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Lee JH, Park S, Perez-Flores MC, Chen Y, Kang M, Choi J, Levine L, Gratton MA, Zhao J, Notterpek L, Yamoah EN. Demyelination and Na + Channel Redistribution Underlie Auditory and Vestibular Dysfunction in PMP22-Null Mice. eNeuro 2024; 11:ENEURO.0462-23.2023. [PMID: 38378628 PMCID: PMC11059428 DOI: 10.1523/eneuro.0462-23.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2023] [Revised: 12/14/2023] [Accepted: 12/15/2023] [Indexed: 02/22/2024] Open
Abstract
Altered expression of peripheral myelin protein 22 (PMP22) results in demyelinating peripheral neuropathy. PMP22 exhibits a highly restricted tissue distribution with marked expression in the myelinating Schwann cells of peripheral nerves. Auditory and vestibular Schwann cells and the afferent neurons also express PMP22, suggesting a unique role in hearing and balancing. Indeed, neuropathic patients diagnosed with PMP22-linked hereditary neuropathies often present with auditory and balance deficits, an understudied clinical complication. To investigate the mechanism by which abnormal expression of PMP22 may cause auditory and vestibular deficits, we studied gene-targeted PMP22-null mice. PMP22-null mice exhibit an unsteady gait, have difficulty maintaining balance, and live for only ∼3-5 weeks relative to unaffected littermates. Histological analysis of the inner ear revealed reduced auditory and vestibular afferent nerve myelination and profound Na+ channel redistribution without PMP22. Yet, Na+ current density was unaltered, in stark contrast to increased K+ current density. Atypical postsynaptic densities and a range of neuronal abnormalities in the organ of Corti were also identified. Analyses of auditory brainstem responses (ABRs) and vestibular sensory-evoked potential (VsEP) revealed that PMP22-null mice had auditory and vestibular hypofunction. These results demonstrate that PMP22 is required for hearing and balance, and the protein is indispensable for the formation and maintenance of myelin in the peripheral arm of the eighth nerve. Our findings indicate that myelin abnormalities and altered signal propagation in the peripheral arm of the auditory nerve are likely causes of auditory deficits in patients with PMP22-linked neuropathies.
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Affiliation(s)
- Jeong Han Lee
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Seojin Park
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
- Prestige BioPharma, Busan 67264, South Korea
| | - Maria C Perez-Flores
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Yingying Chen
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Mincheol Kang
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
- Prestige BioPharma, Busan 67264, South Korea
| | - Jinsil Choi
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Lauren Levine
- Program in Audiology and Communication Sciences, Washington University, St. Louis 63110, Missouri
| | | | - Jie Zhao
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Lucia Notterpek
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
| | - Ebenezer N Yamoah
- Department of Physiology and Cell Biology, School of Medicine, University of Nevada, Reno, Reno 89557, Nevada
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Jang MW, Lim J, Park MG, Lee JH, Lee CJ. Active role of glia-like supporting cells in the organ of Corti: Membrane proteins and their roles in hearing. Glia 2022; 70:1799-1825. [PMID: 35713516 DOI: 10.1002/glia.24229] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2022] [Revised: 05/23/2022] [Accepted: 05/30/2022] [Indexed: 12/13/2022]
Abstract
The organ of Corti, located in the cochlea in the inner ear, is one of the major sensory organs involved in hearing. The organ of Corti consists of hair cells, glia-like supporting cells, and the cochlear nerve, which work in harmony to receive sound from the outer ear and transmit auditory signals to the cochlear nucleus in the auditory ascending pathway. In this process, maintenance of the endocochlear potential, with a high potassium gradient and clearance of electrolytes and biochemicals in the inner ear, is critical for normal sound transduction. There is an emerging need for a thorough understanding of each cell type involved in this process to understand the sophisticated mechanisms of the organ of Corti. Hair cells have long been thought to be active, playing a primary role in the cochlea in actively detecting and transmitting signals. In contrast, supporting cells are thought to be silent and function to support hair cells. However, growing lines of evidence regarding the membrane proteins that mediate ionic movement in supporting cells have demonstrated that supporting cells are not silent, but actively play important roles in normal signal transduction. In this review, we summarize studies that characterize diverse membrane proteins according to the supporting cell subtypes involved in cochlear physiology and hearing. This review contributes to a better understanding of supporting cell functions and facilitates the development of potential therapeutic tools for hearing loss.
