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Turney TS, Li V, Brohawn SG. Structural Basis for pH-gating of the K + channel TWIK1 at the selectivity filter. Nat Commun 2022; 13:3232. [PMID: 35680900 PMCID: PMC9184524 DOI: 10.1038/s41467-022-30853-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2021] [Accepted: 05/20/2022] [Indexed: 11/11/2022] Open
Abstract
TWIK1 (K2P1.1, KCNK1) is a widely expressed pH-gated two-pore domain K+ channel (K2P) that contributes to cardiac rhythm generation and insulin release from pancreatic beta cells. TWIK1 displays unique properties among K2Ps including low basal activity and inhibition by extracellular protons through incompletely understood mechanisms. Here, we present cryo-EM structures of TWIK1 in lipid nanodiscs at high and low pH that reveal a previously undescribed gating mechanism at the K+ selectivity filter. At high pH, TWIK1 adopts an open conformation. At low pH, protonation of an extracellular histidine results in a cascade of conformational changes that close the channel by sealing the top of the selectivity filter, displacing the helical cap to block extracellular ion access pathways, and opening gaps for lipid block of the intracellular cavity. These data provide a mechanistic understanding for extracellular pH-gating of TWIK1 and illustrate how diverse mechanisms have evolved to gate the selectivity filter of K+ channels.
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Affiliation(s)
- Toby S Turney
- Biophysics Graduate Program, University of California Berkeley, Berkeley, CA, 94720, USA
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA
| | - Vivian Li
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA
| | - Stephen G Brohawn
- Department of Molecular & Cell Biology, University of California Berkeley, Berkeley, CA, 94720, USA.
- Helen Wills Neuroscience Institute, University of California Berkeley, Berkeley, CA, 94720, USA.
- California Institute for Quantitative Biosciences (QB3), University of California Berkeley, Berkeley, CA, 94720, USA.
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2
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Kolosov D, O'Donnell MJ. Malpighian tubules of caterpillars: blending RNAseq and physiology to reveal regional functional diversity and novel epithelial ion transport control mechanisms. J Exp Biol 2019; 222:jeb.211623. [PMID: 31636157 DOI: 10.1242/jeb.211623] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2019] [Accepted: 10/16/2019] [Indexed: 12/16/2022]
Abstract
Malpighian tubules (MTs) and hindgut constitute the functional kidney of insects. MTs are outpouches of the gut and in most insects demonstrate proximodistal heterogeneity in function. In most insects, such heterogeneity is confined to ion/fluid secretion in the distal portion and ion/fluid reabsorption in the proximal portion. In contrast, MTs of larval Lepidoptera (caterpillars of butterflies and moths), are comprised of five regions that differ in their association with the gut, their structure, and ion/fluid transport function. Recent studies have shown that several regions can rapidly and reversibly switch between ion secretion and reabsorption. The current study employed RNAseq, pharmacology and electrophysiology to characterize four distinct regions of the MT in larval Trichoplusia ni. Luminal microelectrode measurements indicate changes in [K+], [Na+] and pH as fluid passes through different regions of the tubule. In addition, the regions examined differ in gene ontology enrichment, and demonstrate robust gradients in expression of ion transporters and endocrine ligand receptors. Lastly, the study provides evidence for direct involvement of voltage-gated and ligand-gated ion channels in epithelial ion transport of insect MTs.
