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Kesdoğan AB, Neureiter A, Gaebler AJ, Kalia AK, Körner J, Lampert A. Analgesic effect of Botulinum toxin in neuropathic pain is sodium channel independent. Neuropharmacology 2024; 253:109967. [PMID: 38657946 DOI: 10.1016/j.neuropharm.2024.109967] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2023] [Revised: 02/26/2024] [Accepted: 04/20/2024] [Indexed: 04/26/2024]
Abstract
Botulinum neurotoxin type A BoNT/A is used off-label as a third line therapy for neuropathic pain. However, the mechanism of action remains unclear. In recent years, the role of voltage-gated sodium channels (Nav) in neuropathic pain became evident and it was suggested that block of sodium channels by BoNT/A would contribute to its analgesic effect. We assessed sodium channel function in the presence of BoNT/A in heterologously expressed Nav1.7, Nav1.3, and the neuronal cell line ND7/23 by high throughput automated and manual patch-clamp. We used both the full protein and the isolated catalytic light chain LC/A for acute or long-term extracellular or intracellular exposure. To assess the toxin's effect in a human cellular system, we differentiated induced pluripotent stem cells (iPSC) into sensory neurons from a healthy control and a patient suffering from a hereditary neuropathic pain syndrome (inherited erythromelalgia) carrying the Nav1.7/p.Q875E-mutation and carried out multielectrode-array measurements. Both BoNT/A and the isolated catalytic light chain LC/A showed limited effects in heterologous expression systems and the neuronal cell line ND7/23. Spontaneous activity in iPSC derived sensory neurons remained unaltered upon BoNT/A exposure both in neurons from the healthy control and the mutation carrying patient. BoNT/A may not specifically be beneficial in pain syndromes linked to sodium channel variants. The favorable effects of BoNT/A in neuropathic pain are likely based on mechanisms other than sodium channel blockage and new approaches to understand BoNT/A's therapeutic effects are necessary.
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Affiliation(s)
- Aylin B Kesdoğan
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Anika Neureiter
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Arnim J Gaebler
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Psychiatry, Psychotherapy and Psychosomatics, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Anil K Kalia
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
| | - Jannis Körner
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Anesthesiology, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Department of Intensive and Intermediate Care, Medical Faculty, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany.
| | - Angelika Lampert
- Institute of Neurophysiology, RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany; Scientific Center for Neuropathic Pain Research Aachen, SCN(Aachen), RWTH Aachen University Hospital, Pauwelsstr. 30, 52074, Aachen, Germany
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Spinal cord injury-mediated changes in electrophysiological properties of rat gastric nodose ganglion neurons. Exp Neurol 2022; 348:113927. [PMID: 34798136 PMCID: PMC8727501 DOI: 10.1016/j.expneurol.2021.113927] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Revised: 10/30/2021] [Accepted: 11/11/2021] [Indexed: 02/03/2023]
Abstract
In preclinical rodent models, spinal cord injury (SCI) manifests as gastric vagal afferent dysfunction both acutely and chronically. However, the mechanism that underlies this dysfunction remains unknown. In the current study, we examined the effect of SCI on gastric nodose ganglia (NG) neuron excitability and on voltage-gated Na+ (NaV) channels expression and function in rats after an acute (i.e. 3-days) and chronic (i.e. 3-weeks) period. Rats randomly received either T3-SCI or sham control surgery 3-days or 3-weeks prior to experimentation as well as injections of 3% DiI solution into the stomach to identify gastric NG neurons. Single cell qRT-PCR was performed on acutely dissociated DiI-labeled NG neurons to measure NaV1.7, NaV1.8 and NaV1.9 expression levels. The results indicate that all 3 channel subtypes decreased. Current- and voltage-clamp whole-cell patch-clamp recordings were performed on acutely dissociated DiI-labeled NG neurons to measure active and passive properties of C- and A-fibers as well as the biophysical characteristics of NaV1.8 channels in gastric NG neurons. Acute and chronic SCI did not demonstrate deleterious effects on either passive properties of dissociated gastric NG neurons or biophysical properties of NaV1.8. These findings suggest that although NaV gene expression levels change following SCI, NaV1.8 function is not altered. The disruption throughout the entirety of the vagal afferent neuron has yet to be investigated.
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Koleilat A, Dugdale JA, Christenson TA, Bellah JL, Lambert AM, Masino MA, Ekker SC, Schimmenti LA. L-type voltage-gated calcium channel agonists mitigate hearing loss and modify ribbon synapse morphology in the zebrafish model of Usher syndrome type 1. Dis Model Mech 2020; 13:13/11/dmm043885. [PMID: 33361086 PMCID: PMC7710014 DOI: 10.1242/dmm.043885] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2019] [Accepted: 09/15/2020] [Indexed: 01/19/2023] Open
Abstract
The mariner (myo7aa−/−) mutant is a zebrafish model for Usher syndrome type 1 (USH1). To further characterize hair cell synaptic elements in myo7aa−/− mutants, we focused on the ribbon synapse and evaluated ultrastructure, number and distribution of immunolabeled ribbons, and postsynaptic densities. By transmission electron microscopy, we determined that myo7aa−/− zebrafish have fewer glutamatergic vesicles tethered to ribbon synapses, yet maintain a comparable ribbon area. In myo7aa−/− hair cells, immunolocalization of Ctbp2 showed fewer ribbon-containing cells in total and an altered distribution of Ctbp2 puncta compared to wild-type hair cells. myo7aa−/− mutants have fewer postsynaptic densities – as assessed by MAGUK immunolabeling – compared to wild-type zebrafish. We quantified the circular swimming behavior of myo7aa−/− mutant fish and measured a greater turning angle (absolute smooth orientation). It has previously been shown that L-type voltage-gated calcium channels are necessary for ribbon localization and occurrence of postsynaptic density; thus, we hypothesized and observed that L-type voltage-gated calcium channel agonists change behavioral and synaptic phenotypes in myo7aa−/− mutants in a drug-specific manner. Our results indicate that treatment with L-type voltage-gated calcium channel agonists alter hair cell synaptic elements and improve behavioral phenotypes of myo7aa−/− mutants. Our data support that L-type voltage-gated calcium channel agonists induce morphological changes at the ribbon synapse – in both the number of tethered vesicles and regarding the distribution of Ctbp2 puncta – shift swimming behavior and improve acoustic startle response. Summary: We quantified behavioral and synaptic morphology differences between wild-type zebrafish larvae and the mariner (myo7aa−/−) mutant, finding that these differences can be modified by L-type voltage-gated calcium channel agonists.
