Coherent motion of stereocilia assures the concerted gating of hair-cell transduction channels

TL;DR

This study demonstrates that stereocilia in hair cells move coherently as a unit, ensuring synchronized channel gating, which enhances the sensitivity and amplification of mechanotransduction.

Contribution

It provides direct experimental evidence that stereocilia movements are highly coherent, supporting the model of concerted gating in hair-cell transduction channels.

Findings

High coherence of stereocilia movements across the bundle

Negligible phase lag in stereocilia displacement

Mechanical coupling constrains stereocilia to move as a unit

Abstract

The hair cell's mechanoreceptive organelle, the hair bundle, is highly sensitive because its transduction channels open over a very narrow range of displacements. The synchronous gating of transduction channels also underlies the active hair-bundle motility that amplifies and tunes responsiveness. The extent to which the gating of independent transduction channels is coordinated depends on how tightly individual stereocilia are constrained to move as a unit. Using dual-beam interferometry in the bullfrog's sacculus, we found that thermal movements of stereocilia located as far apart as a bundle's opposite edges display high coherence and negligible phase lag. Because the mechanical degrees of freedom of stereocilia are strongly constrained, a force applied anywhere in the hair bundle deflects the structure as a unit. This feature assures the concerted gating of transduction channels that maximizes the sensitivity of mechanoelectrical transduction and enhances the hair bundle's capacity to amplify its inputs.