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Affiliation(s)
- Dennis Kolosov
- Department of Biology, McMaster University, 524 Life Sciences Building, 1280 Main St West, Hamilton, Ontario, L8S4K1, Canada
| | - Michael J. O'Donnell
- Department of Biology, McMaster University, 524 Life Sciences Building, 1280 Main St West, Hamilton, Ontario, L8S4K1, Canada
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3
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Du Y, Kiyoshi CM, Wang Q, Wang W, Ma B, Alford CC, Zhong S, Wan Q, Chen H, Lloyd EE, Bryan RM, Zhou M. Genetic Deletion of TREK-1 or TWIK-1/TREK-1 Potassium Channels does not Alter the Basic Electrophysiological Properties of Mature Hippocampal Astrocytes In Situ. Front Cell Neurosci 2016; 10:13. [PMID: 26869883 PMCID: PMC4738265 DOI: 10.3389/fncel.2016.00013] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2015] [Accepted: 01/14/2016] [Indexed: 01/03/2023] Open
Abstract
We have recently shown that a linear current-to-voltage (I-V) relationship of membrane conductance (passive conductance) reflects the intrinsic property of K+ channels in mature astrocytes. While passive conductance is known to underpin a highly negative and stable membrane potential (VM) essential for the basic homeostatic function of astrocytes, a complete repertoire of the involved K+ channels remains elusive. TREK-1 two-pore domain K+ channel (K2P) is highly expressed in astrocytes, and covalent association of TREK-1 with TWIK-1, another highly expressed astrocytic K2P, has been reported as a mechanism underlying the trafficking of heterodimer TWIK-1/TREK-1 channel to the membrane and contributing to astrocyte passive conductance. To decipher the individual contribution of TREK-1 and address whether the appearance of passive conductance is conditional to the co-expression of TWIK-1/TREK-1 in astrocytes, TREK-1 single and TWIK-1/TREK-1 double gene knockout mice were used in the present study. The relative quantity of mRNA encoding other astrocyte K+ channels, such as Kir4.1, Kir5.1, and TREK-2, was not altered in these gene knockout mice. Whole-cell recording from hippocampal astrocytes in situ revealed no detectable changes in astrocyte passive conductance, VM, or membrane input resistance (Rin) in either kind of gene knockout mouse. Additionally, TREK-1 proteins were mainly located in the intracellular compartments of the hippocampus. Altogether, genetic deletion of TREK-1 alone or together with TWIK-1 produced no obvious alteration in the basic electrophysiological properties of hippocampal astrocytes. Thus, future research focusing on other K+ channels may shed light on this long-standing and important question in astrocyte physiology.
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Affiliation(s)
- Yixing Du
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, The First Affiliated Hospital of Nanjing Medical UniversityNanjing, China
| | - Conrad M Kiyoshi
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wang
- Department of Neuroscience, The Ohio State University Wexner Medical CenterColumbus, OH, USA; Department of Neurology, Meitan General HospitalXibahe Nanli, Beijing, China
| | - Wei Wang
- Department of Physiology, Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology Wuhan, China
| | - Baofeng Ma
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Catherine C Alford
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Shiying Zhong
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Qi Wan
- Department of Neurology, The First Affiliated Hospital of Nanjing Medical University Nanjing, China
| | - Haijun Chen
- Department of Biological Science, University at Albany, State University of New York Albany, NY, USA
| | - Eric E Lloyd
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Robert M Bryan
- Department of Anesthesiology, Baylor College of Medicine Houston, TX, USA
| | - Min Zhou
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
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New Insights on Astrocyte Ion Channels: Critical for Homeostasis and Neuron-Glia Signaling. J Neurosci 2016; 35:13827-35. [PMID: 26468182 DOI: 10.1523/jneurosci.2603-15.2015] [Citation(s) in RCA: 137] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Initial biophysical studies on glial cells nearly 50 years ago identified these cells as being electrically silent. These first studies also demonstrated a large K(+) conductance, which led to the notion that glia may regulate extracellular K(+) levels homeostatically. This view has now gained critical support from the study of multiple disease models discussed herein. Dysfunction of a major astrocyte K(+) channel, Kir4.1, appears as an early pathological event underlying neuronal phenotypes in several neurodevelopmental and neurodegenerative diseases. An expanding list of other astrocyte ion channels, including the calcium-activated ion channel BEST-1, hemichannels, and two-pore domain K(+) channels, all contribute to astrocyte biology and CNS function and underpin new forms of crosstalk between neurons and glia. Once considered merely the glue that holds the brain together, it is now increasingly recognized that astrocytes contribute in several fundamental ways to neuronal function. Emerging new insights and future perspectives of this active research area are highlighted within. SIGNIFICANCE STATEMENT The critical role of astrocyte potassium channels in CNS homeostasis has been reemphasized by recent studies conducted in animal disease models. Emerging evidence also supports the signaling role mediated by astrocyte ion channels such as BEST1, hemichannels, and two-pore channels, which enable astrocytes to interact with neurons and regulate synaptic transmission and plasticity. This minisymposium highlights recent developments and future perspectives of these research areas.
