1
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Dual Sensing of Physiologic pH and Calcium by EFCAB9 Regulates Sperm Motility. Cell 2019; 177:1480-1494.e19. [PMID: 31056283 PMCID: PMC8808721 DOI: 10.1016/j.cell.2019.03.047] [Citation(s) in RCA: 105] [Impact Index Per Article: 21.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2018] [Revised: 02/08/2019] [Accepted: 03/25/2019] [Indexed: 11/24/2022]
Abstract
Varying pH of luminal fluid along the female reproductive tract is a physiological cue that modulates sperm motility. CatSper is a sperm-specific, pH-sensitive calcium channel essential for hyperactivated motility and male fertility. Multi-subunit CatSper channel complexes organize linear Ca2+ signaling nanodomains along the sperm tail. Here, we identify EF-hand calcium-binding domain-containing protein 9 (EFCAB9) as a bifunctional, cytoplasmic machine modulating the channel activity and the domain organization of CatSper. Knockout mice studies demonstrate that EFCAB9, in complex with the CatSper subunit, CATSPERζ, is essential for pH-dependent and Ca2+-sensitive activation of the CatSper channel. In the absence of EFCAB9, sperm motility and fertility is compromised, and the linear arrangement of the Ca2+ signaling domains is disrupted. EFCAB9 interacts directly with CATSPERζ in a Ca2+-dependent manner and dissociates at elevated pH. These observations suggest that EFCAB9 is a long-sought, intracellular, pH-dependent Ca2+ sensor that triggers changes in sperm motility.
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2
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Bollinger WL, Sial N, Dawson-Scully K. BK channels and a cGMP-dependent protein kinase (PKG) function through independent mechanisms to regulate the tolerance of synaptic transmission to acute oxidative stress at the Drosophila larval neuromuscular junction. J Neurogenet 2018; 32:246-255. [DOI: 10.1080/01677063.2018.1500571] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Affiliation(s)
- Wesley L. Bollinger
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
| | - Nadia Sial
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
- Brain Institute Research Scholars Program, Florida Atlantic University, Boca Raton, FL, USA
| | - Ken Dawson-Scully
- Department of Biological Sciences, Florida Atlantic University, Boca Raton, FL, USA
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3
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Gonçalves-de-Albuquerque SDC, Pessoa-e-Silva R, Trajano-Silva LAM, de Goes TC, de Morais RCS, da C. Oliveira CN, de Lorena VMB, de Paiva-Cavalcanti M. The Equivocal Role of Th17 Cells and Neutrophils on Immunopathogenesis of Leishmaniasis. Front Immunol 2017; 8:1437. [PMID: 29163510 PMCID: PMC5670345 DOI: 10.3389/fimmu.2017.01437] [Citation(s) in RCA: 90] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2017] [Accepted: 10/16/2017] [Indexed: 01/17/2023] Open
Abstract
Advances in the understanding of leishmaniasis progression indicate that cellular interactions more complex than the Th1/Th2 paradigm define the course of infection. Th17 cells are a crucial modulator of adaptive immunity against Leishmania parasites acting mainly on neutrophil recruitment and playing a dual role at the site of infection. This review describes the roles of both these cell types in linking innate defense responses to the establishment of specific immunity. We focus on the Th17-neutrophil interaction as a crucial component of anti-Leishmania immunity, and the clinical evolution of cutaneous or visceral leishmaniasis. To date, information obtained through experimental models and patient evaluations suggests that the influence of the presence of interleukin (IL)-17 (the main cytokine produced by Th17 cells) and neutrophils during Leishmania infections is strictly dependent on the tissue (skin or liver/spleen) and parasite species. Also, the time at which neutrophils are recruited, and the persistence of IL-17 in the infection microenvironment, may also be significant. A clearer understanding of these interactions will enable better measurement of the influence of IL-17 and its regulators, and contribute to the identification of disease/resistance biomarkers.
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Affiliation(s)
| | - Rômulo Pessoa-e-Silva
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Lays A. M. Trajano-Silva
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Tayná Correia de Goes
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Rayana C. S. de Morais
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Cíntia N. da C. Oliveira
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Virgínia M. B. de Lorena
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
| | - Milena de Paiva-Cavalcanti
- Department of Microbiology, Aggeu Magalhães Research Center, Oswaldo Cruz Foundation, Recife, Pernambuco, Brazil
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4
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Understand spiciness: mechanism of TRPV1 channel activation by capsaicin. Protein Cell 2017; 8:169-177. [PMID: 28044278 PMCID: PMC5326624 DOI: 10.1007/s13238-016-0353-7] [Citation(s) in RCA: 181] [Impact Index Per Article: 25.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2016] [Accepted: 11/22/2016] [Indexed: 11/06/2022] Open
Abstract
Capsaicin in chili peppers bestows the sensation of spiciness. Since the discovery of its receptor, transient receptor potential vanilloid 1 (TRPV1) ion channel, how capsaicin activates this channel has been under extensive investigation using a variety of experimental techniques including mutagenesis, patch-clamp recording, crystallography, cryo-electron microscopy, computational docking and molecular dynamic simulation. A framework of how capsaicin binds and activates TRPV1 has started to merge: capsaicin binds to a pocket formed by the channel’s transmembrane segments, where it takes a “tail-up, head-down” configuration. Binding is mediated by both hydrogen bonds and van der Waals interactions. Upon binding, capsaicin stabilizes the open state of TRPV1 by “pull-and-contact” with the S4-S5 linker. Understanding the ligand-host interaction will greatly facilitate pharmaceutical efforts to develop novel analgesics targeting TRPV1.
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5
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Kulke D, von Samson-Himmelstjerna G, Miltsch SM, Wolstenholme AJ, Jex AR, Gasser RB, Ballesteros C, Geary TG, Keiser J, Townson S, Harder A, Krücken J. Characterization of the Ca2+-gated and voltage-dependent K+-channel Slo-1 of nematodes and its interaction with emodepside. PLoS Negl Trop Dis 2014; 8:e3401. [PMID: 25521608 PMCID: PMC4270693 DOI: 10.1371/journal.pntd.0003401] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2014] [Accepted: 11/07/2014] [Indexed: 11/18/2022] Open
Abstract
The cyclooctadepsipeptide emodepside and its parent compound PF1022A are broad-spectrum nematicidal drugs which are able to eliminate nematodes resistant to other anthelmintics. The mode of action of cyclooctadepsipeptides is only partially understood, but involves the latrophilin Lat-1 receptor and the voltage- and calcium-activated potassium channel Slo-1. Genetic evidence suggests that emodepside exerts its anthelmintic activity predominantly through Slo-1. Indeed, slo-1 deficient Caenorhabditis elegans strains are completely emodepside resistant. However, direct effects of emodepside on Slo-1 have not been reported and these channels have only been characterized for C. elegans and related Strongylida. Molecular and bioinformatic analyses identified full-length Slo-1 cDNAs of Ascaris suum, Parascaris equorum, Toxocara canis, Dirofilaria immitis, Brugia malayi, Onchocerca gutturosa and Strongyloides ratti. Two paralogs were identified in the trichocephalids Trichuris muris, Trichuris suis and Trichinella spiralis. Several splice variants encoding truncated channels were identified in Trichuris spp. Slo-1 channels of trichocephalids form a monophyletic group, showing that duplication occurred after the divergence of Enoplea and Chromadorea. To explore the function of a representative protein, C. elegans Slo-1a was expressed in Xenopus laevis oocytes and studied in electrophysiological (voltage-clamp) experiments. Incubation of oocytes with 1-10 µM emodepside caused significantly increased currents over a wide range of step potentials in the absence of experimentally increased intracellular Ca2+, suggesting that emodepside directly opens C. elegans Slo-1a. Emodepside wash-out did not reverse the effect and the Slo-1 inhibitor verruculogen was only effective when applied before, but not after, emodepside. The identification of several splice variants and paralogs in some parasitic nematodes suggests that there are substantial differences in channel properties among species. Most importantly, this study showed for the first time that emodepside directly opens a Slo-1 channel, significantly improving the understanding of the mode of action of this drug class.
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Affiliation(s)
- Daniel Kulke
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
- Global Drug Discovery, Animal Health, Parasiticides, Bayer HealthCare, Leverkusen, Germany
| | | | - Sandra M. Miltsch
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
| | - Adrian J. Wolstenholme
- Department of Infectious Diseases, College of Veterinary Medicine, The University of Georgia, Athens, Georgia, United States of America
| | - Aaron R. Jex
- Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Robin B. Gasser
- Faculty of Veterinary Science, The University of Melbourne, Parkville, Victoria, Australia
| | - Cristina Ballesteros
- Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Timothy G. Geary
- Institute of Parasitology, McGill University, Sainte-Anne-de-Bellevue, Quebec, Canada
| | - Jennifer Keiser
- Department of Medical Parasitology and Infection Biology, Swiss Tropical and Public Health Institute, Basel, Switzerland
| | - Simon Townson
- Tropical Parasitic Diseases Unit, Northwick Park Institute for Medical Research, Harrow, Middlesex, United Kingdom
| | - Achim Harder
- WE Biology, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
| | - Jürgen Krücken
- Institute for Parasitology and Tropical Veterinary Medicine, Freie Universität Berlin, Berlin, Germany
- * E-mail:
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6
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Ligaba A, Dreyer I, Margaryan A, Schneider DJ, Kochian L, Piñeros M. Functional, structural and phylogenetic analysis of domains underlying the Al sensitivity of the aluminum-activated malate/anion transporter, TaALMT1. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2013; 76:766-80. [PMID: 24188189 DOI: 10.1111/tpj.12332] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2013] [Revised: 09/05/2013] [Accepted: 09/09/2013] [Indexed: 05/08/2023]
Abstract
Triticum aestivum aluminum-activated malate transporter (TaALMT1) is the founding member of a unique gene family of anion transporters (ALMTs) that mediate the efflux of organic acids. A small sub-group of root-localized ALMTs, including TaALMT1, is physiologically associated with in planta aluminum (Al) resistance. TaALMT1 exhibits significant enhancement of transport activity in response to extracellular Al. In this study, we integrated structure-function analyses of structurally altered TaALMT1 proteins expressed in Xenopus oocytes with phylogenic analyses of the ALMT family. Our aim is to re-examine the role of protein domains in terms of their potential involvement in the Al-dependent enhancement (i.e. Al-responsiveness) of TaALMT1 transport activity, as well as the roles of all its 43 negatively charged amino acid residues. Our results indicate that the N-domain, which is predicted to form the conductive pathway, mediates ion transport even in the absence of the C-domain. However, segments in both domains are involved in Al(3+) sensing. We identified two regions, one at the N-terminus and a hydrophobic region at the C-terminus, that jointly contribute to the Al-response phenotype. Interestingly, the characteristic motif at the N-terminus appears to be specific for Al-responsive ALMTs. Our study highlights the need to include a comprehensive phylogenetic analysis when drawing inferences from structure-function analyses, as a significant proportion of the functional changes observed for TaALMT1 are most likely the result of alterations in the overall structural integrity of ALMT family proteins rather than modifications of specific sites involved in Al(3+) sensing.
