8 results on '"Kathryn D. Breneman"'
Search Results
2. Hair cell bundles: flexoelectric motors of the inner ear.
- Author
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Kathryn D Breneman, William E Brownell, and Richard D Rabbitt
- Subjects
Medicine ,Science - Abstract
Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the "cochlear amplifier" in mammals.
- Published
- 2009
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3. Dynamic Displacement of Normal and Detached Semicircular Canal Cupula
- Author
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Stephen M. Highstein, Richard Boyle, Curtis King, Angela M. Yamauchi, Richard D. Rabbitt, and Kathryn D. Breneman
- Subjects
Time Factors ,Endolymph ,Motion Perception ,Action Potentials ,Article ,inner ear micromechanics ,Afferent Neurons ,Motion ,03 medical and health sciences ,0302 clinical medicine ,Physical Stimulation ,Afferent ,medicine ,Animals ,Craniocerebral Trauma ,Humans ,Neurons, Afferent ,030304 developmental biology ,Vestibular system ,0303 health sciences ,vestibular ,cupula regeneration ,Semicircular canal ,Chemistry ,Time constant ,Relaxation process ,Anatomy ,Batrachoidiformes ,Adaptation, Physiological ,Semicircular Canals ,Sensory Systems ,angular motion sensation ,medicine.anatomical_structure ,Otorhinolaryngology ,sense organs ,afferent response dynamics ,Displacement (fluid) ,030217 neurology & neurosurgery - Abstract
The dynamic displacement of the semicircular canal cupula and modulation of afferent nerve discharge were measured simultaneously in response to physiological stimuli in vivo. The adaptation time constant(s) of normal cupulae in response to step stimuli averaged 36 s, corresponding to a mechanical lower corner frequency for sinusoidal stimuli of 0.0044 Hz. For stimuli equivalent to 40–200 deg/s of angular head velocity, the displacement gain of the central region of the cupula averaged 53 nm per deg/s. Afferents adapted more rapidly than the cupula, demonstrating the presence of a relaxation process that contributes significantly to the neural representation of angular head motions by the discharge patterns of canal afferent neurons. We also investigated changes in time constants of the cupula and afferents following detachment of the cupula at its apex—mechanical detachment that occurs in response to excessive transcupular endolymph pressure. Detached cupulae exhibited sharply reduced adaptation time constants (300 ms–3 s, n = 3) and can be explained by endolymph flowing rapidly over the apex of the cupula. Partially detached cupulae reattached and normal afferent discharge patterns were recovered 5–7 h following detachment. This regeneration process may have relevance to the recovery of semicircular canal function following head trauma.
- Published
- 2009
4. Hair cell bundles: flexoelectric motors of the inner ear
- Author
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William E. Brownell, Kathryn D. Breneman, and Richard D. Rabbitt
- Subjects
Biophysics/Theory and Simulation ,Cochlear amplifier ,Stereocilia (inner ear) ,Science ,Flexoelectricity ,Models, Biological ,Otolaryngology ,03 medical and health sciences ,0302 clinical medicine ,Biophysics/Macromolecular Assemblies and Machines ,Hair Cells, Auditory ,Molecular motor ,medicine ,otorhinolaryngologic diseases ,Animals ,Inner ear ,Neuroscience/Theoretical Neuroscience ,Mechanical energy ,030304 developmental biology ,Physics ,0303 health sciences ,Multidisciplinary ,Neuroscience/Sensory Systems ,Computational Biology ,Anatomy ,medicine.anatomical_structure ,Ecology/Physiological Ecology ,Ear, Inner ,Biophysics ,Medicine ,Mechanosensitive channels ,Hair cell ,sense organs ,030217 neurology & neurosurgery ,Research Article - Abstract
Microvilli (stereocilia) projecting from the apex of hair cells in the inner ear are actively motile structures that feed energy into the vibration of the inner ear and enhance sensitivity to sound. The biophysical mechanism underlying the hair bundle motor is unknown. In this study, we examined a membrane flexoelectric origin for active movements in stereocilia and conclude that it is likely to be an important contributor to mechanical power output by hair bundles. We formulated a realistic biophysical model of stereocilia incorporating stereocilia dimensions, the known flexoelectric coefficient of lipid membranes, mechanical compliance, and fluid drag. Electrical power enters the stereocilia through displacement sensitive ion channels and, due to the small diameter of stereocilia, is converted to useful mechanical power output by flexoelectricity. This motor augments molecular motors associated with the mechanosensitive apparatus itself that have been described previously. The model reveals stereocilia to be highly efficient and fast flexoelectric motors that capture the energy in the extracellular electro-chemical potential of the inner ear to generate mechanical power output. The power analysis provides an explanation for the correlation between stereocilia height and the tonotopic organization of hearing organs. Further, results suggest that flexoelectricity may be essential to the exquisite sensitivity and frequency selectivity of non-mammalian hearing organs at high auditory frequencies, and may contribute to the "cochlear amplifier" in mammals.
