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Jian L, Zhang Q, Yao D, Wang Q, Chen M, Xia Y, Li S, Shen Y, Cao M, Qin A, Li L, Cao Y. The structural insight into the functional modulation of human anion exchanger 3. Nat Commun 2024; 15:6134. [PMID: 39033175 PMCID: PMC11271275 DOI: 10.1038/s41467-024-50572-x] [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: 02/20/2024] [Accepted: 07/15/2024] [Indexed: 07/23/2024] Open
Abstract
Anion exchanger 3 (AE3) is pivotal in regulating intracellular pH across excitable tissues, yet its structural intricacies and functional dynamics remain underexplored compared to other anion exchangers. This study unveils the structural insights into human AE3, including the cryo-electron microscopy structures for AE3 transmembrane domains (TMD) and a chimera combining AE3 N-terminal domain (NTD) with AE2 TMD (hAE3NTD2TMD). Our analyzes reveal a substrate binding site, an NTD-TMD interlock mechanism, and a preference for an outward-facing conformation. Unlike AE2, which has more robust acid-loading capabilities, AE3's structure, including a less stable inward-facing conformation due to missing key NTD-TMD interactions, contributes to its moderated pH-modulating activity and increased sensitivity to the inhibitor DIDS. These structural differences underline AE3's distinct functional roles in specific tissues and underscore the complex interplay between structural dynamics and functional specificity within the anion exchanger family, enhancing our understanding of the physiological and pathological roles of the anion exchanger family.
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Affiliation(s)
- Liyan Jian
- Department of Orthopaedics, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - Qing Zhang
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
- Structural Biology Program, Memorial Sloan Kettering Cancer Center, 1275 York Avenue, New York, NY, USA
| | - Deqiang Yao
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
- Institute of Aging & Tissue Regeneration, Renji Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China
| | - Qian Wang
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - Moxin Chen
- Department of Ophthalmology, Shanghai Ninth People's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China
- Shanghai Key Laboratory of Orbital Diseases and Ocular Oncology, Shanghai, China
| | - Ying Xia
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - Shaobai Li
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - Yafeng Shen
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - Mi Cao
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China
| | - An Qin
- Department of Orthopaedics, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
- Department of Orthopaedics, Shanghai Frontiers Science Center of Degeneration and Regeneration in Skeletal System, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
| | - Lin Li
- Department of Ophthalmology, Shanghai Ninth People's Hospital, School of Medicine, Shanghai Jiao Tong University, Shanghai, China.
- Shanghai Key Laboratory of Orbital Diseases and Ocular Oncology, Shanghai, China.
| | - Yu Cao
- Department of Orthopaedics, Shanghai Key Laboratory of Orthopaedic Implant, Shanghai Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
- Institute of Precision Medicine, the Ninth People's Hospital, Shanghai Jiao Tong University School of Medicine, 115 Jinzun Road, Shanghai, China.
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Theparambil SM, Begum G, Rose CR. pH regulating mechanisms of astrocytes: A critical component in physiology and disease of the brain. Cell Calcium 2024; 120:102882. [PMID: 38631162 DOI: 10.1016/j.ceca.2024.102882] [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: 03/05/2024] [Revised: 03/28/2024] [Accepted: 03/28/2024] [Indexed: 04/19/2024]
Abstract
Strict homeostatic control of pH in both intra- and extracellular compartments of the brain is fundamentally important, primarily due to the profound impact of free protons ([H+]) on neuronal activity and overall brain function. Astrocytes, crucial players in the homeostasis of various ions in the brain, actively regulate their intracellular [H+] (pHi) through multiple membrane transporters and carbonic anhydrases. The activation of astroglial pHi regulating mechanisms also leads to corresponding alterations in the acid-base status of the extracellular fluid. Notably, astrocyte pH regulators are modulated by various neuronal signals, suggesting their pivotal role in regulating brain acid-base balance in both health and disease. This review presents the mechanisms involved in pH regulation in astrocytes and discusses their potential impact on extracellular pH under physiological conditions and in brain disorders. Targeting astrocytic pH regulatory mechanisms represents a promising therapeutic approach for modulating brain acid-base balance in diseases, offering a potential critical contribution to neuroprotection.
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Affiliation(s)
- Shefeeq M Theparambil
- Faculty of Health and Medicine, Department of Biomedical and Life Sciences, Lancaster University, Lancaster, LA1 4YW, Lancaster, UK.
| | - Gulnaz Begum
- Department of Neurology, The Pittsburgh Institute for Neurodegenerative Diseases, University of Pittsburgh, Pittsburgh, PA, USA
| | - Christine R Rose
- Institute of Neurobiology, Faculty of Mathematics and Natural Sciences, Heinrich Heine University Düsseldorf, 40225, Düsseldorf, Germany
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Zhou C, Hu B, Tang Y, Chen X, Ma Z, Ding Q, Nie G. Genome-wide characterization of the Triplophysa dalaica slc4 gene family and expression profiles in response to salinity changes. BMC Genomics 2022; 23:824. [PMID: 36513970 PMCID: PMC9746111 DOI: 10.1186/s12864-022-09057-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Accepted: 11/29/2022] [Indexed: 12/15/2022] Open
Abstract
BACKGROUND The solute carrier 4 (SLC4) gene family is involved in a variety of physiological processes in organisms and is essential for maintaining acid-base balance in the body. The slc4 genes have been extensively studied in mammals, and they play important roles in intracellular and extracellular pH regulation and in the secretion and uptake of HCO3- and other ions (Na+ and Cl-) between transepithelial cells in different tissues. This study identified and characterized the entire slc4 gene family of Triplophysa dalaica. RESULTS Fifteen slc4 genes were identified in the whole genome of Triplophysa dalaica in this study, including five copies of Na+-independent Cl-/HCO3- transporters, eight members of Na+-dependent HCO3- transporters, and two genes coding Na+-coupled borate transporters. The chromosomal location information, isoelectric points, and molecular weights of the 15 slc4 genes were analyzed. The results for gene structure, domain analysis, and phylogenetic relationships of this gene family showed that the slc4 genes (except for slc4a9, which is missing in teleosts) are significantly expanded in teleosts compared to higher vertebrates. This phenomenon suggests that the slc4 gene family played an important role in the transition from aquatic to terrestrial animals. RT-PCR results showed that different slc4 genes showed diversified expression patterns in the tissues of T. dalaica. For osmotic pressure regulating organs, slc4a1b, slc4a4b, slc4a7, and slc4a11a were highly expressed in gills. In the kidney, slc4a1a, slc4a3, and slc4a10b were highly expressed, suggesting that the slc4 genes play a specific role in the salinity adaptation of T. dalaica. Our study has deciphered the biological roles of the slc4 genes in maintaining ionic and acid-base homeostasis in teleost fishes and provides a foundation for future exploration of the highly differentiated gene family in Triplophysa. CONCLUSIONS The results are relevant for the breeding of alkali-tolerant varieties in saline-alkali areas for aquaculture. Our findings have important implications for the adaptation process of freshwater species to saline-alkali water.
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Affiliation(s)
- Chuanjiang Zhou
- grid.462338.80000 0004 0605 6769College of Life Sciences, Henan Normal University, Xinxiang, 453007 People’s Republic of China
| | - Bo Hu
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
| | - Yongtao Tang
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
| | - Xin Chen
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
| | - Zhigang Ma
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
| | - Qiqi Ding
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
| | - Guoxing Nie
- grid.462338.80000 0004 0605 6769College of Fisheries, Engineering Technology Research Center of Henan Province for Aquatic Animal Cultivation, Henan Normal University, Xinxiang, Henan 453007 People’s Republic of China
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Chloride Channels and Transporters: Roles beyond Classical Cellular Homeostatic pH or Ion Balance in Cancers. Cancers (Basel) 2022; 14:cancers14040856. [PMID: 35205604 PMCID: PMC8870652 DOI: 10.3390/cancers14040856] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2021] [Revised: 01/28/2022] [Accepted: 02/06/2022] [Indexed: 01/04/2023] Open
Abstract
Simple Summary Roles of chloride-associated transporters have been raised in various cancers. Although complicated ion movements, crosstalk among channels/transporters through homeostatic electric regulation, difficulties with experimental implementation such as activity measurement of intracellular location were disturbed to verify the precise modulation of channels/transporters, recently defined cancerous function and communication with tumor microenvironment of chloride channels/transporters should be highlighted beyond classical homeostatic ion balance. Chloride-associated transporters as membrane-associated components of chloride movement, regulations of transmembrane member 16A, calcium-activated chloride channel regulators, transmembrane member 206, chloride intracellular channels, voltage-gated chloride channels, cystic fibrosis transmembrane conductance regulator, voltage-dependent anion channel, volume-regulated anion channel, and chloride-bicarbonate exchangers are discussed. Abstract The canonical roles of chloride channels and chloride-associated transporters have been physiologically determined; these roles include the maintenance of membrane potential, pH balance, and volume regulation and subsequent cellular functions such as autophagy and cellular proliferative processes. However, chloride channels/transporters also play other roles, beyond these classical function, in cancerous tissues and under specific conditions. Here, we focused on the chloride channel-associated cancers and present recent advances in understanding the environments of various types of cancer caused by the participation of many chloride channel or transporters families and discuss the challenges and potential targets for cancer treatment. The modulation of chloride channels/transporters might promote new aspect of cancer treatment strategies.
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Jennings ML. Cell Physiology and Molecular Mechanism of Anion Transport by Erythrocyte Band 3/AE1. Am J Physiol Cell Physiol 2021; 321:C1028-C1059. [PMID: 34669510 PMCID: PMC8714990 DOI: 10.1152/ajpcell.00275.2021] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The major transmembrane protein of the red blood cell, known as band 3, AE1, and SLC4A1, has two main functions: 1) catalysis of Cl-/HCO3- exchange, one of the steps in CO2 excretion; 2) anchoring the membrane skeleton. This review summarizes the 150 year history of research on red cell anion transport and band 3 as an experimental system for studying membrane protein structure and ion transport mechanisms. Important early findings were that red cell Cl- transport is a tightly coupled 1:1 exchange and band 3 is labeled by stilbenesulfonate derivatives that inhibit anion transport. Biochemical studies showed that the protein is dimeric or tetrameric (paired dimers) and that there is one stilbenedisulfonate binding site per subunit of the dimer. Transport kinetics and inhibitor characteristics supported the idea that the transporter acts by an alternating access mechanism with intrinsic asymmetry. The sequence of band 3 cDNA provided a framework for detailed study of protein topology and amino acid residues important for transport. The identification of genetic variants produced insights into the roles of band 3 in red cell abnormalities and distal renal tubular acidosis. The publication of the membrane domain crystal structure made it possible to propose concrete molecular models of transport. Future research directions include improving our understanding of the transport mechanism at the molecular level and of the integrative relationships among band 3, hemoglobin, carbonic anhydrase, and gradients (both transmembrane and subcellular) of HCO3-, Cl-, O2, CO2, pH, and NO metabolites during pulmonary and systemic capillary gas exchange.
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Affiliation(s)
- Michael L Jennings
- Department of Physiology and Cell Biology, University of Arkansas for Medical Sciences, Little Rock, Arkansas, United States
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Engels M, Kalia M, Rahmati S, Petersilie L, Kovermann P, van Putten MJAM, Rose CR, Meijer HGE, Gensch T, Fahlke C. Glial Chloride Homeostasis Under Transient Ischemic Stress. Front Cell Neurosci 2021; 15:735300. [PMID: 34602981 PMCID: PMC8481871 DOI: 10.3389/fncel.2021.735300] [Citation(s) in RCA: 21] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Accepted: 08/23/2021] [Indexed: 12/17/2022] Open
Abstract
High water permeabilities permit rapid adjustments of glial volume upon changes in external and internal osmolarity, and pathologically altered intracellular chloride concentrations ([Cl–]int) and glial cell swelling are often assumed to represent early events in ischemia, infections, or traumatic brain injury. Experimental data for glial [Cl–]int are lacking for most brain regions, under normal as well as under pathological conditions. We measured [Cl–]int in hippocampal and neocortical astrocytes and in hippocampal radial glia-like (RGL) cells in acute murine brain slices using fluorescence lifetime imaging microscopy with the chloride-sensitive dye MQAE at room temperature. We observed substantial heterogeneity in baseline [Cl–]int, ranging from 14.0 ± 2.0 mM in neocortical astrocytes to 28.4 ± 3.0 mM in dentate gyrus astrocytes. Chloride accumulation by the Na+-K+-2Cl– cotransporter (NKCC1) and chloride outward transport (efflux) through K+-Cl– cotransporters (KCC1 and KCC3) or excitatory amino acid transporter (EAAT) anion channels control [Cl–]int to variable extent in distinct brain regions. In hippocampal astrocytes, blocking NKCC1 decreased [Cl–]int, whereas KCC or EAAT anion channel inhibition had little effect. In contrast, neocortical astrocytic or RGL [Cl–]int was very sensitive to block of chloride outward transport, but not to NKCC1 inhibition. Mathematical modeling demonstrated that higher numbers of NKCC1 and KCC transporters can account for lower [Cl–]int in neocortical than in hippocampal astrocytes. Energy depletion mimicking ischemia for up to 10 min did not result in pronounced changes in [Cl–]int in any of the tested glial cell types. However, [Cl–]int changes occurred under ischemic conditions after blocking selected anion transporters. We conclude that stimulated chloride accumulation and chloride efflux compensate for each other and prevent glial swelling under transient energy deprivation.
