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Greenstreet L, Afanassiev A, Kijima Y, Heitz M, Ishiguro S, King S, Yachie N, Schiebinger G. DNA-GPS: A theoretical framework for optics-free spatial genomics and synthesis of current methods. Cell Syst 2023; 14:844-859.e4. [PMID: 37751737 DOI: 10.1016/j.cels.2023.08.005] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2022] [Revised: 04/19/2023] [Accepted: 08/25/2023] [Indexed: 09/28/2023]
Abstract
While single-cell sequencing technologies provide unprecedented insights into genomic profiles at the cellular level, they lose the spatial context of cells. Over the past decade, diverse spatial transcriptomics and multi-omics technologies have been developed to analyze molecular profiles of tissues. In this article, we categorize current spatial genomics technologies into three classes: optical imaging, positional indexing, and mathematical cartography. We discuss trade-offs in resolution and scale, identify limitations, and highlight synergies between existing single-cell and spatial genomics methods. Further, we propose DNA-GPS (global positioning system), a theoretical framework for large-scale optics-free spatial genomics that combines ideas from mathematical cartography and positional indexing. DNA-GPS has the potential to achieve scalable spatial genomics for multiple measurement modalities, and by eliminating the need for optical measurement, it has the potential to position cells in three-dimensions (3D).
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Affiliation(s)
- Laura Greenstreet
- Department of Mathematics, The University of British Columbia, Vancouver, BC, Canada
| | - Anton Afanassiev
- Department of Mathematics, The University of British Columbia, Vancouver, BC, Canada
| | - Yusuke Kijima
- School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada; Department of Aquatic Bioscience, The University of Tokyo, Tokyo, Japan
| | - Matthieu Heitz
- Department of Mathematics, The University of British Columbia, Vancouver, BC, Canada
| | - Soh Ishiguro
- School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada
| | - Samuel King
- School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada
| | - Nozomu Yachie
- School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada; Research Center for Advanced Science and Technology, The University of Tokyo, Tokyo, Japan; Premium Research Institute for Human Metaverse Medicine (WPI-PRIMe), Osaka University, Suita, Osaka, Japan; Graduate School of Media and Governance, Keio University, Fujisawa, Japan.
| | - Geoffrey Schiebinger
- Department of Mathematics, The University of British Columbia, Vancouver, BC, Canada; School of Biomedical Engineering, The University of British Columbia, Vancouver, BC, Canada.
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2
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Abstract
BACKGROUND The pathologic changes that occur as a result of diabetic microangiopathy have been well described for the kidneys and the eyes. Although many studies suggest an association between diabetes mellitus and hearing loss, the pathologic changes in the cochlea in association with the diabetic state remain to be clarified. AIM/OBJECTIVE The aim of this review is to determine the effects of diabetes mellitus on cochlear morphology. METHOD A comprehensive search for relevant articles was carried out on electronic databases of Ovid Medline, Ovid Medline in Process, PubMed, Ovid Embase,or Biosis Preview, The Cochrane Library, ISI Web of Science, and Scopus. Articles published in English between 1940 and June 2010 were eligible to be reviewed. Using predefined inclusion criteria, published articles on histologic changes occurring in the cochlea due to diabetes mellitus were selected and reviewed, and their findings were synthesized. RESULTS Changes were observed in the basement membrane of the capillaries of the stria vascularis and in the basilar membrane, which was remarkably thickened, giving rise to diabetic microangiopathy. Loss of spiral ganglion neurons, organ of Corti cells, and atrophic changes in the stria vascularis were varied and infrequent. CONCLUSION There seems to be variable vulnerability of different cochlear cell types to the DM state. Further studies are required to determine the factors responsible for the differences in the histopathologic observations of cochlear tissues.
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Cura AJ, Carruthers A. Role of monosaccharide transport proteins in carbohydrate assimilation, distribution, metabolism, and homeostasis. Compr Physiol 2013; 2:863-914. [PMID: 22943001 DOI: 10.1002/cphy.c110024] [Citation(s) in RCA: 96] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
The facilitated diffusion of glucose, galactose, fructose, urate, myoinositol, and dehydroascorbicacid in mammals is catalyzed by a family of 14 monosaccharide transport proteins called GLUTs. These transporters may be divided into three classes according to sequence similarity and function/substrate specificity. GLUT1 appears to be highly expressed in glycolytically active cells and has been coopted in vitamin C auxotrophs to maintain the redox state of the blood through transport of dehydroascorbate. Several GLUTs are definitive glucose/galactose transporters, GLUT2 and GLUT5 are physiologically important fructose transporters, GLUT9 appears to be a urate transporter while GLUT13 is a proton/myoinositol cotransporter. The physiologic substrates of some GLUTs remain to be established. The GLUTs are expressed in a tissue specific manner where affinity, specificity, and capacity for substrate transport are paramount for tissue function. Although great strides have been made in characterizing GLUT-catalyzed monosaccharide transport and mapping GLUT membrane topography and determinants of substrate specificity, a unifying model for GLUT structure and function remains elusive. The GLUTs play a major role in carbohydrate homeostasis and the redistribution of sugar-derived carbons among the various organ systems. This is accomplished through a multiplicity of GLUT-dependent glucose sensing and effector mechanisms that regulate monosaccharide ingestion, absorption,distribution, cellular transport and metabolism, and recovery/retention. Glucose transport and metabolism have coevolved in mammals to support cerebral glucose utilization.
