Ciliary bundles of striolar hair cells: are they mechanically specialized

Cotton, John, Silverman, Jen, Peterson, Ellengene and Grant, Wally (2000) Ciliary bundles of striolar hair cells: are they mechanically specialized. Twenty-Third Annual Midwinter Meeting of the Association for Research in Otolaryngology, St. Petersburg Beach, USA. 01 Feb 2000.

Abstract

Vertebrate otolith organs have a specialized region of neuroepithelium, the striola, which is reported to differ from non-striolar regions in a variety of ways including hair cell structure. The functional significance of this specialization is largely unknown. We are addressing this question by analyzing the mechanical characteristics of striolar hair cells in a turtle, P. scripta, using quantitative anatomy of fixed and living bundles combined with computational models of ciliary bundle mechanics. This report describes some structural features of striolar bundles, compares them with the dominant population of extrastriolar bundles, and addresses the mechanical significance of these differences. Ciliary bundles in the striola differ in several ways from bundles in the extra-striolar cotillus (a large, relatively homogeneous area that accounts for 65-75% of the utricular neuroepithelium). Striolar bundles have more stereocilia (75-150 vs. 30-60), and stereocilia form more circular arrays (10 columns of 5-10 stereocilia vs. 5 columns of 9-10 stereocilia). Kinocilia on striolar bundles are shorter (approx. 10 µm vs.15 µm). Stereocilia lengths on striolar bundles fall into two groups: from shortest to longest they (1) increase linearly from 2-5 µm or (2) increase exponentially from 5-10 µm. Stereocilia in the non-striolar cotillus increase linearly from 2-5 µm. These structural differences suggest that bundles in the striola may have different mechanical properties than bundles in the extrastriolar cotillus, but the nature of these differences and their functional significance is unclear. Our computational models suggest that striolar and extra-striolar bundles have distinctive patterns of tip-link tensions across the bundle during deflection and different deformation configurations. Furthermore, striolar bundles with tall stereocilia are approximately an order of magnitude stiffer than the bundles in the non-striolar cotillus (5000 to 10,000 pN/µm vs. 100 to 200 pN/µm), suggesting that higher forces are required to deflect these bundles. Thus, striolar bundles may be specialized for signaling a distinctive range of stimulus intensities.

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