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Affiliation(s)
- Miriam Engels
- Institute of Biological Information Processing, Molekular-und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Manu Kalia
- Applied Analysis, Department of Applied Mathematics, University of Twente, Enschede, Netherlands.,Institute of Neurobiology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Sarah Rahmati
- Institute of Biological Information Processing, Molekular-und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Laura Petersilie
- Institute of Neurobiology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Peter Kovermann
- Institute of Biological Information Processing, Molekular-und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | | | - Christine R Rose
- Institute of Neurobiology, Heinrich Heine University Düsseldorf, Düsseldorf, Germany
| | - Hil G E Meijer
- Applied Analysis, Department of Applied Mathematics, University of Twente, Enschede, Netherlands
| | - Thomas Gensch
- Institute of Biological Information Processing, Molekular-und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
| | - Christoph Fahlke
- Institute of Biological Information Processing, Molekular-und Zellphysiologie (IBI-1), Forschungszentrum Jülich, Jülich, Germany
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7
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Abstract
Our brains consist of 80% water, which is continuously shifted between different compartments and cell types during physiological and pathophysiological processes. Disturbances in brain water homeostasis occur with pathologies such as brain oedema and hydrocephalus, in which fluid accumulation leads to elevated intracranial pressure. Targeted pharmacological treatments do not exist for these conditions owing to our incomplete understanding of the molecular mechanisms governing brain water transport. Historically, the transmembrane movement of brain water was assumed to occur as passive movement of water along the osmotic gradient, greatly accelerated by water channels termed aquaporins. Although aquaporins govern the majority of fluid handling in the kidney, they do not suffice to explain the overall brain water movement: either they are not present in the membranes across which water flows or they appear not to be required for the observed flow of water. Notably, brain fluid can be secreted against an osmotic gradient, suggesting that conventional osmotic water flow may not describe all transmembrane fluid transport in the brain. The cotransport of water is an unconventional molecular mechanism that is introduced in this Review as a missing link to bridge the gap in our understanding of cellular and barrier brain water transport.
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Affiliation(s)
- Nanna MacAulay
- Department of Neuroscience, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
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8
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Auer T, Schreppel P, Erker T, Schwarzer C. Impaired chloride homeostasis in epilepsy: Molecular basis, impact on treatment, and current treatment approaches. Pharmacol Ther 2020; 205:107422. [DOI: 10.1016/j.pharmthera.2019.107422] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2019] [Accepted: 10/07/2019] [Indexed: 12/14/2022]
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9
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Shiozaki A, Hikami S, Ichikawa D, Kosuga T, Shimizu H, Kudou M, Yamazato Y, Kobayashi T, Shoda K, Arita T, Konishi H, Komatsu S, Kubota T, Fujiwara H, Okamoto K, Kishimoto M, Konishi E, Marunaka Y, Otsuji E. Anion exchanger 2 suppresses cellular movement and has prognostic significance in esophageal squamous cell carcinoma. Oncotarget 2018; 9:25993-26006. [PMID: 29899837 PMCID: PMC5995252 DOI: 10.18632/oncotarget.25417] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 04/28/2018] [Indexed: 01/01/2023] Open
Abstract
Background Recent studies have reported essential roles for various intracellular pH regulators in epithelial carcinogenesis and tumor progression. The aims of the present study were to investigate the role of anion exchanger 2 (AE2) in the regulation of tumor progression-related genes and the prognostic value of its expression in esophageal squamous cell carcinoma (ESCC). Results AE2 was strongly expressed in KYSE170 and TE13 cells. The depletion of AE2 in these cells increased cell migration and inhibited the induction of apoptosis. The results of the microarray analysis revealed that various matrix metalloproteinase (MMP) signaling pathway-related genes, such as MMP1, MMP12, and TIMP4, were up- or down-regulated in AE2-depleted KYSE170 cells. Immunohistochemical staining showed that AE2 was primarily located in the cell membranes or cytoplasm of carcinoma cells, and its expression pattern at the invasive front of the tumor was related to the pT category. Prognostic analyses revealed that the low-grade expression of AE2 at the invasive front was associated with shorter postoperative survival. Conclusions The results of the present study suggest that reductions in AE2 in ESCC enhance cellular movement by activating MMP signaling pathways and are related to a poor prognosis in patients with ESCC. Methods In human ESCC cell lines, knockdown experiments were conducted using AE2 siRNA, and the effects on cellular movement and survival were analyzed. The gene expression profiles of cells were examined using a microarray analysis. An immunohistochemical analysis was performed on 61 primary tumor samples obtained from ESCC patients who underwent esophagectomy.
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Affiliation(s)
- Atsushi Shiozaki
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Shoichiro Hikami
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Daisuke Ichikawa
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.,Department of Gastrointestinal, Breast and Endocrine Surgery, Faculty of Medicine, University of Yamanashi, Chuo 409-3898, Japan
| | - Toshiyuki Kosuga
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Hiroki Shimizu
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Michihiro Kudou
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Yuzo Yamazato
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Toshiyuki Kobayashi
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Katsutoshi Shoda
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Tomohiro Arita
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Hirotaka Konishi
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Shuhei Komatsu
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Takeshi Kubota
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Hitoshi Fujiwara
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Kazuma Okamoto
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Mitsuo Kishimoto
- Department of Pathology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Eiichi Konishi
- Department of Pathology, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
| | - Yoshinori Marunaka
- Departments of Molecular Cell Physiology and Bio-Ionomics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan.,Japan Institute for Food Education and Health, St. Agnes' University, Kyoto 602-8013, Japan
| | - Eigo Otsuji
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto 602-8566, Japan
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Pérez-Rodríguez MJ, Velazquez-Lagunas I, Pluma-Pluma A, Barragán-Iglesias P, Granados-Soto V. Anion exchanger 3 in dorsal root ganglion contributes to nerve injury-induced chronic mechanical allodynia and thermal hyperalgesia. J Pharm Pharmacol 2018; 70:374-382. [DOI: 10.1111/jphp.12868] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2017] [Accepted: 11/25/2017] [Indexed: 12/21/2022]
Abstract
Abstract
Objective
To determine the role of anion exchanger 3 (AE3) in dorsal root ganglion (DRG) in nerve injury-induced chronic nociception in the rat.
Methods
Spared nerve injury (SNI) was used to induce neuropathic pain. Von Frey filaments and Hargreaves test were used to assess tactile allodynia and thermal hyperalgesia, respectively. Drugs were given by intrathecal administration. Western blotting was used to determine AE3 expression in DRG.
Key findings
SNI produced long-lasting mechanical allodynia and thermal hyperalgesia. AE3 was found in DRG of sham-operated rats. SNI enhanced baseline AE3 expression in L4 and L5 DRGs at days 7 and 14, respectively. In contrast, SNI did not affect AE3 expression in L6 DRG. AE3 expression returned to baseline levels 21 days after SNI. Intrathecal 4,4′-diisothiocyanatostilbene-2,2′-disulfonic acid (DIDS) (5–50 μg) pretreatment prevented SNI-induced allodynia and, at a lesser extent, hyperalgesia. Moreover, DIDS (50 μg) reduced SNI-induced AE3 upregulation in L4, but not L5, DRGs. Intrathecal DIDS (5–50 μg) or anti-AE3 antibody (1 μg), but not vehicle, post-treatment (6 days) partially reversed SNI-induced allodynia and hyperalgesia. DIDS or anti-AE3 antibody post-treatment diminished SNI-induced AE3 upregulation in L4 and L5 DRGs.
Conclusions
Data suggest that AE3 is present in DRG and contributes to mechanical allodynia and thermal hyperalgesia in neuropathic rats.
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Affiliation(s)
- Marian J Pérez-Rodríguez
- Neurobiology of Pain Laboratory, Departamento de Farmacobiología, Cinvestav, Unidad Coapa, Ciudad de México, Mexico
| | - Isabel Velazquez-Lagunas
- Neurobiology of Pain Laboratory, Departamento de Farmacobiología, Cinvestav, Unidad Coapa, Ciudad de México, Mexico
| | - Alejandro Pluma-Pluma
- Neurobiology of Pain Laboratory, Departamento de Farmacobiología, Cinvestav, Unidad Coapa, Ciudad de México, Mexico
| | - Paulino Barragán-Iglesias
- Neurobiology of Pain Laboratory, Departamento de Farmacobiología, Cinvestav, Unidad Coapa, Ciudad de México, Mexico
- School of Behavioral and Brain Sciences, University of Texas at Dallas, Dallas, TX, USA
| | - Vinicio Granados-Soto
- Neurobiology of Pain Laboratory, Departamento de Farmacobiología, Cinvestav, Unidad Coapa, Ciudad de México, Mexico
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11
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Aoki T. A Comprehensive Review of Our Current Understanding of Red Blood Cell (RBC) Glycoproteins. MEMBRANES 2017; 7:membranes7040056. [PMID: 28961212 PMCID: PMC5746815 DOI: 10.3390/membranes7040056] [Citation(s) in RCA: 42] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 09/20/2017] [Accepted: 09/24/2017] [Indexed: 12/11/2022]
Abstract
Human red blood cells (RBC), which are the cells most commonly used in the study of biological membranes, have some glycoproteins in their cell membrane. These membrane proteins are band 3 and glycophorins A-D, and some substoichiometric glycoproteins (e.g., CD44, CD47, Lu, Kell, Duffy). The oligosaccharide that band 3 contains has one N-linked oligosaccharide, and glycophorins possess mostly O-linked oligosaccharides. The end of the O-linked oligosaccharide is linked to sialic acid. In humans, this sialic acid is N-acetylneuraminic acid (NeuAc). Another sialic acid, N-glycolylneuraminic acid (NeuGc) is present in red blood cells of non-human origin. While the biological function of band 3 is well known as an anion exchanger, it has been suggested that the oligosaccharide of band 3 does not affect the anion transport function. Although band 3 has been studied in detail, the physiological functions of glycophorins remain unclear. This review mainly describes the sialo-oligosaccharide structures of band 3 and glycophorins, followed by a discussion of the physiological functions that have been reported in the literature to date. Moreover, other glycoproteins in red blood cell membranes of non-human origin are described, and the physiological function of glycophorin in carp red blood cell membranes is discussed with respect to its bacteriostatic activity.
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Affiliation(s)
- Takahiko Aoki
- Laboratory of Quality in Marine Products, Graduate School of Bioresources, Mie University, 1577 Kurima Machiya-cho, Mie, Tsu 514-8507, Japan.
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Shiozaki A, Kudou M, Ichikawa D, Shimizu H, Arita T, Kosuga T, Konishi H, Komatsu S, Fujiwara H, Okamoto K, Kishimoto M, Marunaka Y, Otsuji E. Expression and role of anion exchanger 1 in esophageal squamous cell carcinoma. Oncotarget 2017; 8:17921-17935. [PMID: 28160546 PMCID: PMC5392297 DOI: 10.18632/oncotarget.14900] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2016] [Accepted: 01/04/2017] [Indexed: 01/20/2023] Open
Abstract
Recent studies have described important roles for the anion exchanger (AE) in epithelial carcinogenesis and tumor behavior. The objectives of the present study were to investigate the role of AE1 in the regulation of genes involved in tumor progression and the clinicopathological significance of its expression in esophageal squamous cell carcinoma (ESCC). An immunohistochemical analysis was performed on 61 primary tumor samples obtained from ESCC patients who underwent esophagectomy. AE1 was primarily located in the cell membranes or cytoplasm of carcinoma cells, and its distribution pattern was related to the histological degree of the differentiation of SCC or the pT category. Among patients with pT2-3 ESCC, the 5-year survival rate of patients with diffuse AE1 expression (40.2%) was significantly lower than that of patients with focal expression (74.0%). AE1 was strongly expressed in KYSE150 and TE8 human ESCC cells. The depletion of AE1 using siRNA inhibited cell proliferation, migration, and invasion and induced apoptosis. The results of the microarray analysis revealed that MAPK and Hedgehog signaling pathway-related genes, such as DHH, and GLI1, were down-regulated in AE1-depleted KYSE150 cells. In conclusions, the results of the present study suggest that the diffuse expression of AE1 is related to a worse prognosis in patients with advanced ESCC, and that it regulates tumor progression by affecting MAPK and Hedgehog signaling pathways. These results provide an insight into the role of AE1 as a mediator of and/or a biomarker for ESCC.