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Affiliation(s)
- Anthony J Cura
- Department of Biochemistry & Molecular Pharmacology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
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Mistrík P, Daudet N, Morandell K, Ashmore JF. Mammalian prestin is a weak Cl⁻/HCO₃⁻ electrogenic antiporter. J Physiol 2012; 590:5597-610. [PMID: 22890707 DOI: 10.1113/jphysiol.2012.241448] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022] Open
Abstract
The lateral membrane of mammalian cochlear outer hair cells contains prestin, a protein which can act as a fast voltage-driven actuator responsible for electromotility and enhanced sensitivity to sound. The protein belongs to the SLC26 family of transporters whose members are characterised as able to exchange halides for SO(4)(2-) or HCO(3)(-) yet previous analyses of mammalian prestin have suggested that such exchange functions were minimal. Here anion transport is investigated both in guinea-pig outer hair cells (OHCs) and in an expression system where we employ a sensitive intracellular pH (pH(i)) probe, pHluorin, to report HCO(3)(-) transport and to monitor the small pH(i) changes observable in the cells. In the presence of extracellular HCO(3)(-), pH(i) recovered from an acid load 4 times faster in prestin-transfected cells. The acceleration required a chloride gradient established by reducing extracellular chloride to 2 mm. Similar results were also shown using BCECF as an alternative pH(i) sensor, but with recovery only found in those cells expressing prestin. Simultaneous electrophysiological recording of the transfected cells during bicarbonate exposure produced a shift in the reversal potential to more negative potentials, consistent with electrogenic transport. These data therefore suggest that prestin can act as a weak Cl(-)/HCO(3)(-) antiporter and it is proposed that, in addition to participating in wide band cochlear sound amplification, prestin may also be involved in the slow time scale (>10 s) phenomena where changes in cell stiffness and internal pressure have been implicated. The results show the importance of considering the effects of the endogenous bicarbonate buffering system in evaluating the function of prestin in cochlear outer hair cells.
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Affiliation(s)
- P Mistrík
- UCL Ear Institute, 332 Gray’s Inn Road, London WC1E 6BT, UK
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5
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He DZZ, Jia S, Sato T, Zuo J, Andrade LR, Riordan GP, Kachar B. Changes in plasma membrane structure and electromotile properties in prestin deficient outer hair cells. Cytoskeleton (Hoboken) 2010; 67:43-55. [PMID: 20169529 DOI: 10.1002/cm.20423] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Cochlear outer hair cells (OHCs) rapidly change their length and stiffness when their membrane potential is altered. Prestin, the motor protein for this electromotility, is present along the OHC lateral plasma membrane where there is a high density of intra-membrane protein particles (IMPs). However, it is not known to what extent prestin contributes to this unusual dense population of proteins and overall organization of the membrane to generate the unique electromechanical response of OHCs. We investigated the relationship of prestin with the IMPs, the underlying cortical cytoskeletal lattice, and electromotility in prestin-deficient mice. Using freeze-fracture, we observed a reduction in density and size of the IMPs that correlates with the reduction and absence of prestin in the heterozygous and homozygous mice, respectively. We also observed a reduction or absence of electromotility-related charge density, axial stiffness, and piezoelectric properties of the OHC. A comparison of the charge density with the number of IMPs suggests that prestin forms tetramers in the wild type but is likely to form lower number oligomers in the prestin-deficient OHCs from the heterozygous mice. Interestingly, the characteristic actin-based cortical cytoskeletal lattice that underlies the membrane is absent in the prestin-null OHCs, suggesting that prestin is also required for recruiting or maintaining the cortical cytoskeletal lattice. These results suggest that the majority of the IMPs are indeed prestin and that electrically evoked length and stiffness changes are interrelated and dependent on both prestin and on the cortical actin cytoskeletal lattice of the OHC lateral membrane.
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Affiliation(s)
- David Z Z He
- Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, Nebraska, USA.
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Sfondouris J, Rajagopalan L, Pereira FA, Brownell WE. Membrane composition modulates prestin-associated charge movement. J Biol Chem 2008; 283:22473-81. [PMID: 18567583 DOI: 10.1074/jbc.m803722200] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The lateral membrane of the cochlear outer hair cell (OHC) is the site of a membrane-based motor that powers OHC electromotility, enabling amplification and fine-tuning of auditory signals. The OHC membrane protein prestin plays a central role in this process. We have previously shown that membrane cholesterol modulates the peak voltage of prestin-associated nonlinear capacitance in vivo and in vitro. The present study explores the effects of membrane cholesterol and docosahexaenoic acid content on the peak and magnitude of prestin-associated charge movement in a human embryonic kidney (HEK 293) cell model. Increasing membrane cholesterol results in a hyperpolarizing shift in the peak voltage of the nonlinear capacitance (Vpkc) and a decrease in the total charge movement. Both measures depend linearly on membrane cholesterol concentration. Incubation of cholesterol-loaded cells in cholesterol-free media partially restores the Vpkc toward normal values but does not have a compensatory effect on the total charge movement. Decreasing membrane cholesterol results in a depolarizing shift in Vpkc that is restored toward normal values upon incubation in cholesterol-free media. However, cholesterol depletion does not alter the magnitude of charge movement. In contrast, increasing membrane docosahexaenoic acid results in a hyperpolarizing shift in Vpkc that is accompanied by an increase in total charge movement. Our results quantify the relation between membrane cholesterol concentration and prestin-associated charge movement and enhance our understanding of how membrane composition modulates prestin function.
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Affiliation(s)
- John Sfondouris
- Bobby R. Alford Department of Otolaryngology-Head and Neck Surgery, Baylor College of Medicine, Houston, Texas 77030, USA
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Wu X, Wang X, Gao J, Yu Y, Jia S, Zheng J, Dallos P, He DZZ, Cheatham M, Zuo J. Glucose transporter 5 is undetectable in outer hair cells and does not contribute to cochlear amplification. Brain Res 2008; 1210:20-8. [PMID: 18417103 DOI: 10.1016/j.brainres.2008.02.094] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Revised: 02/16/2008] [Accepted: 02/24/2008] [Indexed: 11/29/2022]
Abstract
Glucose transporter 5 (Glut5) is a high-affinity fructose transporter. It was proposed to be a motor protein or part of the motor complex required for cochlear amplification in outer hair cells (OHCs). Here we show that, in contrast to previous reports, Glut5 is undetectable, and possibly absent, in OHCs harvested from wildtype mice. Further, Glut5-deficient mice display normal OHC morphology and motor function (i.e., nonlinear capacitance and electromotility) and normal cochlear sensitivity and frequency selectivity. We conclude that Glut5 is not required for OHC motility or cochlear amplification.
