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Rivera A, Nasburg JA, Shim H, Shmukler BE, Kitten J, Wohlgemuth JG, Dlott JS, Snyder LM, Brugnara C, Wulff H, Alper SL. The erythroid K-Cl cotransport inhibitor [(dihydroindenyl)oxy]acetic acid blocks erythroid Ca 2+-activated K + channel KCNN4. Am J Physiol Cell Physiol 2022; 323:C694-C705. [PMID: 35848620 PMCID: PMC9448282 DOI: 10.1152/ajpcell.00240.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2022] [Revised: 07/07/2022] [Accepted: 07/08/2022] [Indexed: 11/22/2022]
Abstract
Red cell volume is a major determinant of HbS concentration in sickle cell disease. Cellular deoxy-HbS concentration determines the delay time, the interval between HbS deoxygenation and deoxy-HbS polymerization. Major membrane transporter protein determinants of sickle red cell volume include the SLC12/KCC K-Cl cotransporters KCC3/SLC12A6 and KCC1/SLC12A4, and the KCNN4/KCa3.1 Ca2+-activated K+ channel (Gardos channel). Among standard inhibitors of KCC-mediated K-Cl cotransport, only [(dihydroindenyl)oxy]acetic acid (DIOA) has been reported to lack inhibitory activity against the related bumetanide-sensitive erythroid Na-K-2Cl cotransporter NKCC1/SLC12A2. DIOA has been often used to inhibit K-Cl cotransport when studying the expression and regulation of other K+ transporters and K+ channels. We report here that DIOA at concentrations routinely used to inhibit K-Cl cotransport can also abrogate activity of the KCNN4/KCa3.1 Gardos channel in human and mouse red cells and in human sickle red cells. DIOA inhibition of A23187-stimulated erythroid K+ uptake (Gardos channel activity) was chloride-independent and persisted in mouse red cells genetically devoid of the principal K-Cl cotransporters KCC3 and KCC1. DIOA also inhibited YODA1-stimulated, chloride-independent erythroid K+ uptake. In contrast, DIOA exhibited no inhibitory effect on K+ influx into A23187-treated red cells of Kcnn4-/- mice. DIOA inhibition of human KCa3.1 was validated (IC50 42 µM) by whole cell patch clamp in HEK-293 cells. RosettaLigand docking experiments identified a potential binding site for DIOA in the fenestration region of human KCa3.1. We conclude that DIOA at concentrations routinely used to inhibit K-Cl cotransport can also block the KCNN4/KCa3.1 Gardos channel in normal and sickle red cells.
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Affiliation(s)
- Alicia Rivera
- Division of Nephrology and Vascular Biology Research Center, Beth Israel Deaconess Medical Center, Boston, Massachusetts
- Department of Medicine, Harvard Medical School, Boston, Massachusetts
| | - Joshua A Nasburg
- Department of Pharmacology, School of Medicine, University of California, Davis, California
| | - Heesung Shim
- Department of Pharmacology, School of Medicine, University of California, Davis, California
| | - Boris E Shmukler
- Division of Nephrology and Vascular Biology Research Center, Beth Israel Deaconess Medical Center, Boston, Massachusetts
- Department of Medicine, Harvard Medical School, Boston, Massachusetts
| | | | | | | | | | - Carlo Brugnara
- Department of Laboratory Medicine, Boston Children's Hospital, Boston, Massachusetts
- Department of Pathology, Harvard Medical School, Boston, Massachusetts
| | - Heike Wulff
- Department of Pharmacology, School of Medicine, University of California, Davis, California
| | - Seth L Alper
- Division of Nephrology and Vascular Biology Research Center, Beth Israel Deaconess Medical Center, Boston, Massachusetts
- Department of Medicine, Harvard Medical School, Boston, Massachusetts
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Bustamante HA, Ehrich MF, Klein BG. Intracellular potassium depletion enhances apoptosis induced by staurosporine in cultured trigeminal satellite glial cells. Somatosens Mot Res 2021; 38:194-201. [PMID: 34187291 DOI: 10.1080/08990220.2021.1941843] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE Satellite glial cells (SGC) surrounding neurons in sensory ganglia can buffer extracellular potassium, regulating the excitability of injured neurons and possibly influencing a shift from acute to neuropathic pain. SGC apoptosis may be a key component in this process. This work evaluated induction or enhancement of apoptosis in cultured trigeminal SGC following changes in intracellular potassium [K]ic. MATERIALS AND METHODS We developed SGC primary cultures from rat trigeminal ganglia (TG). Purity of our cultures was confirmed using immunofluorescence and western blot analysis for the presence of the specific marker of SGC, glutamine synthetase (GS). SGC [K]ic was depleted using hypo-osmotic shock and 4 mM bumetanide plus 10 mM ouabain. [K]ic was measured using the K+ fluorescent indicator potassium benzofuran isophthalate (PBFI-AM). RESULTS SGC tested positive for GS and hypo-osmotic shock induced a significant decrease in [K]ic at every evaluated time. Cells were then incubated for 5 h with either 2 mM staurosporine (STS) or 20 ng/ml of TNF-α and evaluated for early apoptosis and late apoptosis/necrosis by flow cytometry using annexin V and propidium iodide. A significant increase in early apoptosis, from 16 to 38%, was detected in SGC with depleted [K]ic after incubation with STS. In contrast, TNF-α did not increase early apoptosis in normal or [K]ic depleted SGC. CONCLUSION Hypo-osmotic shock induced a decrease in intracellular potassium in cultured trigeminal SGC and this enhanced apoptosis induced by STS that is associated with the mitochondrial pathway. These results suggest that K+ dysregulation may underlie apoptosis in trigeminal SGC.
