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Schade-Mann T, Münkner S, Eckrich T, Engel J. Calcium signaling in interdental cells during the critical developmental period of the mouse cochlea. Hear Res 2020; 389:107913. [PMID: 32120242 DOI: 10.1016/j.heares.2020.107913] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 02/04/2020] [Accepted: 02/07/2020] [Indexed: 11/18/2022]
Abstract
The tectorial membrane (TM), a complex acellular structure that covers part of the organ of Corti and excites outer hair cells, is required for normal hearing. It consists of collagen fibrils and various glycoproteins, which are synthesized in embryonic and postnatal development by different cochlear cell types including the interdental cells (IDCs). At its modiolar side, the TM is fixed to the apical surfaces of IDCs, which form the covering epithelium of the spiral limbus. We performed confocal membrane imaging and Ca2+ imaging in IDCs of the developing mouse cochlea from birth to postnatal day 18 (P18). Using the fluorescent membrane markers FM 4-64 and CellMask™ Deep Red on explanted whole-mount cochlear epithelium, we identified the morphology of IDCs at different z-levels of the spiral limbus. Ca2+ imaging of Fluo-8 AM-loaded cochlear epithelia revealed spontaneous intracellular Ca2+ transients in IDCs at P0/1, P4/5, and P18. Their relative frequency was lowest on P0/1, increased by a factor of 12.5 on P4/5 and decreased to twice the initial value on P18. At all three ages, stimulation of IDCs with the trinucleotides ATP and UTP at 1 and 10 μM elicited Ca2+ transients of varying amplitude and shape. Before the onset of hearing, IDCs responded with robust Ca2+ oscillations. At P18, after the onset of hearing, ATP stimulation either caused Ca2+ oscillations or an initial Ca2+ peak followed by a plateau while the UTP response was unchanged from that at pre-hearing stage. Parameters of spontaneous and nucleotide-evoked Ca2+ transients such as amplitude, decay time and duration were markedly reduced during cochlear development, whereas the kinetics of the Ca2+ rise did not show relevant changes. Whether low-frequency spontaneous Ca2+ transients are necessary for the formation and maintenance of the tectorial membrane e.g. by regulating gene transcription needs to be elucidated in further studies.
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Affiliation(s)
- Thore Schade-Mann
- Dept. of Biophysics & CIPMM, Hearing Research, Saarland University, Homburg, Germany; Department of Otolaryngology, Head and Neck Surgery, Tübingen University Medical Centre, Germany
| | - Stefan Münkner
- Dept. of Biophysics & CIPMM, Hearing Research, Saarland University, Homburg, Germany
| | - Tobias Eckrich
- Dept. of Biophysics & CIPMM, Hearing Research, Saarland University, Homburg, Germany
| | - Jutta Engel
- Dept. of Biophysics & CIPMM, Hearing Research, Saarland University, Homburg, Germany.
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Stephani F, Scheuer V, Eckrich T, Blum K, Wang W, Obermair GJ, Engel J. Deletion of the Ca 2+ Channel Subunit α 2δ3 Differentially Affects Ca v2.1 and Ca v2.2 Currents in Cultured Spiral Ganglion Neurons Before and After the Onset of Hearing. Front Cell Neurosci 2019; 13:278. [PMID: 31293392 PMCID: PMC6606706 DOI: 10.3389/fncel.2019.00278] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2019] [Accepted: 06/07/2019] [Indexed: 12/14/2022] Open
Abstract
Voltage-gated Ca2+ channels are composed of a pore-forming α1 subunit and auxiliary β and α2δ subunits, which modulate Ca2+ current properties and channel trafficking. So far, the partial redundancy and specificity of α1 for α2δ subunits in the CNS have remained largely elusive. Mature spiral ganglion (SG) neurons express α2δ subunit isoforms 1, 2, and 3 and multiple Ca2+ channel subtypes. Differentiation and in vivo functions of their endbulb of Held synapses, which rely on presynaptic P/Q channels (Lin et al., 2011), require the α2δ3 subunit (Pirone et al., 2014). This led us to hypothesize that P/Q channels may preferentially co-assemble with α2δ3. Using a dissociated primary culture, we analyzed the effects of α2δ3 deletion on somatic Ca2+ currents (ICa) of SG neurons isolated at postnatal day 20 (P20), when the cochlea is regarded to be mature. P/Q currents were the dominating steady-state Ca2+ currents (54% of total) followed by T-type, L-type, N-type, and R-type currents. Deletion of α2δ3 reduced P/Q- and R-type currents by 60 and 38%, respectively, whereas L-type, N-type, and T-type currents were not altered. A subset of ICa types was also analyzed in SG neurons isolated at P5, i.e., before the onset of hearing (P12). Both L-type and N-type current amplitudes of wildtype SG neurons were larger at P5 compared with P20. Deletion of α2δ3 reduced L-type and N-type currents by 23 and 44%, respectively. In contrast, small P/Q currents, which were just being up-regulated at P5, were unaffected by the lack of α2δ3. In summary, α2δ3 regulates amplitudes of L- and N-type currents of immature cultured SG neurons, whereas it regulates P/Q- and R-type currents at P20. Our data indicate a developmental switch from dominating somatic N- to P/Q-type currents in cultured SG neurons. A switch from N- to P/Q-type channels, which has been observed at several central synapses, may also occur at developing endbulbs of Held. In this case, reduction of both neonatal N- (P5) and more mature P/Q-type currents (around/after hearing onset) may contribute to the impaired morphology and function of endbulb synapses in α2δ3-deficient mice.
