source: bhNEWS
Daily India, India - July 14, 2008
Scientist create 3-D image of protein filaments that facilitate
hearing
Berkeley Lab researchers say that they have made a significant advance
towards understanding exactly how hearing works.
The researchers claim that they have for the first time pieced
together the three-dimensional structure of a gossamer-like filament
of proteins
in the inner ear, which enables the sense of hearing and balance.
They say that their work may lead to improved treatments for some
forms of hearing loss, which affect about 10 per cent of people.
The filaments help transform the mechanical vibrations of sound into
electrical signals that can be interpreted by the brain, say the
researchers.
In their study re****t, they have revealed that such filaments are
only four nanometres wide, and 160 nanometres long.
The world becomes silent when enough of them break, the re****t adds.
According to the researchers, the filaments are part of a sensory
system that operates over a range of stimuli spanning six orders of
magnitude, and that they make people capable enough to hear even a pin
drop.
They say that no other sensory system in biology and the electrical
engineering world is capable of this feat.
"It's one of the most beautifully deigned systems in the body. But
how it really works remains a mystery. Our goal is to determine what
the
system looks like, so we can determine how it functions," Science
Daily
quoted Manfred Auer, a researcher in the Berkeley Lab's Life Sciences
Division, as saying.
During the study, the researchers used electron tomography that
acquires hundreds of images of a structure at different angles,
reconstructs
them into a three-dimensional composite, and yields highly detailed
images
of structures at the molecular scale.
Hair cells in the inner ear sprout hair bundles that bob and sway in
fluid when the ear drum absorbs sound waves.
The researchers say that each hair bundle is composed of individual
hairs that are also called stereocilia, and that adjacent stereocilia
are
linked together by protein filaments, also known as tip links.
As the stereocilia sway, the tip links stretch, which momentarily
rips open a transduction channel that allows positively charged ions
to stream
into the hair cell. This initiates a neurotransmitter release that
eventually reaches the nervous system.
In this manner, a mechanical action is converted into an electrical
signal, and eventually something we hear as a chirp, beep, or voice.
"The system is incredible. But we still don't really know what
constitutes the links, and we don't know how the hair bundle operates
at the
molecular level," says Auer.
Auer and colleagues have so far dissect the hair bundle at the
molecular level using electron tomography, reconstructed the hair-
bundle links
in three dimensions, and obtained highly accurate length measurements
of
the links, down to the molecular scale.
"One of the holy grails in structural cell biology is obtaining a
molecular inventory of complex systems, and showing how the proteins
work
together to achieve their marvelous function. We're striving to
develop such an
inventory for the hair bundle," says Auer.
The researchers say that their study enables them to decipher just
how the ear adapt to an extremely loud noise, and then quickly
reconfigure
itself to detect a whisper; and how can it be sensitive enough to
detect the
whisper, but not so sensitive that it detects every molecule colliding
against
the eardrum.
"If the system were any more sensitive, you would hear all of the
molecules in the air bumping onto your ear drum, and go crazy," says
Auer,
adding that their recently obtained images are the first in a series
of electron
tomography explorations of hair cells.
"We know a good deal about how a hair bundle operates through clever
electrophysiology experiments, but we need to know more, and for that
we need to determine its molecular structure. Ultimately, we will get
a
molecular representation of this entire bundle, with all of its
machinery, which will give us a fundamental insight into how the
bundle works -
and how hearing really works," says Auer
The research has been re****ted the Journal of the Association for
Research in Otolaryngology.
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