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Affiliation(s)
- Hedie A Bustamante
- Faculty of Veterinary Sciences, Veterinary Clinical Sciences Institute, Universidad Austral de Chile, Valdivia, Chile
| | - Marion F Ehrich
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
| | - Bradley G Klein
- Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Polytechnic Institute and State University, Blacksburg, VA, USA
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Amador-Muñoz D, Gutiérrez ÁM, Payán-Gómez C, Matheus LM. In silico and in vitro analysis of cation-activated potassium channels in human corneal endothelial cells. Exp Eye Res 2020; 197:108114. [PMID: 32561484 DOI: 10.1016/j.exer.2020.108114] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 06/02/2020] [Accepted: 06/07/2020] [Indexed: 12/31/2022]
Abstract
The corneal endothelium is the inner cell monolayer involved in the maintenance of corneal transparence by the generation of homeostatic dehydration. The glycosaminoglycans of the corneal stroma develop a continuous swelling pressure that should be counteracted by the corneal endothelial cells through active transport mechanisms to move the water to the anterior chamber. Protein transporters for sodium (Na+), potassium (K+), chloride (Cl-) and bicarbonate (HCO3-) are involved in this endothelial "pump function", however despite its physiological importance, the efflux mechanism is not completely understood. There is experimental evidence describing transendothelial diffusion of water in the absence of osmotic gradients. Therefore, it is important to get a deeper understanding of alternative models that drive the fluid transport across the endothelium such as the electrochemical gradients. Three transcriptomic datasets of the corneal endothelium were used in this study to analyze the expression of genes that encode proteins that participate in the transport and the reestablishment of the membrane potential across the semipermeable endothelium. Subsequently, the expression of the identified channels was validated in vitro both at mRNA and protein levels. The results of this study provide the first evidence of the expression of KCNN2, KCNN3 and KCNT2 genes in the corneal endothelium. Differences among the level of expression of KCNN2, KCNT2 and KCNN4 genes were found in a differentially expressed gene analysis of the dataset. Taken together these results underscore the potential importance of the ionic channels in the pathophysiology of corneal diseases. Moreover, we elucidate novel mechanisms that might be involved in the pivotal dehydrating function of the endothelium and in others physiologic functions of these cells using in silico pathways analysis.
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Affiliation(s)
- Diana Amador-Muñoz
- Neuroscience (NEUROS) Research Group, School of Medicine and Health Sciences, Universidad del Rosario, Carrera 24 No. 63 C 69, P.O 111221, Bogotá, Colombia.
| | - Ángela María Gutiérrez
- Escuela Superior de Oftalmología, Instituto Barraquer de América, Calle 100 No. 18 A 51, Bogotá, Colombia.
| | - César Payán-Gómez
- Department of Biology, Faculty of Natural Sciences, Universidad del Rosario, Carrera 24 No. 63 C 69, Bogotá, P.O 111221, Colombia.
| | - Luisa Marina Matheus
- Neuroscience (NEUROS) Research Group, School of Medicine and Health Sciences, Universidad del Rosario, Carrera 24 No. 63 C 69, P.O 111221, Bogotá, Colombia.
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Lauf PK, Sharma N, Adragna NC. Kinetic studies of K-Cl cotransport in cultured rat vascular smooth muscle cells. Am J Physiol Cell Physiol 2019; 316:C274-C284. [PMID: 30649919 DOI: 10.1152/ajpcell.00002.2017] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
During aging, and development of atherosclerosis and cardiovascular disease (CVD), aortic vascular smooth muscle cells (VSMCs) transition from healthy contractile to diseased synthetic phenotypes. K-Cl cotransport (KCC) maintains cell volume and ion homeostasis in growth and differentiation, and hence is important for VSMC proliferation and migration. Therefore, KCC activity may play a role in the contractile-to-synthetic VSMC phenotypic transition. Early, medium, and late synthetic passage VSMCs were tested for specific cytoskeletal protein expression. KCC-mediated ouabain- and bumetanide-insensitive Rb+ (a K+ congener) influx was determined as Cl--dependent Rb+ influx at different external Rb+ and Cl- ion concentrations, [Rb+]o and [Cl-]o. Expressions of the cytoskeletal proteins α-actin, vimentin, and desmin fell from early through late synthetic VSMCs. KCC kinetic parameters, such as maximum velocity ( Vm), and apparent Cl- and Rb+ affinities ( Km), were calculated with Lineweaver-Burk, Hanes-Woolf, and Hill approximations. Vm values of both Rb+- and Cl--dependent influxes were of equal magnitude, commensurate with a KCC stoichiometry of unity, and rose threefold from early to late synthetic VSMCs. Hill coefficients for Rb+ and Cl- correlated with cell passage number, suggesting increased KCC ligand cooperativity. However, Km values for [Cl-]o were strikingly bimodal with 60-80 mM in early, ~20-30 mM in medium, and 60 mM in late passage cells. In contrast, Km values for [Rb+]o remained steady at ~17 mM. Since total KCC isoform expression was similar with cell passage, structure/function changes of the KCC signalosome may accompany the transition of aortic VSMCs from a healthy to a diseased phenotype.
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Affiliation(s)
- Peter K Lauf
- The Cell Biophysics Group, Wright State University , Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University , Dayton, Ohio
- Department of Pathology, Wright State University , Dayton, Ohio
- Boonshoft School of Medicine, Wright State University , Dayton, Ohio
| | - Neelima Sharma
- The Cell Biophysics Group, Wright State University , Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University , Dayton, Ohio
- Boonshoft School of Medicine, Wright State University , Dayton, Ohio
| | - Norma C Adragna
- The Cell Biophysics Group, Wright State University , Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University , Dayton, Ohio
- Boonshoft School of Medicine, Wright State University , Dayton, Ohio
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Sforna L, Megaro A, Pessia M, Franciolini F, Catacuzzeno L. Structure, Gating and Basic Functions of the Ca2+-activated K Channel of Intermediate Conductance. Curr Neuropharmacol 2018; 16:608-617. [PMID: 28875832 PMCID: PMC5997868 DOI: 10.2174/1570159x15666170830122402] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2017] [Revised: 07/21/2017] [Accepted: 07/22/2017] [Indexed: 01/04/2023] Open
Abstract
BACKGROUND The KCa3.1 channel is the intermediate-conductance member of the Ca2+- activated K channel superfamily. It is widely expressed in excitable and non-excitable cells, where it plays a major role in a number of cell functions. This paper aims at illustrating the main structural, biophysical and modulatory properties of the KCa3.1 channel, and providing an account of experimental data on its role in volume regulation and Ca2+ signals. METHODS Research and online content related to the structure, structure/function relationship, and physiological role of the KCa3.1 channel are reviewed. RESULTS Expressed in excitable and non-excitable cells, the KCa3.1 channel is voltage independent, its opening being exclusively gated by the binding of intracellular Ca2+ to calmodulin, a Ca2+- binding protein constitutively associated with the C-terminus of each KCa3.1 channel α subunit. The KCa3.1 channel activates upon high affinity Ca2+ binding, and in highly coordinated fashion giving steep Hill functions and relatively low EC50 values (100-350 nM). This high Ca2+ sensitivity is physiologically modulated by closely associated kinases and phosphatases. The KCa3.1 channel is normally activated by global Ca2+ signals as resulting from Ca2+ released from intracellular stores, or by the refilling influx through store operated Ca2+ channels, but cases of strict functional coupling with Ca2+-selective channels are also found. KCa3.1 channels are highly expressed in many types of cells, where they play major roles in cell migration and death. The control of these complex cellular processes is achieved by KCa3.1 channel regulation of the driving force for Ca2+ entry from the extracellular medium, and by mediating the K+ efflux required for cell volume control. CONCLUSION Much work remains to be done to fully understand the structure/function relationship of the KCa3.1 channels. Hopefully, this effort will provide the basis for a beneficial modulation of channel activity under pathological conditions.
