Auditory Mechanotransduction at the Individual Sterocilium

A number of hereditary and acquired hearing impairments involve disruption or malformation of the hair bundle, a mechanosensory organelle of the inner ear hair cells. A hair bundle consists of stereocilia, microvilli-like protrusions that are hold together by numerous extracellular links. Once the integrity of this structure is compromised, mechanotransduction is usually lost. Consequently, there are no experimental data on the mechanosensitivity of the bundle's constituting elements, such as different individual stereocilia or different links between a pair of stereocilia. Furthermore, it is still a subject of debates whether the mechanotransduction channels migrate from a stereocilium after disruption of stereocilia links. Thus, it is very hard to estimate a potential for functional recovery in a pathologically malformed or disrupted hair bundle. The objective of this application is to implement emerging techniques of nanotechnology, specifically scanning ion conductance microscopy, in order to: 1) investigate mechanotransduction responses evoked by nanoscale deflections of individual stereocilia within a hair bundle of mammalian auditory hair cells, and 2) determine spatial distribution and singlechannel properties of the ion channels populating the surface of these stereocilia before and after disrupting the integrity of the hair bundle. Based on our preliminary results, we hypothesize that the mechanotransduction channels are abundantly expressed at the surface of a stereocilium, but only few of them become functional in the presence of an appropriately attached stereocilia link. Confirmation of this hypothesis would provide an insight into pathophysiological mechanisms of hearing losses that involve damage or malformation of the hair bundle. We expect that the techniques, developed in this study, will open possibility for a different level of experimentation in auditory mechanotransduction: functional studies of individual elements of transduction machinery. The longterm goal of these studies is to understand how different molecular and structural components assemble the transduction apparatus of the mammalian auditory hair cells in normal and pathological conditions.