Tracking the Elusive Sound Channel

When you hear a clap of thunder or a hushed whisper, sound waves are tousling microscopic hairs inside the ear, setting off nerve impulses that crackle to the brain. Neuroscientists have long sought a key player in this chain of events--the cellular pore that opens when the tiny hairs bend and produces an electrical signal. Now, working with fruit flies, they've found a strong candidate.

Hair-cell physiologists don't know yet what the pore--called an ion channel--looks like, but some interesting biophysical properties suggest the channel is very fast and sensitive. When stimulated, the cells' channels open up within microseconds, much faster than most other ion channels in the body. They open when the tip of the cell is deflected by a mere atom's width--akin to bending the tip of the Eiffel Tower by the width of your thumb.

Studying hair-cell channels is tricky, though, partly because they are few and far between. A team led by Charles Zuker of the University of California, San Diego, focused instead on fruit flies, acting on a hunch that the flies' touch-sensitive bristles might contain channels similar to those in sound-sensitive hair cells. In the 24 March Science, the researchers report that they have cloned an intriguing ion channel from the neurons that connect to the bristles. They identified a gene that, when mutated, kept the channel shut or allowed it to open only part way. The gene's sequence suggests that its protein may anchor the channel to the cellular skeleton, a steady framework from which it can detect any jostling.

Although the fruit fly bristle channel behaves a lot like human hair cells, not everyone is convinced. "The anatomy is so different that I wouldn't be surprised if [the hair cell channel] is a completely different molecule, not even a relative," says sensory physiologist Denis Baylor of Stanford Medical School. But James Hudspeth of the Rockefeller University in New York City says that "chances are very good" that the two are related. Hudspeth's team plans to look for genes similar to the bristle gene that might be mutated in people with hereditary deafness.

Posted in Biology