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Wang W, Kiyoshi CM, Du Y, Ma B, Alford CC, Chen H, Zhou M. mGluR3 Activation Recruits Cytoplasmic TWIK-1 Channels to Membrane that Enhances Ammonium Uptake in Hippocampal Astrocytes. Mol Neurobiol 2015; 53:6169-6182. [PMID: 26553349 DOI: 10.1007/s12035-015-9496-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2015] [Accepted: 10/16/2015] [Indexed: 12/29/2022]
Abstract
TWIK-1 two-pore domain K+ channels are highly expressed in mature hippocampal astrocytes. While the TWIK-1 activity is readily detectable on astrocyte membrane, the majority of channels are retained in the intracellular compartments, which raises an intriguing question of whether the membrane TWIK-1 channels could be dynamically regulated for functions yet unknown. Here, the regulation of TWIK-1 membrane expression by Gi/Go-coupled metabotropic glutamate receptor 3 (mGluR3) and its functional impact on ammonium uptake has been studied. Activation of mGluR3 induced a marked translocation of TWIK-1 channels from the cytoplasm to the membrane surface. Consistent with our early observation that membrane TWIK-1 behaves as nonselective monovalent cation channel, mGluR3-mediated TWIK-1 membrane expression was associated with a depolarizing membrane potential (V M). As TWIK-1 exhibits a discernibly high permeability to ammonium (NH4+), a critical substrate in glutamate-glutamine cycle for neurotransmitter replenishment, regulation of NH4+ uptake capacity by TWIK-1 membrane expression was determined by response of astrocyte V M to bath application of 5 mM NH4Cl. Stimulation of mGluR3 potentiated NH4+-induced V M depolarization by ∼30 % in wild type, but not in TWIK-1 knockout astrocytes. Furthermore, activation of mGluR3 mediated a coordinated translocation of TWIK-1 channels with recycling endosomes toward astrocyte membrane and the mGluR3-mediated potentiation of NH4+ uptake required a functional Rab-mediated trafficking pathway. Altogether, we demonstrate that the activation of mGluR3 up-regulates the membrane expression of TWIK-1 that in turn enhances NH4+ uptake in astrocytes, a mechanism potentially important for functional coupling of astrocyte glutamate-glutamine cycle with the replenishment of neurotransmitters in neurons.
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Affiliation(s)
- Wei Wang
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA. .,Department of Physiology, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, 430030, China. .,Institute of Brain Research, School of Basic Medicine, Huazhong University of Science and Technology, Wuhan, China.
| | - Conrad M Kiyoshi
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Yixing Du
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Baofeng Ma
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Catherine C Alford
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA
| | - Haijun Chen
- Department of Biological Sciences, University at Albany, State University of New York, Albany, NY, USA
| | - Min Zhou
- Department of Neuroscience, Ohio State University Wexner Medical Center, Columbus, OH, 43210, USA.
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Walentin K, Hinze C, Werth M, Haase N, Varma S, Morell R, Aue A, Pötschke E, Warburton D, Qiu A, Barasch J, Purfürst B, Dieterich C, Popova E, Bader M, Dechend R, Staff AC, Yurtdas ZY, Kilic E, Schmidt-Ott KM. A Grhl2-dependent gene network controls trophoblast branching morphogenesis. Development 2015; 142:1125-36. [PMID: 25758223 DOI: 10.1242/dev.113829] [Citation(s) in RCA: 53] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
Healthy placental development is essential for reproductive success; failure of the feto-maternal interface results in pre-eclampsia and intrauterine growth retardation. We found that grainyhead-like 2 (GRHL2), a CP2-type transcription factor, is highly expressed in chorionic trophoblast cells, including basal chorionic trophoblast (BCT) cells located at the chorioallantoic interface in murine placentas. Placentas from Grhl2-deficient mouse embryos displayed defects in BCT cell polarity and basement membrane integrity at the chorioallantoic interface, as well as a severe disruption of labyrinth branching morphogenesis. Selective Grhl2 inactivation only in epiblast-derived cells rescued all placental defects but phenocopied intraembryonic defects observed in global Grhl2 deficiency, implying the importance of Grhl2 activity in trophectoderm-derived cells. ChIP-seq identified 5282 GRHL2 binding sites in placental tissue. By integrating these data with placental gene expression profiles, we identified direct and indirect Grhl2 targets and found a marked enrichment of GRHL2 binding adjacent to genes downregulated in Grhl2(-/-) placentas, which encoded known regulators of placental development and epithelial morphogenesis. These genes included that encoding the serine protease inhibitor Kunitz type 1 (Spint1), which regulates BCT cell integrity and labyrinth formation. In human placenta, we found that human orthologs of murine GRHL2 and its targets displayed co-regulation and were expressed in trophoblast cells in a similar domain as in mouse placenta. Our data indicate that a conserved Grhl2-coordinated gene network controls trophoblast branching morphogenesis, thereby facilitating development of the site of feto-maternal exchange. This might have implications for syndromes related to placental dysfunction.