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Affiliation(s)
- Minwoo Wendy Jang
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, Republic of Korea.,Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, Republic of Korea
| | - Jiwoon Lim
- Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, Republic of Korea.,IBS School, University of Science and Technology (UST), Daejeon, Republic of Korea
| | - Mingu Gordon Park
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, Republic of Korea.,Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, Republic of Korea
| | - Jae-Hun Lee
- Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, Republic of Korea
| | - C Justin Lee
- KU-KIST Graduate School of Converging Science and Technology, Korea University, Seoul, Republic of Korea.,Center for Cognition and Sociality, Institute for Basic Science (IBS), Daejeon, Republic of Korea.,IBS School, University of Science and Technology (UST), Daejeon, Republic of Korea
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Optimized Tuning of Auditory Inner Hair Cells to Encode Complex Sound through Synergistic Activity of Six Independent K + Current Entities. Cell Rep 2021; 32:107869. [PMID: 32640234 DOI: 10.1016/j.celrep.2020.107869] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2020] [Revised: 04/08/2020] [Accepted: 06/16/2020] [Indexed: 02/06/2023] Open
Abstract
Auditory inner hair cells (IHCs) convert sound vibrations into receptor potentials that drive synaptic transmission. For the precise encoding of sound qualities, receptor potentials are shaped by K+ conductances tuning the properties of the IHC membrane. Using patch-clamp and computational modeling, we unravel this membrane specialization showing that IHCs express an exclusive repertoire of six voltage-dependent K+ conductances mediated by Kv1.8, Kv7.4, Kv11.1, Kv12.1, and BKCa channels. All channels are active at rest but are triggered differentially during sound stimulation. This enables non-saturating tuning over a far larger potential range than in IHCs expressing fewer current entities. Each conductance contributes to optimizing responses, but the combined activity of all channels synergistically improves phase locking and the dynamic range of intensities that IHCs can encode. Conversely, hypothetical simpler IHCs appear limited to encode only certain aspects (frequency or intensity). The exclusive channel repertoire of IHCs thus constitutes an evolutionary adaptation to encode complex sound through multifaceted receptor potentials.
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Furness DN. Forgotten Fibrocytes: A Neglected, Supporting Cell Type of the Cochlea With the Potential to be an Alternative Therapeutic Target in Hearing Loss. Front Cell Neurosci 2019; 13:532. [PMID: 31866825 PMCID: PMC6908467 DOI: 10.3389/fncel.2019.00532] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2019] [Accepted: 11/15/2019] [Indexed: 12/31/2022] Open
Abstract
Cochlear fibrocytes are a homeostatic supporting cell type embedded in the vascularized extracellular matrix of the spiral ligament, within the lateral wall. Here, they participate in the connective tissue syncytium that enables potassium recirculation into the scala media to take place and ensures development of the endolymphatic potential that helps drive current into hair cells during acoustic stimulation. They have also been implicated in inflammatory responses in the cochlea. Some fibrocytes interact closely with the capillaries of the vasculature in a way which suggests potential involvement, together with the stria vascularis, also in the blood-labyrinth barrier. Several lines of evidence suggests that pathology of the fibrocytes, along with other degenerative changes in this region, contribute to metabolic hearing loss (MHL) during aging that is becoming recognized as distinct from, and potentially a precursor for, sensorineural hearing loss (SNHL). This pathology may underlie a significant proportion of cases of presbycusis. Some evidence points also to an association between fibrocyte degeneration and Ménière’s disease (MD). Fibrocytes are mesenchymal; this characteristic, and their location, make them amenable to potential cell therapy in the form of cell replacement or genetic modification to arrest the process of degeneration that leads to MHL. This review explores the properties and roles of this neglected cell type and suggests potential therapeutic approaches, such as cell transplantation or genetic engineering of fibrocytes, which could be used to prevent this form of presbycusis or provide a therapeutic avenue for MD.
