Department of Earth and Environmental Sciences, Ludwig-Maximilians-University Munich, Munich, Germany.
Proc Natl Acad Sci U S A. 2012 Jul 24;109(30):12022-7. doi: 10.1073/pnas.1205653109. Epub 2012 Jul 9.
Over the past 50 y, behavioral experiments have produced a large body of evidence for the existence of a magnetic sense in a wide range of animals. However, the underlying sensory physiology remains poorly understood due to the elusiveness of the magnetosensory structures. Here we present an effective method for isolating and characterizing potential magnetite-based magnetoreceptor cells. In essence, a rotating magnetic field is employed to visually identify, within a dissociated tissue preparation, cells that contain magnetic material by their rotational behavior. As a tissue of choice, we selected trout olfactory epithelium that has been previously suggested to host candidate magnetoreceptor cells. We were able to reproducibly detect magnetic cells and to determine their magnetic dipole moment. The obtained values (4 to 100 fAm(2)) greatly exceed previous estimates (0.5 fAm(2)). The magnetism of the cells is due to a μm-sized intracellular structure of iron-rich crystals, most likely single-domain magnetite. In confocal reflectance imaging, these produce bright reflective spots close to the cell membrane. The magnetic inclusions are found to be firmly coupled to the cell membrane, enabling a direct transduction of mechanical stress produced by magnetic torque acting on the cellular dipole in situ. Our results show that the magnetically identified cells clearly meet the physical requirements for a magnetoreceptor capable of rapidly detecting small changes in the external magnetic field. This would also explain interference of ac powerline magnetic fields with magnetoreception, as reported in cattle.
在过去的 50 年里，行为实验产生了大量证据，证明在广泛的动物中存在磁感觉。然而，由于磁感觉结构的难以捉摸，其潜在的感觉生理学仍然知之甚少。在这里，我们提出了一种有效分离和表征潜在基于磁铁矿的磁受体细胞的方法。本质上，通过旋转磁场，在分离的组织制剂中，通过细胞的旋转行为来视觉识别含有磁性材料的细胞。作为首选组织，我们选择了鳟鱼嗅觉上皮，先前曾有人提出该组织可能含有候选磁受体细胞。我们能够重复地检测到磁性细胞，并确定它们的磁偶极矩。得到的值（4 到 100 fAm2）大大超过了先前的估计值（0.5 fAm2）。细胞的磁性是由于富含铁的晶体的μm 大小的细胞内结构，很可能是单畴磁铁矿。在共焦反射成像中，这些结构在靠近细胞膜的地方产生明亮的反射点。发现磁性内含物与细胞膜牢固地耦合，从而能够在原位直接转换作用在细胞偶极子上的磁扭矩产生的机械应力。我们的结果表明，被磁识别的细胞显然满足了快速检测外部磁场中微小变化的磁受体的物理要求。这也可以解释交流电电源线磁场对牛磁感应的干扰，正如先前报道的那样。