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Affiliation(s)
- Alaa Koleilat
- College of Continuing and Professional Studies, University of Minnesota, Minneapolis, MN 55108, USA.,Mayo Clinic Graduate School of Biomedical Sciences, Clinical and Translational Science Track, Rochester, MN 55905, USA.,Center for Clinical and Translational Science, Mayo Clinic, Rochester, MN 55905, USA
| | - Joseph A Dugdale
- Department of Otorhinolaryngology, Mayo Clinic, Rochester, MN 55905, USA
| | | | - Jeffrey L Bellah
- Center for Clinical and Translational Science, Mayo Clinic, Rochester, MN 55905, USA.,Department of Genetics and Development, Columbia University, New York City, NY 10032, USA
| | - Aaron M Lambert
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, USA.,Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138, USA
| | - Mark A Masino
- Department of Neuroscience, University of Minnesota, Minneapolis, MN 55455, USA
| | - Stephen C Ekker
- Center for Clinical and Translational Science, Mayo Clinic, Rochester, MN 55905, USA.,Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA
| | - Lisa A Schimmenti
- Department of Otorhinolaryngology, Mayo Clinic, Rochester, MN 55905, USA .,Department of Biochemistry and Molecular Biology, Mayo Clinic, Rochester, MN 55905, USA.,Department of Pediatrics, University of Minnesota, Minneapolis, MN 55455, USA.,Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA.,Department of Ophthalmology and Visual Neuroscience, University of Minnesota, Minneapolis, MN 55454, USA.,Department of Clinical Genomics, Mayo Clinic, Rochester, MN 55905, USA
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Abstract
Voltage-gated sodium channels (VGSC) are critical determinants of cellular electrical activity through the control of initiation and propagation of action potential. To ensure this role, these proteins are not consistently delivered to the plasma membrane but undergo drastic quality controls throughout various adaptive processes such as biosynthesis, anterograde and retrograde trafficking, and membrane targeting. In pathological conditions, this quality control could lead to the retention of functional VGSC and is therefore the target of different pharmacological approaches. The present chapter gives an overview of the current understanding of the facets of VGSC life cycle in the context of both cardiac and neuronal cell types.
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Affiliation(s)
- A Mercier
- Laboratoire de Signalisation et Transports Ioniques Membranaires, Pôle Biologie Santé, Université de Poitiers, CNRS, 1 rue Georges Bonnet, TSA 51106, 86073, Poitiers Cedex 9, France
| | - P Bois
- Laboratoire de Signalisation et Transports Ioniques Membranaires, Pôle Biologie Santé, Université de Poitiers, CNRS, 1 rue Georges Bonnet, TSA 51106, 86073, Poitiers Cedex 9, France
| | - A Chatelier
- Laboratoire de Signalisation et Transports Ioniques Membranaires, Pôle Biologie Santé, Université de Poitiers, CNRS, 1 rue Georges Bonnet, TSA 51106, 86073, Poitiers Cedex 9, France.
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Sun J, Jacobs KM. Knockout of Cyclophilin-D Provides Partial Amelioration of Intrinsic and Synaptic Properties Altered by Mild Traumatic Brain Injury. Front Syst Neurosci 2016; 10:63. [PMID: 27489538 PMCID: PMC4951523 DOI: 10.3389/fnsys.2016.00063] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2016] [Accepted: 07/07/2016] [Indexed: 01/01/2023] Open
Abstract
Mitochondria are central to cell survival and Ca2+ homeostasis due to their intracellular buffering capabilities. Mitochondrial dysfunction resulting in mitochondrial permeability transition pore (mPTP) opening has been reported after mild traumatic brain injury (mTBI). Cyclosporine A provides protection against the mPTP opening through its interaction with cyclophilin-D (CypD). A recent study has found that the extent of axonal injury after mTBI was diminished in neocortex in cyclophilin-D knockout (CypDKO) mice. Here we tested whether this CypDKO could also provide protection from the increased intrinsic and synaptic neuronal excitability previously described after mTBI in a mild central fluid percussion injury mice model. CypDKO mice were crossed with mice expressing yellow fluorescent protein (YFP) in layer V pyramidal neurons in neocortex to create CypDKO/YFP-H mice. Whole cell patch clamp recordings from axotomized (AX) and intact (IN) YFP+ layer V pyramidal neurons were made 1 and 2 days after sham or mTBI in slices from CypDKO/YFP-H mice. Both excitatory post synaptic currents (EPSCs) recorded in voltage clamp and intrinsic cellular properties, including action potential (AP), afterhyperpolarization (AHP), and depolarizing after potential (DAP) characteristics recorded in current clamp were evaluated. There was no significant difference between sham and mTBI for either spontaneous or miniature EPSC frequency, suggesting that CypDKO ameliorates excitatory synaptic abnormalities. There was a partial amelioration of intrinsic properties altered by mTBI. Alleviated were the increased slope of the AP frequency vs. injected current plot, the increased AP, AHP and DAP amplitudes. Other properties that saw a reversal that became significant in the opposite direction include the current rheobase and AP overshoot. The AP threshold remained depolarized and the input resistance remained increased in mTBI compared to sham. Additional altered properties suggest that the CypDKO likely has a direct effect on membrane properties, rather than producing a selective reduction of the effects of mTBI. These results suggest that inhibiting CypD after TBI is an effective strategy to reduce synaptic hyperexcitation, making it a continued target for potential treatment of network abnormalities.