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Affiliation(s)
- Katharina Walentin
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Christian Hinze
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Max Werth
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany Department of Medicine, Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Nadine Haase
- Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Saaket Varma
- Department of Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, 4650 Sunset Blvd., Los Angeles, CA 90027, USA
| | - Robert Morell
- Laboratory of Molecular Genetics, National Institute on Deafness and Other Communication Disorders (NIDCD)/National Institutes of Health (NIH), 5 Research Court, Rockville, MD 20850, USA
| | - Annekatrin Aue
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Elisabeth Pötschke
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - David Warburton
- Department of Developmental Biology and Regenerative Medicine Program, Saban Research Institute, Children's Hospital Los Angeles, 4650 Sunset Blvd., Los Angeles, CA 90027, USA
| | - Andong Qiu
- Department of Medicine, Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Jonathan Barasch
- Department of Medicine, Columbia University College of Physicians and Surgeons, 630 West 168th Street, New York, NY 10032, USA
| | - Bettina Purfürst
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Christoph Dieterich
- Bioinformatics, Max Planck Institute for Biology of Ageing, Robert-Koch-Str. 21, Cologne 50931, Germany
| | - Elena Popova
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Michael Bader
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Ralf Dechend
- Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany
| | - Anne Cathrine Staff
- Department of Gynecology and Obstetrics, Institute of Clinical Medicine, Oslo University Hospital and University of Oslo, Kirkeveien 166, Oslo 0450, Norway
| | - Zeliha Yesim Yurtdas
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Department of Urology, Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin 10117, Germany Berlin Institute of Urologic Research, Berlin 10117, Germany
| | - Ergin Kilic
- Department of Pathology, Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin 10117, Germany
| | - Kai M Schmidt-Ott
- Max Delbrück Center for Molecular Medicine, Robert-Rössle-Str. 10, Berlin 13125, Germany Experimental and Clinical Research Center, a collaboration between the Max Delbrück Center and the Medical Faculty of the Charité, Robert-Rössle-Str. 10, Berlin 13125, Germany Department of Nephrology, Charité-Universitätsmedizin Berlin, Charitéplatz 1, Berlin 10117, Germany
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7
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Sepúlveda FV, Pablo Cid L, Teulon J, Niemeyer MI. Molecular aspects of structure, gating, and physiology of pH-sensitive background K2P and Kir K+-transport channels. Physiol Rev 2015; 95:179-217. [PMID: 25540142 DOI: 10.1152/physrev.00016.2014] [Citation(s) in RCA: 77] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
K(+) channels fulfill roles spanning from the control of excitability to the regulation of transepithelial transport. Here we review two groups of K(+) channels, pH-regulated K2P channels and the transport group of Kir channels. After considering advances in the molecular aspects of their gating based on structural and functional studies, we examine their participation in certain chosen physiological and pathophysiological scenarios. Crystal structures of K2P and Kir channels reveal rather unique features with important consequences for the gating mechanisms. Important tasks of these channels are discussed in kidney physiology and disease, K(+) homeostasis in the brain by Kir channel-equipped glia, and central functions in the hearing mechanism in the inner ear and in acid secretion by parietal cells in the stomach. K2P channels fulfill a crucial part in central chemoreception probably by virtue of their pH sensitivity and are central to adrenal secretion of aldosterone. Finally, some unorthodox behaviors of the selectivity filters of K2P channels might explain their normal and pathological functions. Although a great deal has been learned about structure, molecular details of gating, and physiological functions of K2P and Kir K(+)-transport channels, this has been only scratching at the surface. More molecular and animal studies are clearly needed to deepen our knowledge.
