Mechanical properties and consequences of the stereocilia and the extracellular links in the vestibular hair bundle

¹ Virginia Tech
² Ohio University

^* To whom correspondence should be addressed. E-mail: jcotton{at}vt.edu.

Submitted on May 19, 2005
Revised on July 26, 2005
Accepted on 5 December 2005

	Abstract

While knowledge of the fine structure of vestibular hair bundles is increasing, the mechanical properties and functional significance of those structures remain unclear. In 2004, Bashtanov et al. reported the contribution of different extracellular links to bundle stiffness. We simulated Bashtanov's experimental protocol using a 3-D finite element bundle model with geometry measured from a typical striolar hair cell. Unlike any previous models, we consider separately two types of horizontal links: shaft links (SL) and upper lateral links (UL). Our most important results are as follows. First, we identified the material properties required to match Bashtanov's experiment: stereocilia Young's modulus of 0.74 GPa, tip link assembly (gating spring) stiffness of 5300 pN/µm, and the combined stiffness of shaft links binding two adjacent stereocilia of 750~2250 pN/µm. Second, we conclude that ULs are likely to have non-linear mechanical properties: they have minimal stiffness during small bundle deformations but stiffen as the bundle deflects further. Third, we estimated the stiffness of the gating spring based on our realistic 3-D bundle model rather than a conventional model relying on the parallel arrangement assumption. Our predicted stiffness of the gating spring was greater than the previous estimation.

Key Words: Hair cell, extracellular links, finite element, stiffness, tip link

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