A protein associated with a disorder that causes deafness and blindness in people may be a key to unraveling one of the foremost mysteries of how we hear, says a study in the June 28 issue of the Journal of Neuroscience. Scientists with the National Institute on Deafness and Other Communication Disorders (NIDCD), one of the National Institutes of Health (NIH), and the University of Sussex, Brighton, United Kingdom, have identified protocadherin-15 as a likely player in the moment-of-truth reaction in which sound is converted into electrical signals. (Protocadherin-15 is a protein made by a gene that causes one form of type 1 Usher syndrome, the most common cause of deaf-blindness in humans.) The findings will not only provide insight into how hearing takes place at the molecular level, but also may help us figure out why some people temporarily lose their hearing after being exposed to loud noise, only to regain it a day or two later.
Researchers have long known that hair cells, small sensory cells in the inner ear, convert sound energy into electrical signals that travel to the brain, a process called mechanotransduction. However, the closer one zooms in on the structures involved, the murkier our understanding becomes. When fluid in the inner ear is set into motion by vibrations emanating from the bones of the middle ear, the rippling effect causes bristly structures atop the hair cells to bump up against an overlying membrane and to deflect. Like seats in a three-row stadium, the bristles, called stereocilia, are arranged in tiers, with each lower seat connected to a higher seat by minute, threadlike bridges, or links. As the stereocilia are deflected, pore-like channels on the surface of the stereocilia open up, allowing potassium to rush in, and generating an electrical signal. Because the “tip link” — the link that connects the tip of the shorter stereocilium to the side of the adjacent, taller stereocilium — must be present for the channel to function, scientists believe that this structure may be responsible for opening and closing the channel gate. Researchers suggest that if they can learn the makeup of the tip link, they’ll be that much closer to understanding how the gate mechanism operates.
“This research identifies protocadherin-15 to be one of the proteins associated with the tip link, thus finally answering a question that has been baffling researchers for years,” says James F. Battey, Jr., M.D., Ph.D., director of the NIDCD. “Thanks to the collaborative effort among these researchers, we are now at the closest point we have ever been to understanding the mechanism by which the ear converts mechanical energy — or energy of motion — into a form of energy that the brain can recognize as sound.”
Message posted by: Rashmi Nemade
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