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Machines Like Us

The magnetic sense

Wednesday, 11 July 2012

Migratory birds and fish use the Earth's magnetic field to find their way. LMU researchers have now identified cells with internal compass needles for the perception of the field—and can explain why high-tension cables perturb the magnetic orientation.

Although many animal species can sense the geomagnetic field and exploit it for spatial orientation, efforts to pinpoint the cells that detect the field and convert the information into nerve impulses have so far failed. "The field penetrates the whole organism, so such cells could be located almost anywhere, making them hard to identify," says LMU geophysicist Michael Winklhofer. Together with an international team, he has located magnetosensory cells in the olfactory epithelium of the trout.

The researchers first used enzymes to dissociate the sensory epithelium into single cells. The cell suspension was then stimulated with an artificial, rotating magnetic field. This approach enabled the team to identify and collect single magnetoresponsive cells, and characterize their properties in detail. Much to Winklhofer's surprise, the cells turned out to be more strongly magnetic than previously postulated—a finding that explains the high sensitivity of the magnetic sense.

Magnetite crystals show the way

The cells sense the field by means of micrometer-sized inclusions composed of magnetic crystals, probably made of magnetite. The inclusions are coupled to the cell membrane, which is necessary to change the electrical potential across the membrane when the crystals realign in response to a change in the ambient magnetic field. "This explains why low-frequency magnetic fields generated by powerlines disrupt navigation relative to the geomagnetic field and may induce other physiological effects," says Winklhofer.

The new findings could lead to advances in the sphere of applied sciences, for example in the development of highly sensitive magnetometers. In addition, they raise the question of whether human cells are capable of forming magnetite and if so, how much. "If the answer to the question is yes", Winklhofer speculates, "intracellular magnetite would provide a concrete physiological substrate that could couple to so-called electrosmog." (PNAS, 9. July)