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Affiliation(s)
- Ayalew Ligaba
- Robert W. Holley Center for Agriculture and Health, Agricultural Research Service, US Department of Agriculture, Cornell University, Tower Road, Ithaca, NY, 14853, USA
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7
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Molecular mechanisms of large-conductance ca (2+) -activated potassium channel activation by ginseng gintonin. EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE 2013; 2013:323709. [PMID: 23662129 PMCID: PMC3638619 DOI: 10.1155/2013/323709] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/10/2013] [Revised: 03/05/2013] [Accepted: 03/12/2013] [Indexed: 01/12/2023]
Abstract
Gintonin is a unique lysophosphatidic acid (LPA) receptor ligand
found in Panax ginseng. Gintonin induces transient
[Ca2+]i
through G protein-coupled LPA receptors. Large-conductance Ca2+-activated
K+ (BKCa)
channels are expressed in blood vessels and neurons and
play important roles in blood vessel relaxation and attenuation of
neuronal excitability. BKCa channels are activated by transient
[Ca2+]i
and are regulated by various Ca2+-dependent kinases. We
investigated the molecular mechanisms of BKCa channel activation
by gintonin. BKCa channels are heterologously expressed in
Xenopus oocytes. Gintonin treatment induced BKCa channel activation in
oocytes expressing the BKCa channel α subunit in a
concentration-dependent manner (EC50 = 0.71 ± 0.08 µg/mL).
Gintonin-mediated BKCa channel activation was blocked by a PKC
inhibitor, calphostin, and by the calmodulin inhibitor,
calmidazolium. Site-directed mutations in BKCa channels targeting
CaM kinase II or PKC phosphorylation sites but not PKA
phosphorylation sites attenuated gintonin action. Mutations in the
Ca2+ bowl and the regulator of K+ conductance (RCK) site also
blocked gintonin action. These results indicate that
gintonin-mediated BKCa channel activations are achieved through
LPA1 receptor-phospholipase C-IP3-Ca2+-PKC-calmodulin-CaM kinase
II pathways and calcium binding to the Ca2+ bowl and RCK domain.
Gintonin could be a novel contributor against blood vessel
constriction and over-excitation of neurons.
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8
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Abstract
A thermodynamic approach to studying allosterically regulated ion channels such as the large-conductance voltage- and Ca(2+)-dependent (BK) channel is presented, drawing from principles originally introduced to describe linkage phenomena in hemoglobin. In this paper, linkage between a principal channel component and secondary elements is derived from a four-state thermodynamic cycle. One set of parallel legs in the cycle describes the "work function," or the free energy required to activate the principal component. The second are "lever operations" activating linked elements. The experimental embodiment of this linkage cycle is a plot of work function versus secondary force, whose asymptotes are a function of the parameters (displacements and interaction energies) of an allosteric network. Two essential work functions play a role in evaluating data from voltage-clamp experiments. The first is the conductance Hill energy W(H)([g]), which is a "local" work function for pore activation, and is defined as kT times the Hill transform of the conductance (G-V) curve. The second is the electrical capacitance energy W(C)([q]), representing "global" gating charge displacement, and is equal to the product of total gating charge per channel times the first moment (V(M)) of normalized capacitance (slope of Q-V curve). Plots of W(H)([g]) and W(C)([q]) versus voltage and Ca(2+) potential can be used to measure thermodynamic parameters in a model-independent fashion of the core gating constituents (pore, voltage-sensor, and Ca(2+)-binding domain) of BK channel. The method is easily generalized for use in studying other allosterically regulated ion channels. The feasibility of performing linkage analysis from patch-clamp data were explored by simulating gating and ionic currents of a 17-particle model BK channel in response to a slow voltage ramp, which yielded interaction energies deviating from their given values in the range of 1.3 to 7.2%.
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9
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Singh AK, McMillan J, Bukiya AN, Burton B, Parrill AL, Dopico AM. Multiple cholesterol recognition/interaction amino acid consensus (CRAC) motifs in cytosolic C tail of Slo1 subunit determine cholesterol sensitivity of Ca2+- and voltage-gated K+ (BK) channels. J Biol Chem 2012; 287:20509-21. [PMID: 22474334 DOI: 10.1074/jbc.m112.356261] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Large conductance, Ca(2+)- and voltage-gated K(+) (BK) channel proteins are ubiquitously expressed in cell membranes and control a wide variety of biological processes. Membrane cholesterol regulates the activity of membrane-associated proteins, including BK channels. Cholesterol modulation of BK channels alters action potential firing, colonic ion transport, smooth muscle contractility, endothelial function, and the channel alcohol response. The structural bases underlying cholesterol-BK channel interaction are unknown. Such interaction is determined by strict chemical requirements for the sterol molecule, suggesting cholesterol recognition by a protein surface. Here, we demonstrate that cholesterol action on BK channel-forming Cbv1 proteins is mediated by their cytosolic C tail domain, where we identified seven cholesterol recognition/interaction amino acid consensus motifs (CRAC4 to 10), a distinct feature of BK proteins. Cholesterol sensitivity is provided by the membrane-adjacent CRAC4, where Val-444, Tyr-450, and Lys-453 are required for cholesterol sensing, with hydrogen bonding and hydrophobic interactions participating in cholesterol location and recognition. However, cumulative truncations or Tyr-to-Phe substitutions in CRAC5 to 10 progressively blunt cholesterol sensitivity, documenting involvement of multiple CRACs in cholesterol-BK channel interaction. In conclusion, our study provides for the first time the structural bases of BK channel cholesterol sensitivity; the presence of membrane-adjacent CRAC4 and the long cytosolic C tail domain with several other CRAC motifs, which are not found in other members of the TM6 superfamily of ion channels, very likely explains the unique cholesterol sensitivity of BK channels.
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Affiliation(s)
- Aditya K Singh
- Department of Pharmacology, College of Medicine, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
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10
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Turner RW, Anderson D, Zamponi GW. Signaling complexes of voltage-gated calcium channels. Channels (Austin) 2011; 5:440-8. [PMID: 21832880 DOI: 10.4161/chan.5.5.16473] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Voltage gated calcium channels are key mediators of depolarization induced calcium entry into electrically excitable cells. There is increasing evidence that voltage gated calcium channels, like many other types of ionic channels, do not operate in isolation, but instead forms signaling complexes with signaling molecules, G protein coupled receptors, and other types of ion channels. Furthermore, there appears to be bidirectional signaling within these protein complexes, thus allowing not only for efficient translation of calcium signals into cellular responses, but also for tight control of calcium entry per se. In this review, we will focus predominantly on signaling complexes between G protein-coupled receptors and high voltage activated calcium channels, and on complexes of voltage-gated calcium channels and members of the potassium channel superfamily.
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Affiliation(s)
- Ray W Turner
- Department of Cell Biology and Anatomy, Hotchkiss Brain Institute, University of Calgary, Calgary, AB Canada
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11
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Sakai Y, Harvey M, Sokolowski B. Identification and quantification of full-length BK channel variants in the developing mouse cochlea. J Neurosci Res 2011; 89:1747-60. [PMID: 21800349 DOI: 10.1002/jnr.22713] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2010] [Revised: 04/28/2011] [Accepted: 05/12/2011] [Indexed: 01/03/2023]
Abstract
Maxi-K(+) (BK) channel diversity is attributed to alternative splicing in the kcnma1 gene. The resultant variants manifest themselves in different cell types, tissues, and functions, such as excitation, metabolism, and signaling. Immunoelectron microscopy revealed immunogold particle labeling of BK in apical and basal regions of inner and outer hair cells, respectively. Additional labeling occurs in Deiters' cells and the inner mitochondrial membrane. Identification of full-length sequences reveals 27 BK variants from embryonic and postnatal mouse inner ear, per classification by tail motif, VYR, DEC, and ERL, and by exon usage. Three predicted start codons are found encoding MAN, MSS, and MDA, of which MDA shows the greatest expression through all stages in development, whereas MAN is undetectable. Complex splice sites occur between exons 9 and 10 and between 21 and 23. Spliced-in/out exons between 8 and 10 reveal a short fragment composed of exons 8 + 10, detectable on postnatal day (PD) 14 and PD30, and a longer fragment composed of exons 8 + 9 + 10 that is upregulated on embryonic day (ED) 14. Spliced-in exons 22 or 23 are expressed on ED14 but decrease over time; however, exon 22 increases again on PD34. Using tail-specific primers, qRT-PCR from ED14, PD4, -14, and -30 shows that BK-VYR and -ERL dominate expression on ED14, whereas DEC dominates after birth in all cochlear regions. The localization of BK and the changes in expression of its exons and tail types, by alternative splicing during development, may contribute to cochlear organization, acquisition of hearing, and intracellular signaling.
