Outer hair cell length changes in an external electric field. II. The role of electrokinetic forces on the cell surface

Abstract The effect of an external electric field on the absorption and the double fluorescence of 4-cyano-N,N-dimethylaniline can be understood, taking into account reaction field induced polarizability effects. If a TICT state conformation emits the a-fiuorescence in dioxane, the permanent dipole moment in this state is only slightly larger than in the equilibrium ground state.

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Effectiveness, Active Energy Produced by Molecular Motors, and Nonlinear Capacitance of the Cochlear Outer Hair Cell

Journal of Biomechanical Engineering ◽

10.1115/1.1894233 ◽

2005 ◽

Vol 127 (3) ◽

pp. 391-399 ◽

Cited By ~ 5

Author(s):

Alexander A. Spector

Keyword(s):

Hair Cell ◽

Molecular Motors ◽

Outer Hair Cell ◽

Molecular Motor ◽

Force Production ◽

Outer Hair Cells ◽

Nonlinear Capacitance ◽

Effective Capacitance ◽

Capacitive Properties ◽

Length Changes

Cochlear outer hair cells are crucial for active hearing. These cells have a unique form of motility, named electromotility, whose main features are the cell’s length changes, active force production, and nonlinear capacitance. The molecular motor, prestin, that drives outer hair cell electromotility has recently been identified. We reveal relationships between the active energy produced by the outer hair cell molecular motors, motor effectiveness, and the capacitive properties of the cell membrane. We quantitatively characterize these relationships by introducing three characteristics: effective capacitance, zero-strain capacitance, and zero-resultant capacitance. We show that zero-strain capacitance is smaller than zero-resultant capacitance, and that the effective capacitance is between the two. It was also found that the differences between the introduced capacitive characteristics can be expressed in terms of the active energy produced by the cell’s molecular motors. The effectiveness of the cell and its molecular motors is introduced as the ratio of the motors’ active energy to the energy of the externally applied electric field. It is shown that the effectiveness is proportional to the difference between zero-strain and zero-resultant capacitance. We analyze the cell and motor’s effectiveness within a broad range of cellular parameters and estimate it to be within a range of 12%–30%.

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The role of outer hair cell motility in cochlear tuning

Current Opinion in Neurobiology ◽

10.1016/0959-4388(91)90081-h ◽

1991 ◽

Vol 1 (2) ◽

pp. 215-220 ◽

Cited By ~ 56

Author(s):

Peter Dallos ◽

M.Elizabeth Corey

Keyword(s):

Hair Cell ◽

Cell Motility ◽

Outer Hair Cell ◽

Outer Hair Cell Motility ◽

Cochlear Tuning

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Sound-Evoked Length Changes of the Outer Hair Cell Stereocilia Bundle are Modulated by Endocochlear Currents

10.1063/1.3658056 ◽

2011 ◽

Author(s):

Pierre Hakizimana ◽

William E. Brownell ◽

Stefan Jacob ◽

Anders Fridberger ◽

Christopher A. Shera ◽

...

Keyword(s):

Hair Cell ◽

Outer Hair Cell ◽

Length Changes

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Theory of electrically driven shape changes of cochlear outer hair cells

Journal of Neurophysiology ◽

10.1152/jn.1993.70.1.299 ◽

1993 ◽

Vol 70 (1) ◽

pp. 299-323 ◽

Cited By ~ 86

Author(s):

P. Dallos ◽

R. Hallworth ◽

B. N. Evans

Keyword(s):

Cell Membrane ◽

Hair Cell ◽

Outer Hair Cell ◽

Linear Motor ◽

Outer Hair Cells ◽

Pressure Effects ◽

Model Parameters ◽

Minor Importance ◽

Length Changes ◽

Shape Changes

1. A theory of cochlear outer hair cell electromotility is developed and specifically applied to somatic shape changes elicited in a microchamber. The microchamber permits the arbitrary electrical and mechanical partitioning of the outer hair cell along its length. This means that the two partitioned segments are stimulated with different input voltages and undergo different shape changes. Consequently, by imposing more constraints than other methods, experiments in the microchamber are particularly suitable for testing different theories of outer hair cell motility. 2. The present model is based on simple hypotheses. They include a distributed motor associated with the cell membrane or cortex and the assumption that the displacement generated by the motor is related to the transmembrane voltage across the associated membrane element. It is expected that the force generated by the motor is counterbalanced by an elastic restoring force indigenous to the cell membrane and cortex, and a tensile force due to intracellular pressure. It is assumed that all changes take place while total cell volume is conserved. The above elements of the theory taken together permit the development of qualitative and quantitative predictions about the expected motile responses of both partitioned segments of the cell. Only a DC treatment is offered here. 3. Both a linear motor and an expanded treatment that incorporates a stochastic molecular motor model are considered. The latter is represented by a two-state Boltzmann process. We show that the linear motor treatment is an appropriate extrapolation of the stochastic motor theory for the case of small voltage driving signals. Comparison of experimental results with model responses permits the estimation of model parameters. Good match of data is obtained if it is assumed that the molecular motors undergo conformational length changes of 0.7-1.0 nm, that they have an effective displacement vector at approximately -20 degrees with the long axis of the cell, and that their linear density is approximately 80/microns. 4. An effort is made to parcel out motile response components that are a direct consequence of the motor action from those that are mediated by cytoplasmic pressure changes brought about by the concerted action of the motors. We show that pressure effects are of minor importance, and thus rule out models that rely on radial constriction/expansion-mediated internal pressure change as the primary cause of longitudinal motility. 5. As a consequence of the interaction between the Boltzmann process and the mechanical characteristics of the cell, the electromotile response is asymmetric.(ABSTRACT TRUNCATED AT 400 WORDS)

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Characterization of cochlear outer hair cell turgor

AJP Cell Physiology ◽

10.1152/ajpcell.1994.266.2.c467 ◽

1994 ◽

Vol 266 (2) ◽

pp. C467-C479 ◽

Cited By ~ 44

Author(s):

M. E. Chertoff ◽

W. E. Brownell

Keyword(s):

Hair Cell ◽

Outer Hair Cell ◽

Elastic Shell ◽

Structural Features ◽

Continuous Increase ◽

Cell Turgor ◽

Intracellular Pressure

The cochlear outer hair cell (OHC) is a cylindrical cell with structural features suggestive of a hydraulic skeleton, i.e., an elastic shell with a positive internal pressure. This study characterizes the role of the OHC elevated cytoplasmic pressure in maintaining the cell shape. Intracellular pressure of OHCs from guinea pig is estimated by measuring changes in cell morphology in response to increasing or decreasing osmolarity. Cells collapse when subjected to a continuous increase in osmolarity. Collapse occurs at an average of 8 mosM above the standard medium, suggesting that normal cells have an effective intracellular pressure of 128 mmHg. Fewer cells collapse when exposed to slow rates of osmolarity increase than cells exposed to fast rates of osmolarity increase, although the final change in osmolarity in the perfusion chamber is similar. Furthermore, cells undergo a slow, spontaneous increase in volume on exposure to either no osmolarity change or slow rates of osmolarity increase, suggesting that the cell's internal osmolarity increases in vitro. After volume reduction or elevation, cells do not return to their initial volume.

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