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Affiliation(s)
- David N Furness
- School of Life Sciences, Keele University, Keele, United Kingdom
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Lin EC, Moungey BM, Lim E, Concannon SP, Anderson CL, Kyle JW, Makielski JC, Balijepalli SY, January CT. Mouse ERG K(+) channel clones reveal differences in protein trafficking and function. J Am Heart Assoc 2014; 3:e001491. [PMID: 25497881 PMCID: PMC4338741 DOI: 10.1161/jaha.114.001491] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background The mouse ether‐a‐go‐go‐related gene 1a (mERG1a, mKCNH2) encodes mERG K+ channels in mouse cardiomyocytes. The mERG channels and their human analogue, hERG channels, conduct IKr. Mutations in hERG channels reduce IKr to cause congenital long‐QT syndrome type 2, mostly by decreasing surface membrane expression of trafficking‐deficient channels. Three cDNA sequences were originally reported for mERG channels that differ by 1 to 4 amino acid residues (mERG‐London, mERG‐Waterston, and mERG‐Nie). We characterized these mERG channels to test the postulation that they would differ in their protein trafficking and biophysical function, based on previous findings in long‐QT syndrome type 2. Methods and Results The 3 mERG and hERG channels were expressed in HEK293 cells and neonatal mouse cardiomyocytes and were studied using Western blot and whole‐cell patch clamp. We then compared our findings with the recent sequencing results in the Welcome Trust Sanger Institute Mouse Genomes Project (WTSIMGP). Conclusions First, the mERG‐London channel with amino acid substitutions in regions of highly ordered structure is trafficking deficient and undergoes temperature‐dependent and pharmacological correction of its trafficking deficiency. Second, the voltage dependence of channel gating would be different for the 3 mERG channels. Third, compared with the WTSIMGP data set, the mERG‐Nie clone is likely to represent the wild‐type mouse sequence and physiology. Fourth, the WTSIMGP analysis suggests that substrain‐specific sequence differences in mERG are a common finding in mice. These findings with mERG channels support previous findings with hERG channel structure–function analyses in long‐QT syndrome type 2, in which sequence changes in regions of highly ordered structure are likely to result in abnormal protein trafficking.
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Affiliation(s)
- Eric C Lin
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Brooke M Moungey
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Evi Lim
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Sarah P Concannon
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Corey L Anderson
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - John W Kyle
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Jonathan C Makielski
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Sadguna Y Balijepalli
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
| | - Craig T January
- Division of Cardiovascular Medicine, Department of Medicine, University of Wisconsin, Madison, WI (E.C.L., B.M.M., E.L., S.P.C., C.L.A., J.W.K., J.C.M., S.Y.B., C.T.J.)
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Oak MH, Yi E. Voltage-gated K(+) channels contributing to temporal precision at the inner hair cell-auditory afferent nerve fiber synapses in the mammalian cochlea. Arch Pharm Res 2014; 37:821-33. [PMID: 24925343 DOI: 10.1007/s12272-014-0411-8] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2014] [Accepted: 05/09/2014] [Indexed: 12/16/2022]
Abstract
To perform auditory tasks such as sound localization in the space, auditory neurons in the brain must distinguish sub-millisecond temporal differences in signals from two ears. Such high temporal resolution is possible when each neuron in the ascending auditory pathway fires brief action potential at very accurate timing. Various pre- and postsynaptic machineries ensuring such high temporal precision of auditory synaptic transmission have been identified. Of particular, in this review, the role of K(+) channels in shortening the duration of synaptic potentials will be discussed. First, the contribution of K(+) channels to AP firing of general auditory neurons will be discussed. Then, the focus will be moved to the inner hair cell (IHC)-auditory afferent nerve fiber (ANF) synapses, the first synapses of ascending auditory pathway. Molecular and immunohistological techniques have revealed various K(+) channels in the cell bodies and their processes of ANFs. Since the development of patch-clamp recordings from the ANF dendrites in 2002, it became possible to monitor the IHC-ANF synaptic transmission in greater detail. As revealed in brain auditory synapses, several different K(+) channels appear to participate in reducing the duration of synaptic potentials at the IHC-ANF synapses. In addition, K(+) channels at the ANF dendrites might act as potential targets of efferent feedback from the brain. The hypothesis is that, upon loud sound exposure, efferent neurotransmitters released onto the ANF dendrites activate certain K(+) channels and prevent excitotoxicity of ANFs. Therefore, K(+) channels of the ANF dendrites might provide potential sites of pharmacological actions to prevent noise-induced hearing loss.
