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Dehghani-Ghahnaviyeh S, Zhao Z, Tajkhorshid E. Lipid-mediated prestin organization in outer hair cell membranes and its implications in sound amplification. Nat Commun 2022; 13:6877. [PMID: 36371434 PMCID: PMC9653410 DOI: 10.1038/s41467-022-34596-9] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2022] [Accepted: 10/28/2022] [Indexed: 11/13/2022] Open
Abstract
Prestin is a high-density motor protein in the outer hair cells (OHCs), whose conformational response to acoustic signals alters the shape of the cell, thereby playing a major role in sound amplification by the cochlea. Despite recent structures, prestin's intimate interactions with the membrane, which are central to its function remained unresolved. Here, employing a large set (collectively, more than 0.5 ms) of coarse-grained molecular dynamics simulations, we demonstrate the impact of prestin's lipid-protein interactions on its organization at densities relevant to the OHCs and its effectiveness in reshaping OHCs. Prestin causes anisotropic membrane deformation, which mediates a preferential membrane organization of prestin where deformation patterns by neighboring copies are aligned constructively. The resulting reduced membrane rigidity is hypothesized to maximize the impact of prestin on OHC reshaping. These results demonstrate a clear case of protein-protein cooperative communication in membrane, purely mediated by interactions with lipids.
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Affiliation(s)
- Sepehr Dehghani-Ghahnaviyeh
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
| | - Zhiyu Zhao
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
| | - Emad Tajkhorshid
- grid.35403.310000 0004 1936 9991Theoretical and Computational Biophysics Group, NIH Center for Macromolecular Modeling and Bioinformatics, Beckman Institute for Advanced Science and Technology, Department of Biochemistry, and Center for Biophysics and Quantitative Biology, University of Illinois at Urbana-Champaign, Urbana, IL USA
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2
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Rabbitt RD. Analysis of outer hair cell electromechanics reveals power delivery at the upper-frequency limits of hearing. J R Soc Interface 2022; 19:20220139. [PMID: 35673856 PMCID: PMC9174718 DOI: 10.1098/rsif.2022.0139] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2022] [Accepted: 05/11/2022] [Indexed: 11/12/2022] Open
Abstract
Outer hair cells are the cellular motors in the mammalian inner ear responsible for sensitive high-frequency hearing. Motor function over the frequency range of human hearing requires expression of the protein prestin in the OHC lateral membrane, which imparts piezoelectric properties to the cell membrane. In the present report, electrical power consumption and mechanical power output of the OHC membrane-motor complex are determined using previously published voltage-clamp data from isolated OHCs and membrane patches. Results reveal that power output peaks at a best frequency much higher than implied by the low-pass character of nonlinear capacitance, and much higher than the whole-cell resistive-capacitive corner frequency. High frequency power output is enabled by a -90° shift in the phase of electrical charge displacement in the membrane, manifested electrically as emergence of imaginary-valued nonlinear capacitance.
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Affiliation(s)
- Richard D. Rabbitt
- Biomedical Engineering, Otolaryngology, and Neuroscience Program, University of Utah, 36 S. Wasatch Drive, SMBB 3100, Salt Lake City, UT 84112, USA
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3
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Galassi VV, Wilke N. On the Coupling between Mechanical Properties and Electrostatics in Biological Membranes. MEMBRANES 2021; 11:478. [PMID: 34203412 PMCID: PMC8306103 DOI: 10.3390/membranes11070478] [Citation(s) in RCA: 20] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 06/18/2021] [Accepted: 06/22/2021] [Indexed: 12/24/2022]
Abstract
Cell membrane structure is proposed as a lipid matrix with embedded proteins, and thus, their emerging mechanical and electrostatic properties are commanded by lipid behavior and their interconnection with the included and absorbed proteins, cytoskeleton, extracellular matrix and ionic media. Structures formed by lipids are soft, dynamic and viscoelastic, and their properties depend on the lipid composition and on the general conditions, such as temperature, pH, ionic strength and electrostatic potentials. The dielectric constant of the apolar region of the lipid bilayer contrasts with that of the polar region, which also differs from the aqueous milieu, and these changes happen in the nanometer scale. Besides, an important percentage of the lipids are anionic, and the rest are dipoles or higher multipoles, and the polar regions are highly hydrated, with these water molecules forming an active part of the membrane. Therefore, electric fields (both, internal and external) affects membrane thickness, density, tension and curvature, and conversely, mechanical deformations modify membrane electrostatics. As a consequence, interfacial electrostatics appears as a highly important parameter, affecting the membrane properties in general and mechanical features in particular. In this review we focus on the electromechanical behavior of lipid and cell membranes, the physicochemical origin and the biological implications, with emphasis in signal propagation in nerve cells.
