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Fernandez-Abascal J, Graziano B, Encalada N, Bianchi L. Glial Chloride Channels in the Function of the Nervous System Across Species. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2021; 1349:195-223. [PMID: 35138616 PMCID: PMC11247392 DOI: 10.1007/978-981-16-4254-8_10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Abstract
In the nervous system, the concentration of Cl- in neurons that express GABA receptors plays a key role in establishing whether these neurons are excitatory, mostly during early development, or inhibitory. Thus, much attention has been dedicated to understanding how neurons regulate their intracellular Cl- concentration. However, regulation of the extracellular Cl- concentration by other cells of the nervous system, including glia and microglia, is as important because it ultimately affects the Cl- equilibrium potential across the neuronal plasma membrane. Moreover, Cl- ions are transported in and out of the cell, via either passive or active transporter systems, as counter ions for K+ whose concentration in the extracellular environment of the nervous system is tightly regulated because it directly affects neuronal excitability. In this book chapter, we report on the Cl- channel types expressed in the various types of glial cells focusing on the role they play in the function of the nervous system in health and disease. Furthermore, we describe the types of stimuli that these channels are activated by, the other solutes that they may transport, and the involvement of these channels in processes such as pH regulation and Regulatory Volume Decrease (RVD). The picture that emerges is one of the glial cells expressing a variety of Cl- channels, encoded by members of different gene families, involved both in short- and long-term regulation of the nervous system function. Finally, we report data on invertebrate model organisms, such as C. elegans and Drosophila, that are revealing important and previously unsuspected functions of some of these channels in the context of living and behaving animals.
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Affiliation(s)
- Jesus Fernandez-Abascal
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Bianca Graziano
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Nicole Encalada
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA
| | - Laura Bianchi
- Department Physiology and Biophysics, University of Miami, Miller School of Medicine, Miami, FL, USA.
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Drug development in targeting ion channels for brain edema. Acta Pharmacol Sin 2020; 41:1272-1288. [PMID: 32855530 PMCID: PMC7609292 DOI: 10.1038/s41401-020-00503-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2020] [Accepted: 08/02/2020] [Indexed: 12/18/2022] Open
Abstract
Cerebral edema is a pathological hallmark of various central nervous system (CNS) insults, including traumatic brain injury (TBI) and excitotoxic injury such as stroke. Due to the rigidity of the skull, edema-induced increase of intracranial fluid significantly complicates severe CNS injuries by raising intracranial pressure and compromising perfusion. Mortality due to cerebral edema is high. With mortality rates up to 80% in severe cases of stroke, it is the leading cause of death within the first week. Similarly, cerebral edema is devastating for patients of TBI, accounting for up to 50% mortality. Currently, the available treatments for cerebral edema include hypothermia, osmotherapy, and surgery. However, these treatments only address the symptoms and often elicit adverse side effects, potentially in part due to non-specificity. There is an urgent need to identify effective pharmacological treatments for cerebral edema. Currently, ion channels represent the third-largest target class for drug development, but their roles in cerebral edema remain ill-defined. The present review aims to provide an overview of the proposed roles of ion channels and transporters (including aquaporins, SUR1-TRPM4, chloride channels, glucose transporters, and proton-sensitive channels) in mediating cerebral edema in acute ischemic stroke and TBI. We also focus on the pharmacological inhibitors for each target and potential therapeutic strategies that may be further pursued for the treatment of cerebral edema.
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Slifer ZM, Blikslager AT. The Integral Role of Tight Junction Proteins in the Repair of Injured Intestinal Epithelium. Int J Mol Sci 2020; 21:ijms21030972. [PMID: 32024112 PMCID: PMC7036844 DOI: 10.3390/ijms21030972] [Citation(s) in RCA: 112] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2019] [Revised: 10/10/2019] [Accepted: 10/14/2019] [Indexed: 12/29/2022] Open
Abstract
The intestinal epithelial monolayer forms a transcellular and paracellular barrier that separates luminal contents from the interstitium. The paracellular barrier consists of a highly organized complex of intercellular junctions that is primarily regulated by apical tight junction proteins and tight junction-associated proteins. This homeostatic barrier can be lost through a multitude of injurious events that cause the disruption of the tight junction complex. Acute repair after injury leading to the reestablishment of the tight junction barrier is crucial for the return of both barrier function as well as other cellular functions, including water regulation and nutrient absorption. This review provides an overview of the tight junction complex components and how they link to other plasmalemmal proteins, such as ion channels and transporters, to induce tight junction closure during repair of acute injury. Understanding the components of interepithelial tight junctions and the mechanisms of tight junction regulation after injury is crucial for developing future therapeutic targets for patients experiencing dysregulated intestinal permeability.
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Saberbaghi T, Wong R, Rutka JT, Wang GL, Feng ZP, Sun HS. Role of Cl− channels in primary brain tumour. Cell Calcium 2019; 81:1-11. [DOI: 10.1016/j.ceca.2019.05.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2019] [Revised: 04/28/2019] [Accepted: 05/13/2019] [Indexed: 12/20/2022]
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Okada Y, Okada T, Sato-Numata K, Islam MR, Ando-Akatsuka Y, Numata T, Kubo M, Shimizu T, Kurbannazarova RS, Marunaka Y, Sabirov RZ. Cell Volume-Activated and Volume-Correlated Anion Channels in Mammalian Cells: Their Biophysical, Molecular, and Pharmacological Properties. Pharmacol Rev 2019; 71:49-88. [PMID: 30573636 DOI: 10.1124/pr.118.015917] [Citation(s) in RCA: 60] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
There are a number of mammalian anion channel types associated with cell volume changes. These channel types are classified into two groups: volume-activated anion channels (VAACs) and volume-correlated anion channels (VCACs). VAACs can be directly activated by cell swelling and include the volume-sensitive outwardly rectifying anion channel (VSOR), which is also called the volume-regulated anion channel; the maxi-anion channel (MAC or Maxi-Cl); and the voltage-gated anion channel, chloride channel (ClC)-2. VCACs can be facultatively implicated in, although not directly activated by, cell volume changes and include the cAMP-activated cystic fibrosis transmembrane conductance regulator (CFTR) anion channel, the Ca2+-activated Cl- channel (CaCC), and the acid-sensitive (or acid-stimulated) outwardly rectifying anion channel. This article describes the phenotypical properties and activation mechanisms of both groups of anion channels, including accumulating pieces of information on the basis of recent molecular understanding. To that end, this review also highlights the molecular identities of both anion channel groups; in addition to the molecular identities of ClC-2 and CFTR, those of CaCC, VSOR, and Maxi-Cl were recently identified by applying genome-wide approaches. In the last section of this review, the most up-to-date information on the pharmacological properties of both anion channel groups, especially their half-maximal inhibitory concentrations (IC50 values) and voltage-dependent blocking, is summarized particularly from the standpoint of pharmacological distinctions among them. Future physiologic and pharmacological studies are definitely warranted for therapeutic targeting of dysfunction of VAACs and VCACs.
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Affiliation(s)
- Yasunobu Okada
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Toshiaki Okada
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Kaori Sato-Numata
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Md Rafiqul Islam
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Yuhko Ando-Akatsuka
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Tomohiro Numata
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Machiko Kubo
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Takahiro Shimizu
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Ranohon S Kurbannazarova
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Yoshinori Marunaka
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
| | - Ravshan Z Sabirov
- Departments of Physiology and Systems Bioscience (Y.O.) and Molecular Cell Physiology (Y.M.), Kyoto Prefectural University of Medicine, Kyoto, Japan; Division of Cell Signaling, National Institute for Physiological Sciences, Okazaki, Japan (Y.O., T.O., M.R.I., M.K., R.Z.S.); Department of Physiology, School of Medicine, Fukuoka University, Fukuoka, Japan (K.S.-N., T.N.); Department of Cell Physiology, Faculty of Pharmaceutical Sciences, Suzuka University of Medical Science, Suzuka, Japan (Y.A.-A.); Department of Pharmaceutical Physiology, Graduate School of Medicine and Pharmaceutical Sciences, University of Toyama, Toyama, Japan (T.S.); Laboratory of Molecular Physiology, Institute of Bioorganic Chemistry, Academy of Sciences of Uzbekistan, Tashkent, Uzbekistan (R.S.K., R.Z.S.); and Research Institute for Clinical Physiology, Kyoto Industrial Health Association, Kyoto, Japan (Y.M.)