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Affiliation(s)
- Min-Ho Oak
- College of Pharmacy and Natural Medicine Research Institute, Mokpo National University, 1666 Yeongsan-ro, Cheonggye-Myeon, Muan, Jeonnam, 534-729, Republic of Korea
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7
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Abstract
Normal blood supply to the cochlea is critically important for establishing the endocochlear potential and sustaining production of endolymph. Abnormal cochlear microcirculation has long been considered an etiologic factor in noise-induced hearing loss, age-related hearing loss (presbycusis), sudden hearing loss or vestibular function, and Meniere's disease. Knowledge of the mechanisms underlying the pathophysiology of cochlear microcirculation is of fundamental clinical importance. A better understanding of cochlear blood flow (CoBF) will enable more effective management of hearing disorders resulting from aberrant blood flow. This review focuses on recent discoveries and findings related to the physiopathology of the cochlear microvasculature.
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Affiliation(s)
- Xiaorui Shi
- Oregon Hearing Research Center (NRC04), Department of Otolaryngology/Head & Neck Surgery, Oregon Health & Science University, 3181 SW Sam Jackson Park Road, Portland, OR 97239, USA.
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Lv P, Wei D, Yamoah EN. Kv7-type channel currents in spiral ganglion neurons: involvement in sensorineural hearing loss. J Biol Chem 2010; 285:34699-707. [PMID: 20739290 DOI: 10.1074/jbc.m110.136192] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Alterations in K(v)7-mediated currents in excitable cells result in several diseased conditions. A case in DFNA2, an autosomal dominant version of progressive hearing loss, involves degeneration of hair cells and spiral ganglion neurons (SGNs) from basal to apical cochlea, manifesting as high-to-low frequency hearing loss, and has been ascribed to mutations in K(v)7.4 channels. Analyses of the cellular mechanisms of K(v)7.4 mutations and progressive degeneration of SGNs have been hampered by the paucity of functional data on the role K(v)7 channels play in young and adult neurons. To understand the cellular mechanisms of the disease in SGNs, we examined temporal (young, 0.5 months old, and senescent, 17 months old) and spatial (apical and basal) roles of K(v)7-mediated currents. We report that differential contribution of K(v)7 currents in mice SGNs results in distinct and profound variations of the membrane properties of basal versus apical neurons. The current produces a major impact on the resting membrane potential of basal neurons. Inhibition of the current promotes membrane depolarization, resulting in activation of Ca(2+) currents and a sustained rise in intracellular Ca(2+). Using TUNEL assay, we demonstrate that a sustained increase in intracellular Ca(2+) mediated by inhibition of K(v)7 current results in significant SGN apoptotic death. Thus, this study provides evidence of the cellular etiology and mechanisms of SGN degeneration in DFNA2.
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Affiliation(s)
- Ping Lv
- Department of Anesthesiology and Pain Medicine, School of Medicine, University of California, Davis, California 95618, USA
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9
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Sanguinetti MC. HERG1 channelopathies. Pflugers Arch 2009; 460:265-76. [PMID: 20544339 DOI: 10.1007/s00424-009-0758-8] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2009] [Revised: 11/03/2009] [Accepted: 11/06/2009] [Indexed: 01/08/2023]
Abstract
Human ether a go-go-related gene type 1 (hERG1) K+ channels conduct the rapid delayed rectifier K+ current and mediate action potential repolarization in the heart. Mutations in KCNH2 (the gene that encodes hERG1) causes LQT2, one of the most common forms of long QT syndrome, a disorder of cardiac repolarization that predisposes affected subjects to ventricular arrhythmia and increases the risk of sudden cardiac death. Hundreds of LQT2-associated mutations have been described, and most cause a loss of function by disrupting subunit folding, assembly, or trafficking of the channel to the cell surface. Loss-of-function mutations in hERG1 channels have also recently been implicated in epilepsy. A single gain-of-function mutation has been described that causes short QT syndrome and cardiac arrhythmia. In addition, up-regulation of hERG1 channel expression has been demonstrated in specific tumors and has been associated with skeletal muscle atrophy in mice.
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Affiliation(s)
- Michael C Sanguinetti
- Department of Physiology, Nora Eccles Harrison Cardiovascular Research & Training Institute, University of Utah, 95 South 2000 East, Salt Lake, UT 84112, USA.