- Published
- 2009
5. Piezo- and Flexoelectric Membrane Materials Underlie Fast Biological Motors in the Inner Ear
- Author
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Kathryn D. Breneman and Richard D. Rabbitt
- Subjects
Membrane potential ,Materials science ,Efferent ,Stereocilia (inner ear) ,Nanotechnology ,Article ,Membrane ,medicine.anatomical_structure ,Bundle ,otorhinolaryngologic diseases ,medicine ,Biophysics ,Inner ear ,sense organs ,Hair cell ,Cochlea - Abstract
The mammalian inner ear is remarkably sensitive to quiet sounds, exhibits over 100dB dynamic range, and has the exquisite ability to discriminate closely spaced tones even in the presence of noise. This performance is achieved, in part, through active mechanical amplification of vibrations by sensory hair cells within the inner ear. All hair cells are endowed with a bundle of motile microvilli, stereocilia, located at the apical end of the cell, and the more specialized outer hair cells (OHC's) are also endowed with somatic electromotility responsible for changes in cell length in response to perturbations in membrane potential. Both hair bundle and somatic motors are known to feed energy into the mechanical vibrations in the inner ear. The biophysical origin and relative significance of the motors remains a subject of intense research. Several biological motors have been identified in hair cells that might underlie the motor(s), including a cousin of the classical ATP driven actin-myosin motor found in skeletal muscle. Hydrolysis of ATP, however, is much too slow to be viable at audio frequencies on a cycle-by-cycle basis. Heuristically, the OHC somatic motor behaves as if the OHC lateral wall membrane were a piezoelectric material and the hair bundle motor behaves as if the plasma membrane were a flexoelectric material. We propose these observations from a continuum materials perspective are literally true. To examine this idea, we formulated mathematical models of the OHC lateral wall “piezoelectric” motor and the more ubiquitous “flexoelectric” hair bundle motor. Plausible biophysical mechanisms underlying piezo- and flexoelectircity were established. Model predictions were compared extensively to the available data. The models were then applied to study the power conversion efficiency of the motors. Results show that the material properties of the complex membranes in hair cells provide them with the ability to convert electrical power available in the inner ear cochlea into useful mechanical amplification of sound induced vibrations at auditory frequencies. We also examined how hair cell amplification might be controlled by the brain through efferent synaptic contacts on hair cells and found a simple mechanism to tune hearing to signals of interest to the listener by electrical control of these motors.
- Published
- 2009
6. Ionic Composition of Endolymph and Perilymph in the Inner Ear of the Oyster Toadfish, Opsanus tau
- Author
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H. Mack Brown, Tamer A. Ghanem, Kathryn D. Breneman, and Richard D. Rabbitt
- Subjects
Oyster toadfish ,medicine.medical_specialty ,Endolymph ,Mechanoelectrical transduction ,Perilymph ,Ionic composition ,Article ,Opsanus ,Internal medicine ,medicine ,otorhinolaryngologic diseases ,Animals ,Inner ear ,Ions ,Physiological function ,biology ,biology.organism_classification ,Batrachoidiformes ,medicine.anatomical_structure ,Endocrinology ,Ear, Inner ,sense organs ,General Agricultural and Biological Sciences ,Nuclear chemistry - Abstract
The concentrations of free Na+, K+, Ca(+, and Cl(-)in endolymph and perilymph from the inner ear of the oyster toadfish, Opsanus tau, were measured in vivo using double-barreled ion-selective electrodes. Perilymph concentrations were similar to those measured in other species, while endolymph concentrations were similar to those measured previously in elasmobranch fish, though significantly different from concentrations reported in mammals. Perilymph concentrations (mean +/- std. dev.) were as follows: Na+, 129 mmol l(-1) +/- 20; K+, 4.96 mmol l(-1) +/- 2.67; Ca2+, 1.83 mmol l(-1) +/- 0.27; and Cl(-), 171 mmol l(-1) +/- 20. Saccular endolymph concentrations were Na+, 166 mmol l(-1) +/- 22; K+, 51.4 mmol l(-1) +/- 16.7; Ca2+, 2.88 mmol l(-1) +/- 0.27; and Cl(-), 170 mmol l(-1) +/- 12; and semicircular canal (utricular vestibule) endolymph concentrations were Na+, 122 mmol l(-1) +/- 15; K+, 47.7 mmol l(-1) +/- 13.2; Ca2+, 1.78 mmol l(-1) +/- 0.48; Cl(-), 176 mmol l(-1) +/- 27. The relatively high concentrations of Ca2+ and Na+ in the endolymph may have significant implications for the physiological function of the mechanoelectrical transduction channels in the vestibular hair cells of fish compared to those of their mammalian counterparts.