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Affiliation(s)
- Atsushi Shiozaki
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Michihiro Kudou
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Daisuke Ichikawa
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Hiroki Shimizu
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Tomohiro Arita
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Toshiyuki Kosuga
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Hirotaka Konishi
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Shuhei Komatsu
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Hitoshi Fujiwara
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Kazuma Okamoto
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Mitsuo Kishimoto
- Department of Pathology, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
| | - Yoshinori Marunaka
- Department of Molecular Cell Physiology and Bio-Ionomics, Graduate School of Medical Science, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan.,Japan Institute for Food Education and Health, St. Agnes' University, Kyoto, 602-8013, Japan
| | - Eigo Otsuji
- Division of Digestive Surgery, Department of Surgery, Kyoto Prefectural University of Medicine, Kyoto, 602-8566, Japan
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Vairamani K, Wang HS, Medvedovic M, Lorenz JN, Shull GE. RNA SEQ Analysis Indicates that the AE3 Cl -/HCO 3- Exchanger Contributes to Active Transport-Mediated CO 2 Disposal in Heart. Sci Rep 2017; 7:7264. [PMID: 28779178 PMCID: PMC5544674 DOI: 10.1038/s41598-017-07585-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2017] [Accepted: 06/29/2017] [Indexed: 02/06/2023] Open
Abstract
Loss of the AE3 Cl−/HCO3− exchanger (Slc4a3) in mice causes an impaired cardiac force-frequency response and heart failure under some conditions but the mechanisms are not known. To better understand the functions of AE3, we performed RNA Seq analysis of AE3-null and wild-type mouse hearts and evaluated the data with respect to three hypotheses (CO2 disposal, facilitation of Na+-loading, and recovery from an alkaline load) that have been proposed for its physiological functions. Gene Ontology and PubMatrix analyses of differentially expressed genes revealed a hypoxia response and changes in vasodilation and angiogenesis genes that strongly support the CO2 disposal hypothesis. Differential expression of energy metabolism genes, which indicated increased glucose utilization and decreased fatty acid utilization, were consistent with adaptive responses to perturbations of O2/CO2 balance in AE3-null myocytes. Given that the myocardium is an obligate aerobic tissue and consumes large amounts of O2, the data suggest that loss of AE3, which has the potential to extrude CO2 in the form of HCO3−, impairs O2/CO2 balance in cardiac myocytes. These results support a model in which the AE3 Cl−/HCO3− exchanger, coupled with parallel Cl− and H+-extrusion mechanisms and extracellular carbonic anhydrase, is responsible for active transport-mediated disposal of CO2.
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Affiliation(s)
- Kanimozhi Vairamani
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, 45267, USA
| | - Hong-Sheng Wang
- Department of Pharmacology and Cell Biophysics, University of Cincinnati College of Medicine, Cincinnati, Ohio, 45267, USA
| | - Mario Medvedovic
- Department of Environmental Health, University of Cincinnati College of Medicine, Cincinnati, Ohio, 45267, USA
| | - John N Lorenz
- Department of Cellular and Molecular Physiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, 45267, USA
| | - Gary E Shull
- Department of Molecular Genetics, Biochemistry and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio, 45267, USA.
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14
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Salameh AI, Hübner CA, Boron WF. Role of Cl - -HCO 3- exchanger AE3 in intracellular pH homeostasis in cultured murine hippocampal neurons, and in crosstalk to adjacent astrocytes. J Physiol 2016; 595:93-124. [PMID: 27353306 DOI: 10.1113/jp272470] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/20/2016] [Accepted: 06/20/2016] [Indexed: 12/11/2022] Open
Abstract
KEY POINTS A polymorphism of human AE3 is associated with idiopathic generalized epilepsy. Knockout of AE3 in mice lowers the threshold for triggering epileptic seizures. The explanations for these effects are elusive. Comparisons of cells from wild-type vs. AE3-/- mice show that AE3 (present in hippocampal neurons, not astrocytes; mediates HCO3- efflux) enhances intracellular pH (pHi ) recovery (decrease) from alkali loads in neurons and, surprisingly, adjacent astrocytes. During metabolic acidosis (MAc), AE3 speeds initial acidification, but limits the extent of pHi decrease in neurons and astrocytes. AE3 speeds re-alkalization after removal of MAc in neurons and astrocytes, and speeds neuronal pHi recovery from an ammonium prepulse-induced acid load. We propose that neuronal AE3 indirectly increases acid extrusion in (a) neurons via Cl- loading, and (b) astrocytes by somehow enhancing NBCe1 (major acid extruder). The latter would enhance depolarization-induced alkalinization of astrocytes, and extracellular acidification, and thereby reduce susceptibility to epileptic seizures. ABSTRACT The anion exchanger AE3, expressed in hippocampal (HC) neurons but not astrocytes, contributes to intracellular pH (pHi ) regulation by facilitating the exchange of extracellular Cl- for intracellular HCO3- . The human AE3 polymorphism A867D is associated with idiopathic generalized epilepsy. Moreover, AE3 knockout (AE3-/- ) mice are more susceptible to epileptic seizure. The mechanism of these effects has been unclear because the starting pHi in AE3-/- and wild-type neurons is indistinguishable. The purpose of the present study was to use AE3-/- mice to investigate the role of AE3 in pHi homeostasis in HC neurons, co-cultured with astrocytes. We find that the presence of AE3 increases the acidification rate constant during pHi recovery from intracellular alkaline loads imposed by reducing [CO2 ]. The presence of AE3 also speeds intracellular acidification during the early phase of metabolic acidosis (MAc), not just in neurons but, surprisingly, in adjacent astrocytes. Additionally, AE3 contributes to braking the decrease in pHi later during MAc in both neurons and astrocytes. Paradoxically, AE3 enhances intracellular re-alkalization after MAc removal in neurons and astrocytes, and pHi recovery from an ammonium prepulse-induced acid load in neurons. The effects of AE3 knockout on astrocytic pHi homeostasis in MAc-related assays require the presence of neurons, and are consistent with the hypothesis that the AE3 knockout reduces functional expression of astrocytic NBCe1. These findings suggest a new type of neuron-astrocyte communication, based on the expression of AE3 in neurons, which could explain how AE3 reduces seizure susceptibility.
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Affiliation(s)
- Ahlam I Salameh
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
| | | | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH, 44106, USA
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15
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Downs LM, Webster AR, Moore AT, Michaelides M, Ali RR, Hardcastle AJ, Mellersh CS. Investigation of SLA4A3 as a candidate gene for human retinal disease. J Negat Results Biomed 2016; 15:11. [PMID: 27211793 PMCID: PMC4876561 DOI: 10.1186/s12952-016-0054-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2016] [Accepted: 04/14/2016] [Indexed: 11/10/2022] Open
Abstract
SLC4A3 has been shown to cause retinal degeneration in a genetically engineered knockout mouse, and in a naturally occurring form of canine progressive retinal atrophy considered to be the equivalent of retinitis pigmentosa in humans (RP). This study was undertaken to investigate if SLC4A3 coding variants were implicated in human retinal degeneration. SLC4A3 exons were amplified and sequenced in 200 patients with autosomal recessive retinal degeneration who had no known molecular diagnosis for their condition, which included 197 unrelated individuals with suspected RP and three individuals with other forms of retinal disease. Three rare variants were identified that were predicted to be potentially pathogenic, however each variant was heterozygous in a single patient and therefore not considered disease-causing in isolation. Of these three variants, SNP-3 was the rarest, with an allele frequency of 7.06 x 10(-5) (>46,000 exomes from the ExAC database). In conclusion, no compound heterozygous or homozygous potentially pathogenic variants were identified that would account for recessive RP or retinal degeneration in this cohort, however the possibility remains that the rare variants identified could be acting with as yet undiscovered mutations in introns or regulatory regions. SLC4A3 remains an excellent candidate gene for human retinal degeneration, and with the advent of whole exome and whole genome sequencing of cohorts of molecularly unsolved patients with syndromic and non-syndromic forms of retinal degeneration, SLC4A3 may yet be implicated in human disease.
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Affiliation(s)
- Louise M Downs
- Kennel Club Genetics Centre, Animal Health Trust, Newmarket, UK. .,Present Address: Department of Clinical Studies, School of Veterinary Medicine, University of Pennsylvania, Philadelphia, USA.
| | - Andrew R Webster
- UCL Institute of Ophthalmology, London, UK.,Moorfields Eye Hospital, City Road, London, UK
| | - Anthony T Moore
- UCL Institute of Ophthalmology, London, UK.,Moorfields Eye Hospital, City Road, London, UK
| | - Michel Michaelides
- UCL Institute of Ophthalmology, London, UK.,Moorfields Eye Hospital, City Road, London, UK
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16
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Hosoya M, Fujioka M, Kobayashi R, Okano H, Ogawa K. Overlapping expression of anion exchangers in the cochlea of a non-human primate suggests functional compensation. Neurosci Res 2016; 110:1-10. [PMID: 27091614 DOI: 10.1016/j.neures.2016.04.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 03/27/2016] [Accepted: 04/05/2016] [Indexed: 11/19/2022]
Abstract
Ion homeostasis in the inner ear is essential for proper hearing. Anion exchangers are one of the transporters responsible for the maintenance of homeostasis, but their expression profile in the primate cochlea has not been fully characterized. However, species-specific overlapping expression patterns and functional compensation in other organs, such as the kidney, pancreas and small intestine, have been reported. Here, we determined the expression patterns of the anion exchangers SLC26A4, SLC26A5, SLC26A6, SLC26A7, SLC26A11, SLC4A2 and SLC4A3 in the cochlea of a non-human primate, the common marmoset (Callithrix jacchus). Although the pattern of expression of SLC26A4 and SLC26A5 was similar to that in rodents, SLC26A7, SLC4A2, SLC4A3 exhibited different distributions. Notably, five transporters, SLC26A4, SLC26A6, SLC26A11 SLC4A2 and SLC4A3, were expressed in the cells of the outer sulcus. Our results reveal a species-specific distribution pattern of anion exchangers in the cochlea, particularly in the outer sulcus cells, suggesting functional compensation among these exchangers. This "primate-specific" pattern may be related to the human-specific hearing loss phenotypes of channelopathy disorders, including the SLC26A4-related diseases Pendred syndrome/DFNB4.
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Affiliation(s)
- Makoto Hosoya
- Keio University School of Medicine, Department of Otorhinolaryngology, Head and Neck Surgery, 35 Shinanomachi, Shinjuku-ku 160-8582, Japan
| | - Masato Fujioka
- Keio University School of Medicine, Department of Otorhinolaryngology, Head and Neck Surgery, 35 Shinanomachi, Shinjuku-ku 160-8582, Japan.
| | - Reona Kobayashi
- Keio University School of Medicine, Department of Physiology, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Hideyuki Okano
- Keio University School of Medicine, Department of Physiology, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Kaoru Ogawa
- Keio University School of Medicine, Department of Otorhinolaryngology, Head and Neck Surgery, 35 Shinanomachi, Shinjuku-ku 160-8582, Japan
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17
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Arakawa T, Kobayashi-Yurugi T, Alguel Y, Iwanari H, Hatae H, Iwata M, Abe Y, Hino T, Ikeda-Suno C, Kuma H, Kang D, Murata T, Hamakubo T, Cameron AD, Kobayashi T, Hamasaki N, Iwata S. Crystal structure of the anion exchanger domain of human erythrocyte band 3. Science 2015; 350:680-4. [PMID: 26542571 DOI: 10.1126/science.aaa4335] [Citation(s) in RCA: 175] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Anion exchanger 1 (AE1), also known as band 3 or SLC4A1, plays a key role in the removal of carbon dioxide from tissues by facilitating the exchange of chloride and bicarbonate across the plasma membrane of erythrocytes. An isoform of AE1 is also present in the kidney. Specific mutations in human AE1 cause several types of hereditary hemolytic anemias and/or distal renal tubular acidosis. Here we report the crystal structure of the band 3 anion exchanger domain (AE1(CTD)) at 3.5 angstroms. The structure is locked in an outward-facing open conformation by an inhibitor. Comparing this structure with a substrate-bound structure of the uracil transporter UraA in an inward-facing conformation allowed us to identify the anion-binding position in the AE1(CTD), and to propose a possible transport mechanism that could explain why selected mutations lead to disease.
