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Revuelta M, Urrutia J, Villarroel A, Casis O. Microglia-Mediated Inflammation and Neural Stem Cell Differentiation in Alzheimer's Disease: Possible Therapeutic Role of K V1.3 Channel Blockade. Front Cell Neurosci 2022; 16:868842. [PMID: 35530176 PMCID: PMC9070300 DOI: 10.3389/fncel.2022.868842] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2022] [Accepted: 03/31/2022] [Indexed: 12/14/2022] Open
Abstract
Increase of deposits of amyloid β peptides in the extracellular matrix is landmark during Alzheimer’s Disease (AD) due to the imbalance in the production vs. clearance. This accumulation of amyloid β deposits triggers microglial activation. Microglia plays a dual role in AD, a protective role by clearing the deposits of amyloid β peptides increasing the phagocytic response (CD163, IGF-1 or BDNF) and a cytotoxic role, releasing free radicals (ROS or NO) and proinflammatory cytokines (TNF-α, IL-1β) in response to reactive gliosis activated by the amyloid β aggregates. Microglia activation correlated with an increase KV1.3 channels expression, protein levels and current density. Several studies highlight the importance of KV1.3 in the activation of inflammatory response and inhibition of neural progenitor cell proliferation and neuronal differentiation. However, little is known about the pathways of this activation in neural stem cells differentiation and proliferation and the role in amyloid β accumulation. In recent studies using in vitro cells derived from mice models, it has been demonstrated that KV1.3 blockers inhibit microglia-mediated neurotoxicity in culture reducing the expression and production of the pro-inflammatory cytokines IL-1β and TNF-α through the NF-kB and p38MAPK pathway. Overall, we conclude that KV1.3 blockers change the course of AD development, reducing microglial cytotoxic activation and increasing neural stem cell differentiation. However, further investigations are needed to establish the specific pathway and to validate the use of this blocker as therapeutic treatment in Alzheimer patients.
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Affiliation(s)
- Miren Revuelta
- Department of Physiology, Faculty of Medicine and Nursery, University of the Basque Country (UPV/EHU), Leioa, Spain
| | - Janire Urrutia
- Department of Physiology, Faculty of Medicine and Nursery, University of the Basque Country (UPV/EHU), Leioa, Spain
| | - Alvaro Villarroel
- Instituto Biofisika, Consejo Superior de Investigaciones Científicas (CSIC)-University of the Basque Country/Euskal Herriko Unibertsitatea (UPV/EHU), Leioa, Spain
| | - Oscar Casis
- Department of Physiology, Faculty of Pharmacy, University of the Basque Country (UPV/EHU), Vitoria-Gasteiz, Spain
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Bragança B, Oliveira-Monteiro N, Ferreirinha F, Lima PA, Faria M, Fontes-Sousa AP, Correia-de-Sá P. Ion Fluxes through KCa2 (SK) and Cav1 (L-type) Channels Contribute to Chronoselectivity of Adenosine A1 Receptor-Mediated Actions in Spontaneously Beating Rat Atria. Front Pharmacol 2016; 7:45. [PMID: 27014060 PMCID: PMC4780064 DOI: 10.3389/fphar.2016.00045] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Accepted: 02/18/2016] [Indexed: 11/24/2022] Open
Abstract
Impulse generation in supraventricular tissue is inhibited by adenosine and acetylcholine via the activation of A1 and M2 receptors coupled to inwardly rectifying GIRK/KIR3.1/3.4 channels, respectively. Unlike M2 receptors, bradycardia produced by A1 receptors activation predominates over negative inotropy. Such difference suggests that other ion currents may contribute to adenosine chronoselectivity. In isolated spontaneously beating rat atria, blockade of KCa2/SK channels with apamin and Cav1 (L-type) channels with nifedipine or verapamil, sensitized atria to the negative inotropic action of the A1 agonist, R-PIA, without affecting the nucleoside negative chronotropy. Patch-clamp experiments in the whole-cell configuration mode demonstrate that adenosine, via A1 receptors, activates the inwardly-rectifying GIRK/KIR3.1/KIR3.4 current resulting in hyperpolarization of atrial cardiomyocytes, which may slow down heart rate. Conversely, the nucleoside inactivates a small conductance Ca2+-activated KCa2/SK outward current, which eventually reduces the repolarizing force and thereby prolong action potentials duration and Ca2+ influx into cardiomyocytes. Immunolocalization studies showed that differences in A1 receptors distribution between the sinoatrial node and surrounding cardiomyocytes do not afford a rationale for adenosine chronoselectivity. Immunolabelling of KIR3.1, KCa2.2, KCa2.3, and Cav1 was also observed throughout the right atrium. Functional data indicate that while both A1 and M2 receptors favor the opening of GIRK/KIR3.1/3.4 channels modulating atrial chronotropy, A1 receptors may additionally restrain KCa2/SK activation thereby compensating atrial inotropic depression by increasing the time available for Ca2+ influx through Cav1 (L-type) channels.