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Affiliation(s)
| | | | | | - Fabio Franciolini
- Address correspondence to these authors at the Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Pascoli, 8-06123, Perugia; Tel: 39.075.585.5751; E-mails: and
| | - Luigi Catacuzzeno
- Address correspondence to these authors at the Department of Chemistry, Biology and Biotechnology, University of Perugia, Via Pascoli, 8-06123, Perugia; Tel: 39.075.585.5751; E-mails: and
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Keckeis S, Wernecke L, Salchow DJ, Reichhart N, Strauß O. Activation of a Ca 2+-dependent cation conductance with properties of TRPM2 by reactive oxygen species in lens epithelial cells. Exp Eye Res 2017; 161:61-70. [PMID: 28603015 DOI: 10.1016/j.exer.2017.06.006] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2016] [Revised: 05/23/2017] [Accepted: 06/01/2017] [Indexed: 02/03/2023]
Abstract
Ion channels are crucial for maintenance of ion homeostasis and transparency of the lens. The lens epithelium is the metabolically and electrophysiologically active cell type providing nutrients, ions and water to the lens fiber cells. Ca2+-dependent non-selective ion channels seem to play an important role for ion homeostasis. The aim of the study was to identify and characterize Ca2+- and reactive oxygen species (ROS)-dependent non-selective cation channels in human lens epithelial cells. RT-PCR revealed gene expression of the Ca2+-activated non-selective cation channels TRPC3, TRPM2, TRPM4 and Ano6 in both primary lens epithelial cells and the cell line HLE-B3, whereas TRPM5 mRNA was only found in HLE-B3 cells. Using whole-cell patch-clamp technique, ionomycin evoked non-selective cation currents with linear current-voltage relationship in both cell types. The current was decreased by flufenamic acid (FFA), 2-APB, 9-phenanthrol and miconazole, but insensitive to DIDS, ruthenium red, and intracellularly applied spermine. H2O2 evoked a comparable current, abolished by FFA. TRPM2 protein expression in HLE-B3 cells was confirmed by means of immunocytochemistry and western blot. In summary, we conclude that lens epithelial cells functionally express Ca2+- and H2O2-activated non-selective cation channels with properties of TRPM2.
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Affiliation(s)
- Susanne Keckeis
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Laura Wernecke
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Daniel J Salchow
- Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany
| | - Nadine Reichhart
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany.
| | - Olaf Strauß
- Experimental Ophthalmology, Department of Ophthalmology, Charité University Medicine Berlin, Berlin, Germany.
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Adragna NC, Ravilla NB, Lauf PK, Begum G, Khanna AR, Sun D, Kahle KT. Regulated phosphorylation of the K-Cl cotransporter KCC3 is a molecular switch of intracellular potassium content and cell volume homeostasis. Front Cell Neurosci 2015. [PMID: 26217182 PMCID: PMC4496573 DOI: 10.3389/fncel.2015.00255] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The defense of cell volume against excessive shrinkage or swelling is a requirement for cell function and organismal survival. Cell swelling triggers a coordinated homeostatic response termed regulatory volume decrease (RVD), resulting in K+ and Cl− efflux via activation of K+ channels, volume-regulated anion channels (VRACs), and the K+-Cl− cotransporters, including KCC3. Here, we show genetic alanine (Ala) substitution at threonines (Thr) 991 and 1048 in the KCC3a isoform carboxyl-terminus, preventing inhibitory phosphorylation at these sites, not only significantly up-regulates KCC3a activity up to 25-fold in normally inhibitory isotonic conditions, but is also accompanied by reversal of activity of the related bumetanide-sensitive Na+-K+-2Cl− cotransporter isoform 1 (NKCC1). This results in a rapid (<10 min) and significant (>90%) reduction in intracellular K+ content (Ki) via both Cl-dependent (KCC3a + NKCC1) and Cl-independent [DCPIB (VRAC inhibitor)-sensitive] pathways, which collectively renders cells less prone to acute swelling in hypotonic osmotic stress. Together, these data demonstrate the phosphorylation state of Thr991/Thr1048 in KCC3a encodes a potent switch of transporter activity, Ki homeostasis, and cell volume regulation, and reveal novel observations into the functional interaction among ion transport molecules involved in RVD.
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Affiliation(s)
- Norma C Adragna
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Nagendra B Ravilla
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Peter K Lauf
- Department of Pharmacology and Toxicology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA ; Department of Pathology, Boonshoft School of Medicine, Wright State University Dayton, OH, USA
| | - Gulnaz Begum
- Department of Neurology, University of Pittsburgh Pittsburgh, PA, USA
| | - Arjun R Khanna
- Department of Neurosurgery, Boston Children's Hospital and Harvard Medical School, Harvard University Boston, MA, USA
| | - Dandan Sun
- Department of Neurology, University of Pittsburgh Pittsburgh, PA, USA ; Veterans Affairs Pittsburgh Health Care System, Geriatric Research, Educational and Clinical Center Pittsburgh, PA, USA
| | - Kristopher T Kahle
- Department of Neurosurgery, Boston Children's Hospital and Harvard Medical School, Harvard University Boston, MA, USA ; Manton Center for Orphan Disease Research, Children's Hospital Boston, Harvard University Boston, MA, USA
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Lauf PK, Alqahtani T, Flues K, Meller J, Adragna NC. Interaction between Na-K-ATPase and Bcl-2 proteins BclXL and Bak. Am J Physiol Cell Physiol 2015; 308:C51-60. [DOI: 10.1152/ajpcell.00287.2014] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
In silico analysis predicts interaction between Na-K-ATPase (NKA) and Bcl-2 protein canonical BH3- and BH1-like motifs, consistent with NKA inhibition by the benzo-phenanthridine alkaloid chelerythrine, a BH3 mimetic, in fetal human lens epithelial cells (FHLCs) (Lauf PK, Heiny J, Meller J, Lepera MA, Koikov L, Alter GM, Brown TL, Adragna NC. Cell Physiol Biochem 31: 257–276, 2013). This report establishes proof of concept: coimmunoprecipitation and immunocolocalization showed unequivocal and direct physical interaction between NKA and Bcl-2 proteins. Specifically, NKA antibodies (ABs) coimmunoprecipitated BclXL (B-cell lymphoma extra large) and BAK (Bcl-2 antagonist killer) proteins in FHLCs and A549 lung cancer cells. In contrast, both anti-Bcl-2 ABs failed to pull down NKA. Notably, the molecular mass of BAK1 proteins pulled down by NKA and BclXL ABs appeared to be some 4-kDa larger than found in input monomers. In silico analysis predicts these higher molecular mass BAK1 proteins as alternative splicing variants, encoding 42 amino acid (aa) larger proteins than the known 211-aa long canonical BAK1 protein. These BAK1 variants may constitute a pool separate from that forming mitochondrial pores by specifically interacting with NKA and BclXL proteins. We propose a NKA-Bcl-2 protein ternary complex supporting our hypothesis for a special sensor role of NKA in Bcl-2 protein control of cell survival and apoptosis.