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Verkhratsky A, Nedergaard M. Physiology of Astroglia. Physiol Rev 2018; 98:239-389. [PMID: 29351512 PMCID: PMC6050349 DOI: 10.1152/physrev.00042.2016] [Citation(s) in RCA: 916] [Impact Index Per Article: 152.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2016] [Revised: 03/22/2017] [Accepted: 04/27/2017] [Indexed: 02/07/2023] Open
Abstract
Astrocytes are neural cells of ectodermal, neuroepithelial origin that provide for homeostasis and defense of the central nervous system (CNS). Astrocytes are highly heterogeneous in morphological appearance; they express a multitude of receptors, channels, and membrane transporters. This complement underlies their remarkable adaptive plasticity that defines the functional maintenance of the CNS in development and aging. Astrocytes are tightly integrated into neural networks and act within the context of neural tissue; astrocytes control homeostasis of the CNS at all levels of organization from molecular to the whole organ.
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Affiliation(s)
- Alexei Verkhratsky
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
| | - Maiken Nedergaard
- The University of Manchester , Manchester , United Kingdom ; Achúcarro Basque Center for Neuroscience, IKERBASQUE, Basque Foundation for Science , Bilbao , Spain ; Department of Neuroscience, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain ; Center for Basic and Translational Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen , Copenhagen , Denmark ; and Center for Translational Neuromedicine, University of Rochester Medical Center , Rochester, New York
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Wang H, Xu M, Kong Q, Sun P, Yan F, Tian W, Wang X. Research and progress on ClC‑2 (Review). Mol Med Rep 2017; 16:11-22. [PMID: 28534947 PMCID: PMC5482133 DOI: 10.3892/mmr.2017.6600] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2016] [Accepted: 02/13/2017] [Indexed: 12/22/2022] Open
Abstract
Chloride channel 2 (ClC-2) is one of the nine mammalian members of the ClC family. The present review discusses the molecular properties of ClC‑2, including CLCN2, ClC‑2 promoter and the structural properties of ClC‑2 protein; physiological properties; functional properties, including the regulation of cell volume. The effects of ClC‑2 on the digestive, respiratory, circulatory, nervous and optical systems are also discussed, in addition to the mechanisms involved in the regulation of ClC‑2. The review then discusses the diseases associated with ClC‑2, including degeneration of the retina, Sjögren's syndrome, age‑related cataracts, degeneration of the testes, azoospermia, lung cancer, constipation, repair of impaired intestinal mucosa barrier, leukemia, cystic fibrosis, leukoencephalopathy, epilepsy and diabetes mellitus. It was concluded that future investigations of ClC‑2 are likely to be focused on developing specific drugs, activators and inhibitors regulating the expression of ClC‑2 to treat diseases associated with ClC‑2. The determination of CLCN2 is required to prevent and treat several diseases associated with ClC‑2.
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Affiliation(s)
- Hongwei Wang
- Department of Ophthalmology, People's Hospital of Jingjiang, Jingjiang, Jiangsu 214500, P.R. China
| | - Minghui Xu
- Library, Qiqihar Medical University, Qiqihar, Heilongjiang 161006, P.R. China
| | - Qingjie Kong
- School of Computer Science and Information Technology, Northeast Normal University, Changchun, Jilin 130024, P.R. China
| | - Peng Sun
- Department of Ophthalmology, The First Affiliated Hospital of Jiamusi University, Jiamusi, Heilongjiang 154000, P.R. China
| | - Fengyun Yan
- Assets Division, Harbin University of Science and Technology, Harbin, Heilongjiang 150080, P.R. China
| | - Wenying Tian
- Library, Qiqihar Medical University, Qiqihar, Heilongjiang 161006, P.R. China
| | - Xin Wang
- Library, Qiqihar Medical University, Qiqihar, Heilongjiang 161006, P.R. China
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Saccà SC, Gandolfi S, Bagnis A, Manni G, Damonte G, Traverso CE, Izzotti A. The Outflow Pathway: A Tissue With Morphological and Functional Unity. J Cell Physiol 2016; 231:1876-93. [PMID: 26754581 DOI: 10.1002/jcp.25305] [Citation(s) in RCA: 64] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Accepted: 01/06/2016] [Indexed: 12/17/2022]
Abstract
The trabecular meshwork (TM) plays an important role in high-tension glaucomas. Indeed, the TM is a true organ, through which the aqueous humor flows from the anterior chamber to Schlemm's canal (SC). Until recently, the TM, which is constituted by endothelial-like cells, was described as a kind of passive filter. In reality, it is much more. The cells delineating the structures of the collagen framework of the TM are endowed with a cytoskeleton, and are thus able to change their shape. These cells also have the ability to secrete the extracellular matrix, which expresses proteins and cytokines, and are capable of phagocytosis and autophagy. The cytoskeleton is attached to the nuclear membrane and can, in millionths of a second, send signals to the nucleus in order to alter the expression of genes in an attempt to adapt to biomechanical insult. Oxidative stress, as happens in aging, has a deleterious effect on the TM, leading eventually to cell decay, tissue malfunction, subclinical inflammation, changes in the extracellular matrix and cytoskeleton, altered motility, reduced outflow facility, and (ultimately) increased IOP. TM failure is the most relevant factor in the cascade of events triggering apoptosis in the inner retinal layers, including ganglion cells. J. Cell. Physiol. 231: 1876-1893, 2016. © 2016 Wiley Periodicals, Inc.
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Affiliation(s)
- Sergio Claudio Saccà
- Department of Neuroscience and Sense Organs, Ophthalmology Unit, IRCCS San Martino University Hospital, San Martino Hospital, Genoa, Italy
| | - Stefano Gandolfi
- Department of Biological, Biotechnological and Translational Sciences, Ophthalmology Unit, University of Parma, Parma, Italy
| | - Alessandro Bagnis
- Department of Neuroscience and Sense Organs, Eye Clinic, University of Genoa, Genoa, Italy
| | - Gianluca Manni
- Department of Clinical Science and Translational Medicine, University Tor Vergata, Rome, Italy
| | - Gianluca Damonte
- Department of Experimental Medicine, Section of Biochemistry and Center of Excellence for Biomedical Research, University of Genoa, Genoa, Italy
| | - Carlo Enrico Traverso
- Department of Neuroscience and Sense Organs, Eye Clinic, University of Genoa, Genoa, Italy
| | - Alberto Izzotti
- Department of Health Sciences, Mutagenesis Unit, IRCCS San Martino University Hospital, IST National Institute for Cancer Research, University of Genoa, Genoa, Italy
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Giblin JP, Comes N, Strauss O, Gasull X. Ion Channels in the Eye: Involvement in Ocular Pathologies. ADVANCES IN PROTEIN CHEMISTRY AND STRUCTURAL BIOLOGY 2015; 104:157-231. [PMID: 27038375 DOI: 10.1016/bs.apcsb.2015.11.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The eye is the sensory organ of vision. There, the retina transforms photons into electrical signals that are sent to higher brain areas to produce visual sensations. In the light path to the retina, different types of cells and tissues are involved in maintaining the transparency of avascular structures like the cornea or lens, while others, like the retinal pigment epithelium, have a critical role in the maintenance of photoreceptor function by regenerating the visual pigment. Here, we have reviewed the roles of different ion channels expressed in ocular tissues (cornea, conjunctiva and neurons innervating the ocular surface, lens, retina, retinal pigment epithelium, and the inflow and outflow systems of the aqueous humor) that are involved in ocular disease pathophysiologies and those whose deletion or pharmacological modulation leads to specific diseases of the eye. These include pathologies such as retinitis pigmentosa, macular degeneration, achromatopsia, glaucoma, cataracts, dry eye, or keratoconjunctivitis among others. Several disease-associated ion channels are potential targets for pharmacological intervention or other therapeutic approaches, thus highlighting the importance of these channels in ocular physiology and pathophysiology.