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Affiliation(s)
- Bruno Bragança
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Nádia Oliveira-Monteiro
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Fátima Ferreirinha
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Pedro A Lima
- Departamento de Química e Bioquímica, Faculdade de Ciências, Centro de Química e Bioquímica, Universidade de Lisboa Lisboa, Portugal
| | - Miguel Faria
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Ana P Fontes-Sousa
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
| | - Paulo Correia-de-Sá
- Laboratório de Farmacologia e Neurobiologia - Center for Drug Discovery and Innovative Medicines (MedInUP), Instituto de Ciências Biomédicas Abel Salazar (ICBAS), Universidade do Porto (UP) Porto, Portugal
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Linta L, Boeckers TM, Kleger A, Liebau S. Calcium activated potassium channel expression during human iPS cell-derived neurogenesis. Ann Anat 2013; 195:303-311. [PMID: 23587809 DOI: 10.1016/j.aanat.2013.02.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Revised: 02/05/2013] [Accepted: 02/27/2013] [Indexed: 01/11/2023]
Abstract
The family of calcium activated potassium channels of low and intermediate conductance, known as SK channels, consists of four members (SK1-4). These channels are widely expressed throughout the organism and involved in various cellular processes, such as the afterhyperpolarization in excitable cells but also in differentiation processes of various tissues. To date, the role of SK channels in developmental processes has been merely a marginal focus of investigation, although it is well accepted that cell differentiation and maturation affect the expression patterns of certain ion channels. Recently, several studies from our laboratory delineated the influence of SK channel expression and their respective activity on cytoskeletal reorganization in neural and pluripotent stem cells and regulation of cell fate determination toward the cardiac lineage in human and mouse pluripotent stem cells. Herein, we have now analyzed SK channel expression patterns and distribution at various stages of human induced pluripotent stem cell-derived neurogenesis particularly focusing on undifferentiated iPS cells, neural progenitors and mature neurons. All family members could be detected starting at the iPS cell level and were differentially expressed during the subsequent maturation process. Intriguingly, we found obvious discrepancies between mRNA and protein expression pointing toward a complex regulatory mechanism. Inhibition of SK channels with either apamin or clotrimazol did not have any significant effects on the speed or amount of neurogenesis in vitro. The abundance and specific regulation of SK channel expression during iPS cell differentiation indicates distinct roles of these ion channels not only for the cardiac but also for neuronal cell differentiation and in vitro neurogenesis.
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Affiliation(s)
- Leonhard Linta
- Institute for Anatomy & Cell Biology, Ulm University, Ulm, Germany
| | | | - Alexander Kleger
- Department of Internal Medicine I, Ulm University, Ulm, Germany.
| | - Stefan Liebau
- Institute for Anatomy & Cell Biology, Ulm University, Ulm, Germany.
