Cochlear Outer Hair Cell Motility

Normal hearing depends on sound amplification within the mammalian cochlea. The amplification, without which the auditory system is effectively deaf, can be traced to the correct functioning of a group of motile sensory hair cells, the outer hair cells of the cochlea. Acting like motor cells, outer hair cells produce forces that are driven by graded changes in membrane potential. The forces depend on the presence of a motor protein in the lateral membrane of the cells. This protein, known as prestin, is a member of a transporter superfamily SLC26. The functional and structural properties of prestin are described in this review. Whether outer hair cell motility might account for sound amplification at all frequencies is also a critical question and is reviewed here.

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Passive compliance and active force generation in the guinea pig outer hair cell

Journal of Neurophysiology ◽

10.1152/jn.1995.74.6.2319 ◽

1995 ◽

Vol 74 (6) ◽

pp. 2319-2328 ◽

Cited By ~ 60

Author(s):

R. Hallworth

Keyword(s):

Hair Cell ◽

Cell Motility ◽

Hair Cells ◽

Outer Hair Cell ◽

Outer Hair Cells ◽

Force Generation ◽

Axial Stiffness ◽

Sinusoidal Voltage ◽

Apparent Stiffness ◽

Outer Hair Cell Motility

1. Cochlear outer hair cells 20-80 microns in length were compressed axially in vitro using calibrated glass fibers mounted on a piezoelectric actuator. 2. When driven by rectangular pulses in the compression direction, the motion of the fiber tip consisted of a rapid initial compression that was complete in 10-20 ms followed by a smaller compression of slower time course. 3. The initial fiber deflections were found to be linear in amplitude for compressions up to 400 nm. The axial compliances of outer hair cells were calculated from the difference between the fiber tip motions when unattached and when in contact with a cell. Axial compliances were found to be in the range of 0.04-1.2 km/N for 149 cells. The axial compliance was an increasing function of cell length. 4. The peak forces generated by electrically stimulated outer hair cells were measured from the deflection of a glass fiber when the cells were stimulated by sinusoidal voltage commands. The slope gains of force generation (force generated per mV of command at the cell membrane) were estimated to range from 0.01 to 100 pN/mV. Most of the results fell in the range of 0.1-20 pN/mV. 5. When the apparent stiffness of the fiber was increased by moving the cell closer to the fiber base, the peak amplitude of the fiber deflection generated by the cell decreased and the peak force increased, for the same sinusoidal voltage command. 6. The results of the previous experiment were interpreted in the light of a model of outer hair cell motility in which an ideal extension generating element is in series with an internal stiffness element. This internal stiffness was then calculated for 13 cells. 7. The internal stiffnesses of cells calculated by the above procedure were found to be positively correlated with the axial stiffness measurements obtained for the same cells. 8. The implications of the above results for the effectiveness of outer hair cell motility in vivo are discussed.

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Modeling the Mechanics of Tethers Pulled From the Cochlear Outer Hair Cell Membrane

Journal of Biomechanical Engineering ◽

10.1115/1.2907758 ◽

2008 ◽

Vol 130 (3) ◽

Cited By ~ 6

Author(s):

Kristopher R. Schumacher ◽

Aleksander S. Popel ◽

Bahman Anvari ◽

William E. Brownell ◽

Alexander A. Spector

Keyword(s):

Cell Membrane ◽

Hair Cell ◽

Outer Hair Cell ◽

Lateral Wall ◽

Outer Hair Cells ◽

The Body ◽

Computational Method ◽

Membrane Properties ◽

Bending Modulus ◽

Sound Amplification

Cell membrane tethers are formed naturally (e.g., in leukocyte rolling) and experimentally to probe membrane properties. In cochlear outer hair cells, the plasma membrane is part of the trilayer lateral wall, where the membrane is attached to the cytoskeleton by a system of radial pillars. The mechanics of these cells is important to the sound amplification and frequency selectivity of the ear. We present a modeling study to simulate the membrane deflection, bending, and interaction with the cytoskeleton in the outer hair cell tether pulling experiment. In our analysis, three regions of the membrane are considered: the body of a cylindrical tether, the area where the membrane is attached and interacts with the cytoskeleton, and the transition region between the two. By using a computational method, we found the shape of the membrane in all three regions over a range of tether lengths and forces observed in experiments. We also analyze the effects of biophysical properties of the membrane, including the bending modulus and the forces of the membrane adhesion to the cytoskeleton. The model’s results provide a better understanding of the mechanics of tethers pulled from cell membranes.

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