Migratory
birds and fish use the Earth’s magnetic field to find their way.
Researchers have recently 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 Ludwig Maximilian University 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”.
Magnetic characterization of isolated candidate vertebrate magnetoreceptor cells
Source: Ludwig Maximilian University – Munich