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Affiliation(s)
- Takatoshi Arakawa
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. JST, Research Acceleration Program, Membrane Protein Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Takami Kobayashi-Yurugi
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Yilmaz Alguel
- Division of Molecular Biosciences, Membrane Protein Crystallography group, Imperial College London, London SW7 2AZ, UK. Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Chilton, Oxfordshire OX11 0DE, UK. Research Complex at Harwell Rutherford, Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0FA, UK
| | - Hiroko Iwanari
- Department of Quantitative Biology and Medicine, Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Hinako Hatae
- Faculty of Pharmaceutical Sciences, Nagasaki International University, 2825-7 Huis Ten Bosch-cho, Sasebo, Nagasaki 859-3298, Japan
| | - Momi Iwata
- Division of Molecular Biosciences, Membrane Protein Crystallography group, Imperial College London, London SW7 2AZ, UK. Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Chilton, Oxfordshire OX11 0DE, UK
| | - Yoshito Abe
- Department of Protein Structure, Function and Design, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Tomoya Hino
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Chiyo Ikeda-Suno
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. JST, Research Acceleration Program, Membrane Protein Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Hiroyuki Kuma
- Faculty of Pharmaceutical Sciences, Nagasaki International University, 2825-7 Huis Ten Bosch-cho, Sasebo, Nagasaki 859-3298, Japan
| | - Dongchon Kang
- Department of Clinical Chemistry and Laboratory Medicine, Graduate School of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan
| | - Takeshi Murata
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Chemistry, Graduate School of Science, Chiba University, 1-33 Yayoi-cho, Inage, Chiba 263-8522, Japan
| | - Takao Hamakubo
- Department of Quantitative Biology and Medicine, Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8904, Japan
| | - Alexander D Cameron
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Division of Molecular Biosciences, Membrane Protein Crystallography group, Imperial College London, London SW7 2AZ, UK. Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Chilton, Oxfordshire OX11 0DE, UK. Research Complex at Harwell Rutherford, Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0FA, UK. School of Life Sciences, University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, UK
| | - Takuya Kobayashi
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. JST, Research Acceleration Program, Membrane Protein Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Platform for Drug Discovery, Informatics, and Structural Life Science, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
| | - Naotaka Hamasaki
- Faculty of Pharmaceutical Sciences, Nagasaki International University, 2825-7 Huis Ten Bosch-cho, Sasebo, Nagasaki 859-3298, Japan
| | - So Iwata
- Japan Science and Technology Agency (JST), Exploratory Research for Advanced Technology (ERATO) Human Receptor Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. JST, Research Acceleration Program, Membrane Protein Crystallography Project, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Department of Cell Biology, Kyoto University Faculty of Medicine, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan. Division of Molecular Biosciences, Membrane Protein Crystallography group, Imperial College London, London SW7 2AZ, UK. Membrane Protein Laboratory, Diamond Light Source, Harwell Science and Innovation Campus, Didcot, Chilton, Oxfordshire OX11 0DE, UK. Research Complex at Harwell Rutherford, Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0FA, UK. Platform for Drug Discovery, Informatics, and Structural Life Science, Konoe-cho, Yoshida, Sakyo-ku, Kyoto 606-8501, Japan
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18
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Chloride Cotransporters as a Molecular Mechanism underlying Spreading Depolarization-Induced Dendritic Beading. J Neurosci 2015; 35:12172-87. [PMID: 26338328 DOI: 10.1523/jneurosci.0400-15.2015] [Citation(s) in RCA: 64] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
UNLABELLED Spreading depolarizations (SDs) are waves of sustained neuronal and glial depolarization that propagate massive disruptions of ion gradients through the brain. SD is associated with migraine aura and recently recognized as a novel mechanism of injury in stroke and brain trauma patients. SD leads to neuronal swelling as assessed in real time with two-photon laser scanning microscopy (2PLSM). Pyramidal neurons do not express aquaporins and thus display low inherent water permeability, yet SD rapidly induces focal swelling (beading) along the dendritic shaft by unidentified molecular mechanisms. To address this issue, we induced SD in murine hippocampal slices by focal KCl microinjection and visualized the ensuing beading of dendrites expressing EGFP by 2PLSM. We confirmed that dendritic beading failed to arise during large (100 mOsm) hyposmotic challenges, underscoring that neuronal swelling does not occur as a simple osmotic event. SD-induced dendritic beading was not prevented by pharmacological interference with the cytoskeleton, supporting the notion that dendritic beading may result entirely from excessive water influx. Dendritic beading was strictly dependent on the presence of Cl(-), and, accordingly, combined blockade of Cl(-)-coupled transporters led to a significant reduction in dendritic beading without interfering with SD. Furthermore, our in vivo data showed a strong inhibition of dendritic beading during pharmacological blockage of these cotransporters. We propose that SD-induced dendritic beading takes place as a consequence of the altered driving forces and thus activity for these cotransporters, which by transport of water during their translocation mechanism may generate dendritic beading independently of osmotic forces. SIGNIFICANCE STATEMENT Spreading depolarization occurs during pathological conditions such as stroke, brain injury, and migraine and is characterized as a wave of massive ion translocation between intracellular and extracellular space in association with recurrent transient focal swelling (beading) of dendrites. Numerous ion channels have been demonstrated to be involved in generation and propagation of spreading depolarization, but the molecular machinery responsible for the dendritic beading has remained elusive. Using real-time in vitro and in vivo two-photon laser scanning microscopy, we have identified the transport mechanisms involved in the detrimental focal swelling of dendrites. These findings have clear clinical significance because they may point to a new class of pharmacological targets for prevention of neuronal swelling that consequently will serve as neuroprotective agents.
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19
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Theparambil SM, Naoshin Z, Thyssen A, Deitmer JW. Reversed electrogenic sodium bicarbonate cotransporter 1 is the major acid loader during recovery from cytosolic alkalosis in mouse cortical astrocytes. J Physiol 2015; 593:3533-47. [PMID: 25990710 DOI: 10.1113/jp270086] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 05/17/2015] [Indexed: 12/29/2022] Open
Abstract
KEY POINTS The regulation of H(+) i from cytosolic alkalosis has generally been attributed to the activity of Cl(-) -coupled acid loaders/base extruders in most cell types, including brain cells. The present study demonstrates that outwardly-directed sodium bicarbonate cotransport via electrogenic sodium bicarbonate cotransporter 1 (NBCe1) mediates the major fraction of H(+) i regulation from cytosolic alkalosis in mouse cortical astrocytes. Cl(-) -coupled acid-loading transporters play only a minor role in the regulation of H(+) i from alkalosis in mouse cortical astrocytes. NBCe1-mediated H(+) i regulation from alkalosis was dominant, with the support of intracellular carbonic anhydrase II, even when the intra- and extracellular [HCO3 (-) ] was very low (<1mM), as in nominally CO2 /HCO3 (-) free condition. A reversed NBCe1 in astrocytes may also be significant for stabilizing extracellular pH in brain tissue. ABSTRACT Recovery of intracellular pH from cytosolic alkalosis has been attributed primarily to Cl(-) coupled acid loaders/base extruders such as Cl(-) /HCO3 (-) or Cl(-) /OH(-) exchangers. We have studied this process in cortical astrocytes from wild-type and transgenic mouse models with gene deletion for the electrogenic sodium bicarbonate cotransporter 1 (NBCe1) and for carbonic anhydrase (CA) isoform II. An acute cytosolic alkalosis was induced by the removal of either CO2 /HCO3 (-) or butyric acid, and the subsequent acid loading was analysed by monitoring changes in cytosolic H(+) or Na(+) using ion-sensitive fluorescent dyes. We have identified that NBCe1 reverses during alkalosis and contributes more than 70% to the rate of recovery from alkalosis by extruding Na(+) and HCO3 (-) . After CA inhibition or in CAII-knockout (KO) cells, the rate of recovery was reduced by 40%, and even by 70% in the nominal absence of CO2 /HCO3 (-) . Increasing the extracellular K(+) concentration modulated the rate of acid loading in wild-type cells, but not in NBCe1-KO cells. Removing chloride had only a minor effect on the recovery from alkalosis. Reversal of NBCe1 by reducing pH/[HCO3 (-) ] was demonstrated in astrocytes and in Xenopus oocytes, in which human NBCe1 was heterologously expressed. The results obtained suggest that reversed NBCe1, supported by CAII activity, plays a major role in acid-loading cortical astrocytes to support recovery from cytosolic alkalosis.
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Affiliation(s)
- Shefeeq M Theparambil
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Zinnia Naoshin
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Anne Thyssen
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
| | - Joachim W Deitmer
- Department of General Zoology, Faculty of Biology, University of Kaiserslautern, Kaiserslautern, Germany
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20
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Chloride Accumulators NKCC1 and AE2 in Mouse GnRH Neurons: Implications for GABAA Mediated Excitation. PLoS One 2015; 10:e0131076. [PMID: 26110920 PMCID: PMC4482508 DOI: 10.1371/journal.pone.0131076] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2015] [Accepted: 05/28/2015] [Indexed: 11/30/2022] Open
Abstract
A developmental “switch” in chloride transporters occurs in most neurons resulting in GABAA mediated hyperpolarization in the adult. However, several neuronal cell subtypes maintain primarily depolarizing responses to GABAA receptor activation. Among this group are gonadotropin-releasing hormone-1 (GnRH) neurons, which control puberty and reproduction. NKCC1 is the primary chloride accumulator in neurons, expressed at high levels early in development and contributes to depolarization after GABAA receptor activation. In contrast, KCC2 is the primary chloride extruder in neurons, expressed at high levels in the adult and contributes to hyperpolarization after GABAA receptor activation. Anion exchangers (AEs) are also potential modulators of responses to GABAA activation since they accumulate chloride and extrude bicarbonate. To evaluate the mechanism(s) underlying GABAA mediated depolarization, GnRH neurons were analyzed for 1) expression of chloride transporters and AEs in embryonic, pre-pubertal, and adult mice 2) responses to GABAA receptor activation in NKCC1-/- mice and 3) function of AEs in these responses. At all ages, GnRH neurons were immunopositive for NKCC1 and AE2 but not KCC2 or AE3. Using explants, calcium imaging and gramicidin perforated patch clamp techniques we found that GnRH neurons from NKCC1-/- mice retained relatively normal responses to the GABAA agonist muscimol. However, acute pharmacological inhibition of NKCC1 with bumetanide eliminated the depolarization/calcium response to muscimol in 40% of GnRH neurons from WT mice. In the remaining GnRH neurons, HCO3- mediated mechanisms accounted for the remaining calcium responses to muscimol. Collectively these data reveal mechanisms responsible for maintaining depolarizing GABAA mediated transmission in GnRH neurons.
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Occhipinti R, Boron WF. Mathematical modeling of acid-base physiology. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2015; 117:43-58. [PMID: 25617697 PMCID: PMC4666298 DOI: 10.1016/j.pbiomolbio.2015.01.003] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 01/05/2015] [Accepted: 01/12/2015] [Indexed: 01/22/2023]
Abstract
pH is one of the most important parameters in life, influencing virtually every biological process at the cellular, tissue, and whole-body level. Thus, for cells, it is critical to regulate intracellular pH (pHi) and, for multicellular organisms, to regulate extracellular pH (pHo). pHi regulation depends on the opposing actions of plasma-membrane transporters that tend to increase pHi, and others that tend to decrease pHi. In addition, passive fluxes of uncharged species (e.g., CO2, NH3) and charged species (e.g., HCO3(-), [Formula: see text] ) perturb pHi. These movements not only influence one another, but also perturb the equilibria of a multitude of intracellular and extracellular buffers. Thus, even at the level of a single cell, perturbations in acid-base reactions, diffusion, and transport are so complex that it is impossible to understand them without a quantitative model. Here we summarize some mathematical models developed to shed light onto the complex interconnected events triggered by acids-base movements. We then describe a mathematical model of a spherical cells-which to our knowledge is the first one capable of handling a multitude of buffer reactions-that our team has recently developed to simulate changes in pHi and pHo caused by movements of acid-base equivalents across the plasma membrane of a Xenopus oocyte. Finally, we extend our work to a consideration of the effects of simultaneous CO2 and HCO3(-) influx into a cell, and envision how future models might extend to other cell types (e.g., erythrocytes) or tissues (e.g., renal proximal-tubule epithelium) important for whole-body pH homeostasis.
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Affiliation(s)
- Rossana Occhipinti
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA.