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Affiliation(s)
- Jianli Sun
- Department of Anatomy and Neurobiology, Virginia Commonwealth University Richmond, VA, USA
| | - Kimberle M Jacobs
- Department of Anatomy and Neurobiology, Virginia Commonwealth University Richmond, VA, USA
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Burtscher V, Schicker K, Novikova E, Pöhn B, Stockner T, Kugler C, Singh A, Zeitz C, Lancelot ME, Audo I, Leroy BP, Freissmuth M, Herzig S, Matthes J, Koschak A. Spectrum of Cav1.4 dysfunction in congenital stationary night blindness type 2. BIOCHIMICA ET BIOPHYSICA ACTA 2014; 1838:2053-65. [PMID: 24796500 PMCID: PMC4065569 DOI: 10.1016/j.bbamem.2014.04.023] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/12/2014] [Revised: 04/11/2014] [Accepted: 04/23/2014] [Indexed: 11/26/2022]
Abstract
Defective retinal synaptic transmission in patients affected with congenital stationary night blindness type 2 (CSNB2) can result from different dysfunction phenotypes in Cav1.4 L-type calcium channels. Here we investigated two prototypical Cav1.4 variants from either end of the functional spectrum. Using whole-cell and single-channel patch-clamp techniques, we provide analysis of the biophysical characteristics of the point mutation L860P and the C-terminal truncating mutation R1827X. L860P showed a typical loss-of-function phenotype attributed to a reduced number of functional channels expressed at the plasma membrane as implied by gating current and non-stationary noise analyses. This phenotype can be rationalized, because the inserted proline is predicted to break an amphipatic helix close to the transmembrane segment IIIS1 and thus to reduce channel stability and promote misfolding. In fact, L860P was subject to an increased turnover. In contrast, R1827X displayed an apparent gain-of-function phenotype, i.e., due to a hyperpolarizing shift of the IV-curve and increased single-channel activity. However, truncation also resulted in the loss of functional C-terminal modulation and thus unmasked calcium-dependent inactivation. Thus R1827X failed to support continuous calcium influx. Current inactivation curtails the dynamic range of photoreceptors (e.g., when adapting to variation in illumination). Taken together, the analysis of two representative mutations that occur in CSNB2 patients revealed fundamental differences in the underlying defect. These may explain subtle variations in the clinical manifestation and must be taken into account, if channel function is to be restored by pharmacochaperones or related approaches.
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Affiliation(s)
- Verena Burtscher
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Klaus Schicker
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Elena Novikova
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Birgit Pöhn
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Thomas Stockner
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria
| | - Christof Kugler
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria
| | - Anamika Singh
- University of Innsbruck, Institute of Pharmacy, Pharmacology and Toxicology, Center for Chemistry and Biomedicine, Innrain 80-82/III, 6020 Innsbruck, Austria
| | - Christina Zeitz
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France
| | - Marie-Elise Lancelot
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France
| | - Isabelle Audo
- INSERM, UMR_S968, Paris F-75012, France; CNRS, UMR_7210, Paris F-75012, France; UPMC Univ Paris 06, UMR_S 968, Institut de la Vision, Paris F-75012, France; Centre Hospitalier National d'Ophtalmologie des Quinze-Vingts, INSERM-DHOS CIC 503, Paris F-75012, France; UCL-Institute of Ophthalmology, 11-43 Bath Street, London EC1V 9EL, UK
| | - Bart Peter Leroy
- Dept of Ophthalmology & Center for Medical Genetics, Ghent University Hospital & Ghent University, 9000 Ghent, Belgium
| | - Michael Freissmuth
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Pharmacology, Währingerstrasse 13A, 1090 Wien, Austria
| | - Stefan Herzig
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Jan Matthes
- University of Cologne, Department of Pharmacology and Center of Molecular Medicine, 50931 Cologne, Germany
| | - Alexandra Koschak
- Medical University Vienna, Center for Physiology and Pharmacology, Department of Neurophysiology and -pharmacology, Schwarzspanierstrasse 17, 1090 Vienna, Austria.
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Soudry D, Meir R. The neuronal response at extended timescales: a linearized spiking input-output relation. Front Comput Neurosci 2014; 8:29. [PMID: 24765073 PMCID: PMC3980113 DOI: 10.3389/fncom.2014.00029] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2013] [Accepted: 02/24/2014] [Indexed: 11/16/2022] Open
Abstract
Many biological systems are modulated by unknown slow processes. This can severely hinder analysis – especially in excitable neurons, which are highly non-linear and stochastic systems. We show the analysis simplifies considerably if the input matches the sparse “spiky” nature of the output. In this case, a linearized spiking Input–Output (I/O) relation can be derived semi-analytically, relating input spike trains to output spikes based on known biophysical properties. Using this I/O relation we obtain closed-form expressions for all second order statistics (input – internal state – output correlations and spectra), construct optimal linear estimators for the neuronal response and internal state and perform parameter identification. These results are guaranteed to hold, for a general stochastic biophysical neuron model, with only a few assumptions (mainly, timescale separation). We numerically test the resulting expressions for various models, and show that they hold well, even in cases where our assumptions fail to hold. In a companion paper we demonstrate how this approach enables us to fit a biophysical neuron model so it reproduces experimentally observed temporal firing statistics on days-long experiments.
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Affiliation(s)
- Daniel Soudry
- Laboratory for Network Biology Research, Department of Electrical Engineering Technion, Haifa, Israel
| | - Ron Meir
- Laboratory for Network Biology Research, Department of Electrical Engineering Technion, Haifa, Israel
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Matavel A, Fleury C, Oliveira LC, Molina F, de Lima ME, Cruz JS, Cordeiro MN, Richardson M, Ramos CHI, Beirão PSL. Structure and activity analysis of two spider toxins that alter sodium channel inactivation kinetics. Biochemistry 2009; 48:3078-88. [PMID: 19231838 DOI: 10.1021/bi802158p] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
In this work, Phoneutria nigriventer toxins PnTx2-5 and PnTx2-6 were shown to markedly delay the fast inactivation kinetics of neuronal-type sodium channels. Furthermore, our data show that they have significant differences in their interaction with the channel. PnTx2-6 has an affinity 6 times higher than that of PnTx2-5, and its effects are not reversible within 10-15 min of washing. PnTx2-6 partially (59%) competes with the scorpion alpha-toxin AaHII, but not with the scorpion beta-toxin CssIV, thus suggesting a mode of action similar to that of site 3 toxins. However, PnTx2-6 is not removed by strong depolarizing pulses, as in the known site 3 toxins. We have also established the correct PnTx2-5 amino acid sequence and confirmed the sequence of PnTx2-6, in both cases establishing that the cysteines are in their oxidized form. A structural model of each toxin is proposed. They show structures with poor alpha-helix content. The model is supported by experimental and theoretical tests. A likely binding region on PnTx2-5 and PnTx2-6 is proposed on the basis of their different affinities and sequence differences.