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Affiliation(s)
- Yoshihisa Sakai
- Department of Otolaryngology-Head and Neck Surgery, University of South Florida, Tampa, Florida 33612, USA
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12
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Poulsen AN, Jansen-Olesen I, Olesen J, Klaerke DA. Neuronal fast activating and meningeal silent modulatory BK channel splice variants cloned from rat. Pflugers Arch 2010; 461:65-75. [PMID: 20938677 DOI: 10.1007/s00424-010-0887-0] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2010] [Revised: 09/20/2010] [Accepted: 09/23/2010] [Indexed: 12/25/2022]
Abstract
The big conductance calcium-activated K(+) channel (BK) is involved in regulating neuron and smooth muscle cell excitability. Functional diversity of BK is generated by alpha-subunit splice variation and co-expression with beta subunits. Here, we present six different splice combinations cloned from rat brain or cerebral vascular/meningeal tissues, of which at least three variants were previously uncharacterized (X1, X2(92), and X2(188)). An additional variant was identified by polymerase chain reaction but not cloned. Expression in Xenopus oocytes showed that the brain-specific X1 variant displays reduced current, faster activation, and less voltage sensitivity than the insert-less Zero variant. Other cloned variants Strex and Slo27,3 showed slower activation than Zero. The X1 variant contains sequence inserts in the S1-S2 extracellular loop (8 aa), between intracellular domains RCK1 and RCK2 (4 aa at SS1) and upstream of the calcium "bowl" (27 aa at SS4). Two other truncated variants, X2(92) and X2(188), lacking the intracellular C-terminal (stop downstream of S6), were cloned from cerebral vascular/meningeal tissue. They appear non-functional as no current expression was observed, but the X2(92) appeared to slow the activation of the Zero variant when co-expressed. Positive protein expression of X2(92) was observed in oocytes by immunoblotting and fluorescence using a yellow fluorescent protein-tagged construct. The functional characteristics of the X1 variant may be important for a subpopulation of BK channels in the brain, while the "silent" truncated variants X2(92) and X2(188) may play a role as modulators of other BK channel variants in a way similar to well known beta subunits.
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Affiliation(s)
- Asser Nyander Poulsen
- Department of Animal and Veterinary Basic Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 7, Frederiksberg C, Denmark.
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13
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Abstract
Since the first discovery of Kvbeta-subunits more than 15 years ago, many more ancillary Kv channel subunits were characterized, for example, KChIPs, KCNEs, and BKbeta-subunits. The ancillary subunits are often integral parts of native Kv channels, which, therefore, are mostly multiprotein complexes composed of voltage-sensing and pore-forming Kvalpha-subunits and of ancillary or beta-subunits. Apparently, Kv channels need the ancillary subunits to fulfill their many different cell physiological roles. This is reflected by the large structural diversity observed with ancillary subunit structures. They range from proteins with transmembrane segments and extracellular domains to purely cytoplasmic proteins. Ancillary subunits modulate Kv channel gating but can also have a great impact on channel assembly, on channel trafficking to and from the cellular surface, and on targeting Kv channels to different cellular compartments. The importance of the role of accessory subunits is further emphasized by the number of mutations that are associated in both humans and animals with diseases like hypertension, epilepsy, arrhythmogenesis, periodic paralysis, and hypothyroidism. Interestingly, several ancillary subunits have in vitro enzymatic activity; for example, Kvbeta-subunits are oxidoreductases, or modulate enzymatic activity, i.e., KChIP3 modulates presenilin activity. Thus different modes of beta-subunit association and of functional impact on Kv channels can be delineated, making it difficult to extract common principles underlying Kvalpha- and beta-subunit interactions. We critically review present knowledge on the physiological role of ancillary Kv channel subunits and their effects on Kv channel properties.
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Affiliation(s)
- Olaf Pongs
- Institut für Neurale Signalverarbeitung, Zentrum für Molekulare Neurobiologie Hamburg, Universitätsklinikum Hamburg-Eppendorf, Universität Hamburg, Hamburg, Germany.
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14
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Hill MA, Yang Y, Ella SR, Davis MJ, Braun AP. Large conductance, Ca2+-activated K+ channels (BKCa) and arteriolar myogenic signaling. FEBS Lett 2010; 584:2033-42. [PMID: 20178789 DOI: 10.1016/j.febslet.2010.02.045] [Citation(s) in RCA: 96] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2009] [Accepted: 02/15/2010] [Indexed: 12/22/2022]
Abstract
Myogenic, or pressure-induced, vasoconstriction is critical for local blood flow autoregulation. Underlying this vascular smooth muscle (VSM) response are events including membrane depolarization, Ca(2+) entry and mobilization, and activation of contractile proteins. Large conductance, Ca(2+)-activated K(+) channel (BK(Ca)) has been implicated in several of these steps including, (1) channel closure causing membrane depolarization, and (2) channel opening causing hyperpolarization to oppose excessive pressure-induced vasoconstriction. As multiple mechanisms regulate BK(Ca) activity (subunit composition, membrane potential (Em) and Ca(2+) levels, post-translational modification) tissue level diversity is predicted. Importantly, heterogeneity in BK(Ca) channel activity may contribute to tissue-specific differences in regulation of myogenic vasoconstriction, allowing local hemodynamics to be matched to metabolic requirements. Knowledge of such variability will be important to exploiting the BK(Ca) channel as a therapeutic target and understanding systemic effects of its pharmacological manipulation.
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Affiliation(s)
- Michael A Hill
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO 65211, USA.
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15
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Hou S, Horrigan FT, Xu R, Heinemann SH, Hoshi T. Comparative effects of H+ and Ca2+ on large-conductance Ca2+- and voltage-gated Slo1 K+ channels. Channels (Austin) 2009; 3:249-58. [PMID: 19617704 DOI: 10.4161/chan.3.4.9253] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Large-conductance Ca(2+)- and voltage-gated Slo1 BK channels are allosterically activated by depolarization and intracellular ligands such as Ca(2+). Of the two high-affinity Ca(2+) sensors present in the channel, the RCK1 sensor also mediates H(+)-dependent activation of the channel. In this study, we examined the comparative mechanisms of the channel activation by Ca(2+) and H(+). Steady-state macroscopic conductance-voltage measurements as well as single-channel openings at negative voltages where voltage-sensor activation is negligible showed that at respective saturating concentrations Ca(2+) is more effective in relative stabilization of the open conformation than H(+). Calculations using the Debye-Hückel formalism suggest that small structural changes in the RCK1 sensor, on the order of few angstroms, may accompany the H(+)-mediated opening of the channel. While the efficacy of H(+) in activation of the channel is less than that of Ca(2+), H(+) more effectively accelerates the activation kinetics when examined at the concentrations equipotent on macroscopic voltage-dependent activation. The RCK1 sensor therefore is capable of transducing the nature of the bound ligand and transmits qualitatively different information to the channel's permeation gate.
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Affiliation(s)
- Shangwei Hou
- Department of Physiology, University of Pennsylvania, Philadelphia, PA, USA
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16
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Fodor AA, Aldrich RW. Convergent evolution of alternative splices at domain boundaries of the BK channel. Annu Rev Physiol 2009; 71:19-36. [PMID: 18694345 DOI: 10.1146/annurev.physiol.010908.163124] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Alternative splicing is a widespread mechanism for generating transcript diversity in higher eukaryotic genomes. The alternative splices of the large-conductance calcium-activated potassium (BK) channel have been the subject of a good deal of experimental functional characterization in the Arthropoda, Chordata, and Nematoda phyla. In this review, we examine a list of splices of the BK channel by manual curation of Unigene clusters mapped to mouse, human, chicken, Drosophila, and Caenorhabditis elegans genomes. We find that BK alternative splices do not appear to be conserved across phyla. Despite this lack of conservation, splices occur in both vertebrates and invertebrates at identical regions of the channel at experimentally established domain boundaries. The fact that, across phyla, unique splices occur at experimentally established domain boundaries suggests a prominent role for the convergent evolution of alternative splices that produce functional changes via changes in interdomain communication.
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Affiliation(s)
- Anthony A Fodor
- Bioinformatics Research Center, Cameron Applied Research Center, University of North Carolina, Charlotte, North Carolina 28223, USA.
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17
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Kranjc A, Grillo FW, Rievaj J, Boccaccio A, Pietrucci F, Menini A, Carloni P, Anselmi C. Regulation of bestrophins by Ca2+: a theoretical and experimental study. PLoS One 2009; 4:e4672. [PMID: 19262692 PMCID: PMC2650406 DOI: 10.1371/journal.pone.0004672] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Accepted: 01/26/2009] [Indexed: 01/06/2023] Open
Abstract
Bestrophins are a recently discovered family of Cl(-) channels, for which no structural information is available. Some family members are activated by increased intracellular Ca2+ concentration. Bestrophins feature a well conserved Asp-rich tract in their COOH terminus (Asp-rich domain), which is homologous to Ca2+-binding motifs in human thrombospondins and in human big-conductance Ca2+- and voltage-gated K+ channels (BK(Ca)). Consequently, the Asp-rich domain is also a candidate for Ca2+ binding in bestrophins. Based on these considerations, we constructed homology models of human bestrophin-1 (Best1) Asp-rich domain using human thrombospondin-1 X-ray structure as a template. Molecular dynamics simulations were used to identify Asp and Glu residues binding Ca2+ and to predict the effects of their mutations to alanine. We then proceeded to test selected mutations in the Asp-rich domain of the highly homologous mouse bestrophin-2. The mutants expressed in HEK-293 cells were investigated by electrophysiological experiments using the whole-cell voltage-clamp technique. Based on our molecular modeling results, we predicted that Asp-rich domain has two defined binding sites and that D301A and D304A mutations may impact the binding of the metal ions. The experiments confirmed that these mutations do actually affect the function of the protein causing a large decrease in the Ca2+-activated Cl(-) current, fully consistent with our predictions. In addition, other studied mutations (E306A, D312A) did not decrease Ca2+-activated Cl(-) current in agreement with modeling results.
