Over the last half century, it has been established that fish and migratory birds use the planet's magnetic field to help find their way, an interesting zoological mystery. Researchers have now identified cells with internal compass needles for the perception of the field, and that can explain why high-tension cables perturb their 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 had not been successful.

“The field penetrates the whole organism, so such cells could be located almost anywhere, making them hard to identify,” says geophysicist Michael Winklhofer of Ludwig-Maximilians-Universitaet Muenchen (LMU), who has helped locate 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. The cells turned out to be more strongly magnetic than previously postulated, a finding that explains the high sensitivity of the magnetic sense. 

Electrosmog and the internal compass of magnetite crystals

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.  
They got values of 4 to 100 fAm2, higher than previous estimates of 0.5 fAm2.

“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. Including confusion of cattle when near alternating current transmission lines, they note. 

The new findings could help in understanding the development of highly sensitive magnetometers, though look for mass media scare journalism soon also, like articles worrying that 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.”

 That's a big 'if' that can easily be misconstrued outside science. Use caution when worrying about something that doesn't exist.

Stephan H.K. Eder, Hervé Cadiou, Airina Muhamad, Peter A. McNaughton, Joseph L. Kirschvink, and Michael Winklhofer, 'Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells', PNAS 2012 ; published ahead of print July 9, 2012, doi:10.1073/pnas.1205653109