- Published
- 2008
7. Development of a reinforced porcine elastin composite vascular scaffold
- Author
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Sean J. Kirkpatrick, Ping Cheng Wu, Zhen Ren, Monica T. Hinds, David W. Courtman, Kenton W. Gregory, Jeffrey S. Teach, Rebecca C. Rowe, and Kathryn D. Breneman
- Subjects
Scaffold ,Materials science ,Swine ,Biomedical Engineering ,Thrombogenicity ,Biocompatible Materials ,Fibrin ,Biomaterials ,Blood vessel prosthesis ,Ultimate tensile strength ,Intestine, Small ,medicine ,Animals ,biology ,Metals and Alloys ,Biomaterial ,Blood Vessel Prosthesis ,Elastin ,medicine.anatomical_structure ,Carotid Arteries ,cardiovascular system ,Ceramics and Composites ,biology.protein ,Artery ,Biomedical engineering - Abstract
Elastin, a principal structural component of na- tive arteries, has distinct biological and mechanical advan- tages when used as a biomaterial; however, its low ultimate tensile strength has limited its use as an arterial conduit. We have developed a scaffold, consisting of a purified elastin tubular conduit strengthened with fibrin bonded layers of acellular small intestinal submucosa (aSIS) for potential use as a small diameter vascular graft. The addition of aSIS increased the ultimate tensile strength of the elastin conduits nine-fold. Burst pressures for the elastin composite vascular scaffold (1396 309 mmHg) were significantly higher than pure elastin conduits (162 36 mmHg) and comparable to native saphenous veins. The average suture pullout strength of the elastin composite vascular scaffolds was 14.612 3.677 N, significantly higher than the pure elastin conduit (0.402 0.098 N), but comparable to native porcine carotid arteries (13.994 4.344 N). Cyclic circumferential strain testing indicated that the composite scaffolds were capable of withstanding physiological loading conditions for at least 83 h. Implantation of the elastin composites as carotid inter- position grafts in swine demonstrated its superiority to clin- ically acceptable ePTFE with significantly longer average patency times of 5.23 h compared to 4.15 h. We have devel- oped a biologically based elastin scaffold with suitable me- chanical properties and low thrombogenicity for in vivo implantation, and with the potential for cellular repopula- tion and host integration reestablishing an appropriate elas- tic artery. © 2006 Wiley Periodicals, Inc. J Biomed Mater Res 77A: 458 - 469, 2006
- Published
- 2006
8. The Passive Cable Properties of Hair Cell Stereocilia and Their Contribution to Somatic Capacitance Measurements
- Author
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Richard D. Rabbitt, Kathryn D. Breneman, Richard Boyle, and Stephen M. Highstein
- Subjects
Patch-Clamp Techniques ,Models, Neurological ,Intracellular Space ,Biophysics ,Biophysical Theory and Modeling ,Biology ,Electric Capacitance ,Capacitance ,Membrane Potentials ,Hair Cells, Vestibular ,03 medical and health sciences ,0302 clinical medicine ,Stereocilium tip ,Chinchilla ,Hair Cells, Auditory ,Electric Impedance ,medicine ,otorhinolaryngologic diseases ,Animals ,Computer Simulation ,Cilia ,Vestibular Hair Cell ,030304 developmental biology ,0303 health sciences ,Stereocilium ,Stereocilia ,Anatomy ,Turtles ,medicine.anatomical_structure ,Transducer ,Hair cell ,sense organs ,Algorithms ,030217 neurology & neurosurgery - Abstract
Somatic measurements of whole-cell capacitance are routinely used to understand physiologic events occurring in remote portions of cells. These studies often assume the intracellular space is voltage-clamped. We questioned this assumption in auditory and vestibular hair cells with respect to their stereocilia based on earlier studies showing that neurons, with radial dimensions similar to stereocilia, are not always isopotential under voltage-clamp. To explore this, we modeled the stereocilia as passive cables with transduction channels located at their tips. We found that the input capacitance measured at the soma changes when the transduction channels at the tips of the stereocilia are open compared to when the channels are closed. The maximum capacitance is felt with the transducer closed but will decrease as the transducer opens due to a length-dependent voltage drop along the stereocilium length. This potential drop is proportional to the intracellular resistance and stereocilium tip conductance and can produce a maximum capacitance error on the order of fF for single stereocilia and pF for the bundle.
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