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10
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Erg K+ currents modulate excitability in mouse mitral/tufted neurons. Pflugers Arch 2009; 459:55-70. [DOI: 10.1007/s00424-009-0709-4] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2009] [Revised: 06/13/2009] [Accepted: 07/30/2009] [Indexed: 10/20/2022]
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Feigenspan A, Trümpler J, Dirks P, Weiler R. Ether-à-gogo-related gene (erg1) potassium channels shape the dark response of horizontal cells in the mammalian retina. Pflugers Arch 2008; 458:359-77. [PMID: 18998156 DOI: 10.1007/s00424-008-0609-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2008] [Revised: 09/19/2008] [Accepted: 10/22/2008] [Indexed: 12/11/2022]
Abstract
Postsynaptic to photoreceptors, horizontal cells face prolonged exposure to glutamate in the dark. Therefore, efficient hyperpolarizing mechanisms are crucial to keep horizontal cells within an operating range and to reduce glutamate-induced excitotoxicity. Combining electrophysiology, single-cell reverse transcriptase polymerase chain reaction, and immunocytochemistry, we found that horizontal cell bodies but not their axon terminals express the ether-à-gogo-related gene isoform 1 (erg1) K(+) channel. Erg1-mediated outward currents displayed voltage-dependent activation and C-type inactivation. Recovery from inactivation involved a transient open state. Gating of erg1 channels kept the voltage response to glutamate brief and at physiological amplitudes. With erg1 channels blocked, the response of horizontal cells to the onset of darkness was significantly enhanced. These results indicate a functional dichotomy between horizontal cell bodies and axon terminals in the processing of photoreceptor signals. The dark response thus reflects a finely tuned balance determined by the successive gating of ionotropic glutamate receptors and erg1 channels.
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Affiliation(s)
- Andreas Feigenspan
- Institute of Biology, University of Oldenburg, 26111 Oldenburg, Germany.
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Karolyi IJ, Dootz GA, Halsey K, Beyer L, Probst FJ, Johnson KR, Parlow AF, Raphael Y, Dolan DF, Camper SA. Dietary thyroid hormone replacement ameliorates hearing deficits in hypothyroid mice. Mamm Genome 2007; 18:596-608. [PMID: 17899304 DOI: 10.1007/s00335-007-9038-0] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2007] [Accepted: 05/11/2007] [Indexed: 11/26/2022]
Abstract
Thyroid hormone (TH) insufficiency causes variable hearing impairment and mental deficiency in humans. Rodents lacking TH have congenital hearing deficiency that has been attributed to physiologic, morphologic, and developmental abnormalities of the auditory system. We examined four genetically defined strains of hypothyroid mice for development of hearing and response to TH replacement initiated during late gestation and continued through six weeks of age. Auditory brain stem response studies showed variable hearing impairment in homozygous mutants of each strain at three weeks of age relative to normal littermates. Mutants from three of the strains still had hearing deficiencies at six weeks of age. TH-enriched diet significantly improved hearing in three-week-old mutants of each strain relative to untreated mutants. Differences in the level of hearing impairment between the Prop1df and Pit1dw mutants, which have defects in the same developmental pathway, were determined to be due to genetic background modifier genes. Further physiologic and morphologic studies in the Cgatm1Sac strain indicated that poor hearing was due to cochlear defects. We conclude that TH supplement administered during the critical period of hearing development in mice can prevent deafness associated with congenital hypothyroidism of heterogeneous genetic etiology.
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Affiliation(s)
- I Jill Karolyi
- Department of Human Genetics, University of Michigan Medical School, Ann Arbor, Michigan 48109-0618, USA
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Elmedyb P, Calloe K, Schmitt N, Hansen RS, Grunnet M, Olesen SP. Modulation of ERG Channels by XE991. Basic Clin Pharmacol Toxicol 2007; 100:316-22. [PMID: 17448117 DOI: 10.1111/j.1742-7843.2007.00048.x] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
In neuronal tissue, KCNQ2-5 channels conduct the physiologically important M-current. In some neurones, the M-current may in addition be conducted partly by ERG potassium channels, which have widely overlapping expression with the KCNQ channel subunits. XE991 and linopiridine are known to be standard KCNQ potassium channel blockers. These compounds have been used in many different tissues as specific pharmacological tools to discern native currents conducted by KCNQ channels from other potassium currents. In this article, we demonstrate that ERG1-2 channels are also reversibly inhibited by XE991 in the micromolar range (EC(50) 107 microM for ERG1). The effect has been characterized in Xenopus laevis oocytes expressing ERG1-2 and in the mammalian HEK293 cell line stably expressing ERG1 channels. The IC(50) values for block of KCNQ channels by XE991 range 1-65 microM. In conclusion, great care should be taken when choosing the concentration of XE991 to use for experiments on native potassium channels or animal studies in order to be able to conclude on selective KCNQ channel-mediated effects.