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The interactions of apamin and tetraethylammonium are differentially affected by single mutations in the pore mouth of small conductance calcium-activated potassium (SK) channels. Biochem Pharmacol 2013; 85:560-9. [DOI: 10.1016/j.bcp.2012.12.015] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2012] [Revised: 12/14/2012] [Accepted: 12/17/2012] [Indexed: 10/27/2022]
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Calcium-Activated Potassium Channels, Cardiogenesis of Pluripotent Stem Cells, and Enrichment of Pacemaker-Like Cells. Trends Cardiovasc Med 2011; 21:74-83. [DOI: 10.1016/j.tcm.2012.03.003] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/03/2023]
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Liebau S, Steinestel J, Linta L, Kleger A, Storch A, Schoen M, Steinestel K, Proepper C, Bockmann J, Schmeisser MJ, Boeckers TM. An SK3 channel/nWASP/Abi-1 complex is involved in early neurogenesis. PLoS One 2011; 6:e18148. [PMID: 21464958 PMCID: PMC3064656 DOI: 10.1371/journal.pone.0018148] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2010] [Accepted: 02/27/2011] [Indexed: 12/12/2022] Open
Abstract
Background The stabilization or regulated reorganization of the actin cytoskeleton is essential for cellular structure and function. Recently, we could show that the activation of the SK3-channel that represents the predominant SK-channel in neural stem cells, leads to a rapid local outgrowth of long filopodial processes. This observation indicates that the rearrangement of the actin based cytoskeleton via membrane bound SK3-channels might selectively be controlled in defined micro compartments of the cell. Principal Findings We found two important proteins for cytoskeletal rearrangement, the Abelson interacting protein 1, Abi-1 and the neural Wiskott Aldrich Syndrome Protein, nWASP, to be in complex with SK3- channels in neural stem cells (NSCs). Moreover, this interaction is also found in spines and postsynaptic compartments of developing primary hippocampal neurons and regulates neurite outgrowth during early phases of differentiation. Overexpression of the proteins or pharmacological activation of SK3 channels induces obvious structural changes in NSCs and hippocampal neurons. In both neuronal cell systems SK3 channels and nWASP act synergistic by strongly inducing filopodial outgrowth while Abi-1 behaves antagonistic to its interaction partners. Conclusions Our results give good evidence for a functional interplay of a trimeric complex that transforms incoming signals via SK3-channel activation into the local rearrangement of the cytoskeleton in early steps of neuronal differentiation involving nWASP and Abi-1 actin binding proteins.
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Affiliation(s)
- Stefan Liebau
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Julie Steinestel
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Leonhard Linta
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Alexander Kleger
- Department of Internal Medicine I, Ulm University, Ulm, Germany
- Institute of Molecular Medicine and Max-Planck-Research Group on Stem Cell Aging, Ulm, Germany
| | - Alexander Storch
- Department of Neurology and Center for Regenerative Therapies Dresden (CRTD), Dresden University of Technology, Dresden, Germany
| | - Michael Schoen
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | - Konrad Steinestel
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | | | - Juergen Bockmann
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
| | | | - Tobias M. Boeckers
- Institute for Anatomy and Cell Biology, Ulm University, Ulm, Germany
- * E-mail:
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Weatherall KL, Goodchild SJ, Jane DE, Marrion NV. Small conductance calcium-activated potassium channels: From structure to function. Prog Neurobiol 2010; 91:242-55. [DOI: 10.1016/j.pneurobio.2010.03.002] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2009] [Revised: 03/05/2010] [Accepted: 03/24/2010] [Indexed: 10/19/2022]
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Lamy C, Goodchild SJ, Weatherall KL, Jane DE, Liégeois JF, Seutin V, Marrion NV. Allosteric block of KCa2 channels by apamin. J Biol Chem 2010; 285:27067-27077. [PMID: 20562108 DOI: 10.1074/jbc.m110.110072] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Activation of small conductance calcium-activated potassium (K(Ca)2) channels can regulate neuronal firing and synaptic plasticity. They are characterized by their high sensitivity to the bee venom toxin apamin, but the mechanism of block is not understood. For example, apamin binds to both K(Ca)2.2 and K(Ca)2.3 with the same high affinity (K(D) approximately 5 pM for both subtypes) but requires significantly higher concentrations to block functional current (IC(50) values of approximately 100 pM and approximately 5 nM, respectively). This suggests that steps beyond binding are needed for channel block to occur. We have combined patch clamp and binding experiments on cell lines with molecular modeling and mutagenesis to gain more insight into the mechanism of action of the toxin. An outer pore histidine residue common to both subtypes was found to be critical for both binding and block by the toxin but not for block by tetraethylammonium (TEA) ions. These data indicated that apamin blocks K(Ca)2 channels by binding to a site distinct from that used by TEA, supported by a finding that the onset of block by apamin was not affected by the presence of TEA. Structural modeling of ligand-channel interaction indicated that TEA binds deep within the channel pore, which contrasted with apamin being modeled to interact with the channel outer pore by utilizing the outer pore histidine residue. This multidisciplinary approach suggested that apamin does not behave as a classical pore blocker but blocks using an allosteric mechanism that is consistent with observed differences between binding affinity and potency of block.
