By Penny Stern, MD
NEW YORK, Jan 28 (Reuters Health) -- A more complete understanding of the
nature of hearing and hearing loss may be near, according to Texas researchers.
Drs. William Brownell and John Oghalai, together with colleagues at Baylor
College of Medicine in Houston, Texas, looked at the functioning of the cochlear
outer hair cell, a highly sensitive structure in the inner ear that acts as an
amplifier, allowing people to hear very quiet sounds and those of specific
frequencies.
According to a study in the January 28th issue of Science, they found that
the cells shorten in response to electrical stimuli, and that certain drugs can
also result in changes in the cell's shape. Humans have about 12,000 such cells
in each ear and the cells, which are vulnerable to damage due to noise and
aging, do not regenerate once they are injured. About 28 million Americans have
some degree of hearing loss, much of which can be traced to deterioration of the
outer hair cell.
The thousands of outer hair cells are "responsible for amplifying sounds
of a specific frequency" in a process called electromotility, said Oghalai in an
interview with Reuters Health. The electromotility results in changes in the
fluidity of the hair cell membrane, causing the membrane to undergo rippling,
"much like the folding and unfolding of an accordion's pleats," Oghalai and
Brownell explained.
"The outer hair cells act as microscopic machines that pump up and down in
synchrony with sound waves" which are then amplified to detectable levels,
Oghalai said.
According to Oghalai, "such dynamic changes in membrane fluidity have
never before been demonstrated in any type of cell or membrane."
The team also found that certain drugs, such as aspirin and thorazine (a
type of tranquilizer), can have a significant impact on these cell membranes.
The drugs alter the cell membrane's curvature and affect the membrane fluidity,
according to the researchers.
"It is possible that a large number of the side effects associated with
(drugs such as aspirin) are due to their effect on membrane mechanics," said
Brownell.
The researchers believe that their findings may prompt other scientists to
search for the gene that controls outer hair cell functioning.
"Once this gene is found, it may be possible to insert it into other cells
and cause them to produce electromotility... (providing possible) treatment for
patients who have already had irreversible damage to their outer hair cells, and
have a permanent hearing impairment," Oghalai said.
The new research may also lead to the development of new and more
sophisticated devices to treat hearing loss, but they are only cautiously
optimistic. "It is important to realize that these types of advances may take
longer than we think," Oghalai said.