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Affiliation(s)
- Peter K. Lauf
- Cell Biophysics Group, Wright State University Boonshoft School of Medicine, Dayton, Ohio
- Department of Pathology, Wright State University Boonshoft School of Medicine, Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University Boonshoft School of Medicine, Dayton, Ohio; and
| | - Tariq Alqahtani
- Cell Biophysics Group, Wright State University Boonshoft School of Medicine, Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University Boonshoft School of Medicine, Dayton, Ohio; and
| | - Karin Flues
- Cell Biophysics Group, Wright State University Boonshoft School of Medicine, Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University Boonshoft School of Medicine, Dayton, Ohio; and
| | - Jaroslaw Meller
- Environmental Health, University of Cincinnati Medical Center, Cincinnati, Ohio
| | - Norma C. Adragna
- Cell Biophysics Group, Wright State University Boonshoft School of Medicine, Dayton, Ohio
- Department of Pharmacology and Toxicology, Wright State University Boonshoft School of Medicine, Dayton, Ohio; and
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Medina I, Friedel P, Rivera C, Kahle KT, Kourdougli N, Uvarov P, Pellegrino C. Current view on the functional regulation of the neuronal K(+)-Cl(-) cotransporter KCC2. Front Cell Neurosci 2014; 8:27. [PMID: 24567703 PMCID: PMC3915100 DOI: 10.3389/fncel.2014.00027] [Citation(s) in RCA: 128] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Accepted: 01/18/2014] [Indexed: 12/22/2022] Open
Abstract
In the mammalian central nervous system (CNS), the inhibitory strength of chloride (Cl(-))-permeable GABAA and glycine receptors (GABAAR and GlyR) depends on the intracellular Cl(-) concentration ([Cl(-)]i). Lowering [Cl(-)]i enhances inhibition, whereas raising [Cl(-)]i facilitates neuronal activity. A neuron's basal level of [Cl(-)]i, as well as its Cl(-) extrusion capacity, is critically dependent on the activity of the electroneutral K(+)-Cl(-) cotransporter KCC2, a member of the SLC12 cation-Cl(-) cotransporter (CCC) family. KCC2 deficiency compromises neuronal migration, formation and the maturation of GABAergic and glutamatergic synaptic connections, and results in network hyperexcitability and seizure activity. Several neurological disorders including multiple epilepsy subtypes, neuropathic pain, and schizophrenia, as well as various insults such as trauma and ischemia, are associated with significant decreases in the Cl(-) extrusion capacity of KCC2 that result in increases of [Cl(-)]i and the subsequent hyperexcitability of neuronal networks. Accordingly, identifying the key upstream molecular mediators governing the functional regulation of KCC2, and modifying these signaling pathways with small molecules, might constitute a novel neurotherapeutic strategy for multiple diseases. Here, we discuss recent advances in the understanding of the mechanisms regulating KCC2 activity, and of the role these mechanisms play in neuronal Cl(-) homeostasis and GABAergic neurotransmission. As KCC2 mediates electroneutral transport, the experimental recording of its activity constitutes an important research challenge; we therefore also, provide an overview of the different methodological approaches utilized to monitor function of KCC2 in both physiological and pathological conditions.
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Affiliation(s)
- Igor Medina
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED)Marseille, France
- Aix-Marseille Université, UMR901Marseille, France
| | - Perrine Friedel
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED)Marseille, France
- Aix-Marseille Université, UMR901Marseille, France
| | - Claudio Rivera
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED)Marseille, France
- Aix-Marseille Université, UMR901Marseille, France
- Neuroscience Center, University of HelsinkiHelsinki, Finland
| | - Kristopher T. Kahle
- Department of Cardiology, Manton Center for Orphan Disease Research, Howard Hughes Medical Institute, Boston Children's HospitalBoston, MA, USA
- Department of Neurosurgery, Massachusetts General Hospital and Harvard Medical SchoolBoston, MA, USA
| | - Nazim Kourdougli
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED)Marseille, France
- Aix-Marseille Université, UMR901Marseille, France
| | - Pavel Uvarov
- Institute of Biomedicine, Anatomy, University of HelsinkiHelsinki, Finland
| | - Christophe Pellegrino
- INSERM, Institut de Neurobiologie de la Méditerranée (INMED)Marseille, France
- Aix-Marseille Université, UMR901Marseille, France
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Choi S, Na HY, Kim JA, Cho SE, Suh SH. Contradictory Effects of Superoxide and Hydrogen Peroxide on KCa3.1 in Human Endothelial Cells. THE KOREAN JOURNAL OF PHYSIOLOGY & PHARMACOLOGY : OFFICIAL JOURNAL OF THE KOREAN PHYSIOLOGICAL SOCIETY AND THE KOREAN SOCIETY OF PHARMACOLOGY 2013; 17:181-7. [PMID: 23776393 PMCID: PMC3682077 DOI: 10.4196/kjpp.2013.17.3.181] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 01/14/2013] [Revised: 05/15/2013] [Accepted: 05/20/2013] [Indexed: 01/18/2023]
Abstract
Reactive oxygen species (ROS) are generated in various cells, including vascular smooth muscle and endothelial cells, and regulate ion channel functions. KCa3.1 plays an important role in endothelial functions. However, the effects of superoxide and hydrogen peroxide radicals on the expression of this ion channel in the endothelium remain unclear. In this study, we examined the effects of ROS donors on KCa3.1 expression and the K+ current in primary cultured human umbilical vein endothelial cells (HUVECs). The hydrogen peroxide donor, tert-butyl hydroperoxide (TBHP), upregulated KCa3.1 expression, while the superoxide donors, xanthine/xanthine oxidase mixture (X/XO) and lysopho-sphatidylcholine (LPC), downregulated its expression, in a concentration-dependent manner. These ROS donor effects were prevented by antioxidants or superoxide dismustase. Phosphorylated extracellular signal-regulated kinase (pERK) was upregulated by TBHP and downregulated by X/XO. In addition, repressor element-1-silencing transcription factor (REST) was downregulated by TBHP, and upregulated by X/XO. Furthermore, KCa3.1 current, which was activated by clamping cells with 1 µM Ca2+ and applying the KCa3.1 activator 1-ethyl-2-benzimidazolinone, was further augmented by TBHP, and inhibited by X/XO. These effects were prevented by antioxidants. The results suggest that hydrogen peroxide increases KCa3.1 expression by upregulating pERK and downregulating REST, and augments the K+ current. On the other hand, superoxide reduces KCa3.1 expression by downregulating pERK and upregulating REST, and inhibits the K+ current. ROS thereby play a key role in both physiological and pathological processes in endothelial cells by regulating KCa3.1 and endothelial function.
