A protein deep in the ear is a key factor for normal hearing and could be used to help develop treatments for deafness, US researchers believe.
The inner ear converts sound waves
For decades scientists have been trying to figure out what translates sound into the nerve impulses which are interpreted by the brain.
Now a Harvard Medical School team says it is down to a protein, TRPA1, on the tips of hair cells of the inner ear.
Their animal research findings are published in the journal Nature.
How we hear
Scientists already know that in order to hear, sound waves travel along the passage of the ear until they hit the eardrum and cause it to vibrate.
This causes three tiny bones behind the ear drum, called the ossicles, to start moving.
They, in turn, pass on vibrations to a thin layer of tissue at the entrance of the inner ear called the oval window.
The movement of the oval window then sets off wave-like motions in the fluid in an organ shaped like a snail's shell which is called the cochlea.
The cochlea contains thousands of minute hair cells that are linked up to nerves, which transmit impulses to the brain to interpret the sound.
However, it was unclear exactly how these microscopic hair-like structures in the inner ear convert or "transduce" the sound waves into electrical signals to be transmitted to the brain.
Experts had suspected that the process involved some sort of pore or channel that allows electrical charge to flow into the cells bearing the hairs.
Now Dr David Corey and his Harvard colleagues believe a crucial component of this set-up is a protein called TRPA1.
They studied mice and zebrafish to look at the role and location of TRPA1.
They found it lived on the tips of the hair cells and that cells lacking it were no longer able to generate electrical signals in response to vibration.
By looking at mice embryos, they found its appearance during mouse development coincided with the hair cells' ability to sense vibrations.
Dr Corey said the findings would need to be confirmed by further studies. But he said TRPA1 was the best candidate found so far.
"People have been looking for this protein for decades.
"[This is] the strongest evidence yet that this protein is the hair-cell transducer channel," he said.
He believes the protein forms pores that open and close in sync with sound waves, allowing messenger ions, like sodium and calcium, to flow into the cells and transform the vibrations into electrical signals.
This should help scientists investigate inherited forms of deafness, he said.
Neurobiologist Peter Gillespie, who has conducted similar hearing research at the Oregon Health & Science University, said: "This channel is the jewel everyone would like to find.
"Identifying it is getting at the real kernel of how the inner ear works."