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Affiliation(s)
- Pernille Elmedyb
- Department of Medical Physiology, The Panum Institute, The University of Copenhagen, Denmark
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Wanke E, Restano-Cassulini R. Toxins interacting with ether-à-go-go-related gene voltage-dependent potassium channels. Toxicon 2007; 49:239-48. [PMID: 17097705 DOI: 10.1016/j.toxicon.2006.09.025] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The critical role that ether-à-go-go-related gene (erg) K(+) channels play in mating in Caenorhabditis elegans, neuronal seizures in Drosophila and cardiac action potential repolarization in humans has been well documented. Three erg genes (erg1, erg2 and erg3) have been identified and characterized. A structurally diverse number of compounds block these channels, but do not display specificity among the different channel isoforms. In this review we describe the blocking properties of several peptides, purified from scorpion, sea anemone and spider venoms, which are selective for certain members of the ERG family of channels. These peptides do not behave as classical pore blockers and appear to modify the gating properties of the channel. Genomic studies predict the existence of many other novel peptides with the potential of being more selective for ERG channels than those discussed here.
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Affiliation(s)
- Enzo Wanke
- Dipartimento di Biotecnologie e Bioscienze, Università di Milano-Bicocca, Piazza della Scienza 2, 20126 Milano, Italy.
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Delprat B, Schaer D, Roy S, Wang J, Puel JL, Geering K. FXYD6 is a novel regulator of Na,K-ATPase expressed in the inner ear. J Biol Chem 2007; 282:7450-6. [PMID: 17209044 DOI: 10.1074/jbc.m609872200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The exquisite sensitivity of the cochlea, which mediates the transduction of sound waves into nerve impulses, depends on the endolymph ionic composition and the endocochlear potential. A key protein in the maintenance of the electrochemical composition of the endolymph is the Na,K-ATPase. In this study, we have looked for the presence in the rat inner ear of members of the FXYD protein family, recently identified as tissue-specific modulators of Na,K-ATPase. Only FXYD6 is detected at the protein level. FXYD6 is expressed in various epithelial cells bordering the endolymph space and in the auditory neurons. FXYD6 co-localizes with Na,K-ATPase in the stria vascularis and can be co-immunoprecipitated with Na,K-ATPase. After expression in Xenopus oocytes, FXYD6 associates with Na,K-ATPase alpha1-beta1 and alpha1-beta2 isozymes, which are preferentially expressed in different regions of the inner ear and also with gastric and non-gastric H,K-ATPases. The apparent K(+) and Na(+) affinities of alpha1-beta1 and alpha1-beta2 isozymes are different. Association of FXYD6 with Na,K-ATPase alpha1-beta1 isozymes slightly decreases their apparent K(+) affinity and significantly decreases their apparent Na(+) affinity. On the other hand, association with alpha1-beta2 isozymes increases their apparent K(+) and Na(+) affinity. The effects of FXYD6 on the apparent Na(+) affinity of Na,K-ATPase and the voltage dependence of its K(+) effect are distinct from other FXYD proteins. In conclusion, this study defines the last FXYD protein of unknown function as a modulator of Na,K-ATPase. Among FXYD protein, FXYD6 is unique in its expression in the inner ear, suggesting a role in endolymph composition.
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Affiliation(s)
- Benjamin Delprat
- Department of Pharmacology and Toxicology, University of Lausanne, Rue du Bugnon 27, 1005 Lausanne, Switzerland
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Hibino H, Kurachi Y. Molecular and physiological bases of the K+ circulation in the mammalian inner ear. Physiology (Bethesda) 2006; 21:336-45. [PMID: 16990454 DOI: 10.1152/physiol.00023.2006] [Citation(s) in RCA: 136] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Endolymph, the extracellular solution in cochlea, contains 150 mM K(+) and exhibits a potential of approximately +80 mV relative to neighboring extracellular spaces. This unique situation, essential for hearing, is maintained by K(+) circulation from perilymph to endolymph through the cochlear lateral wall. Recent studies have identified ion-transport molecules involved in the K(+) circulation and their pathophysiological relevance.