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Affiliation(s)
- Friederike Stephani
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, School of Medicine, Saarland University, Homburg, Germany
| | - Veronika Scheuer
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, School of Medicine, Saarland University, Homburg, Germany
| | - Tobias Eckrich
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, School of Medicine, Saarland University, Homburg, Germany
| | - Kerstin Blum
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, School of Medicine, Saarland University, Homburg, Germany
| | - Wenying Wang
- Department of Physiology, School of Medicine, University of Nevada, Reno, NV, United States
| | - Gerald J Obermair
- Department of Physiology and Medical Physics, Medical University Innsbruck, Innsbruck, Austria.,Division Physiology, Karl Landsteiner University of Health Sciences, Krems, Austria
| | - Jutta Engel
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine, School of Medicine, Saarland University, Homburg, Germany
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Sonntag M, Blosa M, Schmidt S, Reimann K, Blum K, Eckrich T, Seeger G, Hecker D, Schick B, Arendt T, Engel J, Morawski M. Synaptic coupling of inner ear sensory cells is controlled by brevican-based extracellular matrix baskets resembling perineuronal nets. BMC Biol 2018; 16:99. [PMID: 30253762 PMCID: PMC6156866 DOI: 10.1186/s12915-018-0566-8] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2018] [Accepted: 08/15/2018] [Indexed: 02/08/2023] Open
Abstract
Background Perineuronal nets (PNNs) are specialized aggregations of extracellular matrix (ECM) molecules surrounding specific neurons in the central nervous system (CNS). PNNs are supposed to control synaptic transmission and are frequently associated with neurons firing at high rates, including principal neurons of auditory brainstem nuclei. The origin of high-frequency activity of auditory brainstem neurons is the indefatigable sound-driven transmitter release of inner hair cells (IHCs) in the cochlea. Results Here, we show that synaptic poles of IHCs are ensheathed by basket-like ECM complexes formed by the same molecules that constitute PNNs of neurons in the CNS, including brevican, aggreccan, neurocan, hyaluronan, and proteoglycan link proteins 1 and 4 and tenascin-R. Genetic deletion of brevican, one of the main components, resulted in a massive degradation of ECM baskets at IHCs, a significant impairment in spatial coupling of pre- and postsynaptic elements and mild impairment of hearing. Conclusions These ECM baskets potentially contribute to control of synaptic transmission at IHCs and might be functionally related to PNNs of neurons in the CNS. Electronic supplementary material The online version of this article (10.1186/s12915-018-0566-8) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Mandy Sonntag
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Maren Blosa
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Sophie Schmidt
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Katja Reimann
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Kerstin Blum
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), School of Medicine, Saarland University, Homburg, Germany
| | - Tobias Eckrich
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), School of Medicine, Saarland University, Homburg, Germany
| | - Gudrun Seeger
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Dietmar Hecker
- Department of Otorhinolaryngology, School of Medicine, Saarland University, Homburg, Germany
| | - Bernhard Schick
- Department of Otorhinolaryngology, School of Medicine, Saarland University, Homburg, Germany
| | - Thomas Arendt
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany
| | - Jutta Engel
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), School of Medicine, Saarland University, Homburg, Germany
| | - Markus Morawski
- Paul-Flechsig-Institute of Brain Research, Medical Faculty, University of Leipzig, Leipzig, Germany.