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA; Department of Medicine, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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22
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Alka K, Casey JR. Bicarbonate transport in health and disease. IUBMB Life 2014; 66:596-615. [PMID: 25270914 DOI: 10.1002/iub.1315] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2014] [Accepted: 09/10/2014] [Indexed: 12/28/2022]
Abstract
Bicarbonate (HCO3(-)) has a central place in human physiology as the waste product of mitochondrial energy production and for its role in pH buffering throughout the body. Because bicarbonate is impermeable to membranes, bicarbonate transport proteins are necessary to enable control of bicarbonate levels across membranes. In humans, 14 bicarbonate transport proteins, members of the SLC4 and SLC26 families, function by differing transport mechanisms. In addition, some anion channels and ZIP metal transporters contribute to bicarbonate movement across membranes. Defective bicarbonate transport leads to diseases, including systemic acidosis, brain dysfunction, kidney stones, and hypertension. Altered expression levels of bicarbonate transporters in patients with breast, colon, and lung cancer suggest an important role of these transporters in cancer.
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Affiliation(s)
- Kumari Alka
- Department of Biochemistry, University of Alberta, Edmonton, AB, Canada
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23
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Wang HS, Chen Y, Vairamani K, Shull GE. Critical role of bicarbonate and bicarbonate transporters in cardiac function. World J Biol Chem 2014; 5:334-345. [PMID: 25225601 PMCID: PMC4160527 DOI: 10.4331/wjbc.v5.i3.334] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/01/2014] [Revised: 03/06/2014] [Accepted: 05/19/2014] [Indexed: 02/05/2023] Open
Abstract
Bicarbonate is one of the major anions in mammalian tissues and extracellular fluids. Along with accompanying H+, HCO3- is generated from CO2 and H2O, either spontaneously or via the catalytic activity of carbonic anhydrase. It serves as a component of the major buffer system, thereby playing a critical role in pH homeostasis. Bicarbonate can also be utilized by a variety of ion transporters, often working in coupled systems, to transport other ions and organic substrates across cell membranes. The functions of HCO3- and HCO3--transporters in epithelial tissues have been studied extensively, but their functions in heart are less well understood. Here we review studies of the identities and physiological functions of Cl-/HCO3- exchangers and Na+/HCO3- cotransporters of the SLC4A and SLC26A families in heart. We also present RNA Seq analysis of their cardiac mRNA expression levels. These studies indicate that slc4a3 (AE3) is the major Cl-/HCO3- exchanger and plays a protective role in heart failure, and that Slc4a4 (NBCe1) is the major Na+/HCO3- cotransporter and affects action potential duration. In addition, previous studies show that HCO3- has a positive inotropic effect in the perfused heart that is largely independent of effects on intracellular Ca2+. The importance of HCO3- in the regulation of contractility is supported by experiments showing that isolated cardiomyocytes exhibit sharply enhanced contractility, with no change in Ca2+ transients, when switched from Hepes-buffered to HCO3-- buffered solutions. These studies demonstrate that HCO3- and HCO3--handling proteins play important roles in the regulation of cardiac function.
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Ruffin VA, Salameh AI, Boron WF, Parker MD. Intracellular pH regulation by acid-base transporters in mammalian neurons. Front Physiol 2014; 5:43. [PMID: 24592239 PMCID: PMC3923155 DOI: 10.3389/fphys.2014.00043] [Citation(s) in RCA: 112] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2013] [Accepted: 01/23/2014] [Indexed: 12/22/2022] Open
Abstract
Intracellular pH (pHi) regulation in the brain is important in both physiological and physiopathological conditions because changes in pHi generally result in altered neuronal excitability. In this review, we will cover 4 major areas: (1) The effect of pHi on cellular processes in the brain, including channel activity and neuronal excitability. (2) pHi homeostasis and how it is determined by the balance between rates of acid loading (JL) and extrusion (JE). The balance between JE and JL determine steady-state pHi, as well as the ability of the cell to defend pHi in the face of extracellular acid-base disturbances (e.g., metabolic acidosis). (3) The properties and importance of members of the SLC4 and SLC9 families of acid-base transporters expressed in the brain that contribute to JL (namely the Cl-HCO3 exchanger AE3) and JE (the Na-H exchangers NHE1, NHE3, and NHE5 as well as the Na+- coupled HCO3− transporters NBCe1, NBCn1, NDCBE, and NBCn2). (4) The effect of acid-base disturbances on neuronal function and the roles of acid-base transporters in defending neuronal pHi under physiopathologic conditions.
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Affiliation(s)
- Vernon A Ruffin
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Ahlam I Salameh
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Walter F Boron
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
| | - Mark D Parker
- Department of Physiology and Biophysics, Case Western Reserve University OH, USA
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25
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Cordat E, Reithmeier RA. Structure, Function, and Trafficking of SLC4 and SLC26 Anion Transporters. CURRENT TOPICS IN MEMBRANES 2014; 73:1-67. [DOI: 10.1016/b978-0-12-800223-0.00001-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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26
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Hübner CA, Holthoff K. Anion transport and GABA signaling. Front Cell Neurosci 2013; 7:177. [PMID: 24187533 PMCID: PMC3807543 DOI: 10.3389/fncel.2013.00177] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2013] [Accepted: 09/21/2013] [Indexed: 12/02/2022] Open
Abstract
Whereas activation of GABAA receptors by GABA usually results in a hyperpolarizing influx of chloride into the neuron, the reversed chloride driving force in the immature nervous system results in a depolarizing efflux of chloride. This GABAergic depolarization is deemed to be important for the maturation of the neuronal network. The concept of a developmental GABA switch has mainly been derived from in vitro experiments and reliable in vivo evidence is still missing. As GABAA receptors are permeable for both chloride and bicarbonate, the net effect of GABA also critically depends on the distribution of bicarbonate. Whereas chloride can either mediate depolarizing or hyperpolarizing currents, bicarbonate invariably mediates a depolarizing current under physiological conditions. Intracellular bicarbonate is quickly replenished by cytosolic carbonic anhydrases. Intracellular bicarbonate levels also depend on different bicarbonate transporters expressed by neurons. The expression of these proteins is not only developmentally regulated but also differs between cell types and even subcellular regions. In this review we will summarize current knowledge about the role of some of these transporters for brain development and brain function.
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Affiliation(s)
- Christian A Hübner
- Institute of Human Genetics, Jena University Hospital, Friedrich Schiller University Jena Jena, Germany
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27
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Romero MF, Chen AP, Parker MD, Boron WF. The SLC4 family of bicarbonate (HCO₃⁻) transporters. Mol Aspects Med 2013; 34:159-82. [PMID: 23506864 DOI: 10.1016/j.mam.2012.10.008] [Citation(s) in RCA: 239] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2012] [Accepted: 08/28/2012] [Indexed: 01/13/2023]
Abstract
The SLC4 family consists of 10 genes (SLC4A1-5; SLC4A7-11). All encode integral membrane proteins with very similar hydropathy plots-consistent with 10-14 transmembrane segments. Nine SLC4 members encode proteins that transport HCO3(-) (or a related species, such as CO3(2-)) across the plasma membrane. Functionally, eight of these proteins fall into two major groups: three Cl-HCO3 exchangers (AE1-3) and five Na(+)-coupled HCO3(-) transporters (NBCe1, NBCe2, NBCn1, NBCn2, NDCBE). Two of the Na(+)-coupled transporters (NBCe1, NBCe2) are electrogenic; the other three Na(+)-coupled HCO3(-) transporters and all three AEs are electroneutral. In addition, two other SLC4 members (AE4, SLC4A9 and BTR1, SLC4A11) do not yet have a firmly established function. Most, though not all, SLC4 members are functionally inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS). SLC4 proteins play important roles many modes of acid-base homeostasis: the carriage of CO2 by erythrocytes, the transport of H(+) or HCO3(-) by several epithelia, as well as the regulation of cell volume and intracellular pH.
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Affiliation(s)
- Michael F Romero
- Physiology & Biomedical Engineering, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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28
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Parker MD, Boron WF. The divergence, actions, roles, and relatives of sodium-coupled bicarbonate transporters. Physiol Rev 2013; 93:803-959. [PMID: 23589833 PMCID: PMC3768104 DOI: 10.1152/physrev.00023.2012] [Citation(s) in RCA: 197] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The mammalian Slc4 (Solute carrier 4) family of transporters is a functionally diverse group of 10 multi-spanning membrane proteins that includes three Cl-HCO3 exchangers (AE1-3), five Na(+)-coupled HCO3(-) transporters (NCBTs), and two other unusual members (AE4, BTR1). In this review, we mainly focus on the five mammalian NCBTs-NBCe1, NBCe2, NBCn1, NDCBE, and NBCn2. Each plays a specialized role in maintaining intracellular pH and, by contributing to the movement of HCO3(-) across epithelia, in maintaining whole-body pH and otherwise contributing to epithelial transport. Disruptions involving NCBT genes are linked to blindness, deafness, proximal renal tubular acidosis, mental retardation, and epilepsy. We also review AE1-3, AE4, and BTR1, addressing their relevance to the study of NCBTs. This review draws together recent advances in our understanding of the phylogenetic origins and physiological relevance of NCBTs and their progenitors. Underlying these advances is progress in such diverse disciplines as physiology, molecular biology, genetics, immunocytochemistry, proteomics, and structural biology. This review highlights the key similarities and differences between individual NCBTs and the genes that encode them and also clarifies the sometimes confusing NCBT nomenclature.
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Affiliation(s)
- Mark D Parker
- Dept. of Physiology and Biophysics, Case Western Reserve University School of Medicine, 10900 Euclid Ave., Cleveland, OH 44106-4970, USA.
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29
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Zhao W, Ji X, Zhang F, Li L, Ma L. Embryonic stem cell markers. Molecules 2012; 17:6196-236. [PMID: 22634835 PMCID: PMC6268870 DOI: 10.3390/molecules17066196] [Citation(s) in RCA: 123] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2012] [Revised: 03/31/2012] [Accepted: 05/04/2012] [Indexed: 02/07/2023] Open
Abstract
Embryonic stem cell (ESC) markers are molecules specifically expressed in ES cells. Understanding of the functions of these markers is critical for characterization and elucidation for the mechanism of ESC pluripotent maintenance and self-renewal, therefore helping to accelerate the clinical application of ES cells. Unfortunately, different cell types can share single or sometimes multiple markers; thus the main obstacle in the clinical application of ESC is to purify ES cells from other types of cells, especially tumor cells. Currently, the marker-based flow cytometry (FCM) technique and magnetic cell sorting (MACS) are the most effective cell isolating methods, and a detailed maker list will help to initially identify, as well as isolate ESCs using these methods. In the current review, we discuss a wide range of cell surface and generic molecular markers that are indicative of the undifferentiated ESCs. Other types of molecules, such as lectins and peptides, which bind to ESC via affinity and specificity, are also summarized. In addition, we review several markers that overlap with tumor stem cells (TSCs), which suggest that uncertainty still exists regarding the benefits of using these markers alone or in various combinations when identifying and isolating cells.
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Affiliation(s)
- Wenxiu Zhao
- Life Science Division, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; (W.Z.); (X.J.); (F.Z.); (L.L.)
| | - Xiang Ji
- Life Science Division, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; (W.Z.); (X.J.); (F.Z.); (L.L.)
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China
| | - Fangfang Zhang
- Life Science Division, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; (W.Z.); (X.J.); (F.Z.); (L.L.)
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China
| | - Liang Li
- Life Science Division, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; (W.Z.); (X.J.); (F.Z.); (L.L.)
- Department of Biological Sciences and Biotechnology, Tsinghua University, Beijing 100084, China
| | - Lan Ma
- Life Science Division, Graduate School at Shenzhen, Tsinghua University, Shenzhen 518055, China; (W.Z.); (X.J.); (F.Z.); (L.L.)
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Effects of acute hypoxia/acidosis on intracellular pH in differentiating neural progenitor cells. Brain Res 2012; 1461:10-23. [PMID: 22608071 DOI: 10.1016/j.brainres.2012.04.043] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Revised: 03/26/2012] [Accepted: 04/20/2012] [Indexed: 01/19/2023]
Abstract
The response of differentiating mouse neural progenitor cells, migrating out from neurospheres, to conditions simulating ischemia (hypoxia and extracellular or intracellular acidosis) was studied. We show here, by using BCECF and single cell imaging to monitor intracellular pH (pH(i)), that two main populations can be distinguished by exposing migrating neural progenitor cells to low extracellular pH or by performing an acidifying ammonium prepulse. The cells dominating at the periphery of the neurosphere culture, which were positive for neuron specific markers MAP-2, calbindin and NeuN had lower initial resting pH(i) and could also easily be further acidified by lowering the extracellular pH. Moreover, in this population, a more profound acidification was seen when the cells were acidified using the ammonium prepulse technique. However, when the cell population was exposed to depolarizing potassium concentrations no alterations in pH(i) took place in this population. In contrast, depolarization caused an increase in pH(i) (by 0.5 pH units) in the cell population closer to the neurosphere body, which region was positive for the radial cell marker (GLAST). This cell population, having higher resting pH(i) (pH 6.9-7.1) also responded to acute hypoxia. During hypoxic treatment the resting pH(i) decreased by 0.1 pH units and recovered rapidly after reoxygenation. Our results show that migrating neural progenitor cells are highly sensitive to extracellular acidosis and that irreversible damage becomes evident at pH 6.2. Moreover, our results show that a response to acidosis clearly distinguishes two individual cell populations probably representing neuronal and radial cells.
