Whether it's a tabby perking up at the distant ratchet of a can opener, or an orchestra conductor cringing from a single wrong note in a Beethoven symphony, mammals have exquisite hearing. Inside the ear, sounds are somehow amplified by "hair" cells that bob like a pogo stick. Now researchers think they have found the key to this remarkable feat: membranes that behave like the bellows of an accordion. The finding, reported in the current Science , may one day lead to ways to protect and restore hearing.
The inner ears of mammals are lined with thousands of so-called outer hair cells, each sprouting a lopsided cluster of cilia like a bad haircut. When sound waves tickle these cilia, the protrusions generate an electrical trigger that makes the cell dance, elongating and shortening with the sound. This unique pumping motion, known as electromotility, amplifies and refines the sounds before the ear dispatches a nerve signal to the brain.
For years, researchers have puzzled over the mechanism that sets the hair cells dancing. With a hunch that the motion originates in the cell membrane, otolaryngology resident John Oghalai and colleagues at Baylor College of Medicine in Houston, Texas, took outer hair cells from guinea pigs and got them boogying with chemicals and jolts of electricity. Using a fluorescent probe, the researchers were able to watch membrane lipids slowing down in response to an electrical signal, a phenomenon unique to these cells. They think this means the membrane wrinkles as the cell twitches.
The team's work is "extremely important" in that it sheds light on the mechanics of electromotility, says Aleksander Popel, a biomechanical engineer at John Hopkins University in Baltimore, Maryland. According to team member William Brownell, damaged outer hair cells are the most common cause of hearing problems, so if researchers can figure out exactly how outer hair cells work, they might be able to protect them. Rock fans, for instance, might be able to pop some prophylactic pills that toughen up their outer hair cells and protect their ears at rib-shaking concerts. Or for fans past their prime, bioengineers might be able to restore hearing with artificial hair cells.