Martin

Active Mechano-sensitivity by Hair Cells in the Inner Ear

Pascal Martin
Scientific keywords: hair cell, hearing, Mechanosensitivity, Molecular motors, oscillations
Technics Used in the Lab: Force measurements with glass microfibers and optical tweezers, microscopy, mathematical modeling.

Our group aims at shedding light on mechano-sensation of sounds (hearing) and head accelerations (balance) by hair cells of the inner ear. Hair cells are named after the tuft of extended microvili —the hair bundle— that protrudes from each cell’s apical surface (see Figure). Mechanosensitivity is initiated by the deflection of the hair bundle, which elicits an electrical signal that then propagates to the brain. By applying force stimuli, we probe the mechanical properties of this organelle. Our experiments demonstrate that the hair bundle can mobilize internal resources of
energy to oscillate spontaneously and actively amplify sinusoidal stimuli. Active hair- bundle motility arises from a dynamic interplay between mechanosensitive ion channels, molecular motors and electro-mechanical feedback by calcium ions. In a complementary bio-mimetic approach, we also develop in vitro, with a minimal set of purified proteins, an autonomous molecular oscillator where oscillations emerge from the collective properties of molecular motors under elastic loading. Our  research promotes a general principle of sound detection that is based on nonlinear amplification by self-sustained “critical” oscillators in the inner ear.

 

A: Hair cell from from a bullfrog’s ear (source: Jim Hudspeth, The Rockefeller University, New York, USA). B: The mechanosensory hair bundle (source: Peter Gillespie, OHSU, Portland, USA).

A: Hair cell from from a bullfrog’s ear (source: Jim Hudspeth, The Rockefeller University, New York,USA). B: The mechanosensory hair bundle (source: Peter Gillespie, OHSU, Portland, USA).