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Holmberg SR, Sakamoto Y, Kato A, Romero MF. The role of Na +-coupled bicarbonate transporters (NCBT) in health and disease. Pflugers Arch 2024; 476:479-503. [PMID: 38536494 DOI: 10.1007/s00424-024-02937-w] [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: 12/15/2023] [Revised: 02/26/2024] [Accepted: 02/27/2024] [Indexed: 04/11/2024]
Abstract
Cellular and organism survival depends upon the regulation of pH, which is regulated by highly specialized cell membrane transporters, the solute carriers (SLC) (For a comprehensive list of the solute carrier family members, see: https://www.bioparadigms.org/slc/ ). The SLC4 family of bicarbonate (HCO3-) transporters consists of ten members, sorted by their coupling to either sodium (NBCe1, NBCe2, NBCn1, NBCn2, NDCBE), chloride (AE1, AE2, AE3), or borate (BTR1). The ionic coupling of SLC4A9 (AE4) remains controversial. These SLC4 bicarbonate transporters may be controlled by cellular ionic gradients, cellular membrane voltage, and signaling molecules to maintain critical cellular and systemic pH (acid-base) balance. There are profound consequences when blood pH deviates even a small amount outside the normal range (7.35-7.45). Chiefly, Na+-coupled bicarbonate transporters (NCBT) control intracellular pH in nearly every living cell, maintaining the biological pH required for life. Additionally, NCBTs have important roles to regulate cell volume and maintain salt balance as well as absorption and secretion of acid-base equivalents. Due to their varied tissue expression, NCBTs have roles in pathophysiology, which become apparent in physiologic responses when their expression is reduced or genetically deleted. Variations in physiological pH are seen in a wide variety of conditions, from canonically acid-base related conditions to pathologies not necessarily associated with acid-base dysfunction such as cancer, glaucoma, or various neurological diseases. The membranous location of the SLC4 transporters as well as recent advances in discovering their structural biology makes them accessible and attractive as a druggable target in a disease context. The role of sodium-coupled bicarbonate transporters in such a large array of conditions illustrates the potential of treating a wide range of disease states by modifying function of these transporters, whether that be through inhibition or enhancement.
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Affiliation(s)
- Shannon R Holmberg
- Physiology & Biomedical Engineering, Mayo Clinic College of Medicine & Science, 200 1st Street SW, Rochester, MN 55905, USA
- Biochemistry & Molecular Biology, Mayo Clinic College of Medicine & Science, 200 1st Street SW, Rochester, MN, USA
| | - Yohei Sakamoto
- School of Life Science and Technology, Tokyo Institute of Technology, Midori-Ku, Yokohama, 226-8501, Japan
| | - Akira Kato
- School of Life Science and Technology, Tokyo Institute of Technology, Midori-Ku, Yokohama, 226-8501, Japan
| | - Michael F Romero
- Physiology & Biomedical Engineering, Mayo Clinic College of Medicine & Science, 200 1st Street SW, Rochester, MN 55905, USA.
- Nephrology & Hypertension, Mayo Clinic College of Medicine & Science, 200 1st Street SW, Rochester, MN, USA.
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2
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Fringuello AR, Colbourn R, Goodman JH, Michelson HB, Ling DSF, Hrabetova S. Rapid volume pulsations of the extracellular space accompany epileptiform activity in trauma-injured neocortex and depend on the sodium-bicarbonate cotransporter NBCe1. Epilepsy Res 2024; 201:107337. [PMID: 38461594 DOI: 10.1016/j.eplepsyres.2024.107337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/29/2023] [Revised: 02/19/2024] [Accepted: 02/29/2024] [Indexed: 03/12/2024]
Abstract
Post traumatic epilepsy (PTE) is a treatment-resistant consequence of traumatic brain injury (TBI). Recently, it has been revealed that epileptiform activity in acute chemoconvulsant seizure models is accompanied by transient shrinkages of extracellular space (ECS) called rapid volume pulsations (RVPs). Shrinkage of the ECS surrounding neurons and glia may contribute to ictogenic hyperexcitability and hypersynchrony during the chronic phase of TBI. Here, we identify the phenomenon of RVPs occurring spontaneously in rat neocortex at ≥ 3 weeks after injury in the controlled cortical impact (CCI) model for PTE. We further report that blocking the electrogenic action of the astrocytic cotransporter NBCe1 with 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS) eliminates both RVPs and epileptiform activity in ex-vivo CCI neocortical brain slices. We conclude that NBCe1-mediated extracellular volume shrinkage may represent a new target for therapeutic intervention in PTE.