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Abstract
SLC4A gene family proteins include bicarbonate transporters that move HCO(3)(-) across the plasma membrane and regulate intracellular pH and transepithelial movement of acid-base equivalents. These transporters are Cl/HCO(3) exchangers, electrogenic Na/HCO(3) cotransporters, electroneutral Na/HCO(3) cotransporters, and Na(+)-driven Cl/HCO(3) exchanger. Studies of the bicarbonate transporters in vitro and in vivo have demonstrated their physiological importance for acid-base homeostasis at the cellular and systemic levels. Recent advances in structure/function analysis have also provided valuable information on domains or motifs critical for regulation, ion translocation, and protein topology. This chapter focuses on the molecular mechanisms of ion transport along with associated structural aspects from mutagenesis of particular residues and from chimeric constructs. Structure/function studies have helped to understand the mechanism by which ion substrates are moved via the transporters. This chapter also describes some insights into the structure of SLC4A1 (AE1) and SLC4A4 (NBCe1) transporters. Finally, as some SLC4A transporters exist in concert with other proteins in the cells, the structural features associated with protein-protein interactions are briefly discussed.
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Affiliation(s)
- Inyeong Choi
- Department of Physiology, Emory University, Atlanta, Georgia, USA.
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Involvement of carboxyl groups in chloride transport and reversible DIDS binding to band 3 protein in human erythrocytes. Cell Mol Biol Lett 2011; 16:342-58. [PMID: 21442446 PMCID: PMC6275994 DOI: 10.2478/s11658-011-0010-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2011] [Accepted: 03/11/2011] [Indexed: 11/24/2022] Open
Abstract
Noncovalent DIDS binding to Band 3 (AE1) protein in human erythrocyte membranes, modified by non-penetrating, water soluble 1-ethyl-3-(4-azonia-4,4-dimethylpentyl)-carbodiimide iodide (EAC), was studied at 0°C in the presence of 165 mM KCl. Under experimental conditions applied up to (48 ± 5) % of irreversible chloride self-exchange inhibition was observed. The apparent dissociation constant, KD, for “DIDS-Band 3” complex, determined from the chloride transport experiments, was (34 ± 3) nM and (80 ± 12) nM for control and EAC-treated resealed ghosts, respectively. The inhibition constant, Ki, for DIDS was (35 ± 6) nM and (60 ± 8) nM in control and EAC-treated ghosts, respectively. The reduced affinity for DIDS reversible binding was not a result of negative cooperativity of DIDS binding sites of Band 3 oligomer since Hill’s coefficients were indistinguishable from 1 (within the limit error) both for control and EAC-treated ghosts. By using tritium-labeled DIDS, 4,4’-diisothiocyanato-2,2’-stilbenedisulfonate ([3H]DIDS), the association rate constant, k+1 (M−1s−1), was measured. The mean values of (4.3 ± 0.7) × 105 M−1s−1 for control and (2.7 ± 0.7) × 105 M−1s−1 for EAC-treated ghosts were obtained. The mean values for KD, evaluated from [3H]DIDS binding measurements, were (37 ± 9) nM and (90 ± 21) nM for control and EAC-modified ghosts, respectively. The results demonstrate that EAC modification of AE1 reduces about 2-fold the affinity of AE1 for DIDS. It is suggested that half of the subunits are modified near the transport site by EAC.
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33
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Roussa E. Channels and transporters in salivary glands. Cell Tissue Res 2010; 343:263-87. [PMID: 21120532 DOI: 10.1007/s00441-010-1089-y] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2010] [Accepted: 11/03/2010] [Indexed: 01/04/2023]
Abstract
According to the two-stage hypothesis, primary saliva, a NaCl-rich plasma-like isotonic fluid is secreted by salivary acinar cells and its ionic composition becomes modified in the duct system. The ducts secrete K(+) and HCO (3) (-) and reabsorb Na(+) and Cl(-) without any water movement, thus establishing a hypotonic final saliva. Salivary secretion depends on the coordinated action of several channels and transporters localized in the apical and basolateral membrane of acinar and duct cells. Early functional studies in perfused glands, followed by the molecular cloning of several transport proteins and the subsequent analysis of mutant mice, have greatly contributed to our understanding of salivary fluid and the electrolyte secretion process. With a few exceptions, most of the key channels and transporters involved in salivary secretion have now been identified and characterized. However, the picture that has emerged from all these studies is one of a complex molecular network characterized by redundancy for several transport proteins, compensatory mechanisms, and adaptive changes in health and disease. Current research is directed to the molecular interactions between the determinants and the ways in which they are regulated by extracellular signals and intracellular mediators. This review focuses on the functionally and molecularly best-characterized channels and transporters that are considered to be involved in transepithelial fluid and electrolyte transport in salivary glands.
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Affiliation(s)
- Eleni Roussa
- Anatomy and Cell Biology II, Department of Molecular Embryology, Albert Ludwigs University Freiburg, 79104, Freiburg i. Br., Germany.
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34
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Makuc D, Albrecht M, Plavec J. Conformational changes of functionalised indole receptors upon their interaction with anions. Supramol Chem 2010. [DOI: 10.1080/10610278.2010.506544] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Damjan Makuc
- a National Institute of Chemistry, Slovenian NMR Centre , Ljubljana, Slovenia
- b EN–FIST Centre of Excellence , Ljubljana, Slovenia
| | | | - Janez Plavec
- a National Institute of Chemistry, Slovenian NMR Centre , Ljubljana, Slovenia
- b EN–FIST Centre of Excellence , Ljubljana, Slovenia
- d Faculty of Chemistry and Chemical Technology, University of Ljubljana , Ljubljana, Slovenia
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Piermarini PM, Grogan LF, Lau K, Wang L, Beyenbach KW. A SLC4-like anion exchanger from renal tubules of the mosquito (Aedes aegypti): evidence for a novel role of stellate cells in diuretic fluid secretion. Am J Physiol Regul Integr Comp Physiol 2009; 298:R642-60. [PMID: 20042685 DOI: 10.1152/ajpregu.00729.2009] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transepithelial fluid secretion across the renal (Malpighian) tubule epithelium of the mosquito (Aedes aegypti) is energized by the vacuolar-type (V-type) H(+)-ATPase and not the Na(+)-K(+)-ATPase. Located at the apical membrane of principal cells, the V-type H(+)-ATPase translocates protons from the cytoplasm to the tubule lumen. Secreted protons are likely to derive from metabolic H(2)CO(3), which raises questions about the handling of HCO(3)(-) by principal cells. Accordingly, we tested the hypothesis that a Cl/HCO(3) anion exchanger (AE) related to the solute-linked carrier 4 (SLC4) superfamily mediates the extrusion of HCO(3)(-) across the basal membrane of principal cells. We began by cloning from Aedes Malpighian tubules a full-length cDNA encoding an SLC4-like AE, termed AeAE. When expressed heterologously in Xenopus oocytes, AeAE is both N- and O-glycosylated and mediates Na(+)-independent intracellular pH changes that are sensitive to extracellular Cl(-) concentration and to DIDS. In Aedes Malpighian tubules, AeAE is expressed as two distinct forms: one is O-glycosylated, and the other is N-glycosylated. Significantly, AeAE immunoreactivity localizes to the basal regions of stellate cells but not principal cells. Concentrations of DIDS that inhibit AeAE activity in Xenopus oocytes have no effects on the unstimulated rates of fluid secretion mediated by Malpighian tubules as measured by the Ramsay assay. However, in Malpighian tubules stimulated with kinin or calcitonin-like diuretic peptides, DIDS reduces the diuretic rates of fluid secretion to basal levels. In conclusion, Aedes Malpighian tubules express AeAE in the basal region of stellate cells, where this transporter may participate in producing diuretic rates of transepithelial fluid secretion.
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Affiliation(s)
- Peter M Piermarini
- Department of Biomedical Sciences, Cornell University, Ithaca, NY 14853, USA.
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36
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Negative shift in the glycine reversal potential mediated by a Ca2+- and pH-dependent mechanism in interneurons. J Neurosci 2009; 29:11495-510. [PMID: 19759298 DOI: 10.1523/jneurosci.1086-09.2009] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Cartwheel cells are glycinergic auditory interneurons which fire Na(+)- and Ca(2+)-dependent spike bursts, termed complex spikes, and which synapse on both principal cells and one another. The reversal potential for glycine (E(gly)) can be hyperpolarizing or depolarizing in cartwheel cells, and many cells are even excited by glycine. We explored the role of spike activity in determining E(gly) in mouse cartwheel cells using gramicidin perforated-patch recording. E(gly) was found to shift toward more negative potentials after a period of complex spiking or Ca(2+) spiking induced by depolarization, thus enhancing glycine's inhibitory effect for approximately 30 s following cessation of spiking. Combined perforated patch electrophysiology and imaging studies showed that the negative E(gly) shift was triggered by a Ca(2+)-dependent intracellular acidification. The effect on E(gly) was likely caused by bicarbonate-Cl(-) exchanger-mediated reduction in intracellular Cl(-), as H(2)DIDS and removal of HCO(3)(-)/CO(2) inhibited the negative E(gly) shift. The outward Cl(-) flux underlying the negative shift in E(gly) opposed a positive shift triggered by passive Cl(-) redistribution during the depolarization. Thus, a Ca(2+)-dependent mechanism serves to maintain or enhance the strength of inhibition in the face of increased excitatory activity.
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Casey JR, Sly WS, Shah GN, Alvarez BV. Bicarbonate homeostasis in excitable tissues: role of AE3 Cl-/HCO3- exchanger and carbonic anhydrase XIV interaction. Am J Physiol Cell Physiol 2009; 297:C1091-102. [PMID: 19692653 DOI: 10.1152/ajpcell.00177.2009] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
Bicarbonate transport and metabolism are key elements of normal cellular function. Two alternate transcripts of anion exchanger 3 (AE3), full-length (AE3fl) and cardiac (AE3c), are expressed in central nervous system (CNS), where AE3 catalyzes electroneutral Cl(-)/HCO(3)(-) exchange across the plasma membrane of neuronal and glial cells of CNS. Anion exchanger isoforms, AE3fl and AE3c, associate with the carbonic anhydrases (CA) CAII and CAIV, forming a HCO(3)(-) transport metabolon, to maximize HCO(3)(-) flux across the plasma membrane. CAXIV, with catalytic domain anchored to the extracellular surface, is also expressed in CNS. Here physical association of AE3 and CAXIV was examined by coimmunoprecipitation experiments, using mouse brain and retinal lysates. CAXIV immunoprecipitated with anti-AE3 antibody, and both AE3 isoforms were immunoprecipitated using anti-CAXIV antibody, indicating CAXIV and AE3 interaction in the CNS. Confocal images revealed colocalization of CAXIV and AE3 in Müller and horizontal cells, in the mouse retina. Cl(-)/HCO(3)(-) exchange activity of AE3fl was investigated in transiently transfected human embryonic kidney 293 cells, using intracellular fluorescence measurements of BCECF, to monitor intracellular pH. CAXIV increased the rate of AE3fl-mediated HCO(3)(-) transport by up to 120%, which was suppressed by the CA inhibitor acetazolamide. Association of AE3 and CAXIV may represent a mechanism to enhance disposal of waste CO(2) and to balance pH in excitable tissues.
