1 mm; rcell = 25 micron) and use a previously described process of ionic and molecular flux rectification to set lower bounds for a threshold exposure. A key assumption is that it is the ability of weak physical fields to alter biochemistry that is limiting, not the ability of a small number of molecules to alter biological systems. Moreover, molecular shot noise, not thermal voltage noise, is the basis of threshold estimates. Models with and without stochastic resonance are used, with a long exposure time, texp = 10(4) s. We also determined the dependence of the threshold on the basal transport rate. By considering both spherical and elongated cells, we find that the lowest bound for the threshold is Emin approximately 9 x 10(-3) V m-1 (9 x 10(-5) V cm-1). Using a conservative value for the loop radius rloop = 0.3 m for induced current, the corresponding lower bound in the human body for a magnetic field exposure is Bmin approximately 6 x 10(-4) T (6 G). Unless large, organized, and electrically amplifying multicellular systems such as the ampullae of Lorenzini of elasmobranch fish are involved, these results strongly suggest that the biophysical mechanism of voltage-gated macromolecules in the membranes of cells can be ruled out as a basis of possible effects of weak ELF electric and magnetic fields in humans.
了解生物系统对极低频（ELF）电场和磁场响应的暴露阈值是一个长期备受关注的基本问题。我们考虑一个孤立细长细胞（Lcell = 1毫米；rcell = 25微米）膜中电压门控通道的双态模型，并使用先前描述的离子和分子通量整流过程来设定阈值暴露的下限。一个关键假设是，限制因素是弱物理场改变生物化学的能力，而非少数分子改变生物系统的能力。此外，分子散粒噪声而非热电压噪声是阈值估计的基础。使用了有无随机共振的模型，曝光时间较长，texp = 10(4) 秒。我们还确定了阈值对基础转运速率的依赖性。通过考虑球形和细长细胞，我们发现阈值的最低下限为Emin约9×10(-3) V m-1（9×10(-5) V cm-1）。对于感应电流，使用保守的回路半径rloop = 0.3米值，人体磁场暴露的相应下限为Bmin约6×10(-4) T（6 G）。除非涉及大型、有组织且电放大的多细胞系统，如板鳃亚纲鱼类的洛伦兹壶腹，这些结果强烈表明，细胞细胞膜中电压门控大分子的生物物理机制可被排除，不作为人类弱ELF电场和磁场可能产生影响的基础。