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Affiliation(s)
- Cédric Lamy
- Laboratory of Pharmacology and Groupe Interdisciplinaire de Génoprotéomique Appliquée Neurosciences, University of Liège, 4000 Liège, Belgium
| | - Samuel J Goodchild
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Kate L Weatherall
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - David E Jane
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom
| | - Jean-François Liégeois
- Laboratory of Medicinal Chemistry and Centre Interfacultaire de Recherche du Medicament, University of Liège, 4000 Liège, Belgium
| | - Vincent Seutin
- Laboratory of Pharmacology and Groupe Interdisciplinaire de Génoprotéomique Appliquée Neurosciences, University of Liège, 4000 Liège, Belgium
| | - Neil V Marrion
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, Bristol BS8 1TD, United Kingdom.
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Krsmanovic LZ, Hu L, Leung PK, Feng H, Catt KJ. Pulsatile GnRH secretion: roles of G protein-coupled receptors, second messengers and ion channels. Mol Cell Endocrinol 2010; 314:158-63. [PMID: 19486924 PMCID: PMC2815227 DOI: 10.1016/j.mce.2009.05.015] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/23/2009] [Revised: 05/21/2009] [Accepted: 05/24/2009] [Indexed: 12/31/2022]
Abstract
The pulsatile secretion of GnRH from normal and immortalized hypothalamic GnRH neurons is highly calcium-dependent and is stimulated by cAMP. It is also influenced by agonist activation of the endogenous GnRH receptor (GnRH-R), which couples to multiple G proteins. This autocrine mechanism could serve as a timer to determine the frequency of pulsatile GnRH release by regulating Ca(2+)- and cAMP-dependent signaling and GnRH neuronal firing. The firing of individual and/or bursts of action potentials (APs) in spontaneously active GnRH neurons is followed by afterhyperpolarization (AHP) that lasts from several milliseconds to several seconds. GnRH-induced activation of GnRH neurons causes a significant increase in medium AHP that is partially sensitive to apamin. GnRH-induced modulation of Ca(2+) influx and the consequent changes in AHP current suggest that the GnRH receptors expressed in hypothalamic GnRH neurons are important modulators of their neuronal excitability. The coexistence of multiple regulatory mechanisms could provide a high degree of redundancy in the maintenance of this crucial component of the reproductive process. It is also conceivable that this multifactorial system could reflect the gradation from simple to more complex neuroendocrine control systems for regulating hypothalamo-pituitary function and gonadal activity during the evolution of the GnRH pulse generator.
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Affiliation(s)
- Lazar Z Krsmanovic
- Section on Hormonal Regulation, PDEGEN, NICHD, NIH, Bethesda, MD 20892, USA.
