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Steady-state stiffness of utricular hair cells depends on macular location and hair bundle structure.

Abstract

Spatial and temporal properties of head movement are encoded by vestibular hair cells in the inner ear. One of the most striking features of these receptors is the orderly structural variation in their mechanoreceptive hair bundles, but the functional significance of this diversity is poorly understood. We tested the hypothesis that hair bundle structure is a significant contributor to hair bundle mechanics by comparing structure and steady-state stiffness of 73 hair bundles at varying locations on the utricular macula. Our first major finding is that stiffness of utricular hair bundles varies systematically with macular locus. Stiffness values are highest in the striola, near the line of hair bundle polarity reversal, and decline exponentially toward the medial extrastriola. Striolar bundles are significantly more stiff than those in medial (median: 8.9 μN/m) and lateral (2.0 μN/m) extrastriolae. Within the striola, bundle stiffness is greatest in zone 2 (106.4 μN/m), a band of type II hair cells, and significantly less in zone 3 (30.6 μN/m), which contains the only type I hair cells in the macula. Bathing bundles in media that break interciliary links produced changes in bundle stiffness with predictable time course and magnitude, suggesting that links were intact in our standard media and contributed normally to bundle stiffness during measurements. Our second major finding is that bundle structure is a significant predictor of steady-state stiffness: the heights of kinocilia and the tallest stereocilia are the most important determinants of bundle stiffness. Our results suggest 1) a functional interpretation of bundle height variability in vertebrate vestibular organs, 2) a role for the striola in detecting onset of head movement, and 3) the hypothesis that differences in bundle stiffness contribute to diversity in afferent response dynamics.

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  • Authors

    Spoon C, Moravec WJ, Rowe MH, Grant JW, Peterson EH

    Institution

    Department of Engineering Science and Mechanics, Virginia Tech, Blacksburg, Virginia, USA.

    Source

    Journal of neurophysiology 106:6 2011 Dec pg 2950-63

    MeSH

    Animals
    Biomechanics
    Chelating Agents
    Cilia
    Egtazic Acid
    Female
    Hair Cells, Vestibular
    Male
    Mechanotransduction, Cellular
    Models, Biological
    Regression (Psychology)
    Saccule and Utricle
    Subtilisin
    Turtles

    Pub Type(s)

    In Vitro
    Journal Article
    Research Support, N.I.H., Extramural

    Language

    eng

    PubMed ID

    21918003