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Affiliation(s)
- Jonathan P Giblin
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | - Nuria Comes
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain
| | | | - Xavier Gasull
- Universitat de Barcelona, Barcelona, Spain; Institut d'Investigacions Biomèdiques August Pi i Sunyer (IDIBAPS), Barcelona, Spain.
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Jin Y, Blikslager AT. ClC-2 regulation of intestinal barrier function: Translation of basic science to therapeutic target. Tissue Barriers 2015; 3:e1105906. [PMID: 26716076 DOI: 10.1080/21688370.2015.1105906] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2015] [Revised: 09/28/2015] [Accepted: 10/01/2015] [Indexed: 02/06/2023] Open
Abstract
The ClC-2 chloride channel is a member of the voltage-gated chloride channel family. ClC-2 is involved in various physiological processes, including fluid transport and secretion, regulation of cell volume and pH, maintaining the membrane potential of the cell, cell-to-cell communication, and tissue homeostasis. Recently, our laboratory has accumulated evidence indicating a critical role of ClC-2 in the regulation of intestinal barrier function by altering inter-epithelial tight junction composition. This review will detail the role of ClC-2 in intestinal barrier function during intestinal disorders, including experimental ischemia/reperfusion injury and dextran sodium sulfate (DSS)-induced inflammatory bowel disease. Details of pharmacological manipulation of ClC-2 via prostone agonists will also be provided in an effort to show the potential therapeutic relevance of ClC-2 regulation, particularly during intestinal barrier disruption.
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Affiliation(s)
- Younggeon Jin
- Department of Clinical Sciences; College of Veterinary Medicine, North Carolina State University ; Raleigh, NC, USA
| | - Anthony T Blikslager
- Department of Clinical Sciences; College of Veterinary Medicine, North Carolina State University ; Raleigh, NC, USA
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Pan F, Guo R, Cheng W, Chai L, Wang W, Cao C, Li S. High glucose inhibits ClC-2 chloride channels and attenuates cell migration of rat keratinocytes. DRUG DESIGN DEVELOPMENT AND THERAPY 2015; 9:4779-91. [PMID: 26355894 PMCID: PMC4560522 DOI: 10.2147/dddt.s84628] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Background Accumulating evidence has demonstrated that migration of keratinocytes is critical to wound epithelialization, and defects of this function result in chronic delayed-healing wounds in diabetes mellitus patients, and the migration has been proved to be associated with volume-activated chloride channels. The aim of the study is to investigate the effects of high glucose (HG, 25 mM) on ClC-2 chloride channels and cell migration of keratinocytes. Methods Newborn Sprague Dawley rats were used to isolate and culture the keratinocyte in this study. Immunofluorescence assay, real-time polymerase chain reaction, and Western blot assay were used to examine the expression of ClC-2 protein or mRNA. Scratch wound assay was used to measure the migratory ability of keratinocytes. Transwell cell migration assay was used to measure the invasion and migration of keratinocytes. Recombinant lentivirus vectors were established and transducted to keratinocytes. Whole-cell patch clamp was used to perform the electrophysiological studies. Results We found that the expression of ClC-2 was significantly inhibited when keratinocytes were exposed to a HG (25 mM) medium, accompanied by the decline of volume-activated Cl− current (ICl,vol), migration potential, and phosphorylated PI3K as compared to control group. When knockdown of ClC-2 by RNAi or pretreatment with wortmannin, similar results were observed, including ICl,vol and migration keratinocytes were inhibited. Conclusion Our study proved that HG inhibited ClC-2 chloride channels and attenuated cell migration of rat keratinocytes via inhibiting PI3K signaling.
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Affiliation(s)
- Fuqiang Pan
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Rui Guo
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Wenguang Cheng
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Linlin Chai
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Wenping Wang
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Chuan Cao
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
| | - Shirong Li
- Department of Plastic and Reconstructive Surgery, Southwestern Hospital, Third Military Medical University, Chongqing, People's Republic of China
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WANG HONGWEI, ZHENG YAJUAN. Effect of CLC-2 on the cytoskeleton in human trabecular meshwork cells. Mol Med Rep 2013; 8:1099-105. [DOI: 10.3892/mmr.2013.1619] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2012] [Accepted: 08/01/2013] [Indexed: 11/06/2022] Open
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Abstract
Vascular remodeling of cerebral arterioles, including proliferation, migration, and apoptosis of vascular smooth muscle cells (VSMCs), is the major cause of changes in the cross-sectional area and diameter of the arteries and sudden interruption of blood flow or hemorrhage in the brain, ie, stroke. Accumulating evidence strongly supports an important role for chloride (Cl(-)) channels in vascular remodeling and stroke. At least three Cl(-) channel genes are expressed in VSMCs: 1) the TMEM16A (or Ano1), which may encode the calcium-activated Cl(-) channels (CACCs); 2) the CLC-3 Cl(-) channel and Cl(-)/H(+) antiporter, which is closely related to the volume-regulated Cl(-) channels (VRCCs); and 3) the cystic fibrosis transmembrane conductance regulator (CFTR), which encodes the PKA- and PKC-activated Cl(-) channels. Activation of the CACCs by agonist-induced increase in intracellular Ca(2+) causes membrane depolarization, vasoconstriction, and inhibition of VSMC proliferation. Activation of VRCCs by cell volume increase or membrane stretch promotes the production of reactive oxygen species, induces proliferation and inhibits apoptosis of VSMCs. Activation of CFTR inhibits oxidative stress and may prevent the development of hypertension. In addition, Cl(-) current mediated by gamma-aminobutyric acid (GABA) receptor has also been implicated a role in ischemic neuron death. This review focuses on the functional roles of Cl(-) channels in the development of stroke and provides a perspective on the future directions for research and the potential to develop Cl(-) channels as new targets for the prevention and treatment of stroke.
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Evidence for sustained ATP release from liver cells that is not mediated by vesicular exocytosis. Purinergic Signal 2011; 7:435-46. [PMID: 21630025 DOI: 10.1007/s11302-011-9240-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2011] [Accepted: 05/23/2011] [Indexed: 10/18/2022] Open
Abstract
Extracellular ATP regulates many important cellular functions in the liver by stimulating purinergic receptors. Recent studies have shown that rapid exocytosis of ATP-enriched vesicles contributes to ATP release from liver cells. However, this rapid ATP release is transient, and ceases in ~30 s after the exposure to hypotonic solution. The purpose of these studies was to assess the role of vesicular exocytosis in sustained ATP release. An exposure to hypotonic solution evoked sustained ATP release that persisted for more than 15 min after the exposure. Using FM1-43 (N-(3-triethylammoniumpropyl)-4-(4-(dibutylamino)styryl)pyridinium dibromide) fluorescence to measure exocytosis, we found that hypotonic solution stimulated a transient increase in FM1-43 fluorescence that lasted ~2 min. Notably, the rate of FM1-43 fluorescence and the magnitude of ATP release were not correlated, indicating that vesicular exocytosis may not mediate sustained ATP release from liver cells. Interestingly, mefloquine potently inhibited sustained ATP release, but did not inhibit an increase in FM1-43 fluorescence evoked by hypotonic solution. Consistent with these findings, when exocytosis of ATP-enriched vesicles was specifically stimulated by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), mefloquine failed to inhibit ATP release evoked by NPPB. Thus, mefloquine can pharmacologically dissociate sustained ATP release and vesicular exocytosis. These results suggest that a distinct mefloquine-sensitive membrane ATP transport may contribute to sustained ATP release from liver cells. This novel mechanism of membrane ATP transport may play an important role in the regulation of purinergic signaling in liver cells.