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Affiliation(s)
- Francisco V Sepúlveda
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - L Pablo Cid
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - Jacques Teulon
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
| | - María Isabel Niemeyer
- Centro de Estudios Científicos, Valdivia, Chile; UPMC Université Paris 06, Team 3, Paris, France; and Institut National de la Santé et de la Recherche Médicale, UMR_S 1138, Paris, France
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8
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Feliciangeli S, Chatelain FC, Bichet D, Lesage F. The family of K2P channels: salient structural and functional properties. J Physiol 2015; 593:2587-603. [PMID: 25530075 DOI: 10.1113/jphysiol.2014.287268] [Citation(s) in RCA: 148] [Impact Index Per Article: 16.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2014] [Accepted: 12/10/2014] [Indexed: 12/11/2022] Open
Abstract
Potassium channels participate in many biological functions, from ion homeostasis to generation and modulation of the electrical membrane potential. They are involved in a large variety of diseases. In the human genome, 15 genes code for K(+) channels with two pore domains (K2P ). These channels form dimers of pore-forming subunits that produce background conductances finely regulated by a range of natural and chemical effectors, including signalling lipids, temperature, pressure, pH, antidepressants and volatile anaesthetics. Since the cloning of TWIK1, the prototypical member of this family, a lot of work has been carried out on their structure and biology. These studies are still in progress, but data gathered so far show that K2P channels are central players in many processes, including ion homeostasis, hormone secretion, cell development and excitability. A growing number of studies underline their implication in physiopathological mechanisms, such as vascular and pulmonary hypertension, cardiac arrhythmias, nociception, neuroprotection and depression. This review gives a synthetic view of the most noticeable features of these channels.
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Affiliation(s)
- Sylvain Feliciangeli
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Frank C Chatelain
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Delphine Bichet
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
| | - Florian Lesage
- LabEx ICST, Institut de Pharmacologie Moléculaire et Cellulaire, CNRS and Université de Nice-Sophia Antipolis, 660 Route des Lucioles, 06560, Valbonne, France
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9
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Silent but not dumb: how cellular trafficking and pore gating modulate expression of TWIK1 and THIK2. Pflugers Arch 2014; 467:1121-31. [PMID: 25339226 DOI: 10.1007/s00424-014-1631-y] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2014] [Revised: 10/09/2014] [Accepted: 10/12/2014] [Indexed: 12/25/2022]
Abstract
Among K2P channels, a few of them turned out to be difficult to express in heterologous systems and were coined "silent subunits". Recent studies have shed light on the mechanisms behind this apparent lack of channel activity at the plasma membrane. For TWIK1 and THIK2 channels, silence is related to a combination of intracellular retention and low intrinsic activity. TWIK1 is constitutively endocytosed from the plasma membrane before being transported to recycling endosomes, whereas THIK2 is restricted to endoplasmic reticulum. These intracellular localizations are related to trafficking signals located in the cytoplasmic parts of the channels. When these motifs are mutated or masked, channels are redistributed at the plasma membrane and produce measurable currents. However, these currents are of modest amplitude. This weak basal activity is due to a hydrophobic barrier in the deep pore that limits water and ions in the conduction pathway. Other silent channels KCNK7, TWIK2, and TASK5 are still under study. Expression and characterization of these K2P channels pave the way for a better understanding of the mechanisms controlling intracellular trafficking of membrane proteins, ion conduction, and channel gating.
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10
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Wang W, Putra A, Schools GP, Ma B, Chen H, Kaczmarek LK, Barhanin J, Lesage F, Zhou M. The contribution of TWIK-1 channels to astrocyte K(+) current is limited by retention in intracellular compartments. Front Cell Neurosci 2013; 7:246. [PMID: 24368895 PMCID: PMC3856854 DOI: 10.3389/fncel.2013.00246] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2013] [Accepted: 11/18/2013] [Indexed: 12/04/2022] Open
Abstract
TWIK-1 two-pore domain K+ channels are expressed abundantly in astrocytes. In the present study, we examined the extent to which TWIK-1 contributes to the linear current-voltage (I–V) relationship (passive) K+ membrane conductance, a dominant electrophysiological feature of mature hippocampal astrocytes. Astrocytes from TWIK-1 knockout mice have a more negative resting potential than those from wild type animals and a reduction in both inward rectification and Cs+ permeability. Nevertheless, the overall whole-cell passive conductance is not altered significantly in TWIK-1 knockout astrocytes. The expression of Kir4.1 and TREK-1, two other major astrocytic K+ channels, or of other two-pore K+ channels is not altered in TWIK-1 knockout mice, suggesting that the mild effect of TWIK-1 knockout does not result from compensation by these channels. Fractionation experiments showed that TWIK-1 is primarily localized in intracellular cytoplasmic fractions (55%) and mildly hydrophobic internal compartment fractions (41%), with only 5% in fractions containing plasma membranes. Our study revealed that TWIK-1 proteins are mainly located in the intracellular compartments of hippocampal astrocyte under physiological condition, therefore a minimal contribution of TWIK-1 channels to whole-cell currents is likely attributable to a relatively low level presence of channels in the plasma membrane.