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Affiliation(s)
- Alessandra Matavel
- Department of Biochemistry and Immunology, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil
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9
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Dominguez B, Felix R, Monjaraz E. Upregulation of voltage-gated Na+ channels by long-term activation of the ghrelin-growth hormone secretagogue receptor in clonal GC somatotropes. Am J Physiol Endocrinol Metab 2009; 296:E1148-56. [PMID: 19223651 DOI: 10.1152/ajpendo.90954.2008] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
A central question in adenohypophyseal cell physiology concerns the role of transmembrane ionic fluxes in the initiation of the hormone secretion process. In the current report, we investigated the effects of the growth hormone (GH) secretagogues ghrelin and GH-releasing peptide-6 (GHRP-6) on the regulation of the functional expression of voltage-gated Na(+) channels using the tumoral somatotrope GC cell line as a model. Cells were cultured under control conditions or in presence of the GH secretagogues (GHS) for 96 h, and Na(+) currents (I(Na)) were characterized in whole cell patch-clamp experiments. GHS treatment significantly increased I(Na) density in a dose-dependent manner. The effects of GHRP-6 were accompanied by an augment in conductance without changes in the kinetics and the voltage dependence of the currents, suggesting an increase in the number of channels in the cell membrane. Sustained inhibition of L-type Ca(2+) channel activity decreased I(Na) density and prevented the effects of the GHS, whereas long-term exposure to an L-channel agonist increased I(Na) density and enhanced the actions of GHRP-6, indicating that Ca(2+) entry through these channels plays a role in the regulation of Na(+) channel expression. Likewise, GHRP-6 failed to enhance Na(+) channel expression in the presence of membrane-permeable inhibitors of protein kinases A and C, as well as the Ca(2+)/calmodulin-dependent kinase II. Conversely, treatment with a cAMP analog or a protein kinase C activator enhanced both basal and GHS-induced secretion of GH measured by enzyme-linked immunoassay, suggesting that GHRP-6 acting through the ghrelin receptor and different signaling pathways enhances Na(+) channel membrane expression, which favors hormone release from GC somatotropes.
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Affiliation(s)
- Belisario Dominguez
- Laboratorio de Neuroendocrinología, Instituto de Fisiología, San Manuel, Puebla, México
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A High Concentration of Resiniferatoxin Inhibits Ion Channel Function in Clonal Neuroendocrine Cells. Anesth Analg 2008; 107:318-24. [DOI: 10.1213/ane.0b013e31816d140a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
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Hervé JC, Derangeon M, Bahbouhi B, Mesnil M, Sarrouilhe D. The connexin turnover, an important modulating factor of the level of cell-to-cell junctional communication: comparison with other integral membrane proteins. J Membr Biol 2007; 217:21-33. [PMID: 17673963 DOI: 10.1007/s00232-007-9054-8] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2007] [Accepted: 06/04/2007] [Indexed: 12/25/2022]
Abstract
The constituent proteins of gap junctions, called "connexins" (Cxs) in chordates, are generally renewed several times a day, in approximately the same rate range as many other integral plasma membrane proteins and the proteins of other channels, other intercellular junctions or different membrane receptors. This permanent renewal turns on a fine-tuned balance among various processes, such as gene transcription, mRNA stability and processing, protein synthesis and oligomerization, posttranslational modifications, transport to the plasma membrane, anchoring to the cytoskeleton, connexon aggregation and docking, regulation of endocytosis and controlled degradations of the proteins. Subtle changes at one or some of these steps would represent an exquisite level of regulation that extends beyond the rapid channel opening and closure events associated with channel gating; membrane channels and receptors are constantly able to answer to physiological requirements to either up- or downregulate their activity. The Cx turnover rate thereby appears to be a key component in the regulation of any protein, particularly of gap junctional proteins. However, the physiological stimuli that control the assembly of Cxs into gap junctions and their degradation remain poorly understood.
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Affiliation(s)
- Jean-Claude Hervé
- Institut de Physiologie et Biologie Cellulaires, Faculté des Sciences Fondamentales et Appliquées, UMR CNRS 6187, Université de Poitiers, 40, avenue du R Pineau, 86022, Poitiers, France.
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Mezey E, Brownstein M. Increased response to high KCl-induced elevation in the intracellular-Ca(2+) concentration in differentiated NG108-15 cell and the inhibitory effect of the L-type Ca(2+) channel blocker, calciseptine. Neurochem Res 2006; 31:127-9. [PMID: 16673173 DOI: 10.1007/s11064-005-9003-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/06/2005] [Indexed: 10/25/2022]
Abstract
Characteristics of the increasing effect for the concentration of intracellular calcium ions ([Ca(2+)](i)) by high-KCl application were investigated in the neuroblastomaxglioma hybrid NG108-15 cell line (NG108-15 cells). The present study confirmed that the increasing effect of [Ca(2+)](i) by high-KCl application in single NG108-15 cells, differentiated with dibutyryl cAMP (Bt(2)cAMP), was significantly enhanced, compared to undifferentiated cells. The following observations were made at first: (1) The response to high-KCl application, in both undifferentiated and differentiated cells, was significantly inhibited by calciseptine (CaS), an L-type Ca(2+) channel blocker, but not by N-, P- and R-type Ca(2+) channel blockers. The IC(50) values for CaS in both undifferentiated and differentiated cell was almost identical. (2) The inhibitory effect of CaS was irreversible. (3) The increasing effect for [Ca(2+)](i) by high-KCl application was completely dependent on the presence of extracellular calcium ions. (4) The increased [Ca(2+)](i) by high-KCl application under a plateau concentration was quickly decreased to basal levels when the high-KCl solution was exchanged for a high-KCl solution containing EGTA (without CaCl(2)). Together, these results suggest that the enhancement of the response effect of [Ca(2+)](i) by high-KCl application in differentiated single NG108-15 cells was mainly due to the quantitative increase of L-type voltage-sensitive calcium channels (VSCCs), which were irreversibly inhibited by CaS.