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Affiliation(s)
- Anthony R Fringuello
- Department of Cell Biology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; Neural and Behavioral Science Graduate Program, SUNY Downstate Health Sciences University, Brooklyn, NY, USA
| | - Robert Colbourn
- Department of Cell Biology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; Neural and Behavioral Science Graduate Program, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; Present address: Department of Pathology and Laboratory Medicine, Hospital of the University of Pennsylvania, Philadelphia, PA, USA
| | - Jeffrey H Goodman
- Department of Developmental Neurobiology, The New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY, USA; Department of Physiology and Pharmacology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; The Robert F. Furchgott Center for Neural and Behavioral Science, SUNY Downstate Health Sciences University, Brooklyn, NY, USA
| | - Hillary B Michelson
- Department of Physiology and Pharmacology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; The Robert F. Furchgott Center for Neural and Behavioral Science, SUNY Downstate Health Sciences University, Brooklyn, NY, USA
| | - Douglas S F Ling
- Department of Physiology and Pharmacology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; The Robert F. Furchgott Center for Neural and Behavioral Science, SUNY Downstate Health Sciences University, Brooklyn, NY, USA
| | - Sabina Hrabetova
- Department of Cell Biology, SUNY Downstate Health Sciences University, Brooklyn, NY, USA; The Robert F. Furchgott Center for Neural and Behavioral Science, SUNY Downstate Health Sciences University, Brooklyn, NY, USA.
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3
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Pethe A, Hamze M, Giannaki M, Heimrich B, Medina I, Hartmann AM, Roussa E. K +/Cl - cotransporter 2 (KCC2) and Na +/ HCO3- cotransporter 1 (NBCe1) interaction modulates profile of KCC2 phosphorylation. Front Cell Neurosci 2023; 17:1253424. [PMID: 37881493 PMCID: PMC10595033 DOI: 10.3389/fncel.2023.1253424] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2023] [Accepted: 09/07/2023] [Indexed: 10/27/2023] Open
Abstract
K+/Cl- cotransporter 2 (KCC2) is a major Cl- extruder in mature neurons and is responsible for the establishment of low intracellular [Cl-], necessary for fast hyperpolarizing GABAA-receptor mediated synaptic inhibition. Electrogenic sodium bicarbonate cotransporter 1 (NBCe1) is a pH regulatory protein expressed in neurons and glial cells. An interactome study identified NBCe1 as a possible interaction partner of KCC2. In this study, we investigated the putative effect of KCC2/NBCe1 interaction in baseline and the stimulus-induced phosphorylation pattern and function of KCC2. Primary mouse hippocampal neuronal cultures from wildtype (WT) and Nbce1-deficient mice, as well as HEK-293 cells stably transfected with KCC2WT, were used. The results show that KCC2 and NBCe1 are interaction partners in the mouse brain. In HEKKCC2 cells, pharmacological inhibition of NBCs with S0859 prevented staurosporine- and 4-aminopyridine (4AP)-induced KCC2 activation. In mature cultures of hippocampal neurons, however, S0859 completely inhibited postsynaptic GABAAR and, thus, could not be used as a tool to investigate the role of NBCs in GABA-dependent neuronal networks. In Nbce1-deficient immature hippocampal neurons, baseline phosphorylation of KCC2 at S940 was downregulated, compared to WT, and exposure to staurosporine failed to reduce pKCC2 S940 and T1007. In Nbce1-deficient mature neurons, baseline levels of pKCC2 S940 and T1007 were upregulated compared to WT, whereas after 4AP treatment, pKCC2 S940 was downregulated, and pKCC2 T1007 was further upregulated. Functional experiments showed that the levels of GABAAR reversal potential, baseline intracellular [Cl-], Cl- extrusion, and baseline intracellular pH were similar between WT and Nbce1-deficient neurons. Altogether, our data provide a primary description of the properties of KCC2/NBCe1 protein-protein interaction and implicate modulation of stimulus-mediated phosphorylation of KCC2 by NBCe1/KCC2 interaction-a mechanism with putative pathophysiological relevance.