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Affiliation(s)
- Wei Wang
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Adhytia Putra
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | | | - Baofeng Ma
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
| | - Haijun Chen
- Department of Biological Sciences, University at Albany, SUNY Albany, NY, USA
| | - Leonard K Kaczmarek
- Department of Pharmacology, Yale University School of Medicine New Haven, CT, USA
| | - Jacques Barhanin
- Centre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis Valbonne, France
| | - Florian Lesage
- Centre National de la Recherche Scientifique, Institut de Pharmacologie Moléculaire et Cellulaire, Université de Nice Sophia Antipolis Valbonne, France
| | - Min Zhou
- Department of Neuroscience, The Ohio State University Wexner Medical Center Columbus, OH, USA
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11
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Abstract
TWIK1 belongs to the family of background K(+) channels with two pore domains. In native and transfected cells, TWIK1 is detected mainly in recycling endosomes. In principal cells in the kidney, TWIK1 gene inactivation leads to the loss of a nonselective cationic conductance, an unexpected effect that was attributed to adaptive regulation of other channels. Here, we show that TWIK1 ion selectivity is modulated by extracellular pH. Although TWIK1 is K(+) selective at neutral pH, it becomes permeable to Na(+) at the acidic pH found in endosomes. Selectivity recovery is slow after restoration of a neutral pH. Such hysteresis makes plausible a role of TWIK1 as a background channel in which selectivity and resulting inhibitory or excitatory influences on cell excitability rely on its recycling rate between internal acidic stores and the plasma membrane. TWIK1(-/-) pancreatic β cells are more polarized than control cells, confirming a depolarizing role of TWIK1 in kidney and pancreatic cells.
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Enyedi P, Czirják G. Molecular background of leak K+ currents: two-pore domain potassium channels. Physiol Rev 2010; 90:559-605. [PMID: 20393194 DOI: 10.1152/physrev.00029.2009] [Citation(s) in RCA: 620] [Impact Index Per Article: 44.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Two-pore domain K(+) (K(2P)) channels give rise to leak (also called background) K(+) currents. The well-known role of background K(+) currents is to stabilize the negative resting membrane potential and counterbalance depolarization. However, it has become apparent in the past decade (during the detailed examination of the cloned and corresponding native K(2P) channel types) that this primary hyperpolarizing action is not performed passively. The K(2P) channels are regulated by a wide variety of voltage-independent factors. Basic physicochemical parameters (e.g., pH, temperature, membrane stretch) and also several intracellular signaling pathways substantially and specifically modulate the different members of the six K(2P) channel subfamilies (TWIK, TREK, TASK, TALK, THIK, and TRESK). The deep implication in diverse physiological processes, the circumscribed expression pattern of the different channels, and the interesting pharmacological profile brought the K(2P) channel family into the spotlight. In this review, we focus on the physiological roles of K(2P) channels in the most extensively investigated cell types, with special emphasis on the molecular mechanisms of channel regulation.
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Affiliation(s)
- Péter Enyedi
- Department of Physiology, Semmelweis University, Budapest, Hungary.