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10
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Goodchild SJ, Lamy C, Seutin V, Marrion NV. Inhibition of K(Ca)2.2 and K(Ca)2.3 channel currents by protonation of outer pore histidine residues. ACTA ACUST UNITED AC 2010; 134:295-308. [PMID: 19786583 PMCID: PMC2757770 DOI: 10.1085/jgp.200910252] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Ion channels are often modulated by changes in extracellular pH, with most examples resulting from shifts in the ionization state of histidine residue(s) in the channel pore. The application of acidic extracellular solution inhibited expressed K(Ca)2.2 (SK2) and K(Ca)2.3 (SK3) channel currents, with K(Ca)2.3 (pIC(50) of approximately 6.8) being approximately fourfold more sensitive than K(Ca)2.2 (pIC(50) of approximately 6.2). Inhibition was found to be voltage dependent, resulting from a shift in the affinity for the rectifying intracellular divalent cation(s) at the inner mouth of the selectivity filter. The inhibition by extracellular protons resulted from a reduction in the single-channel conductance, without significant changes in open-state kinetics or open probability. K(Ca)2.2 and K(Ca)2.3 subunits both possess a histidine residue in their outer pore region between the transmembrane S5 segment and the pore helix, with K(Ca)2.3 also exhibiting an additional histidine residue between the selectivity filter and S6. Mutagenesis revealed that the outer pore histidine common to both channels was critical for inhibition. The greater sensitivity of K(Ca)2.3 currents to protons arose from the additional histidine residue in the pore, which was more proximal to the conduction pathway and in the electrostatic vicinity of the ion conduction pathway. The decrease of channel conductance by extracellular protons was mimicked by mutation of the outer pore histidine in K(Ca)2.2 to an asparagine residue. These data suggest that local interactions involving the outer turret histidine residues are crucial to enable high conductance openings, with protonation inhibiting current by changing pore shape.
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Affiliation(s)
- Samuel J Goodchild
- Department of Physiology and Pharmacology, University of Bristol, England, UK
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Molecular and cellular basis of small--and intermediate-conductance, calcium-activated potassium channel function in the brain. Cell Mol Life Sci 2008; 65:3196-217. [PMID: 18597044 PMCID: PMC2798969 DOI: 10.1007/s00018-008-8216-x] [Citation(s) in RCA: 144] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Small conductance calcium-activated potassium (SK or KCa2) channels link intracellular calcium transients to membrane potential changes. SK channel subtypes present different pharmacology and distribution in the nervous system. The selective blocker apamin, SK enhancers and mice lacking specific SK channel subunits have revealed multifaceted functions of these channels in neurons, glia and cerebral blood vessels. SK channels regulate neuronal firing by contributing to the afterhyperpolarization following action potentials and mediating IAHP, and partake in a calcium-mediated feedback loop with NMDA receptors, controlling the threshold for induction of hippocampal long-term potentiation. The function of distinct SK channel subtypes in different neurons often results from their specific coupling to different calcium sources. The prominent role of SK channels in the modulation of excitability and synaptic function of limbic, dopaminergic and cerebellar neurons hints at their possible involvement in neuronal dysfunction, either as part of the causal mechanism or as potential therapeutic targets.
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Liebau S, Vaida B, Proepper C, Grissmer S, Storch A, Boeckers TM, Dietl P, Wittekindt OH. Formation of cellular projections in neural progenitor cells depends on SK3 channel activity. J Neurochem 2007; 101:1338-1350. [PMID: 17459146 DOI: 10.1111/j.1471-4159.2006.04437.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
Ion channels are potent modulators for developmental processes in progenitor cells. In a screening approach for different ion channels in neural progenitor cells (NPCs) we observed a 1-ethyl-2-benzimidazolinone (1-EBIO) activated inward current, which could be blocked by scyllatoxin (ScTX, IC50=2+/- 0.3 nmol/L). This initial evidence for the expression of the small conductance Ca2+ activated K+-channel SK3 was confirmed by the detection of SK3 transcripts and protein in NPCs. Interestingly, SK3 proteins were highly expressed in non-differentiated NPCs with a focused localization in lamellipodia as well as filopodial structures. The activation of SK3 channels using 1-EBIO lead to an immediate filopodial sprouting and the translocation of the protein into these novel filopodial protrusions. Both effects could be prevented by the pre-incubation of NPCs with ScTX. Our study gives first evidence that the formation and prolongation of filopodia in NPCs is, at least in part, effectively induced and regulated by SK3 channels.