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Affiliation(s)
- Agata Kranjc
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | | | - Juraj Rievaj
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | - Anna Boccaccio
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
| | - Fabio Pietrucci
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
| | - Anna Menini
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
| | - Paolo Carloni
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- Italian Institute of Technology (IIT), SISSA-Unit, Trieste, Italy
- CNR-INFM-DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste, Italy
| | - Claudio Anselmi
- International School for Advanced Studies (SISSA/ISAS), Trieste, Italy
- CNR-INFM-DEMOCRITOS Modeling Center for Research in Atomistic Simulation, Trieste, Italy
- * E-mail:
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18
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Abstract
Large conductance, Ca(2+)-activated potassium (BK) channels are widely expressed throughout the animal kingdom and play important roles in many physiological processes, such as muscle contraction, neural transmission and hearing. These physiological roles derive from the ability of BK channels to be synergistically activated by membrane voltage, intracellular Ca(2+) and other ligands. Similar to voltage-gated K(+) channels, BK channels possess a pore-gate domain (S5-S6 transmembrane segments) and a voltage-sensor domain (S1-S4). In addition, BK channels contain a large cytoplasmic C-terminal domain that serves as the primary ligand sensor. The voltage sensor and the ligand sensor allosterically control K(+) flux through the pore-gate domain in response to various stimuli, thereby linking cellular metabolism and membrane excitability. This review summarizes the current understanding of these structural domains and their mutual interactions in voltage-, Ca(2+)- and Mg(2+)-dependent activation of the channel.
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Affiliation(s)
- J Cui
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, 1 Brookings Drive, St. Louis, Missouri 63130, USA.
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19
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Kubokawa M, Sohma Y, Hirano J, Nakamura K, Kubota T. Intracellular Mg2+ influences both open and closed times of a native Ca2+-activated BK channel in cultured human renal proximal tubule cells. J Membr Biol 2009; 207:69-89. [PMID: 16477529 DOI: 10.1007/s00232-005-0802-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2004] [Revised: 10/20/2005] [Indexed: 12/22/2022]
Abstract
Effects of intracellular Mg2+ on a native Ca(2+)-and voltage-sensitive large-conductance K+ channel in cultured human renal proximal tubule cells were examined with the patch-clamp technique in the inside-out mode. At an intracellular concentration of Ca2+ ([Ca2+](i)) of 10(-5)-10(-4) M, addition of 1-10 mM: Mg2+ increased the open probability (P(o)) of the channel, which shifted the P(o) -membrane potential (V(m)) relationship to the negative voltage direction without causing an appreciable change in the gating charge (Boltzmann constant). However, the Mg(2+)-induced increase in P(o) was suppressed at a relatively low [Ca2+](i) (10(-5.5)-10(-6) M). Dwell-time histograms have revealed that addition of Mg2+ mainly increased P(o) by extending open times at 10(-5) M Ca2+ and extending both open and closed times simultaneously at 10(-5.5) M Ca2+. Since our data showed that raising the [Ca2+](i) from 10(-5) to 10(-4) M increased P(o) mainly by shortening the closed time, extension of the closed time at 10(-5.5) M Ca(2+) would result from the Mg(2+)-inhibited Ca(2+)-dependent activation. At a constant V(m), adding Mg2+ enhanced the sigmoidicity of the P(o)-[Ca2+](i) relationship with an increase in the Hill coefficient. These results suggest that the major action of Mg2+ on this channel is to elevate P(o) by lengthening the open time, while extension of the closed time at a relatively low [Ca2+](i) results from a lowering of the sensitivity to Ca2+ of the channel by Mg2+, which causes the increase in the Hill coefficient.
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Affiliation(s)
- M Kubokawa
- Department of Physiology II, School of Medicine, Iwate Medical University, 19-1, Uchimaru, Morioka, 020-8505, Japan.
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20
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Differential expression of BK channel isoforms and β-subunits in rat neuro-vascular tissues. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2009; 1788:380-9. [DOI: 10.1016/j.bbamem.2008.10.001] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/29/2008] [Revised: 09/18/2008] [Accepted: 10/06/2008] [Indexed: 12/30/2022]
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21
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Abstract
The set of genes that underlie ethanol tolerance (inducible resistance) are likely to overlap with the set of genes responsible for ethanol addiction. Whereas addiction is difficult to recognize in simple model systems, behavioral tolerance is readily identifiable and can be induced in large populations of animals. Thus, tolerance lends itself to analysis in model systems with powerful genetics. Drosophila melanogaster has been used by a variety of laboratories for the identification of genes that interfere with the acquisition of ethanol tolerance. Here, I discuss the genes identified as being important for the production of ethanol tolerance in Drosophila. Some of these genes have also been shown to be important for the production of tolerance in mammals, demonstrating that gene discovery in Drosophila has predictive value for understanding the molecular pathways that generate tolerance in mammals.
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Affiliation(s)
- Nigel S Atkinson
- Section of Neurobiology and The Waggoner Center for Alcohol and Addiction Research, The University of Texas at Austin, Austin, Texas 78712-0248, USA.
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22
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Polyunsaturated fatty acid modulation of voltage-gated ion channels. Cell Biochem Biophys 2008; 52:59-84. [PMID: 18830821 DOI: 10.1007/s12013-008-9027-2] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 09/03/2008] [Indexed: 01/03/2023]
Abstract
Arachidonic acid (AA) was found to inhibit the function of whole-cell voltage-gated (VG) calcium currents nearly 16 years ago. There are now numerous examples demonstrating that AA and other polyunsaturated fatty acids (PUFAs) modulate the function of VG ion channels, primarily in neurons and muscle cells. We will review and extract some common features about the modulation by PUFAs of VG calcium, sodium, and potassium channels and discuss the impact of this modulation on the excitability of neurons and cardiac myocytes. We will describe the fatty acid nature of the membrane, how fatty acids become available to function as modulators of VG channels, and the physiologic importance of this type of modulation. We will review the evidence for molecular mechanisms and assess our current understanding of the structural basis for modulation. With guidance from research on the structure of fatty acid binding proteins, the role of lipids in gating mechanosensitive (MS) channels, and the impact of membrane lipid composition on membrane-embedded proteins, we will highlight some avenues for future investigations.
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23
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Klose A, Huth T, Alzheimer C. 1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122) selectively inhibits Kir3 and BK channels in a phospholipase C-independent fashion. Mol Pharmacol 2008; 74:1203-14. [PMID: 18682550 DOI: 10.1124/mol.108.047837] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-1H-pyrrole-2,5-dione (U73122) is widely used to inhibit phospholipase C (PLC)-mediated signaling, but we and others have also reported a PLC-independent block of Kir3 channels in native cells. To elaborate on this major side effect, we examined the action of U73122 and 1-[6-[[(17beta)-3-methoxyestra-1,3,5(10)-trien-17-yl]amino]hexyl]-2,5-pyrollidinedione (U73343), a structurally related but not PLC-inhibiting analog, on Kir1.1, Kir2.1, or Kir3.1/3.2 channels expressed in HEK293 cells. Both compounds (10 microM) displayed an unusual degree of selectivity for Kir3, superior even to that of tertiapin, which discriminates between Kir3 and Kir2 but also inhibits Kir1.1. Recordings from mutant Kir2 and Kir3 channels showed that U73122 is unlikely to block Kir3 by interfering with binding of phosphatidylinositol 4,5-bisphosphate, and U73122 did not seem to act like a pore blocker. U73122 and U73343 also unexpectedly suppressed Ca(2+)-activated K(+) channels of the large-conductance type (MaxiK, BK) in a PLC-independent fashion. In single-channel recordings, both compounds significantly decreased open probability of BK channels and slowed their ultrafast gating ("flickering") at very depolarized potentials. Alignment of the amino acid sequences of Kir3 and BK channels suggested that the highly selective effect of U73122/U73343 is mediated by a homologous domain within the long C-terminal ends. In fact, mutations in the C-terminal region of Kir2 and Kir3 channels significantly altered their sensitivity to the two compounds. Our data strongly caution against the use of U73122 when exploring signaling pathways involving Kir3 and BK channels. However, the apparent binding of U73122/U73343 to a common structural motif might be exploited to develop drugs selectively targeting Kir3 and BK channels.
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Affiliation(s)
- Angelika Klose
- Department of Physiology, University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany
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24
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Peiter E, Sun J, Heckmann AB, Venkateshwaran M, Riely BK, Otegui MS, Edwards A, Freshour G, Hahn MG, Cook DR, Sanders D, Oldroyd GED, Downie JA, Ané JM. The Medicago truncatula DMI1 protein modulates cytosolic calcium signaling. PLANT PHYSIOLOGY 2007; 145:192-203. [PMID: 17631529 PMCID: PMC1976572 DOI: 10.1104/pp.107.097261] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
In addition to establishing symbiotic relationships with arbuscular mycorrhizal fungi, legumes also enter into a nitrogen-fixing symbiosis with rhizobial bacteria that results in the formation of root nodules. Several genes involved in the development of both arbuscular mycorrhiza and legume nodulation have been cloned in model legumes. Among them, Medicago truncatula DMI1 (DOESN'T MAKE INFECTIONS1) is required for the generation of nucleus-associated calcium spikes in response to the rhizobial signaling molecule Nod factor. DMI1 encodes a membrane protein with striking similarities to the Methanobacterium thermoautotrophicum potassium channel (MthK). The cytosolic C terminus of DMI1 contains a RCK (regulator of the conductance of K(+)) domain that in MthK acts as a calcium-regulated gating ring controlling the activity of the channel. Here we show that a dmi1 mutant lacking the entire C terminus acts as a dominant-negative allele interfering with the formation of nitrogen-fixing nodules and abolishing the induction of calcium spikes by the G-protein agonist Mastoparan. Using both the full-length DMI1 and this dominant-negative mutant protein we show that DMI1 increases the sensitivity of a sodium- and lithium-hypersensitive yeast (Saccharomyces cerevisiae) mutant toward those ions and that the C-terminal domain plays a central role in regulating this response. We also show that DMI1 greatly reduces the release of calcium from internal stores in yeast, while the dominant-negative allele appears to have the opposite effect. This work suggests that DMI1 is not directly responsible for Nod factor-induced calcium changes, but does have the capacity to regulate calcium channels in both yeast and plants.