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Kim KX, Marcus DC. Inward-rectifier chloride currents in Reissner's membrane epithelial cells. Biochem Biophys Res Commun 2010; 394:434-8. [PMID: 20226170 DOI: 10.1016/j.bbrc.2010.03.048] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2010] [Accepted: 03/07/2010] [Indexed: 11/27/2022]
Abstract
Sensory transduction in the cochlea depends on regulated ion secretion and absorption. Results of whole-organ experiments suggested that Reissner's membrane may play a role in the control of luminal Cl(-). We tested for the presence of Cl(-) transport pathways in isolated mouse Reissner's membrane using whole-cell patch clamp recording and gene transcript analyses using RT-PCR. The current-voltage (I-V) relationship in the presence of symmetrical NMDG-Cl was strongly inward-rectifying at negative voltages, with a small outward current at positive voltages. The inward-rectifying component of the I-V curve had several properties similar to those of the ClC-2 Cl(-) channel. It was stimulated by extracellular acidity and inhibited by extracellular Cd2+, Zn2+ and intracellular ClC-2 antibody. Channel transcripts expressed include ClC-2, Slc26a7 and ClC-Ka, but not Cftr, ClC-1, ClCa1, ClCa2, ClCa3, ClCa4, Slc26a9, ClC-Kb, Best1, Best2, Best3 or the beta-subunit of ClC-K, barttin. ClC-2 is the only molecularly-identified channel present that is a strong inward rectifier. This study is the first report of conductive Cl(-) transport in epithelial cells of Reissner's membrane and is consistent with an important role in endolymph anion homeostasis.
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Affiliation(s)
- Kyunghee X Kim
- Cellular Biophysics Laboratory, Kansas State University, Dept. of Anatomy and Physiology, 228 Coles Hall, Manhattan, KS 66506-5802, USA
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Feranchak AP, Lewis MA, Kresge C, Sathe M, Bugde A, Luby-Phelps K, Antich PP, Fitz JG. Initiation of purinergic signaling by exocytosis of ATP-containing vesicles in liver epithelium. J Biol Chem 2010; 285:8138-47. [PMID: 20071341 DOI: 10.1074/jbc.m109.065482] [Citation(s) in RCA: 64] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Extracellular ATP represents an important autocrine/paracrine signaling molecule within the liver. The mechanisms responsible for ATP release are unknown, and alternative pathways have been proposed, including either conductive ATP movement through channels or exocytosis of ATP-enriched vesicles, although direct evidence from liver cells has been lacking. Utilizing dynamic imaging modalities (confocal and total internal reflection fluorescence microscopy and luminescence detection utilizing a high sensitivity CCD camera) at different scales, including confluent cell populations, single cells, and the intracellular submembrane space, we have demonstrated in a model liver cell line that (i) ATP release is not uniform but reflects point source release by a defined subset of cells; (ii) ATP within cells is localized to discrete zones of high intensity that are approximately 1 mum in diameter, suggesting a vesicular localization; (iii) these vesicles originate from a bafilomycin A(1)-sensitive pool, are depleted by hypotonic exposure, and are not rapidly replenished from recycling of endocytic vesicles; and (iv) exocytosis of vesicles in response to cell volume changes depends upon a complex series of signaling events that requires intact microtubules as well as phosphoinositide 3-kinase and protein kinase C. Collectively, these findings are most consistent with an essential role for exocytosis in regulated release of ATP and initiation of purinergic signaling in liver cells.
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Affiliation(s)
- Andrew P Feranchak
- Department of Pediatrics, University of Texas Southwestern Medical Center at Dallas, Dallas, Texas 75390-9030, USA.
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Bao HF, Liu L, Self J, Duke BJ, Ueno R, Eaton DC. A synthetic prostone activates apical chloride channels in A6 epithelial cells. Am J Physiol Gastrointest Liver Physiol 2008; 295:G234-51. [PMID: 18511742 PMCID: PMC2519861 DOI: 10.1152/ajpgi.00366.2007] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
The bicyclic fatty acid lubiprostone (formerly known as SPI-0211) activates two types of anion channels in A6 cells. Both channel types are rarely, if ever, observed in untreated cells. The first channel type was activated at low concentrations of lubiprostone (<100 nM) in >80% of cell-attached patches and had a unit conductance of approximately 3-4 pS. The second channel type required higher concentrations (>100 nM) of lubiprostone to activate, was observed in approximately 30% of patches, and had a unit conductance of 8-9 pS. The properties of the first type of channel were consistent with ClC-2 and the second with CFTR. ClC-2's unit current strongly inwardly rectified that could be best fit by models of the channel with multiple energy barrier and multiple anion binding sites in the conductance pore. The open probability and mean open time of ClC-2 was voltage dependent, decreasing dramatically as the patches were depolarized. The order of anion selectivity for ClC-2 was Cl > Br > NO(3) > I > SCN, where SCN is thiocyanate. ClC-2 was a "double-barreled" channel favoring even numbers of levels over odd numbers as if the channel protein had two conductance pathways that opened independently of one another. The channel could be, at least, partially blocked by glibenclamide. The properties of the channel in A6 cells were indistinguishable from ClC-2 channels stably transfected in HEK293 cells. CFTR in the patches had a selectivity of Cl > Br >> NO(3) congruent with SCN congruent with I. It outwardly rectified as expected for a single-site anion channel. Because of its properties, ClC-2 is uniquely suitable to promote anion secretion with little anion reabsorption. CFTR, on the other hand, could promote either reabsorption or secretion depending on the anion driving forces.
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Affiliation(s)
- Hui Fang Bao
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
| | - Lian Liu
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
| | - Julie Self
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
| | - Billie Jeanne Duke
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
| | - Ryuji Ueno
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
| | - Douglas C. Eaton
- Departments of Physiology and Pediatrics and The Center for Cell and Molecular Signaling, Emory University School of Medicine, Atlanta, Georgia; and Sucampo Pharmaceuticals, Inc., Bethesda, Maryland
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Abstract
In January 2006 the Food and Drug Administration approved lubiprostone for the treatment of chronic constipation in men and women aged 18 and over. Lubiprostone is categorized as a prostone, a bicyclic fatty acid metabolite of prostaglandin E1. Lubiprostone activates a specific chloride channel (ClC-2) in the gastrointestinal (GI) tract to enhance intestinal fluid secretion, which increases GI transit and improves symptoms of constipation. This article reviews the role of chloride channels in the GI tract, describes the structure, function, and pharmacokinetics of lubiprostone, and discusses clinically important data on this new medication.
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Affiliation(s)
- Brian E Lacy
- Section of Gastroenterology and Hepatology, Dartmouth-Hitchcock Medical Center, Lebanon, NH 03756, USA.