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Affiliation(s)
- Abhishek Pethe
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Mira Hamze
- INMED, INSERM, Aix-Marseille University, Marseille, France
| | - Marina Giannaki
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Bernd Heimrich
- Department of Neuroanatomy, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
| | - Igor Medina
- INMED, INSERM, Aix-Marseille University, Marseille, France
| | - Anna-Maria Hartmann
- Division of Neurogenetics, Faculty VI, School of Medicine and Health Sciences, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
- Research Center for Neurosensory Science, Carl von Ossietzky University Oldenburg, Oldenburg, Germany
| | - Eleni Roussa
- Department of Molecular Embryology, Faculty of Medicine, Institute for Anatomy and Cell Biology, Albert-Ludwigs-Universität Freiburg, Freiburg, Germany
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Brady CT, Marshall A, Zhang C, Parker MD. NBCe1-B/C-knockout mice exhibit an impaired respiratory response and an enhanced renal response to metabolic acidosis. Front Physiol 2023; 14:1201034. [PMID: 37405134 PMCID: PMC10315466 DOI: 10.3389/fphys.2023.1201034] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2023] [Accepted: 06/07/2023] [Indexed: 07/06/2023] Open
Abstract
The sodium-bicarbonate cotransporter (NBCe1) has three primary variants: NBCe1-A, -B and -C. NBCe1-A is expressed in renal proximal tubules in the cortical labyrinth, where it is essential for reclaiming filtered bicarbonate, such that NBCe1-A knockout mice are congenitally acidemic. NBCe1-B and -C variants are expressed in chemosensitive regions of the brainstem, while NBCe1-B is also expressed in renal proximal tubules located in the outer medulla. Although mice lacking NBCe1-B/C (KOb/c) exhibit a normal plasma pH at baseline, the distribution of NBCe1-B/C indicates that these variants could play a role in both the rapid respiratory and slower renal responses to metabolic acidosis (MAc). Therefore, in this study we used an integrative physiologic approach to investigate the response of KOb/c mice to MAc. By means of unanesthetized whole-body plethysmography and blood-gas analysis, we demonstrate that the respiratory response to MAc (increase in minute volume, decrease in pCO2) is impaired in KOb/c mice leading to a greater severity of acidemia after 1 day of MAc. Despite this respiratory impairment, the recovery of plasma pH after 3-days of MAc remained intact in KOb/c mice. Using data gathered from mice housed in metabolic cages we demonstrate a greater elevation of renal ammonium excretion and greater downregulation of the ammonia recycling enzyme glutamine synthetase in KOb/c mice on day 2 of MAc, consistent with greater renal acid-excretion. We conclude that KOb/c mice are ultimately able to defend plasma pH during MAc, but that the integrated response is disturbed such that the burden of work shifts from the respiratory system to the kidneys, delaying the recovery of pH.
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Affiliation(s)
- Clayton T. Brady
- Jacobs School of Medicine and Biomedical Sciences, Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, NY, United States
| | - Aniko Marshall
- Jacobs School of Medicine and Biomedical Sciences, Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, NY, United States
| | - Chen Zhang
- Jacobs School of Medicine and Biomedical Sciences, Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, NY, United States
- Department of Biological Sciences, The State University of New York: The University at Buffalo, Buffalo, NY, United States
| | - Mark D. Parker
- Jacobs School of Medicine and Biomedical Sciences, Department of Physiology and Biophysics, The State University of New York: The University at Buffalo, Buffalo, NY, United States
- Jacobs School of Medicine and Biomedical Sciences, Department of Ophthalmology, The State University of New York: The University at Buffalo, Buffalo, NY, United States
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5
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Martinez Ramirez CE, Ruiz-Pérez G, Stollenwerk TM, Behlke C, Doherty A, Hillard CJ. Endocannabinoid signaling in the central nervous system. Glia 2023; 71:5-35. [PMID: 36308424 PMCID: PMC10167744 DOI: 10.1002/glia.24280] [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: 02/01/2022] [Revised: 09/02/2022] [Accepted: 09/29/2022] [Indexed: 11/07/2022]
Abstract
It is hard to overestimate the influence of the endocannabinoid signaling (ECS) system on central nervous system (CNS) function. In the 40 years since cannabinoids were found to trigger specific cell signaling cascades, studies of the ECS system continue to cause amazement, surprise, and confusion! CB1 cannabinoid receptors are expressed widely in the CNS and regulate cell-cell communication via effects on the release of both neurotransmitters and gliotransmitters. CB2 cannabinoid receptors are difficult to detect in the CNS but seem to "punch above their weight" as compounds targeting these receptors have significant effects on inflammatory state and behavior. Positive and negative allosteric modulators for both receptors have been identified and examined in preclinical studies. Concentrations of the endocannabinoid ligands, N-arachidonoylethanolamine and 2-arachidonoylglycerol (2-AG), are regulated by a combination of enzymatic synthesis and degradation and inhibitors of these processes are available and making their way into clinical trials. Importantly, ECS regulates many essential brain functions, including regulation of reward, anxiety, inflammation, motor control, and cellular development. While the field is on the cusp of preclinical discoveries providing impactful clinical and therapeutic insights into many CNS disorders, there is still much to be learned about this remarkable and versatile modulatory system.