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Affiliation(s)
- Shinkyu Choi
- Department of Physiology and Medical Research Institute, School of Medicine, Ewha Womans University, Seoul 158-710, Korea
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Pondugula SR, Kampalli SB, Wu T, De Lisle RC, Raveendran NN, Harbidge DG, Marcus DC. cAMP-stimulated Cl- secretion is increased by glucocorticoids and inhibited by bumetanide in semicircular canal duct epithelium. BMC PHYSIOLOGY 2013; 13:6. [PMID: 23537040 PMCID: PMC3622586 DOI: 10.1186/1472-6793-13-6] [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: 12/14/2012] [Accepted: 03/11/2013] [Indexed: 12/13/2022]
Abstract
Background The vestibular system controls the ion composition of its luminal fluid through several epithelial cell transport mechanisms under hormonal regulation. The semicircular canal duct (SCCD) epithelium has been shown to secrete Cl- under β2-adrenergic stimulation. In the current study, we sought to determine the ion transporters involved in Cl- secretion and whether secretion is regulated by PKA and glucocorticoids. Results Short circuit current (Isc) from rat SCCD epithelia demonstrated stimulation by forskolin (EC50: 0.8 μM), 8-Br-cAMP (EC50: 180 μM), 8-pCPT-cAMP (100 μM), IBMX (250 μM), and RO-20-1724 (100 μM). The PKA activator N6-BNZ-cAMP (0.1, 0.3 & 1 mM) also stimulated Isc. Partial inhibition of stimulated Isc individually by bumetanide (10 & 50 μM), and [(dihydroindenyl)oxy]alkanoic acid (DIOA, 100 μM) were additive and complete. Stimulated Isc was also partially inhibited by CFTRinh-172 (5 & 30 μM), flufenamic acid (5 μM) and diphenylamine-2,2′-dicarboxylic acid (DPC; 1 mM). Native canals of CFTR+/− mice showed a stimulation of Isc from isoproterenol and forskolin+IBMX but not in the presence of both bumetanide and DIOA, while canals from CFTR−/− mice had no responses. Nonetheless, CFTR−/− mice showed no difference from CFTR+/− mice in their ability to balance (rota-rod). Stimulated Isc was greater after chronic incubation (24 hr) with the glucocorticoids dexamethasone (0.1 & 0.3 μM), prednisolone (0.3, 1 & 3 μM), hydrocortisone (0.01, 0.1 & 1 μM), and corticosterone (0.1 & 1 μM) and mineralocorticoid aldosterone (1 μM). Steroid action was blocked by mifepristone but not by spironolactone, indicating all the steroids activated the glucocorticoid, but not mineralocorticoid, receptor. Expression of transcripts for CFTR; for KCC1, KCC3a, KCC3b and KCC4, but not KCC2; for NKCC1 but not NKCC2 and for WNK1 but only very low WNK4 was determined. Conclusions These results are consistent with a model of Cl- secretion whereby Cl- is taken up across the basolateral membrane by a Na+-K+-2Cl- cotransporter (NKCC) and potentially another transporter, is secreted across the apical membrane via a Cl- channel, likely CFTR, and demonstrate the regulation of Cl- secretion by protein kinase A and glucocorticoids.
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13
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Antrobus SP, Lytle C, Payne JA. K+-Cl- cotransporter-2 KCC2 in chicken cardiomyocytes. Am J Physiol Cell Physiol 2012; 303:C1180-91. [PMID: 23034386 PMCID: PMC3530769 DOI: 10.1152/ajpcell.00274.2012] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2012] [Accepted: 09/25/2012] [Indexed: 12/15/2022]
Abstract
Using antibodies prepared against a unique region (exon 22-24) of rat K(+)-Cl(-) cotransporter-2 (KCC2), we confirmed that the ~140-kDa KCC2 protein is exclusively expressed in rat brain, but in chicken, we observed strong reactivity not only with the ~140-kDa KCC2 protein in brain but also a slightly larger ~145-kDa protein in heart. In silico analysis showed that while exon 22 of KCC2 is unique to this isoform in therian mammals, it is retained in KCC2's closest paralog, KCC4, of lower vertebrates, including chicken. To eliminate potential cross-reactivity with chicken KCC4, the antibodies were preadsorbed with blocking peptides prepared over the only two regions showing significant sequence identity to chicken KCC4. This completely eliminated antibody recognition of exogenously expressed chicken KCC4 but not of the ~145-kDa protein in chicken heart, indicating that chicken heart expresses KCC2. Real-time PCR confirmed robust KCC2 transcript expression in both chicken brain and heart. Chicken heart expressed predominantly the longer KCC2a splice variant consistent with the larger ~145-kDa protein in chicken heart. Immunofluorescence microscopy revealed prominent plasma membrane KCC2 labeling in chicken ventricular cardiomyocytes. We hypothesize that KCC2 is an important Cl(-) extrusion pathway in avian cardiomyocytes that counters channel-mediated Cl(-) loading during high heart rates with β-adrenergic stimulation. While KCC2 is absent from mammalian cardiomyocytes, understanding the role that the other KCC isoforms play in Cl(-) homeostasis of these cells represents a nascent area of research.