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Affiliation(s)
- Vanesa Viviana Galassi
- Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza M5500, Argentina;
- Instituto Interdisciplinario de Ciencias Básicas (ICB), Universidad Nacional de Cuyo, CONICET, Mendoza M5500, Argentina
| | - Natalia Wilke
- Departamento de Química Biológica Ranwel Caputto, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Córdoba X5000HUA, Argentina
- Centro de Investigaciones en Química Biológica de Córdoba (CIQUIBIC), Universidad Nacional de Córdoba, CONICET, Córdoba X5000HUA, Argentina
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4
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Pietak A, Levin M. Bioelectrical control of positional information in development and regeneration: A review of conceptual and computational advances. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2018; 137:52-68. [PMID: 29626560 PMCID: PMC10464501 DOI: 10.1016/j.pbiomolbio.2018.03.008] [Citation(s) in RCA: 28] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2018] [Revised: 03/23/2018] [Accepted: 03/26/2018] [Indexed: 12/16/2022]
Abstract
Positional information describes pre-patterns of morphogenetic substances that alter spatio-temporal gene expression to instruct development of growth and form. A wealth of recent data indicate bioelectrical properties, such as the transmembrane potential (Vmem), are involved as instructive signals in the spatiotemporal regulation of morphogenesis. However, the mechanistic relationships between Vmem and molecular positional information are only beginning to be understood. Recent advances in computational modeling are assisting in the development of comprehensive frameworks for mechanistically understanding how endogenous bioelectricity can guide anatomy in a broad range of systems. Vmem represents an extraordinarily strong electric field (∼1.0 × 106 V/m) active over the thin expanse of the plasma membrane, with the capacity to influence a variety of downstream molecular signaling cascades. Moreover, in multicellular networks, intercellular coupling facilitated by gap junction channels may induce directed, electrodiffusive transport of charged molecules between cells of the network to generate new positional information patterning possibilities and characteristics. Given the demonstrated role of Vmem in morphogenesis, here we review current understanding of how Vmem can integrate with molecular regulatory networks to control single cell state, and the unique properties bioelectricity adds to transport phenomena in gap junction-coupled cell networks to facilitate self-assembly of morphogen gradients and other patterns. Understanding how Vmem integrates with biochemical regulatory networks at the level of a single cell, and mechanisms through which Vmem shapes molecular positional information in multicellular networks, are essential for a deep understanding of body plan control in development, regeneration and disease.
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Affiliation(s)
| | - Michael Levin
- Allen Discovery Center at Tufts, USA; Center for Regenerative and Developmental Biology, Tufts University, Medford, MA, USA
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Levin M, Pezzulo G, Finkelstein JM. Endogenous Bioelectric Signaling Networks: Exploiting Voltage Gradients for Control of Growth and Form. Annu Rev Biomed Eng 2017; 19:353-387. [PMID: 28633567 PMCID: PMC10478168 DOI: 10.1146/annurev-bioeng-071114-040647] [Citation(s) in RCA: 142] [Impact Index Per Article: 20.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Living systems exhibit remarkable abilities to self-assemble, regenerate, and remodel complex shapes. How cellular networks construct and repair specific anatomical outcomes is an open question at the heart of the next-generation science of bioengineering. Developmental bioelectricity is an exciting emerging discipline that exploits endogenous bioelectric signaling among many cell types to regulate pattern formation. We provide a brief overview of this field, review recent data in which bioelectricity is used to control patterning in a range of model systems, and describe the molecular tools being used to probe the role of bioelectrics in the dynamic control of complex anatomy. We suggest that quantitative strategies recently developed to infer semantic content and information processing from ionic activity in the brain might provide important clues to cracking the bioelectric code. Gaining control of the mechanisms by which large-scale shape is regulated in vivo will drive transformative advances in bioengineering, regenerative medicine, and synthetic morphology, and could be used to therapeutically address birth defects, traumatic injury, and cancer.