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Affiliation(s)
- Joseph R Casey
- Department of Physiology and Department of Biochemistry, Membrane Protein Research Group, University of Alberta, Edmonton, Canada
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Vilas GL, Johnson DE, Freund P, Casey JR. Characterization of an epilepsy-associated variant of the human Cl-/HCO3(-) exchanger AE3. Am J Physiol Cell Physiol 2009; 297:C526-36. [PMID: 19605733 DOI: 10.1152/ajpcell.00572.2008] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Anion exchanger 3 (AE3), expressed in the brain, heart, and retina, extrudes intracellular HCO(3)(-) in exchange for extracellular Cl(-). The SLC4A3 gene encodes two variants of AE3, brain or full-length AE3 (AE3(fl)) and cardiac AE3 (cAE3). Epilepsy is a heterogeneous group of disorders characterized by recurrent unprovoked seizures that affect about 50 million people worldwide. The AE3-A867D allele in humans has been associated with the development of IGE (IGE), which accounts for approximately 30% of all epilepsies. To examine the molecular basis for the association of the A867D allele with IGE, we characterized wild-type (WT) and AE3(fl)-A867D in transfected human embryonic kidney (HEK)-293 cells. AE3(fl)-A867D had significantly reduced transport activity relative to WT (54 +/- 4%, P < 0.01). Differences in expression levels or the degree of protein trafficking to the plasma membrane did not account for the defect of AE3(fl)-A867D. Treatment with 8-bromo-cAMP (8-Br-cAMP) increased Cl(-)/HCO(3)(-) exchange activity of WT and AE3(fl)-A867D to a similar degree, which was abolished by preincubation with the protein kinase A (PKA)-specific inhibitor H89. This indicates that PKA regulates WT and AE3(fl)-A867D Cl(-)/HCO(3)(-) exchange activity. No difference in Cl(-)/HCO(3)(-) exchange activity was found between cultures of mixed populations of neonatal hippocampal cells from WT and slc4a3(-/-) mice. We conclude that the A867D allele is a functional (catalytic) mutant of AE3 and that the decreased activity of AE3(fl)-A867D may cause changes in cell volume and abnormal intracellular pH. In the brain, these alterations may promote neuron hyperexcitability and the generation of seizures.
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Affiliation(s)
- Gonzalo L Vilas
- Dept. of Physiology, Univ. of Alberta, Edmonton, Alberta T6G 2H7, Canada
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Carbonic anhydrases CA4 and CA14 both enhance AE3-mediated Cl--HCO3- exchange in hippocampal neurons. J Neurosci 2009; 29:3252-8. [PMID: 19279262 DOI: 10.1523/jneurosci.0036-09.2009] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Carbonic anhydrase (CA) activity in the brain extracellular space is attributable mainly to isoforms CA4 and CA14. In brain, these enzymes have been studied mostly in the context of buffering activity-dependent extracellular pH transients. Yet evidence from others has suggested that CA4 acts in a complex with anion exchangers (AEs) to facilitate Cl(-)-HCO(3)(-) exchange in cotransfected cells. To investigate whether CA4 or CA14 plays such a role in hippocampal neurons, we studied NH(4)(+)-induced alkalinization of the cytosol, which is mitigated by Cl(-) entry and HCO(3)(-) exit. The NH(4)(+)-induced alkalinization was enhanced when the extracellular CAs were inhibited by the poorly permeant CA blocker, benzolamide, or by inhibitory antibodies specific for either CA4 or CA14. The NH(4)(+)-induced alkalinization was also increased with inhibition of anion exchange by 4,4*-diisothiocyanostilbene-2,2*-disulfonic acid, or by eliminating Cl(-) from the medium. No effect of benzolamide was seen under these conditions, in which no Cl(-)-HCO(3)(-) exchange was possible. Quantitative PCR on RNA from the neuronal cultures indicated that AE3 was the predominant AE isoform. Single-cell PCR also showed that Slc4a3 (AE3) transcripts were abundant in isolated neurons. In hippocampal neurons dissociated from AE3-null mice, the NH(4)(+)-induced alkalinization was much larger than that seen in neurons from wild-type mice, suggesting little or no Cl(-)-HCO(3)(-) exchange in the absence of AE3. Benzolamide had no effect on the NH(4)(+)-induced alkalinization in the AE3 knock-out neurons. Our results indicate that CA4 and CA14 both play important roles in the regulation of intracellular pH in hippocampal neurons, by facilitating AE3-mediated Cl(-)-HCO(3)(-) exchange.
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Xu WQ, Song LJ, Liu Q, Zhao L, Zheng L, Yan ZW, Fu GH. Expression of anion exchanger 1 is associated with tumor progress in human gastric cancer. J Cancer Res Clin Oncol 2009; 135:1323-30. [PMID: 19330352 DOI: 10.1007/s00432-009-0573-9] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2008] [Accepted: 03/09/2009] [Indexed: 12/28/2022]
Abstract
PURPOSE Anion exchanger 1 (AE1) is a transmembrane glycoprotein which is abundantly expressed in erythrocyte plasma membrane and mediates the electroneutral exchange of Cl(-) and HCO(3) (-). We previously reported that the AE1 protein was unexpectedly expressed in the gastric and colonic cancer and take part in the carcinogenesis of the cancer cells. The aim of the present study is to determine the potential clinical implications of AE1 expression in gastric carcinoma. METHODS Immunohistochemistry assay was used to determine the expression of AE1 protein. The expression of AE1 in normal and malignant tissues from 286 patients with early and advanced gastric carcinoma was examined. The correlations of AE1 expression with clinicopathological parameters, including age, tumor size, location and subtypes, expression frequency, survival period and lymph metastasis were assessed by Chi-squared test and t test analysis. RESULTS AE1 immunoreactivity was negative in normal gastric tissue. Positive immunostaining of AE1 was detected in gastric carcinoma regardless of the location. AE1 was most frequently expressed in the gastric antrum carcinoma compared with gastric body cancer (P = 0.034). Expression of AE1 was significantly associated with bigger tumor size, deeper invasion, shorter survival period, and non-lymph metastasis. In para-cancer tissues of intestinal-type gastric cancer, the expression frequency of AE1 was higher than that in diffuse-type (P = 0.011). CONCLUSION The results showed a strong association of AE1 expression with the onset and progression of the gastric cancer and that may be helpful for improving the tumor classification and the treatment of cancer.
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Affiliation(s)
- Wei-Qing Xu
- Department of Pathology, Institutes of Medical Sciences, Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Shanghai Jiao Tong University School of Medicine, Shanghai 200025, People's Republic of China
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Alper SL. Putative re-entrant loop 1 of AE2 transmembrane domain has a major role in acute regulation of anion exchange by pH. J Biol Chem 2008; 284:6126-39. [PMID: 19103596 DOI: 10.1074/jbc.m802051200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Normal pH sensitivity of the SLC4A2/AE2 anion exchanger requires transmembrane domain (TMD) amino acid (aa) residues not conserved in the homologous but relatively pH-insensitive SLC4A1/AE1 polypeptide. We tested the hypothesis that the nonconserved aa cluster 1075DKPK1078 within the first putative re-entrant loop (RL1) of AE2 TMD contributes to pH sensor function by studying anion exchange function of AE2 mutants in which these and other RL1 aa were systematically substituted with corresponding RL1 aa from AE1. Regulation of Cl-/Cl- and Cl-/HCO(-)3 exchange by intracellular pH (pHi) or extracellular pH (pHo) was measured as 4,4'-di-isothiocyanatostilbene-2,2' disulfonic acid-sensitive 36Cl- efflux from Xenopus oocytes. AE2 RL1 mutants 1075AAAQ1078 and 1075AAAQN1079 showed reduced pHi sensitivity and pHo sensitivity was acid-shifted by approximately 1 pH unit. Individual mutants D1075A and P1077A exhibited moderately altered pH sensitivity, whereas a range of substitutions at conserved AE2 Ile-1079 substantially altered sensitivity to pHo and/or pHi. Substitution of the complete AE1 RL1 with AE2 RL1 failed to confer AE2-like pH sensitivity onto AE1. Replacement, however, of AE1 RL1 763SGPGAAAQ770 with AE2 1071VAPGDKPK1078 restored pHi sensitivity to the chimera AE2(1-920)/AE1(613-929) without affecting its low sensitivity to pHo. The results show that acute regulation of AE2 by pH requires RL1 of the TMD. We propose that critical segments of RL1 constitute part of an AE2 pH sensor that, together with residues within the N-terminal half of the TMD, constrain the AE2 polypeptide in a conformation required for regulation of anion exchange by pHi.
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Affiliation(s)
- Andrew K Stewart
- Department of Medicine, Harvard Medical School, and Molecular and Vascular Medicine Unit, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA
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Prasad V, Bodi I, Meyer JW, Wang Y, Ashraf M, Engle SJ, Doetschman T, Sisco K, Nieman ML, Miller ML, Lorenz JN, Shull GE. Impaired cardiac contractility in mice lacking both the AE3 Cl-/HCO3- exchanger and the NKCC1 Na+-K+-2Cl- cotransporter: effects on Ca2+ handling and protein phosphatases. J Biol Chem 2008; 283:31303-14. [PMID: 18779325 PMCID: PMC2581574 DOI: 10.1074/jbc.m803706200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Revised: 08/27/2008] [Indexed: 12/27/2022] Open
Abstract
To analyze the cardiac functions of AE3, we disrupted its gene (Slc4a3) in mice. Cl(-)/HCO3(-) exchange coupled with Na+-dependent acid extrusion can mediate pH-neutral Na+ uptake, potentially affecting Ca2+ handling via effects on Na+/Ca2+ exchange. AE3 null mice appeared normal, however, and AE3 ablation had no effect on ischemia-reperfusion injury in isolated hearts or cardiac performance in vivo. The NKCC1 Na+-K+-2Cl(-) cotransporter also mediates Na+ uptake, and loss of NKCC1 alone does not impair contractility. To further stress the AE3-deficient myocardium, we combined the AE3 and NKCC1 knock-outs. Double knock-outs had impaired contraction and relaxation both in vivo and in isolated ventricular myocytes. Ca2+ transients revealed an apparent increase in Ca2+ clearance in double null cells. This was unlikely to result from increased Ca2+ sequestration, since the ratio of phosphorylated phospholamban to total phospholamban was sharply reduced in all three mutant hearts. Instead, Na+/Ca2+ exchanger activity was found to be enhanced in double null cells. Systolic Ca2+ was unaltered, however, suggesting more direct effects on the contractile apparatus of double null myocytes. Expression of the catalytic subunit of protein phosphatase 1 was increased in all mutant hearts. There was also a dramatic reversal, between single null and double null hearts, in the carboxymethylation and localization to the myofibrillar fraction, of the catalytic subunit of protein phosphatase 2A, which corresponded to the loss of normal contractility in double null hearts. These data show that AE3 and NKCC1 affect Ca2+ handling, PLN regulation, and expression and localization of major cardiac phosphatases and that their combined loss impairs cardiac function.
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Affiliation(s)
- Vikram Prasad
- Department of Molecular Genetics, Biochemistry, and Microbiology, University of Cincinnati College of Medicine, Cincinnati, Ohio 45267-0524, USA
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43
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Expression and localization of Na-driven Cl-HCO(3)(-) exchanger (SLC4A8) in rodent CNS. Neuroscience 2008; 153:162-74. [PMID: 18359573 DOI: 10.1016/j.neuroscience.2008.02.018] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2007] [Revised: 02/01/2008] [Accepted: 02/13/2008] [Indexed: 11/22/2022]
Abstract
The Na(+)-driven Cl-HCO(3) exchanger (NDCBE or SLC4A8) is a member of the solute carrier 4 (SLC4) family of HCO(3)(-) transporters, which includes products of 10 genes with similar sequences. Most SLC4 members play important roles in regulating intracellular pH (pH(i)). Physiological studies suggest that NDCBE is a major pH(i) regulator in at least hippocampal (HC) pyramidal neurons. We generated a polyclonal rabbit antibody directed against the first 18 residues of the cytoplasmic N terminus (Nt) of human NDCBE. By Western blotting, the antibody distinguishes NDCBE-as a purified Nt peptide or a full-length transporter (expressed in Xenopus oocytes)-from other Na(+)-coupled HCO(3)(-) transporters. By Western blotting, the antiserum recognizes an approximately 135-kDa band in several brain regions of adult mice: the cerebral cortex (CX), subcortex (SCX), cerebellum (CB), and HC. In CX, PNGase F treatment reduces the molecular weight to approximately 116 kDa. By immunocytochemistry, affinity-purified (AP) NDCBE antibody stains the plasma membrane of neuron cell bodies and processes of rat HC neurons in primary culture as well as freshly dissociated mouse HC neurons. The AP antibody does not detect substantial NDCBE levels in freshly dissociated HC astrocytes, or astrocytes in HC or CB sections. By immunohistochemistry, the AP antibody recognizes high levels of NDCBE in neurons of CX, HC (including pyramidal neurons in Cornu Ammonis (CA)1-3 and dentate gyrus), substantial nigra, medulla, cerebellum (especially Purkinje and granular cells), and the basolateral membrane of fetal choroid plexus. Thus, NDCBE is in a position to contribute substantially to pH(i) regulation in multiple CNS neurons.