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Affiliation(s)
- Shane P Antrobus
- Dept. of Physiology and Membrane Biology, School of Medicine, Univ. of California, Davis, CA 95616, USA
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14
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Cruz-Rangel S, Gamba G, Ramos-Mandujano G, Pasantes-Morales H. Influence of WNK3 on intracellular chloride concentration and volume regulation in HEK293 cells. Pflugers Arch 2012; 464:317-30. [PMID: 22864523 DOI: 10.1007/s00424-012-1137-4] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2012] [Revised: 07/06/2012] [Accepted: 07/07/2012] [Indexed: 01/17/2023]
Abstract
The involvement of WNK3 (with no lysine [K] kinase) in cell volume regulation evoked by anisotonic conditions was investigated in two modified stable lines of HEK293 cells: WNK3+, overexpressing WNK3 and WNK3-KD expressing a kinase inactive by a punctual mutation (D294A) at the catalytic site. This different WNK3 functional expression modified intracellular Cl(-) concentration with the following profile: WNK3+ > control > WNK3-KD cells. Stimulated with 15% hypotonic solutions, WNK3+ cells showed less efficient RVD (13.1%), lower Cl(-) efflux and decreased (94.5%) KCC activity. WNK3-KD cells showed 30.1% more efficient RVD, larger Cl(-) efflux and 5-fold higher KCC activity, increased since the isotonic condition. Volume-sensitive Cl(-) currents were similar in controls, WNK3+ cells, and WNK3-KD cells. Taurine efflux was not evoked at H15%. These results show a WNK3 influence on RVD in HEK293 cells via increasing KCC activity. Hypertonic medium induced cell shrinkage and RVI. In both WNK3+ and WNK3-KD cells, RVI and NKCC activity were increased, in WNK3+ cells presumably by enhanced NKCC phosphorylation, and in WNK3-KD cells via the [Cl(-)](i) reduction induced by the higher KCC activity in characteristic of these cells. These results support the role of WNK3 in modulation of intracellular Cl(-) concentration, in RVD, and indirectly on RVI, via its effects on KCC and NKCC activity. WNK3 in HEK293 cells is expressed as puncta at the intercellular junctions and diffusely at the cytosol, while the inactive kinase was found concentrated at the Golgi area. Cells with inactive WNK3 exhibited a marked change of cell phenotype.
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Affiliation(s)
- Silvia Cruz-Rangel
- División de Neurociencias, Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Ciudad Universitaria, Circuito Exterior, 04510, Mexico, DF, Mexico
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15
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Lauf PK, Di Fulvio M, Srivastava V, Sharma N, Adragna NC. KCC2a expression in a human fetal lens epithelial cell line. Cell Physiol Biochem 2012; 29:303-12. [PMID: 22415099 DOI: 10.1159/000337611] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/30/2012] [Indexed: 11/19/2022] Open
Abstract
The fetal human lens epithelial cell (LEC) line (FHL124) possesses all four K(+)Cl(-) (KCC) cotransporter isoforms, KCC1-4, despite KCC2 being typically considered a neuronal isoform. Since at least two spliced variants, KCC2a and KCC2b, are co-expressed in cells of the central nervous system, this study sought to define the KCC2 expression profile in FHL124 cells. KCC2a, but not KCC2b transcripts were detected by reverse transcriptase polymerase chain reaction (RT-PCR). Proteins of molecular weights ranging from 95 to 135 kDa were found by Western blotting using non-variant specific anti-KCC2 antibodies directed against two different regions of the KCC2 proteins, and by biotinylation suggesting membrane expression. Immunofluorescence revealed membrane and punctate cytoplasmic staining for KCC2. Low levels of cytosolic αA and αB crystallines, and neuron-specific enolase were also detected contrasting with the strong membrane immunofluorescence staining for the Na/K ATPase α1 subunit. Since the lack of neuron-specific expression of the KCC2b variant in non-neuronal tissues has been proposed under control of a neuron-restrictive silencing element in the KCC2 gene, we hypothesize that this control may be lifted for the KCC2a variant in the FHL124 epithelial cell culture, a non-neuronal tissue of ectodermal origin.
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Affiliation(s)
- Peter K Lauf
- Cell Biophysics Group, Department of Pathology, Wright State University, Dayton, OH 45435, USA.
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16
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Austin TM, Delpire E. Inhibition of KCC2 in mouse spinal cord neurons leads to hypersensitivity to thermal stimulation. Anesth Analg 2011; 113:1509-15. [PMID: 21965363 PMCID: PMC3224196 DOI: 10.1213/ane.0b013e31822e0a5d] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
BACKGROUND KCC2, a neuronal-specific K-Cl cotransporter, is involved in pain perception physiology through its effects on postsynaptic inhibition in spinal cord neurons. We injected a newly identified, highly potent and selective inhibitor of KCC2 (D4), an inactive structural variant (D4.14), and the Na-K-2Cl cotransporter (NKCC1) inhibitor, bumetanide, into the intrathecal space of mice to measure their effect on heat-evoked nociceptive responses. METHODS Commercially available intrathecal catheters were modified and surgically placed into 2 cohorts of 10 mice. After recovery from the procedure, the mice were injected with D4, D4.14, and bumetanide through this catheter. Nociceptive measurements (hotplate assay, tail flick assay) were performed after injection of each of the test drugs and compared with vehicle controls. RESULTS Two mice in each cohort were omitted because of postprocedure complications. There was a statistically significant decrease (P < 0.01) in withdrawal latency after injection of the active KCC2 inhibitor but not after injection of the inactive compound (P = 0.78), as measured by hotplate assay at 55°C. Injection of bumetanide significantly increased withdrawal latency (P = 0.02) at the same temperature. These results were confirmed using tail flick assays performed at 49°C. CONCLUSIONS Inhibition of KCC2 by D4 led to decreased heat-evoked withdrawal latency in mice, as measured by hotplate and tail flick assays, whereas inhibition of NKCC1 by bumetanide resulted in increased response latencies to heat stimuli as measured by both of these nociceptive tests.