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Affiliation(s)
- Michael Levin
- Biology Department, Tufts University, Medford, Massachusetts 02155-4243;
- Allen Discovery Center, Tufts University, Medford, Massachusetts 02155;
| | - Giovanni Pezzulo
- Institute of Cognitive Sciences and Technologies, National Research Council, Rome 00185, Italy;
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Brownell WE. What Is Electromotility? -The History of Its Discovery and Its Relevance to Acoustics. ACOUSTICS TODAY 2017; 13:20-27. [PMID: 29051713 PMCID: PMC5645053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Subscribe] [Scholar Register] [Indexed: 06/07/2023]
Abstract
Experiments on an inner ear sensory cell revealed that it converts electrical energy directly into mechanical energy at acoustic frequencies.
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Affiliation(s)
- William E Brownell
- Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA
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7
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Membrane prestin expression correlates with the magnitude of prestin-associated charge movement. Hear Res 2016; 339:50-9. [PMID: 27262187 DOI: 10.1016/j.heares.2016.05.016] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/21/2016] [Revised: 05/14/2016] [Accepted: 05/26/2016] [Indexed: 11/20/2022]
Abstract
Full expression of electromotility, generation of non-linear capacitance (NLC), and high-acuity mammalian hearing require prestin function in the lateral wall of cochlear outer hair cells (OHCs). Estimates of the number of prestin molecules in the OHC membrane vary, and a consensus has not emerged about the correlation between prestin expression and prestin-associated charge movement in the OHC. Using an inducible prestin-expressing cell line, we demonstrate that the charge density, but not the voltage at peak capacitance, directly correlates with the amount of prestin in the plasma membrane. This correlation is evident in studies involving a controlled increase of prestin expression with time after induction and inducer dose-response. Conversely, membrane prestin levels and charge density gradually decline together following the reduction of prestin levels from a steady state by removal of the inducer. Thus, charge density directly correlates with the level of membrane prestin expression, whereas changing membrane levels of prestin have no effect on the voltage at peak capacitance in this inducible prestin-expressing cell line.
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8
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Teudt IU, Richter CP. Basilar membrane and tectorial membrane stiffness in the CBA/CaJ mouse. J Assoc Res Otolaryngol 2014; 15:675-94. [PMID: 24865766 PMCID: PMC4164692 DOI: 10.1007/s10162-014-0463-y] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2012] [Accepted: 05/07/2014] [Indexed: 10/25/2022] Open
Abstract
The mouse has become an important animal model in understanding cochlear function. Structures, such as the tectorial membrane or hair cells, have been changed by gene manipulation, and the resulting effect on cochlear function has been studied. To contrast those findings, physical properties of the basilar membrane (BM) and tectorial membrane (TM) in mice without gene mutation are of great importance. Using the hemicochlea of CBA/CaJ mice, we have demonstrated that tectorial membrane (TM) and basilar membrane (BM) revealed a stiffness gradient along the cochlea. While a simple spring mass resonator predicts the change in the characteristic frequency of the BM, the spring mass model does not predict the frequency change along the TM. Plateau stiffness values of the TM were 0.6 ± 0.5, 0.2 ± 0.1, and 0.09 ± 0.09 N/m for the basal, middle, and upper turns, respectively. The BM plateau stiffness values were 3.7 ± 2.2, 1.2 ± 1.2, and 0.5 ± 0.5 N/m for the basal, middle, and upper turns, respectively. Estimations of the TM Young's modulus (in kPa) revealed 24.3 ± 25.2 for the basal turns, 5.1 ± 4.5 for the middle turns, and 1.9 ± 1.6 for the apical turns. Young's modulus determined at the BM pectinate zone was 76.8 ± 72, 23.9 ± 30.6, and 9.4 ± 6.2 kPa for the basal, middle, and apical turns, respectively. The reported stiffness values of the CBA/CaJ mouse TM and BM provide basic data for the physical properties of its organ of Corti.