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Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Division of Molecular and Cellular Pharmacology, Graduate School of Medicine, Osaka University, Osaka, Japan
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Hurley KM, Gaboyard S, Zhong M, Price SD, Wooltorton JRA, Lysakowski A, Eatock RA. M-like K+ currents in type I hair cells and calyx afferent endings of the developing rat utricle. J Neurosci 2006; 26:10253-69. [PMID: 17021181 PMCID: PMC6674627 DOI: 10.1523/jneurosci.2596-06.2006] [Citation(s) in RCA: 79] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2006] [Revised: 08/18/2006] [Accepted: 08/21/2006] [Indexed: 12/17/2022] Open
Abstract
Type I vestibular hair cells have large K+ currents that, like neuronal M currents, activate negative to resting potential and are modulatable. In rodents, these currents are acquired postnatally. In perforated-patch recordings from rat utricular hair cells, immature hair cells [younger than postnatal day 7 (P7)] had a steady-state K+ conductance (g(-30)) with a half-activation voltage (V1/2) of -30 mV. The size and activation range did not change in maturing type II cells, but, by P16, type I cells had added a K conductance that was on average fourfold larger and activated much more negatively. This conductance may comprise two components: g(-60) (V1/2 of -60 mV) and g(-80) (V1/2 of -80 mV). g(-80) washed out during ruptured patch recordings and was blocked by a protein kinase inhibitor. M currents can include contributions from KCNQ and ether-a-go-go-related (erg) channels. KCNQ and erg channel blockers both affected the K+ currents of type I cells, with KCNQ blockers being more potent at younger than P7 and erg blockers more potent at older than P16. Single-cell reverse transcription-PCR and immunocytochemistry showed expression of KCNQ and erg subunits. We propose that KCNQ channels contribute to g(-30) and g(-60) and erg subunits contribute to g(-80). Type I hair cells are contacted by calyceal afferent endings. Recordings from dissociated calyces and afferent endings revealed large K+ conductances, including a KCNQ conductance. Calyx endings were strongly labeled by KCNQ4 and erg1 antisera. Thus, both hair cells and calyx endings have large M-like K+ conductances with the potential to control the gain of transmission.
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Affiliation(s)
- Karen M. Hurley
- The Bobby R. Alford Department of Otorhinolaryngology, Head and Neck Surgery and
| | - Sophie Gaboyard
- Department of Anatomy and Cell Biology, University of Illinois, Chicago, Illinois 60612
| | - Meng Zhong
- The Bobby R. Alford Department of Otorhinolaryngology, Head and Neck Surgery and
| | - Steven D. Price
- Department of Anatomy and Cell Biology, University of Illinois, Chicago, Illinois 60612
| | | | - Anna Lysakowski
- Department of Anatomy and Cell Biology, University of Illinois, Chicago, Illinois 60612
| | - Ruth Anne Eatock
- The Bobby R. Alford Department of Otorhinolaryngology, Head and Neck Surgery and
- Department of Neuroscience, Baylor College of Medicine, Houston, Texas 77030, and
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18
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Wangemann P. Supporting sensory transduction: cochlear fluid homeostasis and the endocochlear potential. J Physiol 2006; 576:11-21. [PMID: 16857713 PMCID: PMC1995626 DOI: 10.1113/jphysiol.2006.112888] [Citation(s) in RCA: 330] [Impact Index Per Article: 18.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Accepted: 07/14/2006] [Indexed: 12/13/2022] Open
Abstract
The exquisite sensitivity of the cochlea, which mediates the transduction of sound waves into nerve impulses, depends on the endocochlear potential and requires a highly specialized environment that enables and sustains sensory function. Disturbance of cochlear homeostasis is the cause of many forms of hearing loss including the most frequently occurring syndromic and non-syndromic forms of hereditary hearing loss, Pendred syndrome and Cx26-related deafness. The occurrence of these and other monogenetic disorders illustrates that cochlear fluid homeostasis and the generation of the endocochlear potential are poorly secured by functional redundancy. This review summarizes the most prominent aspects of cochlear fluid homeostasis. It covers cochlear fluid composition, the generation of the endocochlear potential, K(+) secretion and cycling and its regulation, the role of gap junctions, mechanisms of acid-base homeostasis, and Ca(2+) transport.
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Affiliation(s)
- Philine Wangemann
- Anatomy & Physiology Department, 205 Coles Hall, Kansas State University, Manhattan, 66506, USA.
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