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Affiliation(s)
- Thomas M Austin
- Department of Anesthesiology, Vanderbilt University Medical School, Nashville, TN 37232-2520, USA
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17
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Wei WC, Akerman CJ, Newey SE, Pan J, Clinch NWV, Jacob Y, Shen MR, Wilkins RJ, Ellory JC. The potassium-chloride cotransporter 2 promotes cervical cancer cell migration and invasion by an ion transport-independent mechanism. J Physiol 2011; 589:5349-59. [PMID: 21911617 PMCID: PMC3240877 DOI: 10.1113/jphysiol.2011.214635] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2011] [Accepted: 09/09/2011] [Indexed: 01/24/2023] Open
Abstract
K(+)-Cl(-) cotransporters (KCCs) play a fundamental role in epithelial cell function, both in the context of ionic homeostasis and also in cell morphology, cell division and locomotion. Unlike other ubiquitously expressed KCC isoforms, expression of KCC2 is widely considered to be restricted to neurons, where it is responsible for maintaining a low intracellular chloride concentration to drive hyperpolarising postsynaptic responses to the inhibitory neurotransmitters GABA and glycine. Here we report a novel finding that KCC2 is widely expressed in several human cancer cell lines including the cervical cancer cell line (SiHa). Membrane biotinylation assays and immunostaining showed that endogenous KCC2 is located on the cell membrane of SiHa cells. To elucidate the role of KCC2 in cervical tumuorigenesis, SiHa cells with stable overexpression or knockdown of KCC2 were employed. Overexpression of KCC2 had no significant effect on cell proliferation but dramatically suppressed cell spreading and stress fibre organization, while knockdown of KCC2 showed opposite effects. In addition, insulin-like growth factor 1 (IGF-1)-induced cell migration and invasiveness were significantly increased by overexpression of KCC2. KCC2-induced cell migration and invasion were not dependent on KCC2 transport function since overexpression of an activity-deficient mutant KCC2 still increased IGF-1-induced cell migration and invasion. Moreover, overexpression of KCC2 significantly diminished the number of focal adhesions, while knockdown of KCC2 increased their number. Taken together, our data establish that KCC2 expression and function are not restricted to neurons and that KCC2 serves to increase cervical tumourigenesis via an ion transport-independent mechanism.
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Affiliation(s)
- Wei-Chun Wei
- Department of Physiology, Anatomy and Genetics, University of Oxford, Oxford OX1 3PT, UK
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18
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Park S, Kim JA, Joo KY, Choi S, Choi EN, Shin JA, Han KH, Jung SC, Suh SH. Globotriaosylceramide leads to K(Ca)3.1 channel dysfunction: a new insight into endothelial dysfunction in Fabry disease. Cardiovasc Res 2010; 89:290-9. [PMID: 20971723 DOI: 10.1093/cvr/cvq333] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Excessive endothelial globotriaosylceramide (Gb3) accumulation is associated with endothelial dysfunction and impaired endothelium-dependent relaxation in Fabry disease. In endothelial cells, K(Ca)3.1 channels contribute to endothelium-dependent relaxation. However, the effect of Gb3 on K(Ca)3.1 channels and the underlying mechanisms of Gb3-induced dysfunction are unknown. Herein, we hypothesized that Gb3 accumulation induces K(Ca)3.1 channel dysfunction and aimed to clarify the underlying mechanisms. METHODS AND RESULTS The animal model of Fabry disease, α-galactosidase A (Gla) knockout mice, displayed age-dependent K(Ca)3.1 channel dysfunction. K(Ca)3.1 current and the channel expression were significantly reduced in mouse aortic endothelial cells (MAECs) of aged Gla knockout mice, whereas they were not changed in MAECs of wild-type and young Gla knockout mice. In addition, K(Ca)3.1 current and the channel expression were concentration-dependently reduced in Gb3-treated MAECs. In both Gb3-treated and aged Gla knockout MAECs, extracellular signal-regulated kinase (ERK) and activator protein-1 (AP-1) were down-regulated and repressor element-1 silencing transcription factor (REST) was up-regulated. Gb3 inhibited class III phosphoinositide 3-kinase and decreased intracellular levels of phosphatidylinositol 3-phosphate [PI(3)P]. In addition, endothelium-dependent relaxation was significantly attenuated in Gb3-treated mouse aortic rings. CONCLUSION Gb3 accumulation reduces K(Ca)3.1 channel expression by down-regulating ERK and AP-1 and up-regulating REST and the channel activity by decreasing intracellular levels of PI(3)P. Gb3 thereby evokes K(Ca)3.1 channel dysfunction, and the channel dysfunction in vascular endothelial cells may contribute to vasculopathy in Fabry disease.
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Affiliation(s)
- Seonghee Park
- Department of Physiology, School of Medicine, Ewha Womans University, 911-1 Mok-6-dong, Yang Chun-gu, Seoul 158-710, Republic of Korea
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Barmeyer C, Rahner C, Yang Y, Sigworth FJ, Binder HJ, Rajendran VM. Cloning and identification of tissue-specific expression of KCNN4 splice variants in rat colon. Am J Physiol Cell Physiol 2010; 299:C251-63. [PMID: 20445171 DOI: 10.1152/ajpcell.00091.2009] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
KCNN4 channels that provide the driving force for cAMP- and Ca(2+)-induced anion secretion are present in both apical and basolateral membranes of the mammalian colon. However, only a single KCNN4 has been cloned. This study was initiated to identify whether both apical and basolateral KCNN4 channels are encoded by the same or different isoforms. Reverse transcriptase-PCR (RT-PCR), real-time quantitative-PCR (RT-QPCR), and immunofluorescence studies were used to clone and identify tissue-specific expression of KCNN4 isoforms. Three distinct KCNN4 cDNAs that are designated as KCNN4a, KCNN4b, and KCNN4c encoding 425, 424, and 395 amino acid proteins, respectively, were isolated from the rat colon. KCNN4a differs from KCNN4b at both the nucleotide and the amino acid level with distinct 628 bp at the 3'-untranslated region and an additional glutamine at position 415, respectively. KCNN4c differs from KCNN4b by lacking the second exon that encodes a 29 amino acid motif. KCNN4a and KCNN4b/c are identified as smooth muscle- and epithelial cell-specific transcripts, respectively. KCNN4b and KCNN4c transcripts likely encode basolateral (40 kDa) and apical (37 kDa) membrane proteins in the distal colon, respectively. KCNN4c, which lacks the S2 transmembrane segment, requires coexpression of a large conductance K(+) channel beta-subunit for plasma membrane expression. The KCNN4 channel blocker TRAM-34 inhibits KCNN4b- and KCNN4c-mediated (86)Rb (K(+) surrogate) efflux with an apparent inhibitory constant of 0.6 +/- 0.1 and 7.8 +/- 0.4 muM, respectively. We conclude that apical and basolateral KCNN4 K(+) channels that regulate K(+) and anion secretion are encoded by distinct isoforms in colonic epithelial cells.