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Affiliation(s)
- I. U. Teudt
- />Department of Otolaryngology—Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Searle Building 12-561; 303 East Chicago Avenue, 60611-3008 Chicago, IL USA
- />Department of Otolaryngology—Head and Neck Surgery, University Clinic Hamburg-Eppendorf, Hamburg, Germany
- />Department of Otolaryngology—Head and Neck Surgery, Asklepios Clinic Altona, Hamburg, Germany
| | - C. P. Richter
- />Department of Otolaryngology—Head and Neck Surgery, Feinberg School of Medicine, Northwestern University, Searle Building 12-561; 303 East Chicago Avenue, 60611-3008 Chicago, IL USA
- />Department of Biomedical Engineering, Northwestern University, Evanston, IL USA
- />Hugh Knowles Center, Department of Communication Sciences and Disorders, Northwestern University, Evanston, IL USA
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Mustard J, Levin M. Bioelectrical Mechanisms for Programming Growth and Form: Taming Physiological Networks for Soft Body Robotics. Soft Robot 2014. [DOI: 10.1089/soro.2014.0011] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Affiliation(s)
- Jessica Mustard
- Department of Biology and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts
| | - Michael Levin
- Department of Biology and Center for Regenerative and Developmental Biology, Tufts University, Medford, Massachusetts
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Levin M. Reprogramming cells and tissue patterning via bioelectrical pathways: molecular mechanisms and biomedical opportunities. WILEY INTERDISCIPLINARY REVIEWS. SYSTEMS BIOLOGY AND MEDICINE 2013; 5:657-76. [PMID: 23897652 PMCID: PMC3841289 DOI: 10.1002/wsbm.1236] [Citation(s) in RCA: 79] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Revised: 05/16/2013] [Accepted: 06/21/2013] [Indexed: 12/17/2022]
Abstract
Transformative impact in regenerative medicine requires more than the reprogramming of individual cells: advances in repair strategies for birth defects or injuries, tumor normalization, and the construction of bioengineered organs and tissues all require the ability to control large-scale anatomical shape. Much recent work has focused on the transcriptional and biochemical regulation of cell behavior and morphogenesis. However, exciting new data reveal that bioelectrical properties of cells and their microenvironment exert a profound influence on cell differentiation, proliferation, and migration. Ion channels and pumps expressed in all cells, not just excitable nerve and muscle, establish resting potentials that vary across tissues and change with significant developmental events. Most importantly, the spatiotemporal gradients of these endogenous transmembrane voltage potentials (Vmem ) serve as instructive patterning cues for large-scale anatomy, providing organ identity, positional information, and prepattern template cues for morphogenesis. New genetic and pharmacological techniques for molecular modulation of bioelectric gradients in vivo have revealed the ability to initiate complex organogenesis, change tissue identity, and trigger regeneration of whole vertebrate appendages. A large segment of the spatial information processing that orchestrates individual cells' programs toward the anatomical needs of the host organism is electrical; this blurs the line between memory and decision-making in neural networks and morphogenesis in nonneural tissues. Advances in cracking this bioelectric code will enable the rational reprogramming of shape in whole tissues and organs, revolutionizing regenerative medicine, developmental biology, and synthetic bioengineering.
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Affiliation(s)
- Michael Levin
- Tufts University, Department of Biology and Tufts Center for Regenerative and Developmental Biology, 200 Boston Ave., Suite 4600, Medford, MA 02155
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11
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Abstract
This composite article is intended to give the experts in the field of cochlear mechanics an opportunity to voice their personal opinion on the one mechanism they believe dominates cochlear amplification in mammals. A collection of these ideas are presented here for the auditory community and others interested in the cochlear amplifier. Each expert has given their own personal view on the topic and at the end of their commentary they have suggested several experiments that would be required for the decisive mechanism underlying the cochlear amplifier. These experiments are presently lacking but if successfully performed would have an enormous impact on our understanding of the cochlear amplifier.