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Eckrich T, Blum K, Milenkovic I, Engel J. Fast Ca 2+ Transients of Inner Hair Cells Arise Coupled and Uncoupled to Ca 2+ Waves of Inner Supporting Cells in the Developing Mouse Cochlea. Front Mol Neurosci 2018; 11:264. [PMID: 30104958 PMCID: PMC6077211 DOI: 10.3389/fnmol.2018.00264] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2018] [Accepted: 07/12/2018] [Indexed: 01/29/2023] Open
Abstract
Before the onset of hearing, which occurs around postnatal day 12 (P12) in mice, inner hair cells (IHCs) of the immature cochlea generate sound-independent Ca2+ action potentials (APs), which stimulate the auditory pathway and guide maturation of neuronal circuits. During these early postnatal days, intercellular propagating Ca2+ waves elicited by ATP-induced ATP release are found in inner supporting cells (ISCs). It is debated whether IHCs are able to fire Ca2+ APs independently or require a trigger by an ISC Ca2+ wave. To identify the Ca2+ transients of IHCs underlying Ca2+ APs and to analyze their dependence on ISC Ca2+ waves, we performed fast Ca2+ imaging of Fluo-8 AM-loaded organs of Corti at P4/P5. Fast Ca2+ transients (fCaTs) generated by IHCs were simultaneously imaged with Ca2+ waves in ISCs. ISC Ca2+ waves frequently evoked bursts consisting of >5 fCaTs in multiple adjacent IHCs. Although Ca2+ elevations of small amplitude appeared to be triggered by ISC Ca2+ waves in IHCs of Cav1.3 knockout mice we never observed fCaTs, indicating their requirement for Ca2+ influx through Cav1.3 channels. The Ca2+ wave-triggered Ca2+ upstroke in wildtype IHCs occurred 0.52 ± 0.27 s later than the rise of the Ca2+ signal in the adjacent ISCs. In comparison, superfusion of 1 μM ATP elicited bursts of fCaTs in IHCs starting 0.99 ± 0.34 s prior to Ca2+ elevations in adjacent ISCs. PPADS irreversibly abolished Ca2+ waves in ISCs and reversibly reduced fCaTs in IHCs indicating differential involvement of P2 receptors. IHC and ISC Ca2+ signals were however unaltered in P2X2R/P2X3R double knockout or in P2X7R knockout mice. Together, our data revealed a fairly similar occurrence of fCaTs within a burst (56.5%) compared with 43.5% as isolated single fCaTs or in groups of 2–5 fCaTs (minibursts). We provide evidence that IHCs autonomously generate single fCaTs and minibursts whereas bursts synchronized between neighboring IHCs were mostly triggered by ISC Ca2+ waves. Neonatal IHCs thus spontaneously generate electrical and Ca2+ activity, which is enhanced and largely synchronized by activity of ISCs of Kölliker’s organ indicating two sources of spontaneous activity in the developing auditory system.
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Affiliation(s)
- Tobias Eckrich
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, School of Medicine, Homburg, Germany
| | - Kerstin Blum
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, School of Medicine, Homburg, Germany
| | - Ivan Milenkovic
- Carl-Ludwig-Institute for Physiology, Faculty of Medicine, University of Leipzig, Leipzig, Germany
| | - Jutta Engel
- Department of Biophysics, Center for Integrative Physiology and Molecular Medicine (CIPMM), Saarland University, School of Medicine, Homburg, Germany
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Eckrich T, Varakina K, Johnson SL, Franz C, Singer W, Kuhn S, Knipper M, Holley MC, Marcotti W. Development and function of the voltage-gated sodium current in immature mammalian cochlear inner hair cells. PLoS One 2012; 7:e45732. [PMID: 23029208 PMCID: PMC3446918 DOI: 10.1371/journal.pone.0045732] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2012] [Accepted: 08/14/2012] [Indexed: 12/19/2022] Open
Abstract
Inner hair cells (IHCs), the primary sensory receptors of the mammalian cochlea, fire spontaneous Ca2+ action potentials before the onset of hearing. Although this firing activity is mainly sustained by a depolarizing L-type (CaV1.3) Ca2+ current (ICa), IHCs also transiently express a large Na+ current (INa). We aimed to investigate the specific contribution of INa to the action potentials, the nature of the channels carrying the current and whether the biophysical properties of INa differ between low- and high-frequency IHCs. We show that INa is highly temperature-dependent and activates at around −60 mV, close to the action potential threshold. Its size was larger in apical than in basal IHCs and between 5% and 20% should be available at around the resting membrane potential (−55 mV/−60 mV). However, in vivo the availability of INa could potentially increase to >60% during inhibitory postsynaptic potential activity, which transiently hyperpolarize IHCs down to as far as −70 mV. When IHCs were held at −60 mV and INa elicited using a simulated action potential as a voltage command, we found that INa contributed to the subthreshold depolarization and upstroke of an action potential. We also found that INa is likely to be carried by the TTX-sensitive channel subunits NaV1.1 and NaV1.6 in both apical and basal IHCs. The results provide insight into how the biophysical properties of INa in mammalian cochlear IHCs could contribute to the spontaneous physiological activity during cochlear maturation in vivo.
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Affiliation(s)
- Tobias Eckrich
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Ksenya Varakina
- Department of Otolaryngology, Tübingen Hearing Research Center, Molecular Physiology of Hearing, University of Tübingen, Tübingen, Germany
| | - Stuart L. Johnson
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Christoph Franz
- Department of Otolaryngology, Tübingen Hearing Research Center, Molecular Physiology of Hearing, University of Tübingen, Tübingen, Germany
| | - Wibke Singer
- Department of Otolaryngology, Tübingen Hearing Research Center, Molecular Physiology of Hearing, University of Tübingen, Tübingen, Germany
| | - Stephanie Kuhn
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
| | - Marlies Knipper
- Department of Otolaryngology, Tübingen Hearing Research Center, Molecular Physiology of Hearing, University of Tübingen, Tübingen, Germany
| | - Matthew C. Holley
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
- * E-mail: (MH); (WM)
| | - Walter Marcotti
- Department of Biomedical Science, University of Sheffield, Sheffield, United Kingdom
- * E-mail: (MH); (WM)
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