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Affiliation(s)
- Edgar Peiter
- Biology Department, University of York, York, United Kingdom
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25
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Kim EY, Ridgway LD, Zou S, Chiu YH, Dryer SE. Alternatively spliced C-terminal domains regulate the surface expression of large conductance calcium-activated potassium channels. Neuroscience 2007; 146:1652-61. [PMID: 17478049 PMCID: PMC1995407 DOI: 10.1016/j.neuroscience.2007.03.038] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2007] [Revised: 03/09/2007] [Accepted: 03/13/2007] [Indexed: 01/31/2023]
Abstract
The Slo1 gene, also known as KCNMA1, encodes the pore-forming subunits of large-conductance Ca2+-activated K+ (BK(Ca)) channels. Products of this gene are widely expressed in vertebrate tissues, and occur in a large number (>or=20) of alternatively spliced variants that vary in their gating properties, susceptibility to modulation, and trafficking to the plasma membrane. Motifs in the large cytoplasmic C-terminal are especially important in determining the functional properties of BK(Ca) channels. Here we report that chick ciliary ganglion neurons express transcripts and proteins of two Slo1 splice variants that differ at the extreme C-terminal. We refer to these variants as VEDEC and QEDRL (or QEERL for the orthologous mammalian versions), after the five terminal amino acid residues in each isoform. Individual ciliary ganglion neurons preferentially express these variants in different subcellular compartments. Moreover, QEERL channels show markedly higher levels of constitutive expression on the plasma membrane than VEDEC channels in HEK293T and NG108-15 cells. However, growth factor treatment can stimulate surface expression of VEDEC channels to levels comparable to those seen with QEERL. In addition, we show that co-expression of a soluble protein composed of VEDEC C-terminal tail residues markedly increases cell surface expression of full-length VEDEC channels, suggesting that this region binds to proteins that cause retention of the these channels in intracellular stores.
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Affiliation(s)
| | | | | | | | - Stuart E. Dryer
- Author for correspondence: , +1 713-743-2697 (ph), +1 713-743-2632 (FAX)
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26
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Salkoff L, Butler A, Ferreira G, Santi C, Wei A. High-conductance potassium channels of the SLO family. Nat Rev Neurosci 2007; 7:921-31. [PMID: 17115074 DOI: 10.1038/nrn1992] [Citation(s) in RCA: 409] [Impact Index Per Article: 24.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
High-conductance, 'big' potassium (BK) channels encoded by the Slo gene family are among the largest and most complex of the extended family of potassium channels. The family of SLO channels apparently evolved from voltage-dependent potassium channels, but acquired a large conserved carboxyl extension, which allows channel gating to be altered in response to the direct sensing of several different intracellular ions, and by other second-messenger systems, such as those activated following neurotransmitter binding to G-protein-coupled receptors (GPCRs). This versatility has been exploited to serve many cellular roles, both within and outside the nervous system.
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Affiliation(s)
- Lawrence Salkoff
- Department of Anatomy and Neurobiology, Washington University School of Medicine, 660 S. Euclid Avenue, Saint Louis, Missouri 63110, USA.
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27
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Denson DD, Li J, Eaton DC. Co-localization of the alpha-subunit of BK-channels and c-PLA2 in GH3 cells. Biochem Biophys Res Commun 2006; 350:39-49. [PMID: 16997278 DOI: 10.1016/j.bbrc.2006.08.193] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2006] [Accepted: 08/29/2006] [Indexed: 11/24/2022]
Abstract
Large conductance, calcium-activated potassium channels (maxi K- or BK-channels) can be regulated by arachidonic acid produced by c-Phospholipase A2 (c-PLA2). Since in every excised patch from GH3 cells where there was BK-channel activity, treatment with either a stimulator or inhibitor of c-PLA2 resulted in a corresponding increase or decrease in BK-channel activity, we hypothesized that there must be a close association between BK-channel proteins and c-PLA2 in the cell membrane. To test this hypothesis, we first determined whether the two proteins would co-immunoprecipitate. We then used confocal imaging of fluorescently tagged proteins to determine where in the cells BK-channel proteins and c-PLA2 co-localize. The alpha-subunit of the BK-channel was strongly co-immunoprecipitated by c-PLA2 antibodies, suggesting that most of the BK channel alpha-subunits are associated with c-PLA2. This interaction was not affected by pharmacologically inhibiting c-PLA2 suggesting that the association does not require functionally active c-PLA2. Following dual immunohistochemical labeling and confocal microscopy, image analysis revealed that in the cytosol there was some co-localization, but most of the c-PLA2 was separate from BK-channel proteins. On the other hand, the c-PLA2 and BK-channel proteins at the plasma membrane were strongly co-localized. Immunoprecipitation experiments conducted with plasma membrane proteins support these findings. We conclude that c-PLA2 is likely physically associated with BK-channel proteins at the cell surface.
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Affiliation(s)
- D D Denson
- Department of Anesthesiology, Emory University School of Medicine, Atlanta, GA 30322, USA.
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28
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Yu JY, Upadhyaya AB, Atkinson NS. Tissue-specific alternative splicing of BK channel transcripts in Drosophila. GENES BRAIN AND BEHAVIOR 2006; 5:329-39. [PMID: 16716202 DOI: 10.1111/j.1601-183x.2005.00164.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
BK-type calcium-activated potassium channels are large conductance channels that respond to changes in intracellular calcium and membrane potential. These channels are used in a wide variety of cell types and have recently been linked to drug sensitivity and tolerance. In both Drosophila and mammals, BK channels are encoded by the slowpoke gene. The Drosophila slowpoke gene includes 14 alternative exons distributed among five sites of alternative splicing. Presumably, the purpose of alternative processing is to provide transcripts tailored to the needs of the cell. The slowpoke gene is expressed in nervous, muscle and epithelial tissues. To determine whether splicing is controlled in a tissue- and/or developmental-specific manner, we built tissue- and developmental-specific cDNA libraries that preserved the relative frequency of various slowpoke splice variants. These libraries were screened by colony hybridization using alternative exon-specific DNA probes to document the frequency of individual alternative exons in different developmental stages and distinct tissue types. We demonstrate that slowpoke transcripts undergo tissue- and developmental-specific splicing in Drosophila and some exons are diagnostic for specific tissues.
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Affiliation(s)
- J Y Yu
- Section of Neurobiology, The University of Texas at Austin, Austin, TX 78712-0248, USA
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29
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Ledoux J, Werner ME, Brayden JE, Nelson MT. Calcium-activated potassium channels and the regulation of vascular tone. Physiology (Bethesda) 2006; 21:69-78. [PMID: 16443824 DOI: 10.1152/physiol.00040.2005] [Citation(s) in RCA: 320] [Impact Index Per Article: 17.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Different calcium signals in the endothelium and smooth muscle target different types of Ca2+-sensitive K+ channels to modulate vascular function. These differential calcium signals and targets represent multilayered opportunities for prevention and/or treatment of vascular dysfunctions.
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Affiliation(s)
- Jonathan Ledoux
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington, Vermont, USA
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30
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Ghatta S, Nimmagadda D, Xu X, O'Rourke ST. Large-conductance, calcium-activated potassium channels: structural and functional implications. Pharmacol Ther 2005; 110:103-16. [PMID: 16356551 DOI: 10.1016/j.pharmthera.2005.10.007] [Citation(s) in RCA: 240] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2005] [Accepted: 10/13/2005] [Indexed: 12/16/2022]
Abstract
The large-conductance, calcium-activated potassium channels (BK, also termed BK(Ca), Slo, or MaxiK) distributed in both excitable and non-excitable cells are involved in many cellular functions such as action potential repolarization; neuronal excitability; neurotransmitter release; hormone secretion; tuning of cochlear hair cells; innate immunity; and modulation of the tone of vascular, airway, uterine, gastrointestinal, and urinary bladder smooth muscle tissues. Because of their high conductance, activation of BK channels has a strong effect on membrane potential. BK channels differ from all other potassium (K(+)) channels due to their high sensitivity to both intracellular calcium (Ca(2+)) concentrations and voltage. These features make BK channels ideal negative feedback regulators in many cell types by decreasing voltage-dependent Ca(2+) entry through membrane potential hyperpolarization. The current review aims to give a comprehensive understanding of the structure and molecular biology of BK channels and their relevance to various pathophysiological conditions. The review will also focus on the therapeutic potential and pharmacology of the various BK channel activators and blockers.
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Affiliation(s)
- Srinivas Ghatta
- Department of Pharmaceutical Sciences, College of Pharmacy, North Dakota State University, Fargo, 58105, USA.