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12
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Brownell WE, Qian F, Anvari B. Cell membrane tethers generate mechanical force in response to electrical stimulation. Biophys J 2010; 99:845-52. [PMID: 20682262 PMCID: PMC3297770 DOI: 10.1016/j.bpj.2010.05.025] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2009] [Revised: 03/25/2010] [Accepted: 05/10/2010] [Indexed: 11/22/2022] Open
Abstract
Living cells maintain a huge transmembrane electric field across their membranes. This electric field exerts a force on the membrane because the membrane surfaces are highly charged. We have measured electromechanical force generation by cell membranes using optically trapped beads to detach the plasma membrane from the cytoskeleton and form long thin cylinders (tethers). Hyperpolarizing potentials increased and depolarizing potentials decreased the force required to pull a tether. The membrane tether force in response to sinusoidal voltage signals was a function of holding potential, tether diameter, and tether length. Membrane electromechanical force production can occur at speeds exceeding those of ATP-based protein motors. By harnessing the energy in the transmembrane electric field, cell membranes may contribute to processes as diverse as outer hair cell electromotility, ion channel gating, and transport.
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Affiliation(s)
- William E Brownell
- Bobby R. Alford Department of Otolaryngology, Head & Neck Surgery, and Department of Neuroscience, Baylor College of Medicine, Houston, Texas, USA.
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Harland B, Brownell WE, Spector AA, Sun SX. Voltage-induced bending and electromechanical coupling in lipid bilayers. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2010; 81:031907. [PMID: 20365770 DOI: 10.1103/physreve.81.031907] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/02/2009] [Revised: 01/19/2010] [Indexed: 05/29/2023]
Abstract
The electrical properties of the cellular membrane are important for ion transport across cells and electrophysiology. Plasma membranes also resist bending and stretching, and mechanical properties of the membrane influence cell shape and forces in membrane tethers pulled from cells. There exists a coupling between the electrical and mechanical properties of the membrane. Previous work has shown that applied voltages can induce forces and movements in the lipid bilayer. We present a theory that computes membrane bending deformations and forces as the applied voltage is changed. We discover that electromechanical coupling in lipid bilayers depends on the voltage-dependent adsorption of ions into the region occupied by the phospholipid head groups. A simple model of counter-ion absorption is investigated. We show that electromechanical coupling can be measured using membrane tethers and we use our model to predict the membrane tether tension as a function of applied voltage. We also discuss how electromechanical coupling in membranes may influence transmembrane protein function.
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Affiliation(s)
- Ben Harland
- Department of Mechanical Engineering, The Johns Hopkins University, Baltimore, Maryland 21218, USA
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14
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The passive cable properties of hair cell stereocilia and their contribution to somatic capacitance measurements. Biophys J 2010; 96:1-8. [PMID: 18849411 DOI: 10.1529/biophysj.108.137356] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2008] [Accepted: 08/27/2008] [Indexed: 11/18/2022] Open
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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Brownell WE. WITHDRAWN: Membrane-based amplification in hearing. Hear Res 2009:S0378-5955(09)00240-8. [PMID: 19818390 PMCID: PMC2888686 DOI: 10.1016/j.heares.2009.09.016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/23/2009] [Accepted: 09/30/2009] [Indexed: 10/20/2022]
Abstract
This article has been withdrawn at the request of the author(s) and/or editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at http://www.elsevier.com/locate/withdrawalpolicy.