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Molecular Biology of Background K Channels: Insights from K2P Knockout Mice. J Mol Biol 2009; 385:1331-44. [DOI: 10.1016/j.jmb.2008.11.048] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Revised: 11/07/2008] [Accepted: 11/19/2008] [Indexed: 12/18/2022]
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Heitzmann D, Warth R. Physiology and pathophysiology of potassium channels in gastrointestinal epithelia. Physiol Rev 2008; 88:1119-82. [PMID: 18626068 DOI: 10.1152/physrev.00020.2007] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
Epithelial cells of the gastrointestinal tract are an important barrier between the "milieu interne" and the luminal content of the gut. They perform transport of nutrients, salts, and water, which is essential for the maintenance of body homeostasis. In these epithelia, a variety of K(+) channels are expressed, allowing adaptation to different needs. This review provides an overview of the current literature that has led to a better understanding of the multifaceted function of gastrointestinal K(+) channels, thereby shedding light on pathophysiological implications of impaired channel function. For instance, in gastric mucosa, K(+) channel function is a prerequisite for acid secretion of parietal cells. In epithelial cells of small intestine, K(+) channels provide the driving force for electrogenic transport processes across the plasma membrane, and they are involved in cell volume regulation. Fine tuning of salt and water transport and of K(+) homeostasis occurs in colonic epithelia cells, where K(+) channels are involved in secretory and reabsorptive processes. Furthermore, there is growing evidence for changes in epithelial K(+) channel expression during cell proliferation, differentiation, apoptosis, and, under pathological conditions, carcinogenesis. In the future, integrative approaches using functional and postgenomic/proteomic techniques will help us to gain comprehensive insights into the role of K(+) channels of the gastrointestinal tract.
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Affiliation(s)
- Dirk Heitzmann
- Institute of Physiology and Clinic and Policlinic for Internal Medicine II, Regensburg, Germany
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Lachheb S, Cluzeaud F, Bens M, Genete M, Hibino H, Lourdel S, Kurachi Y, Vandewalle A, Teulon J, Paulais M. Kir4.1/Kir5.1 channel forms the major K+ channel in the basolateral membrane of mouse renal collecting duct principal cells. Am J Physiol Renal Physiol 2008; 294:F1398-407. [PMID: 18367659 DOI: 10.1152/ajprenal.00288.2007] [Citation(s) in RCA: 99] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
K(+) channels in the basolateral membrane of mouse cortical collecting duct (CCD) principal cells were identified with patch-clamp technique, real-time PCR, and immunohistochemistry. In cell-attached membrane patches, three K(+) channels with conductances of approximately 75, 40, and 20 pS were observed, but the K(+) channel with the intermediate conductance (40 pS) predominated. In inside-out membrane patches exposed to an Mg(2+)-free medium, the current-voltage relationship of the intermediate-conductance channel was linear with a conductance of 38 pS. Addition of 1.3 mM internal Mg(2+) had no influence on the inward conductance (G(in) = 35 pS) but reduced outward conductance (G(out)) to 13 pS, yielding a G(in)/G(out) of 3.2. The polycation spermine (6 x 10(-7) M) reduced its activity on inside-out membrane patches by 50% at a clamp potential of 60 mV. Channel activity was also dependent on intracellular pH (pH(i)): a sigmoid relationship between pH(i) and channel normalized current (NP(o)) was observed with a pK of 7.24 and a Hill coefficient of 1.7. By real-time PCR on CCD extracts, inwardly rectifying K(+) (Kir)4.1 and Kir5.1, but not Kir4.2, mRNAs were detected. Kir4.1 and Kir5.1 proteins cellularly colocalized with aquaporin 2 (AQP2), a specific marker of CCD principal cells, while AQP2-negative cells (i.e., intercalated cells) showed no staining. Dietary K(+) had no influence on the properties of the intermediate-conductance channel, but a Na(+)-depleted diet increased its open probability by approximately 25%. We conclude that the Kir4.1/Kir5.1 channel is a major component of the K(+) conductance in the basolateral membrane of mouse CCD principal cells.
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MESH Headings
- Animals
- Cell Polarity/physiology
- Cloning, Molecular
- Immunohistochemistry
- In Vitro Techniques
- Kidney Cortex/physiology
- Kidney Tubules, Collecting/cytology
- Kidney Tubules, Collecting/physiology
- Male
- Mice
- Mice, Inbred Strains
- Models, Biological
- Patch-Clamp Techniques
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Potassium, Dietary/pharmacokinetics
- RNA, Messenger/metabolism
- Sodium, Dietary/pharmacokinetics
- Kir5.1 Channel
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Affiliation(s)
- Sahran Lachheb
- Université Pierre et Marie Curie, 75720 Paris Cedex 06, France
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