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Marder E, Goaillard JM. Variability, compensation and homeostasis in neuron and network function. Nat Rev Neurosci 2006; 7:563-74. [PMID: 16791145 DOI: 10.1038/nrn1949] [Citation(s) in RCA: 746] [Impact Index Per Article: 41.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Neurons in most animals live a very long time relative to the half-lives of all of the proteins that govern excitability and synaptic transmission. Consequently, homeostatic mechanisms are necessary to ensure stable neuronal and network function over an animal's lifetime. To understand how these homeostatic mechanisms might function, it is crucial to understand how tightly regulated synaptic and intrinsic properties must be for adequate network performance, and the extent to which compensatory mechanisms allow for multiple solutions to the production of similar behaviour. Here, we use examples from theoretical and experimental studies of invertebrates and vertebrates to explore several issues relevant to understanding the precision of tuning of synaptic and intrinsic currents for the operation of functional neuronal circuits.
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Affiliation(s)
- Eve Marder
- Volen Center and Biology Department, MS 013 Brandeis University, 415 South Street, Waltham, Massachusetts 02454, USA.
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14
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Imanishi T, Matsushima K, Kawaguchi A, Wada T, Masuko T, Yoshida S, Ichida S. Enhancement of veratridine-induced sodium dynamics in NG108-15 cells during differentiation. Biol Pharm Bull 2006; 29:701-4. [PMID: 16595902 DOI: 10.1248/bpb.29.701] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Developmental changes in dynamics of Na+ were studied in neuroblastomaxglioma hybrid NG108-15 cells during differentiation which was induced by dibutyryl cAMP (Bt2cAMP). Ratiometric Na+ imaging with a Na+-sensitive fluorescent dye SBFI (sodium-binding benzofuran isophthalate) revealed that the intracellular Na+ concentration ([Na+]i) was not affected by the application of high K+ (60 mM) solution to either control or differentiated cells. When cells were exposed to 50 microM veratridine (Vtd), an agonist of voltage-sensitive sodium channels (VSSCs), a significant increase in [Na+]i was observed in differentiated but not in undifferentiated cells. Calculated mean [Na+]i value increased from the basal 10.4 to 44.1 mM in response to 50 microM Vtd. This Vtd response was reversibly inhibited by tetrodotoxin (TTX), a specific blocker for VSSCs, in a dose-dependent manner (IC50 = 1 nM). It is suggested that VSSCs in NG108-15 cells are sensitive to TTX and Vtd and that the number of VSSCs increases during differentiation.
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Affiliation(s)
- Takashi Imanishi
- Department of Biological Chemistry, School of Pharmaceutical Sciences, Kinki University, Kowakae, Higashiosaka, Japan
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15
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López-Domínguez AM, Espinosa JL, Navarrete A, Avila G, Cota G. Nerve growth factor affects Ca2+ currents via the p75 receptor to enhance prolactin mRNA levels in GH3 rat pituitary cells. J Physiol 2006; 574:349-65. [PMID: 16690703 PMCID: PMC1817754 DOI: 10.1113/jphysiol.2006.110791] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
In clonal pituitary GH(3) cells, spontaneous action potentials drive the opening of Ca(v)1 (L-type) channels, leading to Ca(2+) transients that are coupled to prolactin gene transcription. Nerve growth factor (NGF) has been shown to stimulate prolactin synthesis by GH(3) cells, but the underlying mechanisms are unknown. Here we studied whether NGF influences prolactin gene expression and Ca(2+) currents. By using RT-PCR, NGF (50 ng ml(-1)) was found to augment prolactin mRNA levels by approximately 80% when applied to GH(3) cells for 3 days. A parallel change in the prolactin content was detected by Western blotting. Both NGF-induced responses were mimicked by an agonist (Bay K 8644) and prevented by a blocker (nimodipine) of L-type channels. In whole-cell patch-clamp experiments, NGF enhanced the L-type Ca(2+) current by approximately 2-fold within 60 min. This effect reversed quickly upon growth factor withdrawal, but was maintained for days in the continued presence of NGF. In addition, chronic treatment (>or= 24 h) with NGF amplified the T-type current, which flows through Ca(v)3 channels and is thought to support pacemaking activity. Thus, NGF probably increases the amount of Ca(2+) that enters per action potential and may also induce a late increase in spike frequency. MC192, a specific antibody for the p75 neurotrophin receptor, but not tyrosine kinase inhibitors (K252a and lavendustin A), blocked the effects of NGF on Ca(2+) currents. Overall, the results indicate that NGF activates the p75 receptor to cause a prolonged increase in Ca(2+) influx through L-type channels, which in turn up-regulates the prolactin mRNA.
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Affiliation(s)
- Adriana M López-Domínguez
- Department of Physiology, Biophysics and Neurosciences, Cinvestav-IPN, AP 14-740, Mexico, DF 07000, Mexico
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16
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Moody WJ, Bosma MM. Ion Channel Development, Spontaneous Activity, and Activity-Dependent Development in Nerve and Muscle Cells. Physiol Rev 2005; 85:883-941. [PMID: 15987798 DOI: 10.1152/physrev.00017.2004] [Citation(s) in RCA: 274] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
At specific stages of development, nerve and muscle cells generate spontaneous electrical activity that is required for normal maturation of intrinsic excitability and synaptic connectivity. The patterns of this spontaneous activity are not simply immature versions of the mature activity, but rather are highly specialized to initiate and control many aspects of neuronal development. The configuration of voltage- and ligand-gated ion channels that are expressed early in development regulate the timing and waveform of this activity. They also regulate Ca2+influx during spontaneous activity, which is the first step in triggering activity-dependent developmental programs. For these reasons, the properties of voltage- and ligand-gated ion channels expressed by developing neurons and muscle cells often differ markedly from those of adult cells. When viewed from this perspective, the reasons for complex patterns of ion channel emergence and regression during development become much clearer.