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Affiliation(s)
- Stefan Liebau
- Department of Anatomy and Cell Biology, University of Ulm, Ulm, Germany
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13
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Nolting A, Ferraro T, D'hoedt D, Stocker M. An amino acid outside the pore region influences apamin sensitivity in small conductance Ca2+-activated K+ channels. J Biol Chem 2006; 282:3478-86. [PMID: 17142458 PMCID: PMC1849974 DOI: 10.1074/jbc.m607213200] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Small conductance calcium-activated potassium channels (SK, K(Ca)) are a family of voltage-independent K+ channels with a distinct physiology and pharmacology. The bee venom toxin apamin inhibits exclusively the three cloned SK channel subtypes (SK1, SK2, and SK3) with different affinity, highest for SK2, lowest for SK1, and intermediate for SK3 channels. The high selectivity of apamin made it a valuable tool to study the molecular makeup and function of native SK channels. Three amino acids located in the outer vestibule of the pore are of particular importance for the different apamin sensitivities of SK channels. Chimeric SK1 channels, enabling the homomeric expression of the rat SK1 (rSK1) subunit and containing the core domain (S1-S6) of rSK1, are apamin-insensitive. By contrast, channels formed by the human orthologue human SK1 (hSK1) are sensitive to apamin. This finding hinted at the involvement of regions beyond the pore as determinants of apamin sensitivity, because hSK1 and rSK1 have an identical amino acid sequence in the pore region. Here we investigated which parts of the channels outside the pore region are important for apamin sensitivity by constructing chimeras between apamin-insensitive and -sensitive SK channel subunits and by introducing point mutations. We demonstrate that a single amino acid situated in the extracellular loop between the transmembrane segments S3 and S4 has a major impact on apamin sensitivity. Our findings enabled us to convert the hSK1 channel into a channel that was as sensitive for apamin as SK2, the SK channel with the highest sensitivity.
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Affiliation(s)
- Andreas Nolting
- Laboratory of Molecular Pharmacology, Department of Pharmacology, University College London, Gower Street, London WC1E 6BT, United Kingdom
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Kelly T, Church J. Relationships Between Calcium and pH in the Regulation of the Slow Afterhyperpolarization in Cultured Rat Hippocampal Neurons. J Neurophysiol 2006; 96:2342-53. [PMID: 16885515 DOI: 10.1152/jn.01269.2005] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The Ca2+-dependent slow afterhyperpolarization (AHP) is an important determinant of neuronal excitability. Although it is established that modest changes in extracellular pH (pHo) modulate the slow AHP, the relative contributions of changes in the priming Ca2+ signal and intracellular pH (pHi) to this effect remain poorly defined. To gain a better understanding of the modulation of the slow AHP by changes in pHo, we performed simultaneous recordings of intracellular free calcium concentration ([Ca2+]i), pHi, and the slow AHP in cultured rat hippocampal neurons coloaded with the Ca2+- and pH-sensitive fluorophores fura-2 and SNARF-5F, respectively, and whole cell patch-clamped using the perforated patch technique. Decreasing pHo from 7.2 to 6.5 lowered pHi, reduced the magnitude of depolarization-evoked [Ca2+]i transients, and inhibited the subsequent slow AHP; opposite effects were observed when pHo was increased from 7.2 to 7.5. Although decreases and increases in pHi (at a constant pHo) reduced and augmented, respectively, the slow AHP in the absence of marked changes in preceding [Ca2+]i transients, the inhibition of the slow AHP by decreases in pHo was correlated with low pHo-dependent reductions in [Ca2+]i transients rather than the decreases in pHi that accompanied the decreases in pHo. In contrast, high pHo-induced increases in the slow AHP were correlated with the accompanying increases in pHi rather than high pHo-dependent increases in [Ca2+]i transients. The results indicate that changes in pHo modulate the slow AHP in a manner that depends on the direction of the pHo change and substantiate a role for changes in pHi in modulating the slow AHP during changes in pHo.
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Affiliation(s)
- Tony Kelly
- Department of Cellular and Physiological Sciences, The University of British Columbia, 2350 Health Sciences Mall, Vancouver, B.C., Canada V6T 1Z3
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