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Searing the heart for the better
By Nathan Seppa
Talk about heartburn. Using a catheter
with a charged tip, doctors can sizzle wayward heart cells and correct an irregular
heartbeat better than standard drugs can,
a head-to-head comparison shows. The
report appears in the Jan. 27 Journal of
the American Medical Association.
The procedure has been used for more
than 20 years to correct atrial fibrillation — a weak, rapid heartbeat that carries health risks. But despite its long
track record, the U.S. medical community
hasn’t fully accepted the technique.
“There are doctors who take a more
conservative view and continue to try
drugs” to treat atrial fibrillation, says
cardiologist David Wilber of Loyola
University Health Center in Maywood,
Ill., who coauthored the new study. As
a result, the procedure, called catheter
ablation, has remained a second-line
treatment and continues to undergo
testing, he says, even though about half of
patients fail to control their atrial fibril-
lation with medication.
Pore propulsion
helps out sperm
Study suggests possible link
between marijuana, infertility
By Laura Sanders
Fancy goggles, a swim cap or the latest
high-tech suit won’t help human sperm
power through their race to fertilize an
egg. Instead, the tiny cells rely on a pro-ton-shedding pore to speed toward their
target, a study in the Feb. 5 Cell finds.
The study also reports that a compound similar to the active ingredient in
marijuana might interfere with this channel, suggesting a molecular link between
habitual marijuana use and male infertility. Finding other compounds that open
or close the channel may offer new ways
to control reproduction, the authors say.
Researchers knew that powerful sperm
swimming depends on protons leaving
the sperm cell, thereby lowering its acidity. The concentration of protons inside
The proton channel Hv1 (green) is found
on the tails of human sperm. DNA (blue)
and mitochondria (red) are also shown.
a sperm is roughly 1,000 times higher
than outside, says Yuriy Kirichok of the
University of California, San Francisco,
a coauthor of the new study. As protons
flood out of the cell, a host of changes kick
the sperm into high gear. But just how the
protons escaped was a mystery.
“This is an important paper because it
reveals how human spermatozoa lower
intracellular acidity,” comments David
Clapham, a Howard Hughes Medical
Institute investigator at Harvard Medical School.
Kirichok and colleagues examined the
electrical properties of mature human
sperm by using an electrode to record
proton movement across the cell membranes. The electrical properties of the
sperm were similar to those of certain
immune cells that are known to discharge
protons through a channel called Hv1.
To verify that Hv1 was the right channel
in sperm, the team stained the channel
with green fluorescent antibodies. The
tails of the sperm glowed green, indicating Hv1 was abundant there. The team
also looked for substances that changed
Hv1’s behavior. A compound called anandamide, similar to the active ingredient in
marijuana, opened the channel.
“It’s been known for quite some time
that marijuana reduces fertility, but
nobody knows why this happens,” says
Kirichok. “We for the first time show the
presence of a molecule on sperm that can
be directly activated by anandamide.”
He speculates that habitual marijuana
use may activate sperm cells prematurely,
leaving them burned out and unable to
swim when it counts.
Y. KIRICHOK
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