Elsevier

Hearing Research

Volume 6, Issue 3, April 1982, Pages 277-289
Hearing Research

Preservation and visualization of actin-containing filaments in the apical zone of cochlear sensory cells

https://doi.org/10.1016/0378-5955(82)90060-0Get rights and content

Abstract

The fine filamentous structure in the apical zone of cochlear sensory cells of the guinea pig was investigated under transmission electron microscopy (TEM) using various fixation methods. The true form of this structure, which is that of a dense core of sensory hairs and cuticular plates containing hair rootlets, has been hitherto unknown because of the selectively destructive effect of ordinary fixatives. We revealed the fine filamentous structure in great detail by fixing the specimens in tannic acid or by the modified glutaraldehyde-osmium fixation method, which can preserve actin filaments during the procedures required to prepare the specimen for TEM. The filamentous structure gives the impression of a negatively stained image when prepared in this way. Filaments were packed regularly and tightly into dense cores which projected down deep into the cuticular plate as hair rootlets. Cross-striations were seen at intervals of 360 ± 28 Å along the packed filaments, a distance which is comparable to the periodicity of an actin paracrystal. The overall diameter of each filament was 83 Å. In fact, the structure of dense cores and hair rootlets proved to be composed of actin paracrystals, probably containing some regulatory proteins. Cross-sectioned actin filaments in the paracrystal were arranged in an extremely regular hexagonal pattern. The characteristic filamentous texture in the cuticular plate was best seen in tissues that were pretreated with EDTA, and then fixed by tannic acid. It is probable that the greater part of the cuticular plate is composed of actin filaments and actin monomers, both containing Ca2+-dependent regulatory proteins. Utilizing the above ultrastructural findings, some functional models of this zone are proposed.

References (32)

  • Å. Flock et al.

    Studies on the sensory hairs of receptor cells in the inner ear

    Acta Otolaryngol.

    (1977)
  • J. Hanson

    Evidence from electron microscope studies on actin paracrystals concerning the origin of the cross-striation in the thin filaments of vertebrate skeletal muscle

  • B.E. Hull et al.

    The terminal web

    J. Cell Biol.

    (1979)
  • H. Ishikawa et al.

    Formation of arrowhead complexes with heavy meromyosin in a variety of cell types

    J. Cell Biol.

    (1969)
  • H. Ishikawa

    Identification and distribution of intracellular filaments

  • M. Itoh et al.

    Structure of the hair rootlets on cochlear sensory cells by tannic acid fixation

    Acta Otolaryngol.

    (1980)
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