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Moeser AJ, Nighot PK, Engelke KJ, Ueno R, Blikslager AT. Recovery of mucosal barrier function in ischemic porcine ileum and colon is stimulated by a novel agonist of the ClC-2 chloride channel, lubiprostone. Am J Physiol Gastrointest Liver Physiol 2007; 292:G647-56. [PMID: 17053162 DOI: 10.1152/ajpgi.00183.2006] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Previous studies utilizing an ex vivo porcine model of intestinal ischemic injury demonstrated that prostaglandin (PG)E(2) stimulates repair of mucosal barrier function via a mechanism involving Cl(-) secretion and reductions in paracellular permeability. Further experiments revealed that the signaling mechanism for PGE(2)-induced mucosal recovery was mediated via type-2 Cl(-) channels (ClC-2). Therefore, the objective of the present study was to directly investigate the role of ClC-2 in mucosal repair by evaluating mucosal recovery in ischemia-injured intestinal mucosa treated with the selective ClC-2 agonist lubiprostone. Ischemia-injured porcine ileal mucosa was mounted in Ussing chambers, and short-circuit current (I(sc)) and transepithelial electrical resistance (TER) were measured in response to lubiprostone. Application of 0.01-1 microM lubiprostone to ischemia-injured mucosa induced concentration-dependent increases in TER, with 1 microM lubiprostone stimulating a twofold increase in TER (DeltaTER = 26 Omega.cm(2); P < 0.01). However, lubiprostone (1 microM) stimulated higher elevations in TER despite lower I(sc) responses compared with the nonselective secretory agonist PGE(2) (1 microM). Furthermore, lubiprostone significantly (P < 0.05) reduced mucosal-to-serosal fluxes of (3)H-labeled mannitol to levels comparable to those of normal control tissues and restored occludin localization to tight junctions. Activation of ClC-2 with the selective agonist lubiprostone stimulated elevations in TER and reductions in mannitol flux in ischemia-injured intestine associated with structural changes in tight junctions. Prostones such as lubiprostone may provide a selective and novel pharmacological mechanism of accelerating recovery of acutely injured intestine compared with the nonselective action of prostaglandins such as PGE(2).
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Affiliation(s)
- Adam J Moeser
- Department of Clinical Sciences, College of Veterinary Medicine, North Carolina State University, Raleigh, NC 27606, USA
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Kimelberg HK, MacVicar BA, Sontheimer H. Anion channels in astrocytes: biophysics, pharmacology, and function. Glia 2006; 54:747-757. [PMID: 17006903 PMCID: PMC2556042 DOI: 10.1002/glia.20423] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The chloride/anion channels that have been so far identified in cultured astrocytes and those that have been confirmed in situ by a combination of mRNA identification, immunocytochemistry, and biophysical studies are reviewed. It is emphasized that we are just beginning to describe such channels and analyze their functions in astrocytes. The best-studied anion channels studied so far are those known as volume-regulated anion channels (VRACs). These, as for most channels, have been mainly studied in cultured astrocytes, but some correlative studies have been done in situ, because these channels have been emphasized as release routes for transmitters; namely, excitatory amino acids and ATP. They are activated by cell shape changes and cell swelling, and the release of amino acids and ATP and chloride currents, measured by whole cell clamping, by these processes has been well described, as is also their activation by low concentrations of extracellular ATP. However, the identity of these channels in astrocytes, as in all other cells, remains elusive. The potential involvement of VRACs in pathological states such as stroke, metastasis, and spreading depression is also discussed.
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Affiliation(s)
- Harold K Kimelberg
- Neural and Vascular Biology Theme, Ordway Research Institute, Albany, New York
| | - Brian A MacVicar
- Brain Research Centre, University of British Columbia, Vancouver, British Columbia, Canada
| | - Harald Sontheimer
- Department of Neurobiology and Civitan International Research Center, University of Alabama at Birgmingham, Birmingham, Alabama
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Benfenati V, Nicchia GP, Svelto M, Rapisarda C, Frigeri A, Ferroni S. Functional down-regulation of volume-regulated anion channels in AQP4 knockdown cultured rat cortical astrocytes. J Neurochem 2006; 100:87-104. [PMID: 17064359 DOI: 10.1111/j.1471-4159.2006.04164.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In the brain, the astroglial syncytium is crucially involved in the regulation of water homeostasis. Accumulating evidence indicates that a dysregulation of the astrocytic processes controlling water homeostasis has a pathogenetic role in several brain injuries. Here, we have analysed by RNA interference technology the functional interactions occurring between the most abundant water channel in the brain, aquaporin-4 (AQP4), and the swelling-activated Cl(-) current expressed by cultured rat cortical astrocytes. We show that in primary cultured rat cortical astrocytes transfected with control small interfering RNA (siRNA), hypotonic shock promotes an increase in cellular volume accompanied by augmented membrane conductance mediated by volume-regulated anion channels (VRAC). Conversely, astroglia in which AQP4 was knocked down (AQP4 KD) by transfection with AQP4 siRNA changed their morphology from polygonal to process-bearing, and displayed normal cell swelling but reduced VRAC activity. Pharmacological manipulations of actin cytoskeleton in rat astrocytes, and functional analysis in mouse astroglial cells, which retain their morphology upon knockdown of AQP4, suggest that stellation of AQP4 KD rat cortical astrocytes was not causally linked to reduction of VRAC current. Molecular analysis of possible candidates of swelling-activated Cl(-) current provided evidence that in AQP4 KD astrocytes, there was a down-regulation of chloride channel-2 (CIC-2), which, however, was not involved in VRAC conductance. Inclusion of ATP in the intracellular saline restored VRAC activity upon hypotonicity. Collectively, these results support the view that in cultured astroglial cells, plasma membrane proteins involved in cell volume homeostasis are assembled in a functional platform.
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Affiliation(s)
- Valentina Benfenati
- Department of Human and General Physiology, University of Bologna, Bologna, Italy
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Comes N, Abad E, Morales M, Borrás T, Gual A, Gasull X. Identification and functional characterization of ClC-2 chloride channels in trabecular meshwork cells. Exp Eye Res 2006; 83:877-89. [PMID: 16769051 DOI: 10.1016/j.exer.2006.04.008] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2005] [Revised: 04/18/2006] [Accepted: 04/19/2006] [Indexed: 11/24/2022]
Abstract
In the eye, trabecular meshwork (TM) cell volume may be an important determinant of aqueous humor outflow. Among their functions, ClC-2 chloride channels are thought to be involved in regulation of cellular volume and intracellular [Cl(-)]. We characterized the properties and modulation of an inwardly rectifying chloride current activated in these cells. Patch-clamp recordings revealed inwardly rectifying chloride currents activated by membrane hyperpolarization in primary cultures of both bovine (BTM) and human (HTM) TM cells. Electrophysiological properties and anion permeability sequence (Cl(-)>Br(-)>I(-)>F(-)) were in agreement with previous data for ClC-2 in other cells. The currents were blocked by Cd(2+) and enhanced by extracellular acidification, 8Br-cAMP and cell swelling, while extracellular alkalinization decreased them. RT-PCR experiments using total RNA revealed the molecular expression of ClC-2 channels. Previously we reported the involvement of swelling-activated chloride channels (Cl(swell)) and Ca(2+)-activated K(+) channels (BK(Ca)) in cell volume and outflow facility regulation. However, in the present analysis, cell volume experiments in calcein-loaded cells and outflow facility studies performed in bovine anterior segments revealed that ClC-2 channels do not make a significant contribution to the recovery of cellular volume or to the regulation of the outflow facility. Nevertheless, ClC-2 modulation by different stimuli may contribute to intracellular [Cl(-)] regulation and other cellular functions yet to be determined in the TM.