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Affiliation(s)
- Xudong Wu
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN 38105, 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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9
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Mio K, Kubo Y, Ogura T, Yamamoto T, Arisaka F, Sato C. The motor protein prestin is a bullet-shaped molecule with inner cavities. J Biol Chem 2007; 283:1137-45. [PMID: 17998209 DOI: 10.1074/jbc.m702681200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Prestin is a transmembrane motor protein localized at the outer hair cells (OHCs) of the mammalian inner ear. Voltage-dependent conformational changes in prestin generate changes in the length of OHCs. A loss of prestin function is reported to induce severe auditory deficiencies, suggesting prestin-dependent changes of OHC length may be at least a part of cochlear amplification. Here we expressed the recombinant FLAG-fused prestin proteins in Sf9 cells and purified to particles of a uniform size in EM. The square-shaped top view of purified prestin, the binding of multiple anti-FLAG antibodies to each prestin particle, the native-PAGE analysis, and the much larger molecular weight obtained from size exclusion chromatography than the estimation for the monomer all support that prestin is a tetramer (Zheng, J., Du, G. G., Anderson, C. T., Keller, J. P., Orem, A., Dallos, P., and Cheatham, M. (2006) J. Biol. Chem. 281, 19916-19924). From negatively stained prestin particles, the three-dimensional structure was reconstructed at 2 nm resolution assuming 4-fold symmetry. Prestin is shown to be a bullet-shaped particle with a large cytoplasmic domain. The surface representation demonstrates indentations on the molecule, and the slice images indicate the inner cavities of sparse densities. The dimensions, 77 x 77 x 115 A, are consistent with the previously reported sizes of motor proteins on the surface of OHCs.
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Affiliation(s)
- Kazuhiro Mio
- Neuroscience Research Institute and Biological Information Research Center, National Institute of Advanced Industrial Science and Technology, Umezono 1-1-4, Tsukuba, Ibaraki 305-8568, Japan
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Rajagopalan L, Greeson JN, Xia A, Liu H, Sturm A, Raphael RM, Davidson AL, Oghalai JS, Pereira FA, Brownell WE. Tuning of the outer hair cell motor by membrane cholesterol. J Biol Chem 2007; 282:36659-70. [PMID: 17933870 DOI: 10.1074/jbc.m705078200] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Cholesterol affects diverse biological processes, in many cases by modulating the function of integral membrane proteins. We observed that alterations of cochlear cholesterol modulate hearing in mice. Mammalian hearing is powered by outer hair cell (OHC) electromotility, a membrane-based motor mechanism that resides in the OHC lateral wall. We show that membrane cholesterol decreases during maturation of OHCs. To study the effects of cholesterol on hearing at the molecular level, we altered cholesterol levels in the OHC wall, which contains the membrane protein prestin. We show a dynamic and reversible relationship between membrane cholesterol levels and voltage dependence of prestin-associated charge movement in both OHCs and prestin-transfected HEK 293 cells. Cholesterol levels also modulate the distribution of prestin within plasma membrane microdomains and affect prestin self-association in HEK 293 cells. These findings indicate that alterations in membrane cholesterol affect prestin function and functionally tune the outer hair cell.
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Affiliation(s)
- Lavanya Rajagopalan
- Bobby R. Alford Department of Otolaryngology-Head and Neck Surgery, Huffington Center on Aging and Molecular and Cellular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
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11
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Wu X, Currall B, Yamashita T, Parker LL, Hallworth R, Zuo J. Prestin-prestin and prestin-GLUT5 interactions in HEK293T cells. Dev Neurobiol 2007; 67:483-97. [PMID: 17443803 DOI: 10.1002/dneu.20357] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The remarkable hearing sensitivity and frequency selectivity in mammals is attributed to cochlear amplifier in the outer hair cells (OHCs). Prestin, a membrane protein in the lateral wall of OHC plasma membrane, is required for OHC electromotility and cochlear amplifier. In addition, GLUT5, a fructose transporter, is reported to be abundant in the plasma membrane of the OHC lateral wall and has been originally proposed as the OHC motor protein. Here we provide evidence of interactions between prestin/prestin and prestin/GLUT5 in transiently transfected HEK293T cells. We used a combination of techniques: (1) membrane colocalization by confocal microscopy, (2) fluorescence resonance energy transfer (FRET) by fluorescence activated cell sorting (FACS), (3) FRET by acceptor photobleaching, (4) FRET by fluorescence lifetime imaging (FRET-FLIM), and (5) coimmunoprecipitation. Our results suggest that homomeric and heteromeric prestin interactions occur in native OHCs to facilitate its electromotile function and that GLUT5 interacts with prestin for its elusive function.
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Affiliation(s)
- Xudong Wu
- Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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12
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Abe T, Kakehata S, Kitani R, Maruya SI, Navaratnam D, Santos-Sacchi J, Shinkawa H. Developmental expression of the outer hair cell motor prestin in the mouse. J Membr Biol 2007; 215:49-56. [PMID: 17415610 PMCID: PMC4154540 DOI: 10.1007/s00232-007-9004-5] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2006] [Accepted: 01/22/2007] [Indexed: 10/23/2022]
Abstract
The development of motor protein activity in the lateral membrane of the mouse outer hair cell (OHC) from postnatal day 5 (P5) to P18 was investigated under whole-cell voltage clamp. Voltage-dependent, nonlinear capacitance (C (v)), which represents the conformational fluctuations of the motor molecule, progressively increased during development. At P12, the onset of hearing in the mouse, C (v) was about 70% of the mature level. C (v) saturated at P18 when hearing shows full maturation. On the other hand, C (lin), which represents the membrane area of the OHC, showed a relatively small increase with development, reaching steady state at P10. This early maturation of linear capacitance is further supported by morphological estimates of surface area during development. These results, in light of recent prestin knockout experiments and our results with quantitative polymerase chain reaction, suggest that, rather than the incorporation of new motors into the lateral membrane after P10, molecular motors mature to augment nonlinear capacitance. Thus, current estimates of motor protein density based on charge movement may be exaggerated. A corresponding indicator of motor maturation, the motor's operating voltage midpoint, V (pkcm), tended to shift to depolarized potentials during postnatal development, although it was unstable prior to P10. However, after P14, V (pkcm) reached a steady-state level near -67 mV, suggesting that intrinsic membrane tension or intracellular chloride, each of which can modulate V (pkcm), may mature at P14. These developmental data significantly alter our understanding of the cellular mechanisms that control cochlear amplification and provide a foundation for future analysis of genetic modifications of mouse auditory development.
