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 A high-powered electromagnet allowed researchers to increase, eliminate and even decrease the effects of gravity on live paramecia in a vial of pond water. Image: Karine Guevorkian and James Valles.
For many single-celled organisms
living in water, the force is always against them. The classic example is the
slipper-shaped paramecium, which consistently swims harder going up than going
down, just to keep from sinking. Now physicists Karine Guevorkian and James
Valles of Brown University have worked out a way to turn gravity on its head and
see how the creatures respond.
The researchers placed a vial with pond water and live paramecia
inside a high-powered electromagnet at the National High Magnetic Field
Laboratory in Tallahassee, Fla. The organisms are less susceptible to a magnetic
field than plain water is, so the magnetic field generated inside the vial
“pulls” harder on the water than on the cells. If the field is
pulling down, the cells float. If it’s pulling up, they sink.
Using water alone, Valles and Guevorkian were able to increase
the effect of gravity by about 50 percent. To increase the effect even further,
they added a compound called Gadolinium-diethylene-triamine-pentaacetate
(Gd-DTPA) to the water. Gd-DPTA is highly susceptible to induced magnetic fields
such as those generated in electromagnets. This allowed the researchers to make
the water much “heavier” or “lighter,” relative to the
paramecia, achieving an effect up to 10 times that of normal gravity. The
magnetic field is continuously adjustable, so Valles and Guevorkian were also
able to create conditions simulating zero-gravity and inverse-gravity.
By dialing the magnetic field up or down, the researchers could
change the swimming behavior of the paramecia dramatically. In high gravity, the
organisms swam upward mightily to maintain their place in the water column. In
zero gravity, they swam up and down equally. And in reverse gravity, they dove
for where the sediments ought to be.
“If you want to make something float more,” said
Valles, “you put it in a fluid and you pull the fluid down harder than you
pull the thing down. And that’s what we basically do with the magnet. That
causes the cell to float more – and that turns gravity upside down for the
cell.”
Cranking the field intensity even higher, Valles and Guevorkian
could test the limits of protozoan endurance. At about eight times normal
gravity, the little swimmers stalled, swimming upward, but making no progress.
At this break-even point, the physicists could measure the force needed to
counter the gravitational effect: 0.7 nano-Newtons. For comparison, the force
required to press a key on a computer keyboard is about 22 Newtons or more than 3
billion times as strong.
Space-based research has demonstrated many puzzling biological
effects related to reduced gravity, such as changes in bone cell development and
gene expression. But methods for manipulating gravity in the Earth-based
laboratory have been few and troublesome, hindering further research in these
areas. This new method will allow researchers to subject small biological
systems to gravitational effects similar to those encountered in space, allowing
less expensive and more complex experiments on the biological response to
altered gravity.
See also three short film clips:
Enhanced gravity:
Paramecia swimming in a 20-tesla magnetic field, oriented to increase
the effect of gravity five-fold (5G). Upward-swimming paramecia work
much harder than they would in normal gravity (1G).
Inverted Gravity:
Paramecia swimming in a 25-tesla magnetic field, oriented to create an
inverse gravity effect. If they weren’t swimming, the paramecia would
move quickly to the top of the frame, but in fact most paramecia swim
downward, against the reversed effect of gravity.
Stalling Force:
Paramecia swimming in a 30-tesla magnetic field, which increases the
effect of gravity 10-fold. At this level, the increased effect of
gravity equals the cells’ swimming force, effectively stalling the
paramecia.
Source: Brown University
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