Mechanical Analysis of Hair Cell Microstructure and Motility

Steele, Charles R.; Jen, D. H.

doi:10.1007/978-1-4684-5640-0_8

Cited by 3 publications

(2 citation statements)

References 17 publications

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“…Increased intracellular calcium (entering the hair cell in its apical region) could trigger reactions within or interactions among these proteins to increase stereocilia stiffness. It has recently been suggested that the elastic modulus of F-actin in the stereocilia may be increased directly by calcium ions (34), and if this occurs it would stiffen the hair bundles. It is also possible that intracellular calcium activates contractile proteins in the cuticular plate which pull on the rootlet of the sensory hairs and stiffen them (35).…”

Section: Discussionmentioning

confidence: 99%

Intra- and extracellular calcium modulates stereocilia stiffness on chick cochlear hair cells.

Pae

Saunders

1994

Proc. Natl. Acad. Sci. U.S.A.

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Segments of the chick basilar papilla were isolated and maintained in culture medium. The sensory hair bundle of individual hair cells was observed with light microscopy and stimulated with a water microjet at 600 Hz. Hair bundle motion was slowed by illuminating the microscope with stroboscopic light, and water jet intensity was systematically varied in decibel (dB) steps until a visual detection level (VDL) threshold of hair bundle motion was achieved. The VDL threshold of many hair cells was measured in each isolated papilla. However, only one of eight extracellular calcium concentrations (0.0, 0.0001, 0.001, 0.01, 0.1, 1.25, 6.0, and 12.0 mM) was used with each papilla. In a second series, a calcium ionophore (ionomycin) was added to the culture medium, and VDL thresholds were again measured at seven of these extracellular calcium concentrations. With extracellular calcium alone, the stimulus level needed to achieve threshold was reduced by 2.73 dB between 0.1 and 0.01 mM. This change in threshold represented a 1.37-fold decrease in hair bundle stiffness. When ionomycin was added to the culture medium, a progressively greater stimulus intensity was needed to achieve threshold as calcium concentration increased. The 11.7-dB increase in threshold, with the addition of ionomycin, between 0.0001 and 6.0 mM extracellular calcium was equivalent to a 3.85-fold increase in bundle stiffness. These large changes in hair-bundle stiffness, as a function of the extra-or intracellular calcium environment, may play an important role in the micromechanical behavior of the hair cell during sound simulation.

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Section: Discussionmentioning

confidence: 99%

Intra- and extracellular calcium modulates stereocilia stiffness on chick cochlear hair cells.

Pae

Saunders

1994

Proc. Natl. Acad. Sci. U.S.A.

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“…The same concern calls into question the role of the outer hair cells in the generation of otoacoustic emissions particularly when some stimulated otoacoustic emissions have been measured in response to acoustic stimulation well below the threshold for hearing (Wilson, 1979;Zwicker & Manley, 1981). The movements of isolated outer hair cells are governed by the mechanical properties of the outer hair cell and the electromotile forcegenerating mechanism (Steele & Jen, 1988). The transfer af force and the resulting movements of the cochlear partition will be determined by its mechanical properties.…”

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confidence: 99%

Outer Hair Cell Electromotility and Otoacoustic Emissions

1990

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Outer hair cell electromotility is a rapid, force generating, length change in response to electrical stimulation. DC electrical pulses either elongate or shorten the cell and sinusoidal electrical stimulation results in mechanical oscillations at acoustic frequencies. The mechanism underlying outer hair cell electromotility is thought to be the origin of spontaneous otoacoustic emissions. The ability of the cell to change its length requires that it be mechanically flexible. At the same time the structural integrity of the organ of Corti requires that the cell possess considerable compressive rigidity along its major axis. Evolution appears to have arrived at novel solutions to the mechanical requirements imposed on the outer hair cell. Segregation of cytoskeletal elements in specific intracellular domains facilitates the rapid movements. Compressive strength is provided by a unique hydraulic skeleton in which a positive hydrostatic pressure in the cytoplasm stabilizes a flexible elastic cortex with circumferential tensile strength. Cell turgor is required in order that the pressure gradients associated with the electromotile response can be communicated to the ends of the cell. A loss in turgor leads to loss of outer hair cell electromotility. Concentrations of salicylate equivalent to those that abolish spontaneous otoacoustic emissions in patients weaken the outer hair cell's hydraulic skeleton. There is a significant diminution in the electromotile response associated with the loss in cell turgor. Aspirin's effect on outer hair cell electromotility attests to the role of the outer hair cell in generating otoacoustic emissions and demonstrates how their physiology can influence the propagation of otoacoustic emissions. THERE HAS BEEN a dramatic change in our understanding of the biophysics of the mammalian inner ear over the past decade. The concept of the cochlea as a passive organ that converts the mechanical vibrations of sound into neural energy has been altered by the startling finding that outer hair cells possess a unique electromotile capacity (Brownell, 1983 ;1984 ;Brownell, Bader, Bertrand, & de Ribaupierre, 1985). The electromotility appears to be responsible for the cochlea's surprising ability to generate sound (Kemp, 1978; see also other articles in this issue). The hearing science community now accepts the presence of otoacoustic emissions after nearly a decade of experimental confirmation. Skepticism from the more general sensory science community is understandable. The fact that the ear can make sound is, at one level, equivalent to the eye producing light or the nose expelling odors. Energy conversion in both directions (bidirectional transduction) appears unique to hearing and is thought to contribute to the remarkable sensitivity and exquisite frequency selectivity of mammalian hearing. This contribution is discussed below in a brief review of the evidence implicating outer hair cells in generating otoacoustic emissions. The physiological characteristics of outer hair cell electro...

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Elastic Behavior of the Outer Hair Cell Wall

Steele

1990

Lecture Notes in Biomathematics

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Mechanical Analysis of Hair Cell Microstructure and Motility

Cited by 3 publications

References 17 publications

Intra- and extracellular calcium modulates stereocilia stiffness on chick cochlear hair cells.

Intra- and extracellular calcium modulates stereocilia stiffness on chick cochlear hair cells.

Outer Hair Cell Electromotility and Otoacoustic Emissions

Elastic Behavior of the Outer Hair Cell Wall

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