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Affiliation(s)
- Takahisa Abe
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Seiji Kakehata
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Rei Kitani
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Shin-ichiro Maruya
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
| | - Dhasakumar Navaratnam
- Department of Neurology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Joseph Santos-Sacchi
- Department of Otolaryngology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA
| | - Hideichi Shinkawa
- Department of Otorhinolaryngology, Hirosaki University School of Medicine, Hirosaki 036-8562, Japan
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13
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Abstract
Mechanosensory outer hair cells play an essential role in the amplification of sound-induced vibrations within the mammalian cochlea due to their ability to contract or elongate following changes of the intracellular potential. This unique property of outer hair cells is known as electromotility. Selective efferent innervation of these cells within the organ of Corti suggests that regulation of outer hair cell electromotility may be the primary function of the efferent control in the cochlea. A number of studies demonstrate that outer hair cell electromotility is indeed modulated by the efferent neurotransmitter, acetylcholine. The effects of acetylcholine on outer hair cells include cell hyperpolarization and a decrease of the axial stiffness, both mediated by intracellular Ca(2+). This article reviews these results and considers other potential mechanisms that may regulate electromotility, such as direct modification of the plasma membrane molecular motors, alteration of intracellular pressure, and modification of intracellular chloride concentration.
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Affiliation(s)
- Gregory I Frolenkov
- Department of Physiology, University of Kentucky, MS508, Chandler Medical Center, 800 Rose Street, Lexington, 40536, USA.
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14
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Murakoshi M, Gomi T, Iida K, Kumano S, Tsumoto K, Kumagai I, Ikeda K, Kobayashi T, Wada H. Imaging by atomic force microscopy of the plasma membrane of prestin-transfected Chinese hamster ovary cells. J Assoc Res Otolaryngol 2006; 7:267-78. [PMID: 16761115 PMCID: PMC2504612 DOI: 10.1007/s10162-006-0041-z] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2005] [Accepted: 04/26/2006] [Indexed: 11/27/2022] Open
Abstract
The high sensitivity of mammalian hearing is achieved by amplification of the motion of the cochlear partition. This cochlear amplification is thought to be generated by the elongation and contraction of outer hair cells (OHCs) in response to acoustical stimulation. This motility is made possible by a membrane protein embedded in the lateral membrane of OHCs. Although a fructose transporter, GLUT-5, was initially proposed to be this protein, a later study identified the gene of the motor protein distributed throughout the OHC plasma membrane. This protein has been named "prestin." However, although previous morphological studies by electron microscopy and atomic force microscopy (AFM) found the lateral wall of OHCs to be covered with 10-nm particles, believed to be motor proteins, it is unknown whether such particles consist only of prestin or are a complex of GLUT-5 and prestin molecules. To determine if the 10-nm particles are indeed constituted only of prestin, plasma membranes of prestin-transfected and untransfected Chinese hamster ovary (CHO) cells, which do not express GLUT-5, were observed by AFM. First, the cells attached to a substrate were sonicated so that only the plasma membrane remained on the substrate. The cytoplasmic face of the cell was observed by the tapping mode of the AFM in liquid. As a result, particle-like structures were recognized on the plasma membranes of both the prestin-transfected and untransfected CHO cells. Comparison of the difference in the frequency distribution of these structures between those two cells showed approximately 75% of the particle-like structures with a diameter of 8-12 nm in the prestin-transfected CHO cells to be possibly constituted only by prestin molecules. Our data suggest that the densely packed 10-nm particles observed on the OHC lateral wall are likely to be constituted only of prestin molecules.
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Affiliation(s)
- Michio Murakoshi
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Takashi Gomi
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Koji Iida
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Shun Kumano
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
| | - Kouhei Tsumoto
- Department of Medical Genome Sciences, Graduate School of Frontier Sciences, The University of Tokyo, 5-1-5 Kashiwanoha, Kashiwa, 277-8652 Japan
| | - Izumi Kumagai
- Department of Biomolecular Engineering, Tohoku University, 6-6-11 Aoba-yama, Sendai, 980-8579 Japan
| | - Katsuhisa Ikeda
- Department of Otorhinolaryngology, Juntendo University School of Medicine, 2-1-1 Hongo, Tokyo, 113-8421 Japan
| | - Toshimitsu Kobayashi
- Department of Otorhinolaryngology–Head and Neck Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryo-machi, Sendai, 980-8574 Japan
| | - Hiroshi Wada
- Department of Bioengineering and Robotics, Tohoku University, 6-6-01 Aoba-yama, Sendai, 980-8579 Japan
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15
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He DZZ, Zheng J, Kalinec F, Kakehata S, Santos-Sacchi J. Tuning in to the amazing outer hair cell: membrane wizardry with a twist and shout. J Membr Biol 2006; 209:119-34. [PMID: 16773497 DOI: 10.1007/s00232-005-0833-9] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2005] [Indexed: 11/29/2022]
Affiliation(s)
- D Z Z He
- Hair Cell Biophysics Laboratory, Department of Biomedical Sciences, Creighton University School of Medicine, Omaha, NE 68178, USA
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16
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Abstract
The voltage-dependent activity of prestin, the outer hair cell (OHC) motor protein essential for its electromotility, enhances the mammalian inner ear's auditory sensitivity. We investigated the effect of prestin's activity on the plasma membrane's (PM) susceptibility to electroporation (EP) via cell-attached patch-clamping. Guinea pig OHCs, TSA201 cells, and prestin-transfected TSA cells were subjected to incremental 50 mus and/or 50 ms voltage pulse trains, or ramps, at rates from 10 V/s to 1 kV/s, to a maximum transmembrane potential of +/-1000 mV. EP was determined by an increase in capacitance to whole-cell levels. OHCs were probed at the prestin-rich lateral PM or prestin-devoid basal portion; TSA cells were patched at random points. OHCs were consistently electroporated with 50 ms pulses, with significant resistance to depolarizing pulses. Although EP rarely occurred with 50 mus pulses, prior stimulation with this protocol had a significant effect on the sensitivity to EP with 50 ms pulses, regardless of polarity or PM domain. Consistent with these results, resistance to EP with depolarizing 10-V/s ramps was also found. Our findings with TSA cells were comparable, showing resistance to EP with both depolarizing 50-ms pulses and 10 V/s ramps. We conclude prestin significantly affects susceptibility to EP, possibly via known biophysical influences on specific membrane capacitance and/or membrane stiffness.