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31
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Hu L, Yang H, Shi J, Cui J. Effects of multiple metal binding sites on calcium and magnesium-dependent activation of BK channels. ACTA ACUST UNITED AC 2005; 127:35-49. [PMID: 16344323 PMCID: PMC2151482 DOI: 10.1085/jgp.200509317] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
BK channels are activated by physiological concentrations of intracellular Ca2+ and Mg2+ in a variety of cells. Previous studies have identified two sites important for high-affinity Ca2+ sensing between [Ca2+]i of 0.1–100 μM and a site important for Mg2+ sensing between [Mg2+]i of 0.1–10 mM. BK channels can be also activated by Ca2+ and Mg2+ at concentrations >10 mM so that the steady-state conductance and voltage (G-V) relation continuously shifts to more negative voltage ranges when [Mg2+]i increases from 0.1–100 mM. We demonstrate that a novel site is responsible for metal sensing at concentrations ≥10 mM, and all four sites affect channel activation independently. As a result, the contributions of these sites to channel activation are complex, depending on the combination of Ca2+ and Mg2+ concentrations. Here we examined the effects of each of these sites on Ca2+ and Mg2+-dependent activation and the data are consistent with the suggestion that these sites are responsible for metal binding. We provide an allosteric model for quantitative estimation of the contributions that each of these putative binding sites makes to channel activation at any [Ca2+]i and [Mg2+]i.
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Affiliation(s)
- Lei Hu
- Department of Biomedical Engineering and Cardiac Bioelectricity and Arrhythmia Center, Washington University, St. Louis, MO 63130, USA
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32
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Suzuki M. The Drosophila tweety family: molecular candidates for large-conductance Ca2+-activated Cl- channels. Exp Physiol 2005; 91:141-7. [PMID: 16219661 DOI: 10.1113/expphysiol.2005.031773] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Calcium-activated chloride currents (I(Cl(Ca))) can be recorded in almost all cells, but the molecular identity of the channels underlying this Cl- conductance is still incompletely understood. Here, I report that tweety, a gene located in Drosophila flightless, possesses five or six transmembrane segments, and that a human homologue of tweety (hTTYH3) is a novel large-conductance Ca2+-activated Cl- channel, while the related gene, hTTYH1, is a swelling-activated Cl- current. hTTYH3 is expressed in excitable tissues, including the heart, brain and skeletal muscle, whereas hTTYH1 is expressed mainly in the brain. Expression of hTTYH3 in CHO cells generated a unique Cl- current activated by an increase in the intracellular Ca2+ concentration. The hTTYH3-induced Cl- current had a linear current-voltage (I-V) relationship, a large single-channel conductance (260 pS) and the anion permeability sequence I- > Br- > Cl-. Like native Ca2+-activated Cl- channels, the hTTYH3 channel showed complex gating kinetics and voltage-dependent inactivation, and was dependent on micromolar intracellular Ca2+ concentration. Expression in CHO cells of an hTTYH1 splice variant that lacks the C-terminal glutamate-rich domain of hTTYH1 (hTTYH1sv) generated a swelling-activated Cl- current. I conclude that investigation of the tweety family will provide important information about large-conductance Cl- channel molecules.
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Affiliation(s)
- Makoto Suzuki
- Department of Pharmacology, Division of Molecular Pharmacology, Jichi Medical School 3311-1, Yakushiji, Minamikawachi, Tochigi, 329-0498, Japan.
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Chen L, Tian L, MacDonald SHF, McClafferty H, Hammond MSL, Huibant JM, Ruth P, Knaus HG, Shipston MJ. Functionally Diverse Complement of Large Conductance Calcium- and Voltage-activated Potassium Channel (BK) α-Subunits Generated from a Single Site of Splicing. J Biol Chem 2005; 280:33599-609. [PMID: 16081418 DOI: 10.1074/jbc.m505383200] [Citation(s) in RCA: 136] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The pore-forming alpha-subunits of large conductance calcium- and voltage-activated potassium (BK) channels are encoded by a single gene that undergoes extensive alternative pre-mRNA splicing. However, the extent to which differential exon usage at a single site of splicing may confer functionally distinct properties on BK channels is largely unknown. Here we demonstrated that alternative splicing at site of splicing C2 in the mouse BK channel C terminus generates five distinct splice variants: ZERO, e20, e21(STREX), e22, and a novel variant deltae23. Splice variants display distinct patterns of tissue distribution with e21(STREX) expressed at the highest levels in adult endocrine tissues and e22 at embryonic stages of mouse development. deltae23 is not functionally expressed at the cell surface and acts as a dominant negative of cell surface expression by trapping other BK channel splice variant alpha-subunits in the endoplasmic reticulum and perinuclear compartments. Splice variants display a range of biophysical properties. e21(STREX) and e22 variants display a significant left shift (>20 mV at 1 microM [Ca2+]i) in half-maximal voltage of activation compared with ZERO and e20 as well as considerably slower rates of deactivation. Splice variants are differentially sensitive to phosphorylation by endogenous cAMP-dependent protein kinase; ZERO, e20, and e22 variants are all activated, whereas e21 (STREX) is the only variant that is inhibited. Thus alternative pre-mRNA splicing from a single site of splicing provides a mechanism to generate a physiologically diverse complement of BK channel alpha-subunits that differ dramatically in their tissue distribution, trafficking, and regulation.
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Affiliation(s)
- Lie Chen
- Centre for Integrative Physiology, Membrane Biology Group, University of Edinburgh, Hugh Robson Building, Edinburgh EH8 9XD, Scotland, United Kingdom
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Thorneloe KS, Nelson MT. Ion channels in smooth muscle: regulators of intracellular calcium and contractility. Can J Physiol Pharmacol 2005; 83:215-42. [PMID: 15870837 DOI: 10.1139/y05-016] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Smooth muscle (SM) is essential to all aspects of human physiology and, therefore, key to the maintenance of life. Ion channels expressed within SM cells regulate the membrane potential, intracellular Ca2+ concentration, and contractility of SM. Excitatory ion channels function to depolarize the membrane potential. These include nonselective cation channels that allow Na+ and Ca2+ to permeate into SM cells. The nonselective cation channel family includes tonically active channels (Icat), as well as channels activated by agonists, pressure-stretch, and intracellular Ca2+ store depletion. Cl--selective channels, activated by intracellular Ca2+ or stretch, also mediate SM depolarization. Plasma membrane depolarization in SM activates voltage-dependent Ca2+ channels that demonstrate a high Ca2+ selectivity and provide influx of contractile Ca2+. Ca2+ is also released from SM intracellular Ca2+ stores of the sarcoplasmic reticulum (SR) through ryanodine and inositol trisphosphate receptor Ca2+ channels. This is part of a negative feedback mechanism limiting contraction that occurs by the Ca2+-dependent activation of large-conductance K+ channels, which hyper polarize the plasma membrane. Unlike the well-defined contractile role of SR-released Ca2+ in skeletal and cardiac muscle, the literature suggests that in SM Ca2+ released from the SR functions to limit contractility. Depolarization-activated K+ chan nels, ATP-sensitive K+ channels, and inward rectifier K+ channels also hyperpolarize SM, favouring relaxation. The expression pattern, density, and biophysical properties of ion channels vary among SM types and are key determinants of electrical activity, contractility, and SM function.
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Affiliation(s)
- Kevin S Thorneloe
- Department of Pharmacology, College of Medicine, University of Vermont, Burlington 05405, USA.
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Krishnamoorthy G, Shi J, Sept D, Cui J. The NH2 terminus of RCK1 domain regulates Ca2+-dependent BK(Ca) channel gating. ACTA ACUST UNITED AC 2005; 126:227-41. [PMID: 16103277 PMCID: PMC2266574 DOI: 10.1085/jgp.200509321] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Large conductance, voltage- and Ca2+-activated K+ (BKCa) channels regulate blood vessel tone, synaptic transmission, and hearing owing to dual activation by membrane depolarization and intracellular Ca2+. Similar to an archeon Ca2+-activated K+ channel, MthK, each of four α subunits of BKCa may contain two cytosolic RCK domains and eight of which may form a gating ring. The structure of the MthK channel suggests that the RCK domains reorient with one another upon Ca2+ binding to change the gating ring conformation and open the activation gate. Here we report that the conformational changes of the NH2 terminus of RCK1 (AC region) modulate BKCa gating. Such modulation depends on Ca2+ occupancy and activation states, but is not directly related to the Ca2+ binding sites. These results demonstrate that AC region is important in the allosteric coupling between Ca2+ binding and channel opening. Thus, the conformational changes of the AC region within each RCK domain is likely to be an important step in addition to the reorientation of RCK domains leading to the opening of the BKCa activation gate. Our observations are consistent with a mechanism for Ca2+-dependent activation of BKCa channels such that the AC region inhibits channel activation when the channel is at the closed state in the absence of Ca2+; Ca2+ binding and depolarization relieve this inhibition.
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Affiliation(s)
- Gayathri Krishnamoorthy
- Department of Biomedical Engineering, Case Western Reserve University, Cleveland, OH 44106, USA
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36
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Abstract
Potassium channels are integral membrane proteins that selectively transport K+ across the cell membrane. They are present in all mammalian cells and have a wide variety of roles in both excitable and nonexcitable cells. The phenotypic diversity required to accomplish their various roles is created by differences in conductance, the timecourse and mechanisms of different gating events, and the interaction of channels with a variety of accessory proteins. Through the integration of biophysical, molecular, structural, and theoretical studies, significant progress has been made toward understanding the structural basis of K+ channel function, and diseases associated with K+ channel dysfunction.
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Affiliation(s)
- Stephen J Korn
- Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT 06269, USA.
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Xia XM, Zhang X, Lingle CJ. Ligand-dependent activation of Slo family channels is defined by interchangeable cytosolic domains. J Neurosci 2004; 24:5585-91. [PMID: 15201331 PMCID: PMC6729329 DOI: 10.1523/jneurosci.1296-04.2004] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Large-conductance Ca2+- and voltage-regulated K+ channels (Slo1 BK-type) are controlled by two physiological stimuli, membrane voltage and cytosolic Ca2+. Regulation by voltage is similar to that in voltage-dependent K+ channels, arising from positively charged amino acids primarily within the S4 transmembrane helices. The basis for regulation by Ca2+ remains controversial. One viewpoint suggests that the extensive cytosolic C terminus contains the Ca2+ regulatory machinery, whereas another suggests that the pore-forming module contains the Ca2+-sensing elements. To address this issue, we take advantage of another Slo family member, the pH-regulated homolog Slo3. We reason that if the ligand-sensing apparatus is uniquely associated with a particular domain (either the pore or the cytosolic domain), exchange of those domains between Slo1 and Slo3 should result in exchange of ligand dependence in association with the key domain. The results show that the Slo3 cytosolic module confers pH-dependent regulation on the Slo1 pore module, whereas the Slo1 cytosolic module confers Ca2+-dependent regulation on the Slo3 pore module. Thus, ligand-specific regulation is defined by interchangeable cytosolic regulatory modules.