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Liu CJ, Hwang JM, Wu TT, Hsieh YH, Wu CC, Hsieh YS, Tsai CH, Wu HC, Huang CY, Liu JY. Anion exchanger inhibitor DIDS induces human poorly-differentiated malignant hepatocellular carcinoma HA22T cell apoptosis. Mol Cell Biochem 2007; 308:117-25. [DOI: 10.1007/s11010-007-9619-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Accepted: 10/03/2007] [Indexed: 10/22/2022]
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Chen LM, Choi I, Haddad GG, Boron WF. Chronic continuous hypoxia decreases the expression of SLC4A7 (NBCn1) and SLC4A10 (NCBE) in mouse brain. Am J Physiol Regul Integr Comp Physiol 2007; 293:R2412-20. [PMID: 17928512 DOI: 10.1152/ajpregu.00497.2007] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
In the mammalian CNS, hypoxia causes a wide range of physiological effects, and these effects often depend on the stage of development. Among the effects are alterations in pH homeostasis. Na+-coupled HCO3(-) transporters can play critical roles in intracellular pH regulation and several, such as NCBE and NBCn1, are expressed abundantly in the central nervous system. In the present study, we examined the effect of chronic continuous hypoxia on the expression of two electroneutral Na-coupled HCO3(-) transporters, SLC4a7 (NBCn1) and SLC4a10 (NCBE), in mouse brain, the first such study on any acid-base transporter. We placed the mice in normobaric chambers and either maintained normoxia (21% inspired O2) or imposed continuous chronic hypoxia (11% O2) for a duration of either 14 days or 28 days, starting from ages of either postnatal age 2 days (P2) or P90. We assessed protein abundance by Western blot analysis, loading equal amounts of total protein for each condition. In most cases, hypoxia reduced NBCn1 levels by 20-50%, and NCBE levels by 15-40% in cerebral cortex, subcortex, cerebellum, and hippocampus, both after 14 and 28 days, and in both pups and adults. We hypothesize that these decreases, which are out of proportion to the expected overall decreases in brain protein levels, may especially be important for reducing energy consumption.
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Affiliation(s)
- Li-Ming Chen
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, Connecticut, USA.
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46
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Stewart AK, Kurschat CE, Vaughan-Jones RD, Shmukler BE, Alper SL. Acute regulation of mouse AE2 anion exchanger requires isoform-specific amino acid residues from most of the transmembrane domain. J Physiol 2007; 584:59-73. [PMID: 17690150 PMCID: PMC2277056 DOI: 10.1113/jphysiol.2007.136119] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The widely expressed anion exchanger polypeptide AE2/SLC4A2 is acutely inhibited by acidic intracellular (pH(i)), by acidic extracellular pH (pH(o)), and by the calmodulin inhibitor, calmidazolium, whereas it is acutely activated by NH(4)(+). The homologous erythroid/kidney AE1/SLC4A1 polypeptide is insensitive to these regulators. Each of these AE2 regulatory responses requires the presence of AE2's C-terminal transmembrane domain (TMD). We have now measured (36)Cl(-) efflux from Xenopus oocytes expressing bi- or tripartite AE2-AE1 chimeras to define TMD subregions in which AE2-specific sequences contribute to acute regulation. The chimeric AE polypeptides were all functional at pH(o) 7.4, with the sole exception of AE2((1-920))/AE1((613-811))/AE2((1120-1237)). Reciprocal exchanges of the large third extracellular loops were without effect. AE2 regulation by pH(i), pH(o) and NH(4)(+) was retained after substitution of C-terminal AE2 amino acids 1120-1237 (including the putative second re-entrant loop, two TM spans and the cytoplasmic tail) with the corresponding AE1 sequence. In contrast, the presence of this AE2 C-terminal sequence was both necessary and sufficient for inhibition by calmidazolium. All other tested TMD substitutions abolished AE2 pH(i) sensitivity, abolished or severely attenuated sensitivity to pH(o) and removed sensitivity to NH(4)(+). Loss of AE2 pH(i) sensitivity was not rescued by co-expression of a complementary AE2 sequence within separate full-length chimeras or AE2 subdomains. Thus, normal regulation of AE2 by pH and other ligands requires AE2-specific sequence from most regions of the AE2 TMD, with the exceptions of the third extracellular loop and a short C-terminal sequence. We conclude that the individual TMD amino acid residues previously identified as influencing acute regulation of AE2 exert that influence within a regulatory structure requiring essential contributions from multiple regions of the AE2 TMD.
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Affiliation(s)
- A K Stewart
- Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA
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47
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Morgan PE, Pastoreková S, Stuart-Tilley AK, Alper SL, Casey JR. Interactions of transmembrane carbonic anhydrase, CAIX, with bicarbonate transporters. Am J Physiol Cell Physiol 2007; 293:C738-48. [PMID: 17652430 DOI: 10.1152/ajpcell.00157.2007] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Association of some plasma membrane bicarbonate transporters with carbonic anhydrase enzymes forms a bicarbonate transport metabolon to facilitate metabolic CO(2)-HCO(3)(-) conversions and coupled HCO(3)(-) transport. The transmembrane carbonic anhydrase, CAIX, with its extracellular catalytic site, is highly expressed in parietal and other cells of gastric mucosa, suggesting a role in acid secretion. We examined in transfected HEK293 cells the functional and physical interactions between CAIX and the parietal cell Cl(-)/HCO(3)(-) exchanger AE2 or the putative Cl(-)/HCO(3)(-) exchanger SLC26A7. Coexpression of CAIX increased AE2 transport activity by 28 +/- 7% and also activated transport mediated by AE1 and AE3 (32 +/- 10 and 37 +/- 9%, respectively). In contrast, despite a transport rate comparable to that of AE3, coexpressed CAIX did not alter transport associated with SLC26A7. The CAIX-associated increase of AE2 activity did not result from altered AE2 expression or cell surface processing. CAIX was coimmunoprecipitated with the coexpressed SLC4 polypeptides AE1, AE2, and AE3, but not with SLC26A7. GST pull-down assays with a series of domain-deleted forms of CAIX revealed that the catalytic domain of CAIX mediated interaction with AE2. AE2 and CAIX colocalized in human gastric mucosa, as indicated by coimmunofluorescence. This is the first example of a functional and physical interaction between a bicarbonate transporter and a transmembrane carbonic anhydrase. We conclude that CAIX can bind to some Cl(-)/HCO(3)(-) exchangers to form a bicarbonate transport metabolon.
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Affiliation(s)
- Patricio E Morgan
- Membrane Protein Research Group, Dept of Physiology, University of Alberta, Edmonton, Alberta, Canada
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Wang Y, Wu SF, Chen GQ, Fu GH. Effect of block deletions in the C-terminus on the functional expression of human anion exchanger 1 (AE1). Mol Membr Biol 2007; 24:65-73. [PMID: 17453414 DOI: 10.1080/09687860600945263] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The human anion exchanger 1 (AE1) is the most abundant integral membrane protein in red cells and is responsible for the exchange of Cl(-) for HCO(3)(-). However, the detailed role played by the AE1 C-terminal region in the anion translocation and membrane trafficking process remains unclear. In this paper, we created four mutants in the human AE1 C-terminus by deletion of the residues Ala(891)-Phe(895), Asp(896)-Glu(899), Asp(902)-Glu(906) and Val(907)-Val(911), to investigate the role of these sequences in functional expression of AE1. WT AE1 and its deletion mutant constructs were expressed in HEK 293 cells. Western blotting showed that deletions of Ala(891)-Phe(895), Asp(896)-Glu(899), and Val(907)-Val(911) induced high expression of AE1, whereas loss of Asp(902)-Glu(906) results in stable low expression. Pulse chase assays of WT AE1 and its mutants showed that the stability of protein is unaffected by the levels of expression of the AE1 and its mutants. Ala(891)-Phe(895), Asp(902)-Glu(906) and Val(907)-Val(911) mutants exhibited lower levels of trafficking to the plasma membrane compared with WT AE1, while the Asp(896)-Glu(899) mutant was more highly expressed at the plasma membrane. The decreased ability of the mutants to mediate Cl(-)/HCO(3)(-) exchange in transfected cells revealed that the deletion sequences have an important role in transport activity. These results demonstrate that the studied residues in the AE1 C-terminus differently affect the expression, membrane trafficking and functional folding of AE1.
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Affiliation(s)
- Yong Wang
- Key Laboratory of Cell Differentiation and Apoptosis of Chinese Ministry of Education, Rui-Jin Hospital, Shanghai Jiao-Tong University, School of Medicine/Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, PR China
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Stewart AK, Kurschat CE, Alper SL. Role of nonconserved charged residues of the AE2 transmembrane domain in regulation of anion exchange by pH. Pflugers Arch 2007; 454:373-84. [PMID: 17492309 DOI: 10.1007/s00424-007-0220-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2006] [Revised: 01/15/2007] [Accepted: 01/22/2007] [Indexed: 11/29/2022]
Abstract
The ubiquitous AE2/SLC4A2 anion exchanger is acutely and independently regulated by intracellular (pH(i)) and extracellular pH (pH(o)), whereas the closely related AE1/SLC4A1 of the red cell and renal intercalated cell is relatively pH-insensitive. We have investigated the contribution of nonconserved charged residues within the C-terminal transmembrane domain (TMD) of AE2 to regulation by pH through mutation to the corresponding AE1 residues. AE2-mediated Cl(-)/Cl(-) exchange was measured as 4,4'-di-isothiocyanatostilbene-2,2'-disulfonic acid-sensitive (36)Cl(-) efflux from Xenopus oocytes by varying pH(i) at constant pH(o), and by varying pH(o) at near-constant pH(i). All mutations of nonconserved charged residues of the AE2 TMD yielded functional protein, but mutations of some conserved charged residues (R789E, R1056A, R1134C) reduced or abolished function. Individual mutation of AE2 TMD residues R921, F922, P1077, and R1107 exhibited reduced pH(i) sensitivity compared to wt AE2, whereas TMD mutants K1153R, R1155K, R1202L displayed enhanced sensitivity to acidic pH(i). In addition, pH(o) sensitivity was significantly acid- shifted when nonconserved AE2 TMD residues E981, K982, and D1075 were individually converted to the corresponding AE1 residues. These results demonstrate that multiple conserved charged residues are important for basal transport function of AE2 and that certain nonconserved charged residues of the AE2 TMD are essential for wild-type regulation of anion exchange by pH(i) and pH(o).
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Affiliation(s)
- A K Stewart
- Molecular and Vascular Medicine Unit and Renal Unit, Department of Medicine, Harvard Medical School, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
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50
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Stewart AK, Kurschat CE, Burns D, Banger N, Vaughan-Jones RD, Alper SL. Transmembrane domain histidines contribute to regulation of AE2-mediated anion exchange by pH. Am J Physiol Cell Physiol 2007; 292:C909-18. [PMID: 17005605 DOI: 10.1152/ajpcell.00265.2006] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Activity of the AE2/SLC4A2 anion exchanger is modulated acutely by pH, influencing the transporter's role in regulation of intracellular pH (pHi) and epithelial solute transport. In Xenopus oocytes, heterologous AE2-mediated Cl−/Cl−and Cl−/HCO3−exchange are inhibited by acid pHior extracellular pH (pHo). We have investigated the importance to pH sensitivity of the eight histidine (His) residues within the AE2 COOH-terminal transmembrane domain (TMD). Wild-type mouse AE2-mediated Cl−/Cl−exchange, measured as DIDS-sensitive36Cl−efflux from Xenopus oocytes, was experimentally altered by varying pHiat constant pHoor varying pHo. Pretreatment of oocytes with the His modifier diethylpyrocarbonate (DEPC) reduced basal36Cl−efflux at pHo7.4 and acid shifted the pHovs. activity profile of wild-type AE2, suggesting that His residues might be involved in pH sensing. Single His mutants of AE2 were generated and expressed in oocytes. Although mutation of H1029 to Ala severely reduced transport and surface expression, other individual His mutants exhibited wild-type or near-wild-type levels of Cl−transport activity with retention of pHosensitivity. In contrast to the effects of DEPC on wild-type AE2, pHosensitivity was significantly alkaline shifted for mutants H1144Y and H1145A and the triple mutants H846/H849/H1145A and H846/H849/H1160A. Although all functional mutants retained sensitivity to pHi, pHisensitivity was enhanced for AE2 H1145A. The simultaneous mutation of five or more His residues, however, greatly decreased basal AE2 activity, consistent with the inhibitory effects of DEPC modification. The results show that multiple TMD His residues contribute to basal AE2 activity and its sensitivity to pHiand pHo.
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Affiliation(s)
- A K Stewart
- Beth Israel Deaconess Medical Center, 330 Brookline Ave., E/RW763, Boston, MA 02215, USA.
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