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Affiliation(s)
- William J Moody
- Department of Biology, University of Washington, Seattle, Washington 98195, USA.
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17
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Ooi GT, Tawadros N, Escalona RM. Pituitary cell lines and their endocrine applications. Mol Cell Endocrinol 2004; 228:1-21. [PMID: 15541569 DOI: 10.1016/j.mce.2004.07.018] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/17/2004] [Accepted: 07/15/2004] [Indexed: 10/26/2022]
Abstract
The pituitary gland is an important component of the endocrine system, and together with the hypothalamus, exerts considerable influence over the functions of other endocrine glands. The hypothalamus either positively or negatively regulates hormonal productions in the pituitary through its release of various trophic hormones which act on specific cell types in the pituitary to secrete a variety of pituitary hormones that are important for growth and development, metabolism, reproductive and nervous system functions. The pituitary is divided into three sections-the anterior lobe which constitute the majority of the pituitary mass and is composed primarily of five hormone-producing cell types (thyrotropes, lactotropes, corticotropes, somatotropes and gonadotropes) each secreting thyrotropin, prolactin, ACTH, growth hormone and gonadotropins (FSH and LH) respectively. There is also a sixth cell type in the anterior lobe-the non-endocrine, agranular, folliculostellate cells. The intermediate lobe produces melanocyte-stimulating hormone and endorphins, whereas the posterior lobe secretes anti-diuretic hormone (vasopressin) and oxytocin. Representative cell lines of all the six cell types of the anterior pituitary have been established and have provided valuable information on genealogy of the various cell lineages, endocrine feedback control of hormone synthesis and secretions, intrapituitary interactions between the various cell types, as well as the role of specific transcription factors that determine each differentiated cell phenotype. In this review, we will discuss the morphology and function of the cell types that make up the anterior pituitary, and the characteristics of the various functional anterior pituitary cell systems that have been established to be representative of each anterior pituitary cell lineage.
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Affiliation(s)
- Guck T Ooi
- Prince Henry's Institute of Medical Research, Monash Medical Centre, Block E, Level 4, 246 Clayton Road, Clayton, Victoria 3168, Australia.
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18
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Schwab Y, Jahke R, Jover E. Expression of tetrodotoxin-sensitive and resistant sodium channels by rat melanotrophs. Neuroreport 2004; 15:1219-23. [PMID: 15129178 DOI: 10.1097/00001756-200405190-00028] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
Rat melanotrophs fire Na+ and Ca2(+)-dependent action potentials. Whereas the molecular identity of Ca2+ channels expressed by these cells is well documented, less is known about Na channels. We characterize the expression of seven sodium channel alpha-subunit and the beta1- and beta2-subunit mRNAs. The tetrodotoxin-resistant Nav1.8 and Nav1.9 alpha subunit mRNAs are detected in the newborn intermediate lobe and in cultured melanotrophs. Electrophysiological recordings further demonstrate the expression of both tetrodotoxin-sensitive and tetrodotoxin-resistant currents by dissociated melanotrophs. Moreover, activated sodium channels are able to elicit intracellular calcium waves, both in the absence or in the presence of tetrodotoxin. This work shows that rat melanotrophs express functional tetrodotoxin-resistant sodium channels, whose activation can lead to the generation of intracellular calcium waves.
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Affiliation(s)
- Yannick Schwab
- UMR-CNRS-ULP 7519, Laboratoire de Neurophysiologie Cellulaire et Intégrée, Université Louis Pasteur 21, rue René Descartes F-67084 Strasbourg-Cedex, France.
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19
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Galindo CA, Sitges M. Dihydropiridines mechanism of action in striatal isolated nerve endings: comparison with omega-agatoxin IVA. Neurochem Res 2004; 29:659-69. [PMID: 15098927 DOI: 10.1023/b:nere.0000018836.82122.23] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
The relative contribution of Ca2+ and Na+ channels to the mechanism underlying the action of the dihydropiridines (DHPs), nimodipine, nitrendipine and nifedipine was investigated in rat striatum synaptosomes. The rise in internal Ca2+ (Ca(i), as determined with fura-2) induced by high K+ was unchanged by the DHPs, which like tetrodotoxin (TTX) inhibited both the rise in internal Na+ (Na(i), as determined with the Na+ selective indicator dye, SBFI) and the rise in Ca(i) induced by veratridine. Nimodipine and nitrendipine were much more potent than nifedipine. Oppositely to TTX and to the DHPs, the P/Q type Ca2+ channel blocker, omega-agatoxin IVA did not inhibit the rise in Ca(i) induced by veratridine, but inhibited the rise in Ca(i) induced by high K+. Veratridine-evoked release of dopamine, GABA, Glu, and Asp (detected by HPLC) was inhibited by nimodipine, nitrendipine, and TTX, while high K+-evoked release was unchanged by the DHPs or TTX. It is concluded that the reduction in presynaptic Na+ channel permeability might contribute to the cerebral effects of DHPs.
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Affiliation(s)
- C A Galindo
- Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, Ciudad Universitaria, México
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20
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Murgia AR, Batista CVF, Prestipino G, Possani LD. Amino acid sequence and function of a new α-toxin from the Amazonian scorpion Tityus cambridgei. Toxicon 2004; 43:737-40. [PMID: 15109895 DOI: 10.1016/j.toxicon.2004.02.014] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2003] [Revised: 02/06/2004] [Accepted: 02/13/2004] [Indexed: 11/26/2022]
Abstract
A toxic peptide earlier denominated Tc48b [Toxicon 40 (2002) 557] was purified to homogeneity and its amino acid sequence determined. It has 64 amino acid residues stabilized by four disulfide bridges with a molecular weight of 7,385.2 atomic mass units (a.m.u.). It affects Na(+)-permeability in pituitary GH3 cells in culture, in a similar fashion as those reported for alpha-scorpion toxins, contrary to most of the New World scorpion toxins that are beta-toxins.
