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BP: Fachverband Biologische Physik

BP 25: Oscillatory Systems

BP 25.1: Invited Talk

Thursday, March 29, 2007, 14:30–15:00, H44

Mechanical amplification by sensory hair cells from the vertebrate ear — •Pascal Martin — Institut Curie recherche\CNRS - Laboratoire PCC (UMR168), 26 rue d'Ulm 75005 Paris, France

The dazzling sensitivity and frequency selectivity of the vertebrate ear rely on mechanical amplification of small sounds by hair cells, the sensory receptors of the inner ear that transduce mechanical stimuli into electrical signals that will then be received by the brain. As revealed by spontaneous oscillations and forms of mechanical excitability in response to force steps, the hair bundle that adorns each hair cell is both a mechano-sensory antenna and a force generator. To study active hair-bundle motility, we use flexible glass micro-fibers to stimulate mechanically in vitro a single hair bundle from the bullfrog's sacculus. We find that an oscillatory hair bundle amplifies its response to small stimuli at frequencies near that of the spontaneous oscillation. By combining measurements of force-displacement relations with Ca2+ iontophoresis, we show that the location of a bundle's operating point within its nonlinear force-displacement relation controls the type of movements observed. We have developed a simple theoretical description that can account for the various incarnations of active hair-bundle motility. There, mechanical activity stems solely from myosin-based adaptation, the process by which molecular motors (myosins) in the hair bundle set the open probability of mechano-sensitive ion channels at steady state. By taking intrinsic hair-bundle fluctuations into account, we could reach quantitative agreement between calculated and experimentally measured response functions.