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Affiliation(s)
- Xiao-Ming Xia
- Department of Anesthesiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA
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38
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Bao L, Kaldany C, Holmstrand EC, Cox DH. Mapping the BKCa channel's "Ca2+ bowl": side-chains essential for Ca2+ sensing. ACTA ACUST UNITED AC 2004; 123:475-89. [PMID: 15111643 PMCID: PMC2234491 DOI: 10.1085/jgp.200409052] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
There is controversy over whether Ca2+ binds to the BKCa channel's intracellular domain or its integral-membrane domain and over whether or not mutations that reduce the channel's Ca2+ sensitivity act at the point of Ca2+ coordination. One region in the intracellular domain that has been implicated in Ca2+ sensing is the “Ca2+ bowl”. This region contains many acidic residues, and large Ca2+-bowl mutations eliminate Ca2+ sensing through what appears to be one type of high-affinity Ca2+-binding site. Here, through site-directed mutagenesis we have mapped the residues in the Ca2+ bowl that are most important for Ca2+ sensing. We find acidic residues, D898 and D900, to be essential, and we find them essential as well for Ca2+ binding to a fusion protein that contains a portion of the BKCa channel's intracellular domain. Thus, much of our data supports the conclusion that Ca2+ binds to the BKCa channel's intracellular domain, and they define the Ca2+ bowl's essential Ca2+-sensing motif. Overall, however, we have found that the relationship between mutations that disrupt Ca2+ sensing and those that disrupt Ca2+ binding is not as strong as we had expected, a result that raises the possibility that, when examined by gel-overlay, the Ca2+ bowl may be in a nonnative conformation.
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Affiliation(s)
- Lin Bao
- Molecular Cardiology Research Institute, New England Medical Center, Department of Neuroscience, Tufts University School of Medicine, Boston, MA 02111, USA
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39
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40
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Zhang Y, Joiner WJ, Bhattacharjee A, Rassendren F, Magoski NS, Kaczmarek LK. The Appearance of a Protein Kinase A-regulated Splice Isoform of slo Is Associated with the Maturation of Neurons That Control Reproductive Behavior. J Biol Chem 2004; 279:52324-30. [PMID: 15375169 DOI: 10.1074/jbc.m408543200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
In response to brief synaptic stimulation that activates protein kinase A (PKA), the bag cell neurons of Aplysia trigger the onset of reproductive behaviors by generating a prolonged afterdischarge. In juvenile animals, such afterdischarges are inhibited by a high density of Ca2+ -activated K+ (BK) channels, encoded by the slo gene. An increase in this current also follows an afterdischarge in mature animals, contributing to a subsequent refractory state that limits reproductive behaviors. Using a bag cell cDNA library, we have isolated two alternative transcripts of the slo gene, differing in the presence (slo-a) or absence (slo-b) of a consensus phosphorylation site for PKA. Expression of either isoform in Chinese hamster ovary cells produced Ca2+ - and voltage-dependent channels with macroscopic and unitary properties matching those in bag cell neurons. The isoforms differed, however, in their response to application of the catalytic subunit of PKA, which reduced the open probability of Slo-a, an effect that was reversed by a PKA inhibitor. In contrast, PKA had no effect on Slo-b. By immunocytochemistry, we determined that the PKA-regulated Slo-a subunit is present in adult, but not juvenile, bag cell neurons. Patch clamp recordings from adult and juvenile bag cell neurons confirmed that PKA decreases BK channel activity only in adults. Our findings suggest that a change in the identity of Slo isoforms expressed during development allows mature neurons to generate afterdischarges that are required for reproduction.
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Affiliation(s)
- Yalan Zhang
- Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06520, USA
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41
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Jow F, Zhang ZH, Kopsco DC, Carroll KC, Wang K. Functional coupling of intracellular calcium and inactivation of voltage-gated Kv1.1/Kvbeta1.1 A-type K+ channels. Proc Natl Acad Sci U S A 2004; 101:15535-40. [PMID: 15486093 PMCID: PMC524431 DOI: 10.1073/pnas.0402081101] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Voltage-gated Kv1.1/Kvbeta1.1 A-type channels, as a natural complex, can switch from fast to slow inactivation under oxidation/reduction conditions. The mode-switching of inactivation, which is mediated by a cysteine residue in the inactivation ball domain of the Kvbeta1.1 N terminus, can regulate membrane electrical excitability. In the present study, we identified a mechanism whereby inactivation in Kv1.1/Kvbeta1.1 channels is regulated by calcium influx. The rise in intracellular calcium, due to either influx from extracellular space or release from intracellular stores, eliminates fast inactivation induced by Kvbeta1.1, resulting in slower inactivation and increased steady-state current. This oxidation-independent calcium effect is mediated through the Kvbeta1.1 N terminus, not the C terminus. We propose that a coupling between calcium influx and inactivation of voltage-gated A-type K+ channels occurs as a result of membrane depolarization and may contribute to afterhyperpolarization as negative feedback to control neuronal excitability.
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Affiliation(s)
- Flora Jow
- Neuroscience Discovery Research, Wyeth Research, CN-8000, Princeton, NJ 08543, USA
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42
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Niu X, Qian X, Magleby KL. Linker-gating ring complex as passive spring and Ca(2+)-dependent machine for a voltage- and Ca(2+)-activated potassium channel. Neuron 2004; 42:745-56. [PMID: 15182715 DOI: 10.1016/j.neuron.2004.05.001] [Citation(s) in RCA: 139] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2003] [Revised: 02/24/2004] [Accepted: 04/16/2004] [Indexed: 12/19/2022]
Abstract
Ion channels are proteins that control the flux of ions across cell membranes by opening and closing (gating) their pores. It has been proposed that channels gated by internal agonists have an intracellular gating ring that extracts free energy from agonist binding to open the gates using linkers that directly connect the gating ring to the gates. Here we find for a voltage- and Ca(2+)-activated K+ (BK) channel that shortening the linkers increases channel activity and lengthening the linkers decreases channel activity, both in the presence and absence of intracellular Ca2+. These observations are consistent with a mechanical model in which the linker-gating ring complex forms a passive spring that applies force to the gates in the absence of Ca2+ to modulate the voltage-dependent gating. Adding Ca2+ then changes the force to further activate the channel. Both the passive and Ca(2+)-induced forces contribute to the gating of the channel.
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MESH Headings
- Allosteric Regulation
- Amino Acid Sequence
- Animals
- Calcium/metabolism
- Cell Line
- Cloning, Molecular/methods
- Dose-Response Relationship, Drug
- Electric Conductivity
- Embryo, Mammalian
- Embryo, Nonmammalian
- Humans
- Ion Channel Gating/physiology
- Kidney
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Models, Biological
- Mutation/physiology
- Oocytes
- Patch-Clamp Techniques/methods
- Potassium Channels, Calcium-Activated/chemistry
- Potassium Channels, Calcium-Activated/metabolism
- Potassium Channels, Voltage-Gated/chemistry
- Potassium Channels, Voltage-Gated/metabolism
- Protein Conformation
- Protein Structure, Tertiary/physiology
- Transfection/methods
- Xenopus
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Affiliation(s)
- Xiaowei Niu
- Department of Physiology and Biophysics, University of Miami School of Medicine, P.O. Box 016430, Miami, Florida 33101, USA
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43
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Park SM, Liu G, Kubal A, Fury M, Cao L, Marx SO. Direct interaction between BKCa potassium channel and microtubule-associated protein 1A. FEBS Lett 2004; 570:143-8. [PMID: 15251455 DOI: 10.1016/j.febslet.2004.06.037] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Accepted: 06/14/2004] [Indexed: 10/26/2022]
Abstract
The BKCa channel, a potassium channel that is allosterically activated by voltage and calcium, is expressed in both excitable and non-excitable cells. The channel plays an important role in regulating membrane excitability. The channel activity can be modulated by post-translational modifications such as phosphorylation. Recently, hippocampal BKCa channels were shown to be directly modulated by assembly/disassembly of the submembranous actin cytoskeleton. Here, we report that the BKCa channel physically interacts with the light chain of microtubule associated protein 1A (MAP1A). The light chain was isolated in a yeast two-hybrid screen of a human brain cDNA library. The specificity of the interaction was demonstrated in biochemical experiments utilizing GST fusion protein pulldown assays and reciprocal co-immunoprecipitations from rat brain. Furthermore, utilizing immunofluorescence, the BKCa channel and MAP1A co-localize in the Purkinje cell layer of the cerebellum. These studies identify a novel interaction between the C-terminal tail of the BKCa channel and the light chain of MAP1A, which enables channel association with and modulation by the cytoskeleton.
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Affiliation(s)
- Soo Mi Park
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY, USA
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44
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Abstract
Calcium-activated potassium channels are a large family of potassium channels that are found throughout the central nervous system and in many other cell types. These channels are activated by rises in cytosolic calcium largely in response to calcium influx via voltage-gated calcium channels that open during action potentials. Activation of these potassium channels is involved in the control of a number of physiological processes from the firing properties of neurons to the control of transmitter release. These channels form the target for modulation for a range of neurotransmitters and have been implicated in the pathogenesis of neurological and psychiatric disorders. Here the authors summarize the varieties of calcium-activated potassium channels present in central neurons and their defining molecular and biophysical properties.