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Affiliation(s)
- Anna Rosa Murgia
- Istituto di Biofisica, C.N.R., via De Marini 6, 16149 Genoa, Italy
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21
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Klein JP, Tendi EA, Dib-Hajj SD, Fields RD, Waxman SG. Patterned electrical activity modulates sodium channel expression in sensory neurons. J Neurosci Res 2003; 74:192-8. [PMID: 14515348 DOI: 10.1002/jnr.10768] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Peripheral nerve injury induces changes in the level of gene expression for sodium channels Nav1.3, Nav1.8, and Nav1.9 within dorsal root ganglion (DRG) neurons, which may contribute to the development of hyperexcitability, ectopic neuronal discharge, and neuropathic pain. The mechanism of this change in sodium channel expression is unclear. Decreased availability of neurotrophic factors following axotomy contributes to these changes in gene transcription, but the question of whether changes in intrinsic neuronal activity levels alone can trigger changes in the expression of these sodium channels has not been addressed. We examined the effect of electrical stimulation on the expression of Nav1.3, Nav1.8, and Nav1.9 by using cultured embryonic mouse sensory neurons under conditions in which nerve growth factor (NGF) was not limiting. Expression of Nav1.3 was not significantly changed following stimulation. In contrast, we observed activity-dependent down-regulation of Nav1.8 and Nav1.9 mRNA and protein levels after stimulation, as demonstrated by quantitative polymerase chain reaction and immunocytochemistry. These results show that a change in neuronal activity can alter the expression of sodium channel genes in a subtype-specific manner, via a mechanism independent of NGF withdrawal.
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Affiliation(s)
- Joshua P Klein
- Department of Neurology and PVA/EPVA Center for Neuroscience and Regeneration Research, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
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22
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Kenney AM, Widlund HR, Rowitch DH. Hedgehog and PI-3 kinase signaling converge on Nmyc1 to promote cell cycle progression in cerebellar neuronal precursors. Development 2003; 131:217-28. [PMID: 14660435 DOI: 10.1242/dev.00891] [Citation(s) in RCA: 177] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
Neuronal precursor cells in the developing cerebellum require activity of the sonic hedgehog (Shh) and phosphoinositide-3-kinase (PI3K) pathways for growth and survival. Synergy between the Shh and PI3K signaling pathways are implicated in the cerebellar tumor medulloblastoma. Here, we describe a mechanism through which these disparate signaling pathways cooperate to promote proliferation of cerebellar granule neuron precursors. Shh signaling drives expression of mRNA encoding the Nmyc1 oncoprotein (previously N-myc), which is essential for expansion of cerebellar granule neuron precursors. The PI3K pathway stabilizes Nmyc1 protein via inhibition of GSK3-dependent Nmyc1 phosphorylation and degradation. The effects of PI3K activity on Nmyc1 stabilization are mimicked by insulin-like growth factor, a PI3K agonist with roles in central nervous system precursor growth and tumorigenesis. These findings indicate that Shh and PI3K signaling pathways converge on N-Myc to regulate neuronal precursor cell cycle progression. Furthermore, they provide a rationale for therapeutic targeting of PI3K signaling in medulloblastoma.
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Affiliation(s)
- Anna Marie Kenney
- Department of Pediatric Oncology, Dana-Farber Cancer Institute and Harvard Medical School, Boston, MA 02115, USA
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23
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Avila G, Monjaraz E, Espinosa JL, Cota G. Downregulation of voltage-gated sodium channels by dexamethasone in clonal rat pituitary cells. Neurosci Lett 2003; 339:21-4. [PMID: 12618291 DOI: 10.1016/s0304-3940(02)01460-x] [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: 11/24/2022]
Abstract
The effect of chronic dexamethasone (DEX) treatment (4-5 days) on Na(+) channel expression was examined in a clonal strain of rat pituitary cells secreting growth hormone (GH) and prolactin (GH3 cells). Using whole-cell patch clamp recording, we found that DEX (1 microM) induces an 80% decrease in Na(+) current density. No concomitant changes in current kinetics or voltage dependence of Na(+) channel function were detected. Instead, the decrease in current density was accompanied by a similar reduction in maximal Na(+) conductance, suggesting the loss of Na(+) channels from the plasma membrane. Accordingly, saxitoxin binding assays carried out on intact cells showed that the average number of Na(+) channels per cell is markedly decreased by DEX. Thus, this glucocorticoid inhibits the cell surface expression of Na(+) channels when chronically applied to GH3 cells.
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Affiliation(s)
- Guillermo Avila
- Department of Biochemistry, Cinvestav-IPN, AP 14-740, DF 07000, Mexico City, Mexico
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24
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Massensini AR, Suckling J, Brammer MJ, Moraes-Santos T, Gomez MV, Romano-Silva MA. Tracking sodium channels in live cells: confocal imaging using fluorescently labeled toxins. J Neurosci Methods 2002; 116:189-96. [PMID: 12044668 DOI: 10.1016/s0165-0270(02)00040-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
One particularly important class of ion channels in excitable cells are the voltage-dependent sodium channels (VDSC). Knowledge of the distribution of VDSC in living cells is important for studies of neuronal excitability, development, and plasticity. Here, we demonstrate a new method for visualizing the spatial distribution of VDSC in living cells. To illustrate the capabilities of the technique, the distribution of VDSC in GH3 cells was revealed with fluorescent derivatives of the alpha-type and beta-type scorpion toxins in conjunction with laser scanning confocal microscopy. Cells exhibited fluorescent hot spots on the surface of the membrane. This characteristic staining pattern was prevented by pre-incubation with unlabeled native toxins and blocked by membrane depolarization for alpha-type toxins. Labeling was not observed in cells lacking sodium channels (HEK 293) after incubation with fluorescent-labeled toxins. Image processing techniques were applied to identify the location of each cluster of labeled VDSC in these cells. The proposed method eliminates artefacts commonly introduced during sample preparation for immunostaining and should prove to be a valuable research tool for investigating VDSC distribution in living specimens.