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Affiliation(s)
- Enrique G Navarrete
- Department of Cell and Molecular Biology, House Ear Institute, Los Angeles, California, USA
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17
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Abstract
The amplification of acoustic stimuli is a feature of hair cells that evolved early on in vertebrates. Though standard stereocilia mechanisms to promote such amplification may persist in the mammal, an additional mechanism evolved to enhance high frequency sensation. Only in mammals, a special cell type, the outer hair cell, arose that possesses a remarkably fast somatic mechanical response, which probably endows the passive cochlea with a boost in sensitivity by a factor of 100 (40dB), at least. Experiments conducted over the past few years have shed light on many aspects of outer hair cell electromotility, including the molecular identification of the motor, the effects of a knockout, and underlying mechanisms of action. A review of this remarkable progress is attempted.
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Affiliation(s)
- Joseph Santos-Sacchi
- Yale University School of Medicine, Otolaryngology and Neurobiology, BML 244 333 Cedar Street, New Haven, CT 06510, USA.
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18
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Chambard JM, Ashmore JF. Sugar transport by mammalian members of the SLC26 superfamily of anion-bicarbonate exchangers. J Physiol 2003; 550:667-77. [PMID: 12938672 PMCID: PMC2343088 DOI: 10.1113/jphysiol.2003.039321] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The mammalian cochlea contains a population of outer hair cells (OHCs) whose electromotility depends on an assembly of 'motor' molecules in the basolateral membrane of the cell. Named 'prestin', the molecule is a member of the SLC26 anion transporter superfamily. We show both directly and indirectly that SLC26A5, rat prestin, takes up hexoses when expressed in several cell lines. Direct measurements of labelled fructose transport into COS-7 cells expressing prestin are reported here. Indirect measurements, using imaging techniques, show that transfected HEK-293 or CHO-Ki cells undergo reversible volume changes when exposed to isosmotic glucose-fructose exchange. The observations are consistent with the sugar transport. A similar transport was observed using a C-terminal green fluorescent protein (GFP)-tagged pendrin (SLC26A4) construct. Cells transfected with GFP alone did not respond to sugars. The data are consistent with fructose being transported by prestin with an apparent Km=24 nm. From the voltage-dependent capacitance of transfected cells, we estimate that 250,000 prestin molecules were present and hence that the single transport rate is not more than 3000 fructose molecules s(-1). Comparison of the transfected cell swelling rates induced by fructose and by osmotic steps indicates that water was co-transported with sugar. We suggest that the structure of SLC26 family members allows them to act as neutral substrate transporters and may explain observed properties of cochlear hair cells.
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Affiliation(s)
- J-M Chambard
- Department of Physiology, University College London, UK
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19
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Abstract
Active feedback mechanisms in the ears of mammals amplify and tune the auditory response to sound stimuli, allowing these organisms to enjoy both exquisite sensitivity and sharp frequency selectivity. A requisite component of this feedback pathway has recently been identified. Targeted deletion of pres, the gene that encodes the novel membrane-bound motor protein prestin, has revealed a hundred-fold loss in hearing sensitivity suggesting that it might be part of the elusive cochlear amplifier.
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Affiliation(s)
- Gwénaëlle S G Géléoc
- Department of Neuroscience, University of Virginia, PO Box 801392, Charlottesville, VA 22908, USA
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20
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Affiliation(s)
- Ruth Anne Eatock
- The Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine, Houston, Texas 77030, USA
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21
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Zuo J. Transgenic and gene targeting studies of hair cell function in mouse inner ear. JOURNAL OF NEUROBIOLOGY 2002; 53:286-305. [PMID: 12382282 DOI: 10.1002/neu.10128] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Despite the rapid discovery of a large number of genes in sensory hair cells of the inner ear, the functional roles of these genes in hair cells remain largely undetermined. Recent advances in transgenic and gene targeting technologies in mice have offered unprecedented opportunities to genetically manipulate the expression of these genes and to study their functional roles in hair cells in vivo. Transgenic analyses have revealed the presence of hair-cell-specific promoters in the genes encoding Math1, myosin VIIa, Pou4f3, and the alpha9 subunit of the acetylcholine receptor (alpha9 AChR). Targeted inactivation using embryonic stem cell technology and transgenic expression studies have revealed the roles of several genes involved in hair cell lineage (Math1), differentiation (Pou4f3), mechanotransduction (Myo1c, and Myo7a), electromotility (Prestin), and efferent modulation (Chrna9, encoding alpha9 AChR). Although many of these genes also play roles in other tissues, inactivation of these genes in hair cells alone will soon be possible by using the Cre-loxP system. Also imminent is the development of genetic methods to inactivate genes specifically in mouse hair cells at a desired time, by using inducible systems established in other types of neurons. Combining these types of manipulation of gene expression will enable hearing researchers to elucidate some of the fundamental and unique features of hair cell function such as mechanotransduction, frequency tuning, active mechanical amplification, and efferent modulation.
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Affiliation(s)
- Jian Zuo
- Department of Developmental Neurobiology, St Jude Children's Research Hospital, 332 North Lauderdale Street, Memphis, Tennessee 38105-2794, USA.