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Affiliation(s)
- William E Brownell
- Bobby R. Alford Department of Otolaryngology - Head & Neck Surgery, Baylor College of Medicine, Houston, TX, USA
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16
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Schumacher KR, Popel AS, Anvari B, Brownell WE, Spector AA. Computational analysis of the tether-pulling experiment to probe plasma membrane-cytoskeleton interaction in cells. PHYSICAL REVIEW. E, STATISTICAL, NONLINEAR, AND SOFT MATTER PHYSICS 2009; 80:041905. [PMID: 19905340 PMCID: PMC4990357 DOI: 10.1103/physreve.80.041905] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/09/2008] [Revised: 06/09/2009] [Indexed: 05/28/2023]
Abstract
Tethers are thin membrane tubes that can be formed when relatively small and localized forces are applied to cellular membranes and lipid bilayers. Tether pulling experiments have been used to better understand the fine membrane properties. These include the interaction between the plasma membrane and the underlying cytoskeleton, which is an important factor affecting membrane mechanics. We use a computational method aimed at the interpretation and design of tether pulling experiments in cells with a strong membrane-cytoskeleton attachment. In our model, we take into account the detailed information in the topology of bonds connecting the plasma membrane and the cytoskeleton. We compute the force-dependent piecewise membrane deflection and bending as well as modes of stored energy in three major regions of the system: body of the tether, membrane-cytoskeleton attachment zone, and the transition zone between the two. We apply our method to three cells: cochlear outer hair cells (OHCs), human embryonic kidney (HEK) cells, and Chinese hamster ovary (CHO) cells. OHCs have a special system of pillars connecting the membrane and the cytoskeleton, and HEK and CHO cells have the membrane-cytoskeleton adhesion arrangement via bonds (e.g., PIP2), which is common to many other cells. We also present a validation of our model by using experimental data on CHO and HEK cells. The proposed method can be an effective tool in the analyses of experiments to probe the properties of cellular membranes.
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Affiliation(s)
| | - Aleksander S. Popel
- Department of Biomedical Engineering, Johns Hopkins
University, Baltimore, Maryland 21205, USA
| | - Bahman Anvari
- Department of Bioengineering, University of
California-Riverside, Riverside, California 92521, USA
| | - William E. Brownell
- Bobby R. Alford Department of Otolaryngology – Head
and Neck Surgery, Baylor College of Medicine, Houston, Texas 77030, USA
| | - Alexander A. Spector
- Department of Biomedical Engineering, Johns Hopkins
University, Baltimore, Maryland 21205, USA
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17
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Sachs F, Brownell WE, Petrov AG. Membrane Electromechanics in Biology, with a Focus on Hearing. MRS BULLETIN 2009; 34:665. [PMID: 20165559 PMCID: PMC2822359 DOI: 10.1557/mrs2009.178] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
Cells are ion conductive gels surrounded by a ~5-nm-thick insulating membrane, and molecular ionic pumps in the membrane establish an internal potential of approximately -90 mV. This electrical energy store is used for high-speed communication in nerve and muscle and other cells. Nature also has used this electric field for high-speed motor activity, most notably in the ear, where transduction and detection can function as high as 120 kHz. In the ear, there are two sets of sensory cells: the "inner hair cells" that generate an electrical output to the nervous system and the more numerous "outer hair cells" that use electromotility to counteract viscosity and thus sharpen resonance to improve frequency resolution. Nature, in a remarkable exhibition of nanomechanics, has made out of soft, aqueous materials a microphone and high-speed decoder capable of functioning at 120 kHz, limited only by thermal noise. Both physics and biology are only now becoming aware of the material properties of biomembranes and their ability to perform work and sense the environment. We anticipate new examples of this biopiezoelectricity will be forthcoming.
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18
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Okoruwa OE, Weston MD, Sanjeevi DC, Millemon AR, Fritzsch B, Hallworth R, Beisel KW. Evolutionary insights into the unique electromotility motor of mammalian outer hair cells. Evol Dev 2008; 10:300-15. [PMID: 18460092 DOI: 10.1111/j.1525-142x.2008.00239.x] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Prestin (SLC26A5) is the molecular motor responsible for cochlear amplification by mammalian cochlea outer hair cells and has the unique combined properties of energy-independent motility, voltage sensitivity, and speed of cellular shape change. The ion transporter capability, typical of SLC26A members, was exchanged for electromotility function and is a newly derived feature of the therian cochlea. A putative minimal essential motif for the electromotility motor (meEM) was identified through the amalgamation of comparative genomic, evolution, and structural diversification approaches. Comparisons were done among nonmammalian vertebrates, eutherian mammalian species, and the opossum and platypus. The opossum and platypus SLC26A5 proteins were comparable to the eutherian consensus sequence. Suggested from the point-accepted mutation analysis, the meEM motif spans all the transmembrane segments and represented residues 66-503. Within the eutherian clade, the meEM was highly conserved with a substitution frequency of only 39/7497 (0.5%) residues, compared with 5.7% in SLC26A4 and 12.8% in SLC26A6 genes. Clade-specific substitutions were not observed and there was no sequence correlation with low or high hearing frequency specialists. We were able to identify that within the highly conserved meEM motif two regions, which are unique to all therian species, appear to be the most derived features in the SLC26A5 peptide.
