Hearing Discrepancy Probed

摘要

A sound wave that hits your ear can only be perceived after it has been converted from mechanical to electrical energy through a process called mechanotransduction, which is carried out by hair cells within the cochlea, the snail shell-shape canal of the inner ear. To study hair cells, researchers typically excise a portion of the cochlea and use a tiny probe to stimulate bundles of stereocilia that protrude from the tops of the hair cells into the central duct of the cochlea. Stereocilia movement opens up potassium ion channels on the hair cell membrane, resulting in a change in membrane voltage, which in turn allows an influx of calcium ions that scientists can measure with electrodes. Although these methods have yielded much information about how stereocilia work, in vitro techniques often give results that suggest stereocilia are much less sensitive than researchers know them to be from early in vivo and whole-cochlear explant studies. "[It's] kind of a paradox that the movement of the bundle that you need to open up the channels [in vitro] is larger than the needed movement to open them up in vivo," says Anthony Ricci, who studies the molecular mechanisms of hearing at Stanford University. He says that in vivo, the stereocilia bundles need only move a few nanometers to transduce a signal, but in studies using a microprobe, that measurement is "offby several orders of magnitude."