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22
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Brownell WE, Spector AA, Raphael RM, Popel AS. Micro- and nanomechanics of the cochlear outer hair cell. Annu Rev Biomed Eng 2002; 3:169-94. [PMID: 11447061 DOI: 10.1146/annurev.bioeng.3.1.169] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Outer hair cell electromotility is crucial for the amplification, sharp frequency selectivity, and nonlinearities of the mammalian cochlea. Current modeling efforts based on morphological, physiological, and biophysical observations reveal transmembrane potential gradients and membrane tension as key independent variables controlling the passive and active mechanics of the cell. The cell's mechanics has been modeled on the microscale using a continuum approach formulated in terms of effective (cellular level) mechanical and electric properties. Another modeling approach is nanostructural and is based on the molecular organization of the cell's membranes and cytoskeleton. It considers interactions between the components of the composite cell wall and the molecular elements within each of its components. The methods and techniques utilized to increase our understanding of the central role outer hair cell mechanics plays in hearing are also relevant to broader research questions in cell mechanics, cell motility, and cell transduction.
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Affiliation(s)
- W E Brownell
- Bobby R. Alford Department of Otorhinolaryngology and Communicative Sciences, Baylor College of Medicine and Department of Bioengineering, Rice University, Houston, Texas 77030, USA.
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23
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Ashmore JF, Chambard JM, Richmond S. Cochlear transduction: from models to molecules and back again. Audiol Neurootol 2002; 7:6-8. [PMID: 11914517 DOI: 10.1159/000046854] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The strides made over the last few years towards understanding many details of cochlear function still leave a number of issues unresolved. Integrating the information from molecular, genetic and, increasingly, genomic sources requires models that provide close matching between data and theory. For both theoretical and experimental reasons, the difficult area in cochlear physiology has been to understand how sensory transduction operates at the basal end of the mammalian cochlea. The identification of candidate motor proteins in outer hair cells (OHCs) draws attention to the question of whether we understand cochlear tuning. Nevertheless, the association of the cloned motor protein 'prestin' with an anion transporter superfamily provides clues about the molecular nature of the OHC motor in the basolateral membrane, the utilisation of chloride in hair cells and the long-term stability of small basal turn cochlear hair cells.
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24
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Abstract
Understanding how the cochlea works as a system has become increasingly important. We need to know this before integrating new information from genetic, physiological and clinical sources. This chapter will show how the cochlea should be seen as a device for carrying out a frequency analysis built from cells that have been adapted for specialist purposes. Sensory hair cells convert mechanical displacements into the neural code. The transducer channel remains to be identified. The biomechanics of the cochlear duct depends on an energy-dependent feedback from the sensory outer hair cells. The molecular basis for outer hair cell feedback depends on a protein that has recently been identified. The auditory signal encoded by the cochlea is further modified by membrane properties of the hair cells and cochlear supporting cells. The interplay between techniques of genetics, molecular biology and cell physiology has started to reveal which ion channels and transporters in the cochlea are mutated in certain forms of deafness. The interpretation of these mutations requires the cell physiology of the cochlear partition to be better characterised in the future.
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25
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Zheng J, Madison LD, Oliver D, Fakler B, Dallos P. Prestin, the motor protein of outer hair cells. Audiol Neurootol 2002; 7:9-12. [PMID: 11914518 DOI: 10.1159/000046855] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Prestin is a gene recently cloned from mammalian cochlear outer hair cells (OHC) using a single cell type, outer minus inner hair cell, specific suppressive subtractive hybridization procedure. The localization and gene expression profile of the prestin protein fits the pattern of OHC's development of electromotility. When prestin is abundantly expressed in normally nonmotile kidney cells, nonlinear capacitance and motility that are normally only seen in OHCs can be recorded. Furthermore, both nonlinear capacitance and motility can be reduced by salicylate, a well-known inhibitor of electromotility. These data suggest that prestin is the motor protein of OHCs. Amino acid sequence and gene structure analysis indicate that prestin is the fifth member of a newly discovered anion transport family (SLC26) that includes PDS, DRA and DTDST, which are chloride-iodide transporters, Cl-/HCO3- exchangers or sulfate transporters. Prestin shares overall structure similarity with this anion transporter family. Recently, intracellular anions (chloride or bicarbonate) were found to be essential for OHC electromotility and prestin's function.
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Affiliation(s)
- Jing Zheng
- Department of Communication Sciences and Disorders, Auditory Physiology Laboratory, The Hugh Knowles Center, Northwestern University, Evanston, Ill 60208, USA.
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26
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Abstract
We propose a three-dimensional (3D) model to simulate outer hair cell electromotility. In our model, the major components of the composite cell wall are explicitly represented. We simulate the activity of the particles/motor complexes in the plasma membrane by generating active strains inside them and compute the overall response of the cell. We also consider the constrained wall and compute the generated active force. We estimate the parameters of our model by matching the predicted longitudinal and circumferential electromotile strains with those observed in the microchamber experiment. In addition, we match the earlier estimated values of the active force and cell wall stiffness. The computed electromotile strains in the plasma membrane and other components of the wall are in agreement with experimental observations in trypsinized cells and in nonmotile cells transfected with Prestin. We discover several features of the 3D mechanism of outer hair cell electromotilty. Because of the constraints under which the motors operate, the motor-related strains have to be 2-3 times larger than the observable strains. The motor density has a strong effect on the electromotile strain. Such effect on the active force is significantly lower because of the interplay between the active and passive properties of the cell wall.
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Affiliation(s)
- A A Spector
- Department of Biomedical Engineering, Center for Computational Medicine and Biology and Center for Hearing Sciences, Johns Hopkins University, Baltimore, Maryland 21205, USA.
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28
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Ludwig J, Oliver D, Frank G, Klöcker N, Gummer AW, Fakler B. Reciprocal electromechanical properties of rat prestin: the motor molecule from rat outer hair cells. Proc Natl Acad Sci U S A 2001; 98:4178-83. [PMID: 11274441 PMCID: PMC31199 DOI: 10.1073/pnas.071613498] [Citation(s) in RCA: 109] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2000] [Indexed: 11/18/2022] Open
Abstract
Cochlear outer hair cells (OHCs) are responsible for the exquisite sensitivity, dynamic range, and frequency-resolving capacity of the mammalian hearing organ. These unique cells respond to an electrical stimulus with a cycle-by-cycle change in cell length that is mediated by molecular motors in the cells' basolateral membrane. Recent work identified prestin, a protein with similarity to pendrin-related anion transporters, as the OHC motor molecule. Here we show that heterologously expressed prestin from rat OHCs (rprestin) exhibits reciprocal electromechanical properties as known for the OHC motor protein. Upon electrical stimulation in the microchamber configuration, rprestin generates mechanical force with constant amplitude and phase up to a stimulus frequency of at least 20 kHz. Mechanical stimulation of rprestin in excised outside-out patches shifts the voltage dependence of the nonlinear capacitance characterizing the electrical properties of the molecule. The results indicate that rprestin is a molecular motor that displays reciprocal electromechanical properties over the entire frequency range relevant for mammalian hearing.