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Affiliation(s)
- Núria Comes
- Laboratory of Neurophysiology, Department of Physiological Sciences I-Institute of Biomedical Investigations August Pi i Sunyer, IDIBAPS, School of Medicine, University of Barcelona, Casanova 143, E-08036 Barcelona, Spain
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Comes N, Gasull X, Gual A, Borrás T. Differential expression of the human chloride channel genes in the trabecular meshwork under stress conditions. Exp Eye Res 2005; 80:801-13. [PMID: 15939036 DOI: 10.1016/j.exer.2004.12.009] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2004] [Revised: 10/07/2004] [Accepted: 12/13/2004] [Indexed: 11/19/2022]
Abstract
Among other channels, voltage-gated chloride channels (ClC) regulate cell volume, membrane potential and cellular transport. Because changes in trabecular meshwork (TM) cell volume influence outflow facility and because the relative abundance of a gene's transcript is an indication of the relevance of the gene's function, we investigated the presence and relative expression of seven members of the CLCN gene family in the human TM. To elucidate the role of ClC-2 and ClC-3 in cell swelling, we studied changes in their mRNA levels after hypotonic shock. In addition, to examine the potential involvement of these two channels in conditions associated with glaucoma, we determined their transcripts levels in response to elevated intraocular pressure (IOP) and dexamethasone (DEX). For our evaluations, we used non-transformed human TM cells and perfused human anterior segments from post-mortem donors. For hypotonic shock, cells were exposed to 260 mOsm kg(-1) medium for 15 and 30 min. For DEX, cells were treated with 0.1 microm DEX for 1, 4 and 10 days. For elevated IOP, one eye of each pair of perfused human anterior segments was subjected to DeltaP 38+/-4 mm Hg for 1 hr, 4 and 7 days while the contralateral remained at baseline pressure as a control. ClCs transcripts were determined by relative quantitative RT-PCR. Our results showed that all transcripts but ClC-1 were detected in HTM cells. ClC-2 and ClC-3 were the most abundant and comprised about twice the amount of ClC-6 and ClC-7 and four times that of ClC-4 and ClC-5. Hypotonic conditions consistently up regulated CLCN2 and slightly up regulated CLCN3. After short periods of elevated pressure, ClC-2 and ClC-3 transcripts were increased but ClC-2 induction was significantly higher than that of ClC-3. In contrast, after long pressure insults (7 days), ClC-3 mRNA was significantly increased while CLCN2 was not changed. DEX treatment markedly down regulated CLCN3 and little, if any, reduced ClC-2. The extent of response of the CLCN2 and CLCN3 to these conditions was markedly affected by individual traits but at all times maintained the relative expression pattern of both genes. CLCN2 gene expression was predominantly influenced by cell volume regulation while that of CLCN3 was preferentially affected by conditions associated with TM pathology.
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Affiliation(s)
- Núria Comes
- Department of Ophthalmology, University of North Carolina School of Medicine, 6109 Neuroscience Research Building CB 7041, 103 Mason Farm Road, Chapel Hill, NC 27599-7041, USA
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McWilliams RR, Breusegem SY, Brodsky KF, Kim E, Levi M, Doctor RB. Shank2E binds NaP(i) cotransporter at the apical membrane of proximal tubule cells. Am J Physiol Cell Physiol 2005; 289:C1042-51. [PMID: 15917299 DOI: 10.1152/ajpcell.00568.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Proteins expressing postsynaptic density (PSD)-95/Drosophila disk large (Dlg)/zonula occludens-1 (ZO-1) (PDZ) domains are commonly involved in moderating receptor, channel, and transporter activities at the plasma membrane in a variety of cell types. At the apical membrane of renal proximal tubules (PT), the type IIa NaP(i) cotransporter (NaP(i)-IIa) binds specific PDZ domain proteins. Shank2E is a spliceoform of a family of PDZ proteins that is concentrated at the apical domain of liver and pancreatic epithelial cell types and is expressed in kidney. In the present study, immunoblotting of enriched plasma membrane fractions and immunohistology found Shank2E concentrated at the brush border membrane of rat PT cells. Confocal localization of Flag-Shank2E and enhanced green fluorescent protein-NaP(i)-IIa in cotransfected OK cells showed these proteins colocalized in the apical microvilli of this PT cell model. Shank2E co-immunoprecipitated with NaP(i)-IIa from rat renal cortex tissue and HA-NaP(i)-IIa coprecipitated with Flag-Shank2E in cotransfected human embryonic kidney HEK cells. Domain analysis showed that the PDZ domain of Shank2E specifically bound NaP(i)-IIa and truncation of the COOH-terminal TRL motif from NaP(i)-IIa abolished this binding, and Far Western blotting showed that the Shank2E- NaP(i)-IIa interaction occurred directly between the two proteins. NaP(i)-IIa activity is regulated by moderating its abundance in the apical membrane. High-P(i) conditions induce NaP(i)-IIa internalization and degradation. In both rat kidney PT cells and OK cells, shifting to high-P(i) conditions induced an acute internal redistribution of Shank2E and, in OK cells, a significant degree of degradation. In sum, Shank2E is concentrated in the apical domain of renal PT cells, specifically binds NaP(i)-IIa via PDZ interactions, and undergoes P(i)-induced internalization.
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Affiliation(s)
- Ryan R McWilliams
- Department of Medicine, University of Colorado Health Sciences Center, 4200 E. 9th St., Denver, Colorado 80262, USA
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Lan WZ, Abbas H, Lam HD, Lemay AM, Hill CE. Contribution of a time-dependent and hyperpolarization-activated chloride conductance to currents of resting and hypotonically shocked rat hepatocytes. Am J Physiol Gastrointest Liver Physiol 2005; 288:G221-9. [PMID: 15358597 DOI: 10.1152/ajpgi.00226.2004] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Hepatocellular Cl- flux is integral to maintaining cell volume and electroneutrality in the face of the many transport and metabolic activities that describe the multifaceted functions of these cells. Although a significant volume-regulated Cl- current (VRAC) has been well described in hepatocytes, the Cl- channels underlying the large resting anion conductance have not been identified. We used a combination of electrophysiological and molecular approaches to describe potential candidates for this conductance. Anion currents in rat hepatocytes and WIF-B and HEK293T cells were measured under patch electrode-voltage clamp. With K+-free salts of Cl- comprising the major ions externally and internally, hyperpolarizing steps between -40 and -140 mV activated a time-dependent inward current in hepatocytes. Steady-state activation was half-maximal at -63 mV and 28-38% of maximum at -30 to -45 mV, previously reported hepatocellular resting potentials. Gating was dependent on cytosolic Cl-, shifting close to 58 mV/10-fold change in Cl- concentration. Time-dependent inward Cl- currents and a ClC-2-specific RT-PCR product were also observed in WIF-B cells but not HEK293T cells. All cell types exhibited typical VRAC in response to dialysis with hypertonic solutions. DIDS (0.1 mM) inhibited the hepatocellular VRAC but not the inward time-dependent current. Antibodies against the COOH terminus of ClC-2 reacted with a protein between 90 and 100 kDa in liver plasma membranes. The results demonstrate that rat hepatocytes express a time-dependent inward Cl- channel that could provide a significant depolarizing influence in the hepatocyte.
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Affiliation(s)
- Wen-Zhi Lan
- Gastrointestinal Diseases Research Unit, Hotel Dieu Hospital, Queen's University, Kingston, Ontario, Canada
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Puljak L, Pagliassotti MJ, Wei Y, Qadri I, Parameswara V, Esser V, Fitz JG, Kilic G. Inhibition of cellular responses to insulin in a rat liver cell line. A role for PKC in insulin resistance. J Physiol 2005; 563:471-82. [PMID: 15649984 PMCID: PMC1665596 DOI: 10.1113/jphysiol.2004.080333] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The initial response of liver cells to insulin is mediated through exocytosis of Cl- channel-containing vesicles and a subsequent opening of plasma membrane Cl- channels. Intracellular accumulation of fatty acids leads to profound defects in metabolism, and is closely associated with insulin resistance. It is not known whether the activity of Cl- channels is altered in insulin resistance and by which mechanisms. We studied the effects of fatty acid accumulation on Cl- channel opening in a model liver cell line. Overnight treatment with amiodarone increased the fat content by approximately 2-fold, and the rates of gluconeogenesis by approximately 5-fold. The ability of insulin to suppress gluconeogenesis was markedly reduced indicating that amiodarone treatment induces insulin resistance. Western blot analysis showed that these cells express the same number of insulin receptors as control cells. However, insulin failed to activate exocytosis and Cl- channel opening. These inhibitory effects were mimicked in control cells by exposures to arachidonic acid (15 microm). Further studies demonstrated that fatty acids stimulate the PKC activity, and inhibition of PKC partially restored exocytosis and Cl- channel opening in insulin-resistant cells. Accordingly, activation of PKC with PMA in control cells potently inhibited the insulin responses. These results suggest that stimulation of PKC activity in insulin resistance contributes to the inhibition of cellular responses to insulin in liver cells.