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Affiliation(s)
- Oseremen E Okoruwa
- Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE 68178, USA
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Abstract
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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Affiliation(s)
- Jonathan Ashmore
- Department of Physiology and UCL Ear Institute, University College London, London, United Kingdom.
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Drexl M, Lagarde MMM, Zuo J, Lukashkin AN, Russell IJ. The role of prestin in the generation of electrically evoked otoacoustic emissions in mice. J Neurophysiol 2008; 99:1607-15. [PMID: 18234980 DOI: 10.1152/jn.01216.2007] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Electrically evoked otoacoustic emissions are sounds emitted from the inner ear when alternating current is injected into the cochlea. Their temporal structure consists of short- and long-delay components and they have been attributed to the motile responses of the sensory-motor outer hair cells of the cochlea. The nature of these motile responses is unresolved and may depend on either somatic motility, hair bundle motility, or both. The short-delay component persists after almost complete elimination of outer hair cells. Outer hair cells are thus not the sole generators of electrically evoked otoacoustic emissions. We used prestin knockout mice, in which the motor protein prestin is absent from the lateral walls of outer hair cells, and Tecta(Delta ENT/Delta ENT) mice, in which the tectorial membrane, a structure with which the hair bundles of outer hair cells normally interact, is vestigial and completely detached from the organ of Corti. The amplitudes and delay spectra of electrically evoked otoacoustic emissions from Tecta(Delta ENT/Delta ENT) and Tecta(+/+) mice are very similar. In comparison with prestin(+/+) mice, however, the short-delay component of the emission in prestin(-/-) mice is dramatically reduced and the long-delay component is completely absent. Emissions are completely suppressed in wild-type and Tecta(Delta ENT/Delta ENT) mice at low stimulus levels, when prestin-based motility is blocked by salicylate. We conclude that near threshold, the emissions are generated by prestin-based somatic motility.
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Affiliation(s)
- Markus Drexl
- University of Sussex, School of Life Sciences, Brighton, UK
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21
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Jensen-Smith H, Hallworth R. Lateral wall protein content mediates alterations in cochlear outer hair cell mechanics before and after hearing onset. ACTA ACUST UNITED AC 2007; 64:705-17. [PMID: 17615570 PMCID: PMC1992524 DOI: 10.1002/cm.20217] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Specialized outer hair cells (OHCs) housed within the mammalian cochlea exhibit active, nonlinear, mechanical responses to auditory stimulation termed electromotility. The extraordinary frequency resolution capacity of the cochlea requires an exquisitely equilibrated mechanical system of sensory and supporting cells. OHC electromotile length change, stiffness, and force generation are responsible for a 100-fold increase in hearing sensitivity by augmenting vibrational input to non-motile sensory inner hair cells. Characterization of OHC mechanics is crucial for understanding and ultimately preventing permanent functional deficits due to overstimulation or as a consequence of various cochlear pathologies. The OHCs' major structural assembly is a highly-specialized lateral wall. The lateral wall consists of three structures; a plasma membrane highly-enriched with the motor-protein prestin, an actin-spectrin cortical lattice, and one or more layers of subsurface cisternae. Technical difficulties in independently manipulating each lateral wall constituent have constrained previous attempts to analyze the determinants of OHCs' mechanical properties. Temporal separations in the accumulation of each lateral wall constituent during postnatal development permit associations between lateral wall structure and OHC mechanics. We compared developing and adult gerbil OHC axial stiffness using calibrated glass fibers. Alterations in each lateral wall component and OHC stiffness were correlated as a function of age. Reduced F-actin labeling was correlated with reduced OHC stiffness before hearing onset. Prestin incorporation into the PM was correlated with increased OHC stiffness at hearing onset. Our data indicate lateral wall F-actin and prestin are the primary determinants of OHC mechanical properties before and after hearing onset, respectively.
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Affiliation(s)
- Heather Jensen-Smith
- Department of Biomedical Sciences, Creighton University, Omaha, Nebraska 68178, USA.
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