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Affiliation(s)
- J Ludwig
- Department of Physiology II, Ob dem Himmelreich 7, 72074 Tübingen, Germany
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29
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Frolenkov GI, Mammano F, Kachar B. Action of 2,3-butanedione monoxime on capacitance and electromotility of guinea-pig cochlear outer hair cells. J Physiol 2001; 531:667-76. [PMID: 11251049 PMCID: PMC2278492 DOI: 10.1111/j.1469-7793.2001.0667h.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Whole-cell patch-clamp recordings were obtained from isolated cochlear outer hair cells (OHCs) while applying 2,3-butanedione monoxime (BDM) by pressure. BDM (5 mM) shifted the range of voltage sensitivity of membrane capacitance and cell length in the hyperpolarised direction by -49.6 +/- 4.0 mV (n = 12; mean +/- S.E.M.), without appreciable effects on membrane conductance. The shift was completely reversible and dose dependent, with a Hill coefficient of 1.8 /- 0.4 and a half-maximal dose of 3.0 +/- 0.8 mM (values +/- S.D). 2. The shift of the capacitance curve was also reproducible in cells whose natural turgor had been removed. BDM had no detectable effect on the capacitance of Deiters' cells, a non-sensory cell type of the organ of Corti. 3. The effect of BDM on membrane capacitance was faster than that of salicylate. At similar saturating concentrations (20 mM), the time constant of the capacitance changes was 1.8 +/- 0.3 s (n = 3) for salicylate and 0.75 +/- 0.06 s (n = 3) for BDM. The recovery periods were 13 +/- 1 s and 1.7 +/- 0.4 s, respectively (means +/- S.E.M.). 4. The effect of BDM, a known inorganic phosphatase, was compared to the effects of okadaic acid, trifluoperazine and W-7, which are commonly used in studies of protein phosphorylation. Incubation of OHCs with okadaic acid (1 microM, 30-60 min) shifted the voltage sensitivity of the membrane capacitance in the hyperpolarised direction. Incubation with trifluoperazine (30 microM) and W-7 (150 microM) shifted it in the opposite, depolarised direction. BDM induced hyperpolarising shifts even in the presence of W-7. 5. Simultaneous measurement of membrane capacitance and intracellular free Ca2+ concentration ([Ca2+]i) showed that BDM action on OHC voltage-dependent capacitance and electromotility is not mediated by changes of [Ca2+]i. 6. Our results suggest that: (a) the effects of BDM are unrelated to its inorganic phosphatase properties, cell turgor conditions or Ca2+ release from intracellular stores; and (b) BDM may target directly the voltage sensor of the OHC membrane motor protein.
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Affiliation(s)
- G I Frolenkov
- Section on Structural Cell Biology, Laboratory of Cellular Biology, NIDCD-NIH, Bethesda, MD 20892-4163, USA
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30
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Santos-Sacchi J, Shen W, Zheng J, Dallos P. Effects of membrane potential and tension on prestin, the outer hair cell lateral membrane motor protein. J Physiol 2001; 531:661-6. [PMID: 11251048 PMCID: PMC2278494 DOI: 10.1111/j.1469-7793.2001.0661h.x] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
1. Under whole-cell voltage clamp, the effects of initial voltage conditions and membrane tension on gating charge and voltage-dependent capacitance were studied in human embryonic kidney cells (TSA201 cell line) transiently transfected with the gene encoding the gerbil protein prestin. Conformational changes in this membrane-bound protein probably provide the molecular basis of the outer hair cell (OHC) voltage-driven mechanical activity, which spans the audio spectrum. 2. Boltzmann characteristics of the charge movement in transfected cells were similar to those reported for OHCs (Q(max) = 0.99 +/- 0.16 pC, z = 0.88 +/- 0.02; n = 5, means +/- S.E.M.). Unlike that of the adult OHC, the voltage at peak capacitance (V(pkcm)) was very negative (-74.7 +/- 3.8 mV). Linear capacitance in transfected cells was 43.7 +/- 13.8 pF and membrane resistance was 458 +/- 123 Mohms. 3. Voltage steps from the holding potential preceding the measurement of capacitance-voltage functions caused a time- and voltage-dependent shift in V(pkcm). For a prepulse to -150 mV, from a holding potential of 0 mV, V(pkcm) shifted 6.4 mV, and was fitted by a single exponential time constant of 45 ms. A higher resolution analysis of this time course was made by measuring the change in capacitance during a fixed voltage step and indicated a double exponential shift (tau(0) = 51.6 ms, tau(1) = 8.5 s) similar to that of the native gerbil OHC. 4. Membrane tension, delivered by increasing pipette pressure, caused a positive shift in V(pkcm). A maximal shift of 7.5 mV was obtained with 2 kPa of pressure. The effect was reversible. 5. Our results show that the sensitivity of prestin to initial voltage and membrane tension, though present, is less than that observed in adult OHCs. It remains possible that some other interacting molecular species within the lateral plasma membrane of the native OHC amplifies the effect of tension and prior voltage on prestin's activity.
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Affiliation(s)
- J Santos-Sacchi
- Sections of Otolaryngology and Neurobiology, Yale University School of Medicine, New Haven, CT 06510, USA.