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Affiliation(s)
- Christian Barmeyer
- Department of Internal Medicine, Yale University, New Haven, Connecticut, USA
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Chimote AA, Adragna NC, Lauf PK. Ion transport in a human lens epithelial cell line exposed to hyposmotic and apoptotic stress. J Cell Physiol 2010; 223:110-22. [PMID: 20049853 DOI: 10.1002/jcp.22015] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Membrane transport changes in human lens epithelial (HLE-B3) cells under hyposmotic and apoptotic stress were compared. Cell potassium content, K(i), uptake of the K congener rubidium, Rb(i), and water content were measured after hyposmotic stress induced by hypotonicity, and apoptotic stress by the protein-kinase inhibitor staurosporine (STP). Cell water increased in hyposmotic (150 mOsm) as compared to isosmotic (300 mOsm) balanced salt solution (BSS) by >2-fold at 5 min and decreased within 15 min to baseline values accompanied by a 40% K(i) loss commensurate with cell swelling and subsequent cell shrinkage likely due to regulatory volume decrease (RVD). Loss of K(i), and accompanying water, and Rb(i) uptake in hyposmotic BSS were prevented by clotrimazole (CTZ) suggesting water shifts associated with K and Rb flux via intermediate conductance K (IK) channels, also detected at the mRNA and protein level. In contrast, 2 h after 2 microM STP exposure, the cells lost approximately 40% water and approximately 60% K(i), respectively, consistent with apoptotic volume decrease (AVD). Indeed, water and K(i) loss was at least fivefold greater after hyposmotic than after apoptotic stress. High extracellular K and 2 mM 4-aminopyridine (4-AP) but not CTZ significantly reduced apoptosis. Annexin labeling phosphatidylserine (PS) at 15 min suggested loss of lipid asymmetry. Quantitative PCR revealed significant IK channel expression during prolonged hyposmotic stress. Results suggest in HLE-B3 cells, IK channels likely partook in and were down regulated after RVD, whereas pro-apoptotic STP-activation of 4-AP-sensitive voltage-gated K channels preceded or accompanied PS externalization before subsequent apoptosis.
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Affiliation(s)
- Ameet A Chimote
- Cell Biophysics Group, Boonshoft School of Medicine, Wright State University, Dayton, Ohio 45435, USA
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Hoffmann EK, Lambert IH, Pedersen SF. Physiology of cell volume regulation in vertebrates. Physiol Rev 2009; 89:193-277. [PMID: 19126758 DOI: 10.1152/physrev.00037.2007] [Citation(s) in RCA: 1014] [Impact Index Per Article: 67.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The ability to control cell volume is pivotal for cell function. Cell volume perturbation elicits a wide array of signaling events, leading to protective (e.g., cytoskeletal rearrangement) and adaptive (e.g., altered expression of osmolyte transporters and heat shock proteins) measures and, in most cases, activation of volume regulatory osmolyte transport. After acute swelling, cell volume is regulated by the process of regulatory volume decrease (RVD), which involves the activation of KCl cotransport and of channels mediating K(+), Cl(-), and taurine efflux. Conversely, after acute shrinkage, cell volume is regulated by the process of regulatory volume increase (RVI), which is mediated primarily by Na(+)/H(+) exchange, Na(+)-K(+)-2Cl(-) cotransport, and Na(+) channels. Here, we review in detail the current knowledge regarding the molecular identity of these transport pathways and their regulation by, e.g., membrane deformation, ionic strength, Ca(2+), protein kinases and phosphatases, cytoskeletal elements, GTP binding proteins, lipid mediators, and reactive oxygen species, upon changes in cell volume. We also discuss the nature of the upstream elements in volume sensing in vertebrate organisms. Importantly, cell volume impacts on a wide array of physiological processes, including transepithelial transport; cell migration, proliferation, and death; and changes in cell volume function as specific signals regulating these processes. A discussion of this issue concludes the review.
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Affiliation(s)
- Else K Hoffmann
- Department of Biology, University of Copenhagen, Copenhagen, Denmark.
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22
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Lauf PK, Chimote AA, Adragna NC. Lithium fluxes indicate presence of Na-Cl cotransport (NCC) in human lens epithelial cells. Cell Physiol Biochem 2008; 21:335-46. [PMID: 18453742 DOI: 10.1159/000129627] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/07/2008] [Indexed: 11/19/2022] Open
Abstract
During regulatory volume decrease (RVD) of human lens epithelial cells (hLECs) by clotrimazole (CTZ)-sensitive K fluxes, Na-K-2Cl cotransport (NKCC) remains active and K-Cl cotransport (KCC) inactive. To determine whether such an abnormal behavior was caused by RVD-induced cell shrinkage, NKCC was measured in the presence of either CTZ or in high K media to prevent RVD. NKCC transports RbCl + NaCl, and LiCl + KCl; thus ouabain-insensitive, bumetanide-sensitive (BS) or Cl-dependent (ClD) Rb and Li fluxes were determined in hyposmotic high NaCl media with CTZ, or in high KCl media alone, or with sulfamate (Sf) or nitrate as Cl replacement at varying Rb, Li or Cl mol fractions (MF). Unexpectedly, NKCC was inhibited by 80% with CTZ (IC(50) = 31 microM). In isosmotic (300 mOsM) K, Li influx was approximately 1/3 of Rb influx in Na, 50% lower in Sf, and bumetanide-insensitive (BI). In hypotonic (200 mOsM) K, only the ClD but not BS Li fluxes were detected. At Li MFs from 0.1-1, Li fluxes fitted a bell-shaped curve maxing at approximately 0.6 Li MF, with the BS fluxes equaling approximately 1/4 of the ClD-Li influx. The difference, i.e. the BI/ClD Li influx, saturated with increasing Li and Cl MFs, with K(ms) for Li of 11 with, and 7 mM without K, and of approximately 46 mM for Cl. Inhibition of this K-independent Li influx by thiazides was weak whilst furosemide (<100 microM) was ineffective. Reverse transcription polymerase chain reaction and Western blots verified presence of both NKCC1 and Na-Cl cotransport (NCC). In conclusion, in hyposmotic high K media, which prevents CTZ-sensitive K flux-mediated RVD in hLECs, NKCC1, though molecularly expressed, was functionally silent. However, a K-independent and moderately thiazide-sensitive ClD-Li flux, i.e. LiCC, likely occurring through NCC was detected operationally and molecularly.
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Affiliation(s)
- Peter K Lauf
- Cell Biophysics Group, Department of Pathology, Boonshoft School of Medicine, Wright State University, Dayton, OH 45435, USA.
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