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Affiliation(s)
- Livia Puljak
- Department of Internal Medicine, University of Texas South-western Medical Center, 5323 Harry Hines Blvd, Dallas, TX 75390-8887, USA
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Cuppoletti J, Malinowska DH, Tewari KP, Li QJ, Sherry AM, Patchen ML, Ueno R. SPI-0211 activates T84 cell chloride transport and recombinant human ClC-2 chloride currents. Am J Physiol Cell Physiol 2004; 287:C1173-83. [PMID: 15213059 DOI: 10.1152/ajpcell.00528.2003] [Citation(s) in RCA: 205] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
The purpose of this study was to determine the mechanism of action of SPI-0211 (lubiprostone), a novel bicyclic fatty acid in development for the treatment of bowel dysfunction. Adult rabbit intestine was shown to contain mRNA for ClC-2 using RT-PCR, Northern blot analysis, and in situ hybridization. T84 cells grown to confluence on permeable supports were shown to express ClC-2 channel protein in the apical membrane. SPI-0211 increased electrogenic Cl- transport across the apical membrane of T84 cells, with an EC50 of approximately 18 nM measured by short-circuit current (Isc) after permeabilization of the basolateral membrane with nystatin. SPI-0211 effects on Cl- currents were also measured by whole cell patch clamp using the human embryonic kidney (HEK)-293 cell line stably transfected with either recombinant human ClC-2 or recombinant human cystic fibrosis transmembrane regulator (CFTR). In these studies, SPI-0211 activated ClC-2 Cl- currents in a concentration-dependent manner, with an EC50 of approximately 17 nM, and had no effect in nontransfected HEK-293 cells. In contrast, SPI-0211 had no effect on CFTR Cl- channel currents measured in CFTR-transfected HEK-293 cells. Activation of ClC-2 by SPI-0211 was independent of PKA. Together, these studies demonstrate that SPI-0211 is a potent activator of ClC-2 Cl- channels and suggest a physiologically relevant role for ClC-2 Cl- channels in intestinal Cl- transport after SPI-0211 administration.
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Affiliation(s)
- John Cuppoletti
- Department of Molecular and Cellular Physiology, College of Medicine, University of Cincinnati, Cincinnati, Ohio 45267-0576, USA.
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Jin NG, Kim JK, Yang DK, Cho SJ, Kim JM, Koh EJ, Jung HC, So I, Kim KW. Fundamental role of ClC-3 in volume-sensitive Cl- channel function and cell volume regulation in AGS cells. Am J Physiol Gastrointest Liver Physiol 2003; 285:G938-48. [PMID: 12842831 DOI: 10.1152/ajpgi.00470.2002] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Volume regulation is essential for cell function, but it is unknown which channels are involved in a regulatory volume decrease (RVD) in human gastric epithelial cells. Exposure to a hypotonic solution caused the increase in AGS cell volume, followed by the activation of a current. The reversal potential of the swelling-induced current suggested that Cl- was the primary charge carrier. The selectivity sequence for different anions was I- > Br- > Cl- > F- > gluconate. This current was inhibited by flufenamate, DIDS, tamoxifen, and 5-nitro-2-(3-phenylpropylamino)benzoate. Intracellular dialysis of three different anti-ClC-3 antibodies abolished or attenuated the Cl- current and disrupted RVD, whereas the current and RVD was unaltered by anti-ClC-2 antibody. Immunoblot studies demonstrated the presence of ClC-3 protein in Hela and AGS cells. RT-PCR analysis detected expression of ClC-3, MDR-1, and pICln mRNA in AGS cells. These results suggest a fundamental role of endogenous ClC-3 in the swelling-activated Cl- channels function and cell volume regulation in human gastric epithelial cells.
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Affiliation(s)
- Nan Ge Jin
- Dept. of Physiology and Biophysics, Seoul National Univ. College of Medicine, 28 Yongon-Dong, Chongro-Gu, Seoul, Korea 110-799
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Spiegel S, Phillipper M, Rossmann H, Riederer B, Gregor M, Seidler U. Independence of apical Cl-/HCO3- exchange and anion conductance in duodenal HCO3- secretion. Am J Physiol Gastrointest Liver Physiol 2003; 285:G887-97. [PMID: 12842823 DOI: 10.1152/ajpgi.00083.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Reduced gastrointestinal HCO3- secretion contributes to malabsorption and obstructive syndromes in cystic fibrosis. The apical HCO3- transport pathways in these organs have not been defined. We therefore assessed the involvement of apical Cl-/HCO3- exchangers and anion conductances in basal and cAMP-stimulated duodenal HCO3- secretion. Muscle-stripped rat and rabbit proximal duodena were mounted in Ussing chambers, and electrical parameters, HCO3- secretion rates, and 36Cl-, 22Na+, and 3H+ mannitol fluxes were assessed. mRNA expression levels were measured by a quantitative PCR technique. Removal of Cl- from or addition of 1 mM DIDS to the luminal perfusate markedly decreased basal HCO3- secretion but did not influence the HCO3- secretory response to 8-bromo-cAMP, which was inhibited by luminal 5-nitro-2-(3-phenylpropylamino)-benzoate. Bidirectional 22Na+ and 36Cl- flux measurements demonstrated an inhibition rather than a stimulation of apical anion exchange during cAMP-stimulated HCO3- secretion. The ratio of Cl- to HCO3- in the anion secretory response was compatible with both Cl- and HCO3- being secreted via the CFTR anion channel. CFTR expression was very high in the duodenal mucosa of both species. We conclude that in rat and rabbit duodena, an apical Cl-/HCO3- exchanger mediates a significant part of basal HCO3- secretion but is not involved in the HCO3- secretory response to cAMP analogs. The inhibitor profile, the strong predominance of Cl- over HCO3- in the anion secretory response, and the high duodenal CFTR expression levels suggest that a major portion of cAMP-stimulated duodenal HCO3- secretion is directly mediated by CFTR.
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Affiliation(s)
- S Spiegel
- Zentrum Innere Medizin, Abteilung IV, der Medizinischen Hochschule Hannover, Carl-Neuberg Str. 1, 30625 Hannover, Germany
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Affiliation(s)
- Andrew P Feranchak
- Department of Pediatrics, Children's Hospital and the University of Colorado Health Sciences Center, Denver, CO 80262, USA.