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Affiliation(s)
- E S Louise Faber
- Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, Australia
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45
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Spreadbury IC, Kros CJ, Meech RW. Effects of trypsin on large-conductance Ca2+-activated K+ channels of guinea-pig outer hair cells. Hear Res 2004; 190:115-27. [PMID: 15051134 DOI: 10.1016/s0378-5955(03)00376-9] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/19/2003] [Accepted: 11/13/2003] [Indexed: 11/18/2022]
Abstract
High-conductance Ca(2+)-activated K(+) (BK(Ca)) channels from isolated adult guinea-pig outer hair cells were studied in inside-out membrane patches. They had a 300 pS unitary conductance and were inhibited by tetraethyl ammonium (1 mM), iberiotoxin (33 nM) and charybdotoxin (50 nM). In symmetrical 144 mM KCl their K(+) permeability (P(K)) was 5.4 x 10(-13) cm(3)/s; this was reduced to around 4.5 x 10(-13) cm(3)/s with 160 mM Na(+) in place of K(+) on either internal or external membrane surface. BK(Ca) channels from trypsin-isolated hair cells had a high open probability, that depended on both membrane voltage (16 mV/e-fold change) and the concentration of calcium ions at their intracellular surface ([Ca(2+)](i)). The Hill coefficient was 3-4. About 50% of BK(Ca) channels from mechanically isolated outer hair cells had similar characteristics; the remainder had the same high conductance but a low open probability. Trypsin (<0.5 mg/ml) applied to the intracellular face of these 'inactive' channels markedly increased their open probability. It is possible that exposure to trypsin during cell isolation removes an inactivating beta subunit. This would account for the absence of 'inactive' BK(Ca) channels in trypsin-isolated cells.
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Affiliation(s)
- I C Spreadbury
- Neurosciences Group, Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, Headington, Oxford, UK.
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46
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Suzuki M, Mizuno A. A novel human Cl(-) channel family related to Drosophila flightless locus. J Biol Chem 2004; 279:22461-8. [PMID: 15010458 DOI: 10.1074/jbc.m313813200] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Large conductance chloride (maxi-Cl(-)) currents have been recorded in some cells, but there is still little information on the molecular nature of the channel underlying this conductance. We report here that tweety, a gene located in Drosophila flightless, has a structure similar to those of known channels and that human homologues of tweety (hTTYH1-3) are novel maxi-Cl(-) channels. hTTYH3 mRNA was found to be distributed in excitable tissues. The whole cell current of hTTYH3 was large enough to be discriminated from the control but emerged only after treatment with ionomycin. Analysis of pore mutants suggested that positively charged amino acids contributed to anion selectivity. Like a maxi-Cl(-) channel in situ, the hTTYH3 single channel showed 26-picosiemen linear current voltage, complex kinetics, 4,4'-diisothiocyanato-stilbene-2,2'-disulfonic acid sensitivity, subconductance, and the permeability order of I(-) > Br(-) > Cl(-). Similarly, hTTYH2 encoded an ionomycin-induced maxi-Cl(-) channel, but TTYH1 encoded a Ca(2+)-independent and swelling-activated maxi-Cl(-) channel. Therefore, the hTTYH family encoded maxi-Cl(-) channels of mammals. Further studies on the hTTYH family should lead to the elucidation of physiological and pathophysiological roles of novel Cl(-) channel molecules.
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Affiliation(s)
- Makoto Suzuki
- Department of Pharmacology, Jichi Medical School 3311-1, Yakushiji, Minamikawachi, Tochigi 329-0498, Japan
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47
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Tang XD, Garcia ML, Heinemann SH, Hoshi T. Reactive oxygen species impair Slo1 BK channel function by altering cysteine-mediated calcium sensing. Nat Struct Mol Biol 2004; 11:171-8. [PMID: 14745441 DOI: 10.1038/nsmb725] [Citation(s) in RCA: 136] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2003] [Accepted: 12/16/2003] [Indexed: 01/19/2023]
Abstract
Vascular dysfunction is a hallmark of many diseases, including coronary heart disease, stroke and diabetes. The underlying mechanisms of these disorders, which are intimately associated with inflammation and oxidative stress caused by excess reactive oxygen species (ROS), have remained elusive. Here we report that ROS are powerful inhibitors of vascular smooth muscle calcium-dependent Slo1 BK or Maxi-K potassium channels, an important physiological determinant of vascular tone. By targeting a cysteine residue near the Ca(2+) bowl of the BK alpha subunit, H(2)O(2) virtually eliminates physiological activation of the channel, with an inhibitory potency comparable to a knockout of the auxiliary subunit BK beta 1. These results reveal a molecular structural basis for the vascular dysfunction involving oxidative stress and provide a solid rationale for a potential use of BK openers in the prevention and treatment of cardiovascular disorders.
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Affiliation(s)
- Xiang Dong Tang
- Department of Physiology, University of Pennsylvania, 3700 Hamilton Walk, Philadelphia, Pennsylvania 19104, USA
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48
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Lesage F, Hibino H, Hudspeth AJ. Association of beta-catenin with the alpha-subunit of neuronal large-conductance Ca2+-activated K+ channels. Proc Natl Acad Sci U S A 2003; 101:671-5. [PMID: 14701909 PMCID: PMC327206 DOI: 10.1073/pnas.0307681100] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
The association of Ca(2+)-activated K(+) channels with voltage-gated Ca(2+) channels at the presynaptic active zones of hair cells, photoreceptors, and neurons contributes to rapid repolarization of the membrane after excitation. Ca(2+) channels have been shown to bind to a large set of synaptic proteins, but the proteins interacting with Ca(2+)-activated K(+) channels remain unknown. Here, we report that the large-conductance Ca(2+)-activated K(+) channel of the chicken's cochlear hair cell interacts with beta-catenin. Yeast two-hybrid assays identified the S10 region of the K(+) channel's alpha-subunit and the ninth armadillo repeat and carboxyl terminus of beta-catenin as necessary for the interaction. An antiserum directed against the alpha-subunit specifically coprecipitated beta-catenin from brain synaptic proteins. beta-Catenin is known to associate with the synaptic protein Lin7/Velis/MALS, whose interaction partner Lin2/CASK also binds voltage-gated Ca(2+) channels. beta-Catenin may therefore provide a physical link between the two types of channels at the presynaptic active zone.
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Affiliation(s)
- F Lesage
- Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, New York, NY 10021, USA
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49
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Hu S, Labuda MZ, Pandolfo M, Goss GG, McDermid HE, Ali DW. Variants of the KCNMB3 regulatory subunit of maxi BK channels affect channel inactivation. Physiol Genomics 2003; 15:191-8. [PMID: 14612589 DOI: 10.1152/physiolgenomics.00110.2003] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The steady-state and kinetic properties of the KCNMB3 regulatory subunits associated with calcium-activated potassium channels (BK channels) are presented. BK channels containing four sequence variants (V1-V4) in the four different isoforms of the beta-subunit (beta3a, beta3b, beta3c, and beta3d) were expressed in Xenopus oocytes. Reconstituted BK channel inactivation ranged from none to around 90% inactivation. In particular, channels expressing the beta3b-V4 variant displayed a right shift in the potassium current voltage-dependence of activation and inactivated to about 30% of the maximum conductance, compared with wild-type beta3b channels that showed no inactivation. When the membrane potential was depolarized, BK channels inactivated with a very rapid time course (approximately 2-6 ms). This same variant was previously demonstrated to show subtly higher incidence in patients with idiopathic epilepsy (IE) compared with controls, especially when combined with variant V2 (combined heterozygotes). Furthermore, the gene maps to a region containing a susceptibility factor for this disorder. Taken together, these data suggest that neurons expressing BK channels composed of the beta3b-V4 variant subunit may experience reduced levels of inhibition and may therefore play permissive roles in high levels of neuronal activity that is characteristic of epilepsy.
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Affiliation(s)
- Song Hu
- Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada
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Dulhunty AF, Pouliquin P. What we don't know about the structure of ryanodine receptor calcium release channels. Clin Exp Pharmacol Physiol 2003; 30:713-23. [PMID: 14516409 DOI: 10.1046/j.1440-1681.2003.03904.x] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
1. The ryanodine receptor (RyR) is the Ca2+ release channel in the sarcoplamic reticulum of skeletal and cardiac muscle and is essential for respiration and heart beat. The RyR channel releases Ca2+ from intracellular stores in a variety of other cell types, where it normally coexists with the inositiol 1,4,5-trisphosphate receptor (IP3R). The RyR and IP3R, forming a superfamily of homotetrameric ligand-gated intracellular Ca2+ channels, serve discrete functions: they can be located in independent Ca2+ stores with different activation mechanisms and can be coupled to different signalling pathways. 2. Although functional characteristics of the RyR have been investigated intensely, there remain major gaps in our knowledge about the structure of the protein, its ion-conducting pore, its ligand-binding sites and sites supporting the many protein/protein interactions that underlie the in vivo function of the channel. 3. Of particular importance are the transmembrane segments that form the membrane-spanning domain of the protein and the pore, define the conductance and selectivity of the channel and dictate the cytoplasmic and luminal domains and the overall protein structure. Hydropathy profiles predict between four and 12 transmembrane segments. One popular model shows four transmembrane segments in the C-terminal one-tenth of the protein. However, there is substantial evidence for a larger number of membrane-spanning segments located in both the C-terminal and central parts of the protein. 4. A model of the RyR pore based on the Streptomyces lividans KcsA channel structure is presented. Protein/protein interactions between the RyR and other regulatory proteins, as well as within the RyR subunit, are discussed.
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Affiliation(s)
- Angela F Dulhunty
- The Muscle Research Group, John Curtin School of Medical Research, Australian National University, Canberra, Australian Capital Territory, Australia.
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