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Affiliation(s)
- Andre R Massensini
- Brain Image Analysis Unit, Institute of Psychiatry, King's College London, London, UK
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25
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Katsura M, Mohri Y, Shuto K, Hai-Du Y, Amano T, Tsujimura A, Sasa M, Ohkuma S. Up-regulation of L-type voltage-dependent calcium channels after long term exposure to nicotine in cerebral cortical neurons. J Biol Chem 2002; 277:7979-88. [PMID: 11756415 DOI: 10.1074/jbc.m109466200] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Effects of long term (72-h) exposure to low concentration (0.1 mum) of nicotine on various types of voltage-dependent Ca(2+) channels (VDCCs) and neuronal nicotinic acetylcholine receptors (nnAChRs) were examined using primary cultures of mouse cerebral cortical neurons. High potassium (30 mm KCl)-stimulated (45)Ca(2+) influx into the neurons increased with increasing the duration of nicotine exposure and its concentrations. The maximal increase of the KCl-stimulated (45)Ca(2+) influx was found 24 h after the initiation of exposure and thereafter maintained up to 72 h. This enhancement of KCl-induced (45)Ca(2+) influx after 72-h exposure to 0.1 mum nicotine was completely abolished by concomitant exposure with mecamylamine, an inhibitor for nnAChRs. Only the component of the KCl-induced (45)Ca(2+) influx observed after long term exposure to nicotine, which was sensitive to nifedipine, an inhibitor of L-type VDCCs, was facilitated, while the (45)Ca(2+) influx through P/Q- and N-type VDCCs showed no changes. Moreover, enhanced immunoreactivity against antibody for the alpha(1C) subunit of L-type VDCCs was recognized, whereas no changes in immunoreactivities against antibodies for alpha(1A) and alpha(1B) subunits of other types of VDCCs were noted. In addition, a Western blot analysis showed an increase of immunoreactivities against antibodies for alpha(1D) and alpha(2)/delta(1), and expression of mRNA for L-type VDCC subunit, alpha(1F), was also enhanced, although beta(4) mRNA expression was not changed. Whole cell patch clamp analysis revealed that the increase of the amplitude of Ba(2+) currents was also recognized in the neurons exposed to nicotine, and nicardipine reduced this increased amplitude to the level of the amplitude detected in nontreated neurons with nicardipine. The up-regulation of alpha(4) and beta(2) subunits, but not the alpha(3) subunit of nnAChRs, was also noted after the nicotine exposure when examining by the Western blot analysis. Taken together, these results indicate that the long term exposure of the neurons to a low concentration of nicotine induces both increased (45)Ca(2+) influx through up-regulated L-type VDCCs and nnAChR up-regulation.
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MESH Headings
- 3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester/pharmacology
- Animals
- Barium/metabolism
- Blotting, Western
- Calcium/metabolism
- Calcium Channel Agonists/pharmacology
- Calcium Channel Blockers/pharmacology
- Calcium Channels, L-Type/metabolism
- Cells, Cultured
- Cerebral Cortex/drug effects
- Cerebral Cortex/metabolism
- DNA, Complementary/metabolism
- Dose-Response Relationship, Drug
- Electrophysiology
- Enzyme Inhibitors/pharmacology
- Ganglionic Stimulants/pharmacology
- Immunoblotting
- Kinetics
- Mice
- Neurons/drug effects
- Neurons/metabolism
- Nicotine/pharmacology
- Potassium Chloride/pharmacology
- Protein Binding
- RNA, Messenger/metabolism
- Time Factors
- Up-Regulation
- Verapamil/pharmacology
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Affiliation(s)
- Masashi Katsura
- Department of Pharmacology, Kawasaki Medical School, Matsushima, Kurashiki 701-0192, Japan
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26
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Hanson JE, Smith Y. Subcellular distribution of high-voltage-activated calcium channel subtypes in rat globus pallidus neurons. J Comp Neurol 2002; 442:89-98. [PMID: 11754164 DOI: 10.1002/cne.10075] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Globus pallidus (GP) neurons receive dense inhibitory synaptic inputs interspersed with sparse excitatory inputs distributed across the entire extent of their somata and dendrites. Yet, despite this predominance of inhibitory influence, GP neurons fire at a high tonic rate, suggesting that intrinsic properties play an important role in determining the physiological characteristics of these neurons. High-voltage-activated (HVA) calcium channels represent an important class of conductances that plays roles in controlling neurotransmitter release, postsynaptic excitability, and intracellular calcium signaling. To better understand the intrinsic properties of GP neurons, we examined the subcellular localization of HVA calcium channels by using immunocytochemistry at the electron microscopic level. Peroxidase labeling with antibodies against P/Q-, N-, and R-type HVA calcium channels demonstrated the presence of these channels in both proximal and distal dendrites of GP neurons. P/Q-, N-, and R-type channels were also found in presynaptic terminals, whereas L-type channels were found exclusively postsynaptically in neuronal elements. Immunogold labeling demonstrated that, although the density of intracellular L-type calcium channel labeling remains constant throughout the proximal-distal extent of the dendritic tree of GP neurons, the density of plasma membrane-bound channels is greater in distal dendrites. The finding of HVA calcium channels distributed throughout the whole dendritic tree of GP neurons indicates that these channels may interact with synaptic inputs to allow rich processing possibilities for GP neuron dendrites. Furthermore, the finding of a greater density of plasma membrane-bound L-type channels in distal dendrites expands the view that L-type channels are important only in somatic and proximal locations.
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Affiliation(s)
- Jesse E Hanson
- Yerkes Regional Primate Research Center, Division of Neuroscience and Department of Neurology, Emory University, Atlanta, Georgia 30322, USA
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