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Abstract
Voltage-gated chloride channels have recently been implicated as being important for cell proliferation and invasive cell migration of primary brain tumors cells. In the present study we provide several lines of evidence that glioma Cl- currents are primarily mediated by ClC-2 and ClC-3, two genes that belong to the ClC superfamily. Transcripts for ClC-2 thru ClC-7 were detected in a human glioma cell line by PCR, whereas only ClC-2, ClC-3, and ClC-5 protein could be identified by Western blot. Prominent ClC-2, -3, and -5 channel expression was also detected in acute patient biopsies from low- and high-grade malignant gliomas. Immunogold electron microscopic studies as well as digital confocal imaging localized a portion of these ClC channels to the plasma membrane. Whole-cell patch-clamp recordings show the presence of two pharmacologically and biophysically distinct Cl- currents that could be specifically reduced by 48 hr exposure of cells to channel-specific antisense oligonucleotides. ClC-3 antisense selectively and significantly reduced the expression of outwardly rectifying current with pronounced voltage-dependent inactivation. Such currents were sensitive to DIDS (200-500 microm) and 5-nitro-2-(3-phenylpropylamino) benzoic acid (165 microm). ClC-2 antisense significantly reduced expression of inwardly rectifying currents, which were potentiated by hyperpolarizing prepulses and inhibited by Cd2+ (200-500 microm). Currents that were mediated by ClC-5 could not be demonstrated. We suggest that ClC-2 and ClC-3 channels are specifically upregulated in glioma membranes and endow glioma cells with an enhanced ability to transport Cl-. This may in turn facilitate rapid changes in cell size and shape as cells divide or invade through tortuous extracellular brain spaces.
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Zonia L, Feijó JA. State and spectral properties of chloride oscillations in pollen. Biophys J 2003; 84:1387-98. [PMID: 12547818 PMCID: PMC1302714 DOI: 10.1016/s0006-3495(03)74953-4] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2002] [Accepted: 09/27/2002] [Indexed: 12/15/2022] Open
Abstract
Pollen tube growth is a dynamic system expressing a number of oscillating circuits. Our recent work identified a new circuit, oscillatory efflux of Cl(-) anion from the pollen tube apex. Cl(-) efflux is the first ion signal found to be coupled in phase with growth oscillations. Functional analyses indicate an active role for Cl(-) flux in pollen tube growth. In this report the dynamical properties of Cl(-) efflux are examined. Phase space analysis demonstrates that the system trajectory converges on a limit cycle. Fourier analysis reveals that two harmonic frequencies characterize normal growth. Cl(-) efflux is inhibited by the channel blocker DIDS, is stimulated by hypoosmotic treatment, and is antagonized by the signal encoded in inositol 3,4,5,6-tetrakisphosphate. These perturbations induce transitions of the limit cycle to new metastable states or cause system collapse to a static attractor centered near the origin. These perturbations also transform the spectral profile, inducing subharmonic frequencies, transitions to period doubling and tripling, superharmonic resonance, and chaos. These results indicate that Cl(-) signals in pollen tubes display features that are characteristic of active oscillators that carry frequency-encoded information. A reaction network of the Cl(-) oscillator coupled to two nonlinear feedback circuits that may drive pollen tube growth oscillations is considered.
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Affiliation(s)
- Laura Zonia
- Institute of Experimental Botany, Academy of Sciences of the Czech Republic, Na Pernikarce 15, 160 00 Prague 6, Czech Republic.
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Abstract
Hepatocytes possess chloride channels at the plasma membrane and in multiple intracellular compartments. These channels are required for cell volume regulation and acidification of intracellular organelles. Evidence also supports a role of chloride channels in modulation of apoptosis and cell growth. Swelling- and Ca(2+)-activated chloride channels have been identified in hepatocyte plasma membranes, and chloride channels have been observed in the membranes of lysosomes, endosomes, Golgi, endoplasmic reticulum, mitochondria, and the nucleus. This review summarizes the functions of these channels and discusses the specific channel molecules they may represent. Chloride channel molecules shown to be expressed in hepatocytes include members of the ClC channel family (ClC-2, ClC-3, ClC-5, and ClC-7), members of the newly identified CLIC family of intracellular chloride channels (CLIC-1 and CLIC-4), the mitochondrial voltage-dependent anion channel, and a newly identified intracellular channel, MCLC (Mid-1 related chloride channel). Current understanding does not include a molecular identification of most of the observed channel functions, but details of the molecular properties of these channel molecules should allow future identification and further understanding of chloride channel function in hepatocytes.
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Affiliation(s)
- Xinhua Li
- Department of Physiology and Biophysics University of Texas Medical Branch, Galveston, Texas 77555-0641, USA.
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Kilic G, Fitz JG. Heterotrimeric G-proteins activate Cl- channels through stimulation of a cyclooxygenase-dependent pathway in a model liver cell line. J Biol Chem 2002; 277:11721-7. [PMID: 11812774 DOI: 10.1074/jbc.m108631200] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Circulating hormones produce rapid changes in the Cl(-) permeability of liver cells through activation of plasma membrane receptors coupled to heterotrimeric G-proteins. The resulting effects on intracellular pH, membrane potential, and Cl(-) content are important contributors to the overall metabolic response. Consequently, the purpose of these studies was to evaluate the mechanisms responsible for G-protein-mediated changes in membrane Cl(-) permeability using HTC hepatoma cells as a model. Using patch clamp techniques, intracellular dialysis with 0.3 mm guanosine 5'-O-(3-thiotriphosphate) (GTPgammaS) increased membrane conductance from 10 to 260 picosiemens/picofarads due to activation of Ca(2+)-dependent Cl(-) currents that were outwardly rectifying and exhibited slow activation at depolarizing potentials. These effects were mimicked by intracellular AlF(4)(-) (0.03 mm) and inhibited by pertussis toxin (PTX), consistent with current activation through Galpha(i). Studies using defined agonists and inhibitors indicate that Cl(-) channel activation by GTPgammaS occurs through an indomethacin-sensitive pathway involving sequential activation of phospholipase C, mobilization of Ca(2+) from inositol 1,4,5-trisphosphate-sensitive stores, and stimulation of phospholipase A(2) and cyclooxygenase (COX). Accordingly, the conductance responses to GTPgammaS or to intracellular Ca(2+) were inhibited by COX inhibitors. These results indicate that PTX-sensitive G-proteins regulate the Cl(-) permeability of HTC cells through Ca(2+)-dependent stimulation of COX activity. Thus, receptor-mediated activation of Galpha(i) may be essential for hormonal regulation of liver transport and metabolism through COX-dependent opening of a distinct population of plasma membrane Cl(-) channels.
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Affiliation(s)
- Gordan Kilic
- Department of Medicine, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
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Jentsch TJ, Stein V, Weinreich F, Zdebik AA. Molecular structure and physiological function of chloride channels. Physiol Rev 2002; 82:503-68. [PMID: 11917096 DOI: 10.1152/physrev.00029.2001] [Citation(s) in RCA: 934] [Impact Index Per Article: 42.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cl- channels reside both in the plasma membrane and in intracellular organelles. Their functions range from ion homeostasis to cell volume regulation, transepithelial transport, and regulation of electrical excitability. Their physiological roles are impressively illustrated by various inherited diseases and knock-out mouse models. Thus the loss of distinct Cl- channels leads to an impairment of transepithelial transport in cystic fibrosis and Bartter's syndrome, to increased muscle excitability in myotonia congenita, to reduced endosomal acidification and impaired endocytosis in Dent's disease, and to impaired extracellular acidification by osteoclasts and osteopetrosis. The disruption of several Cl- channels in mice results in blindness. Several classes of Cl- channels have not yet been identified at the molecular level. Three molecularly distinct Cl- channel families (CLC, CFTR, and ligand-gated GABA and glycine receptors) are well established. Mutagenesis and functional studies have yielded considerable insights into their structure and function. Recently, the detailed structure of bacterial CLC proteins was determined by X-ray analysis of three-dimensional crystals. Nonetheless, they are less well understood than cation channels and show remarkably different biophysical and structural properties. Other gene families (CLIC or CLCA) were also reported to encode Cl- channels but are less well characterized. This review focuses on molecularly identified Cl- channels and their physiological roles.
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Affiliation(s)
- Thomas J Jentsch
- Zentrum für Molekulare Neurobiologie Hamburg, Universität Hamburg, Hamburg, Germany.
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