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31
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Evans MG, Kros CJ. Hey presto! Electrophysiological characterisation of prestin, a motor protein from outer hair cells, transfected into kidney cells. J Physiol 2001; 531:582. [PMID: 11251040 PMCID: PMC2278505 DOI: 10.1111/j.1469-7793.2001.0582h.x] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Affiliation(s)
- M G Evans
- MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, Keele, Staffs ST5 5BG, UK
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32
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Manley GA, Kirk DL, Köppl C, Yates GK. In vivo evidence for a cochlear amplifier in the hair-cell bundle of lizards. Proc Natl Acad Sci U S A 2001; 98:2826-31. [PMID: 11226325 PMCID: PMC30224 DOI: 10.1073/pnas.041604998] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Vertebrate sensory hair cells achieve high sensitivity and frequency selectivity by adding self-generated mechanical energy to low-level signals. This allows them to detect signals that are smaller than thermal molecular motion and to achieve significant resonance amplitudes and frequency selectivity despite the viscosity of the surrounding fluid. In nonmammals, a great deal of in vitro evidence indicates that the active process responsible for this amplification is intimately associated with the hair cells' transduction channels in the stereovillar bundle. Here, we provide in vivo evidence of hair-cell bundle involvement in active processes. Electrical stimulation of the inner ear of a lizard at frequencies typical for this hearing organ induced low-level otoacoustic emissions that could be modulated by low-frequency sound. The unique modulation pattern permitted the tracing of the active process involved to the stereovillar bundles of the sensory hair cells. This supports the notion that, in nonmammals, the cochlear amplifier in the hair cells is driven by a bundle motor system.
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Affiliation(s)
- G A Manley
- Institut für Zoologie, Technische Universität München, 85747 Garching, Germany.
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33
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Abstract
The distinguishing feature of the mammalian outer hair cells (OHCs) is to elongate and shorten at acoustic frequencies, when their intracellular potential is changed. This "electromotility" or "electromechanics" depends critically on positive intracellular pressure (turgor), maintained by the inflow of water through yet uncharacterized water pathways. We measured the water volume flow, J(v), across the plasma membrane of isolated guinea pig and rat OHCs after osmotic challenges and estimated the osmotic water permeability coefficient, P(f), to be approximately 10(-2) cm/sec. This value is within the range reported for osmotic flow mediated by the water channel proteins, aquaporins. J(v) was inhibited by HgCl(2), which is known to block aquaporin-mediated water transport. P(f) values that were estimated for OHCs from neonatal rats were of the order of approximately 2 x 10(-3) cm/sec, equivalent to that of membranes lacking water channel proteins. In an immunofluorescence assay we showed that an anti-peptide antibody specific for aquaporins labels the lateral plasma membrane of the OHC in the region in which electromotility is generated. Using patch-clamp recording, we found that water influx into the OHC is regulated by intracellular voltage. We also found that the most pronounced increases of the electromotility-associated charge movement and of the expression of OHC water channels occur between postnatal days 8 and 12, preceding the onset of hearing function in the rat. Our data indicate that electromotility and water transport in OHCs may influence each other structurally and functionally.
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34
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Abstract
Little is known of the molecular basis of normal auditory function. In contrast to the visual or olfactory senses, in which reasonable amounts of sensory tissue can be gathered, the auditory system has proven difficult to access through biochemical routes, mainly because such small amounts of tissue are available for analysis. Key molecules, such as the transduction channel, may be present in only a few tens of copies per sensory hair cell, compounding the difficulty. Moreover, fundamental differences in the mechanism of stimulation and, most importantly, the speed of response of audition compared with other senses means that we have no well-understood models to provide good candidate molecules for investigation. For these reasons, a genetic approach is useful for identifying the key components of auditory transduction, as it makes no assumptions about the nature or expression level of molecules essential for hearing. We review here some of the major advances in our understanding of auditory function resulting from the recent rapid progress in identification of genes involved in deafness.
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Affiliation(s)
- K P Steel
- Medical Research Council Institute of Hearing Research, University of Nottingham, Nottingham, UK.
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35
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Ashmore JF, Géléoc GS, Harbott L. Molecular mechanisms of sound amplification in the mammalian cochlea. Proc Natl Acad Sci U S A 2000; 97:11759-64. [PMID: 11050206 PMCID: PMC34346 DOI: 10.1073/pnas.97.22.11759] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Mammalian hearing depends on the enhanced mechanical properties of the basilar membrane within the cochlear duct. The enhancement arises through the action of outer hair cells that act like force generators within the organ of Corti. Simple considerations show that underlying mechanism of somatic motility depends on local area changes within the lateral membrane of the cell. The molecular basis for this phenomenon is a dense array of particles that are inserted into the basolateral membrane and that are capable of sensing membrane potential field. We show here that outer hair cells selectively take up fructose, at rates high enough to suggest that a sugar transporter may be part of the motor complex. The relation of these findings to a recent candidate for the molecular motor is also discussed.
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Affiliation(s)
- J F Ashmore
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, United Kingdom.
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36
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Affiliation(s)
- C M Hackney
- MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, Keele, Staffordshire, UK
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37
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Zheng J, Shen W, He DZ, Long KB, Madison LD, Dallos P. Prestin is the motor protein of cochlear outer hair cells. Nature 2000; 405:149-55. [PMID: 10821263 DOI: 10.1038/35012009] [Citation(s) in RCA: 880] [Impact Index Per Article: 36.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
The outer and inner hair cells of the mammalian cochlea perform different functions. In response to changes in membrane potential, the cylindrical outer hair cell rapidly alters its length and stiffness. These mechanical changes, driven by putative molecular motors, are assumed to produce amplification of vibrations in the cochlea that are transduced by inner hair cells. Here we have identified an abundant complementary DNA from a gene, designated Prestin, which is specifically expressed in outer hair cells. Regions of the encoded protein show moderate sequence similarity to pendrin and related sulphate/anion transport proteins. Voltage-induced shape changes can be elicited in cultured human kidney cells that express prestin. The mechanical response of outer hair cells to voltage change is accompanied by a 'gating current', which is manifested as nonlinear capacitance. We also demonstrate this nonlinear capacitance in transfected kidney cells. We conclude that prestin is the motor protein of the cochlear outer hair cell.
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Affiliation(s)
- J Zheng
- The Hugh Knowles Center, Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208, USA
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38
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