The tectorial membrane (TM) of the mammalian cochlea is a complex extracellular matrix which, in response toacoustic stimulation, displaces the hair bundles of outer hair cells (OHCs), thereby initiating sensory transduction and amplification.Here, using TM segments from the basal, high-frequency region of the cochleae of genetically modified mice (includingmodels of human hereditary deafness) with missing or modified TM proteins, we demonstrate that frequency-dependent stiffeningis associated with the striated sheet matrix (SSM). Frequency-dependent stiffening largely disappeared in all three TMmutations studied where the SSM was absent either entirely or at least from the stiffest part of the TM overlying the OHCs.In all three TM mutations, dissipation of energy is decreased at low (<8 kHz) and increased at high (>8 kHz) stimulusfrequencies. The SSM is composed of polypeptides carrying fixed charges, and electrostatic interaction between them mayaccount for frequency-dependent stiffness changes in the material properties of the TM. Through comparison with previousin vivo measurements, it is proposed that implementation of frequency-dependent stiffening of the TM in the OHC attachmentregion facilitates interaction among tones, backward transmission of energy, and amplification in the cochlea.
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- School of Pharmacy and Biomolecular Sci - Professor of Neurobiology
- Centre for Stress and Age-Related Disease
- Sensory Neuroscience Research and Enterprise Group