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Affiliation(s)
- César E Martinez Ramirez
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Gonzalo Ruiz-Pérez
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Todd M Stollenwerk
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Christina Behlke
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Ashley Doherty
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
| | - Cecilia J Hillard
- Neuroscience Research Center and Department of Pharmacology and Toxicology, Medical College of Wisconsin, Milwaukee, Wisconsin, USA
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6
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Du L, Zahra A, Jia M, Wang Q, Wu J. Understanding the Functional Expression of Na+-Coupled SLC4 Transporters in the Renal and Nervous Systems: A Review. Brain Sci 2021; 11:1276. [PMID: 34679341 PMCID: PMC8534249 DOI: 10.3390/brainsci11101276] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2021] [Revised: 09/16/2021] [Accepted: 09/23/2021] [Indexed: 11/25/2022] Open
Abstract
Acid-base homeostasis is crucial for numerous physiological processes. Na+/HCO3- cotransporters (NBCs) belong to the solute carrier 4 (SLC4) family, which regulates intracellular pH as well as HCO3- absorption and secretion. However, knowledge of the structural functions of these proteins remains limited. Electrogenic NBC (NBCe-1) is thought to be the primary factor promoting the precise acid-base equilibrium in distinct cell types for filtration and reabsorption, as well as the function of neurons and glia. NBC dysregulation is strongly linked to several diseases. As such, the need for special drugs that interfere with the transmission function of NBC is becoming increasingly urgent. In this review, we focus on the structural and functional characteristics of NBCe1, and discuss the roles of NBCe1 in the kidney, central nervous system (CNS), and related disorders, we also summarize the research on NBC inhibitors. NBCe1 and the related pathways should be further investigated, so that new medications may be developed to address the related conditions.
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Affiliation(s)
- Le Du
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
| | - Aqeela Zahra
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
| | - Meng Jia
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
| | - Qun Wang
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
| | - Jianping Wu
- School of Chemistry, Chemical Engineering and Life Sciences, Wuhan University of Technology, Wuhan 430070, China; (L.D.); (A.Z.)
- Beijing Tiantan Hospital, Capital Medical University, Beijing 100070, China; (M.J.); (Q.W.)
- Advanced Innovation Center for Human Brain Protection, Capital Medical University, Beijing 100070, China
- National Clinical Research Center for Neurological Disease, Beijing 100070, China
- Health Science Center, Yangtze University, Jingzhou 434023, China
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7
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The electrogenic sodium bicarbonate cotransporter and its roles in the myocardial ischemia-reperfusion induced cardiac diseases. Life Sci 2021; 270:119153. [PMID: 33539911 DOI: 10.1016/j.lfs.2021.119153] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 01/06/2021] [Accepted: 01/22/2021] [Indexed: 12/19/2022]
Abstract
Cardiac tissue ischemia/hypoxia increases glycolysis and lactic acid accumulation in cardiomyocytes, leading to intracellular metabolic acidosis. Sodium bicarbonate cotransporters (NBCs) play a vital role in modulating intracellular pH and maintaining sodium ion concentrations in cardiomyocytes. Cardiomyocytes mainly express electrogenic sodium bicarbonate cotransporter (NBCe1), which has been demonstrated to participate in myocardial ischemia/reperfusion (I/R) injury. This review outlines the structural and functional properties of NBCe1, summarizes the signaling pathways and factors that may regulate the activity of NBCe1, and reviews the roles of NBCe1 in the pathogenesis of I/R-induced cardiac diseases. Further studies revealing the regulatory mechanisms of NBCe1 activity should provide novel therapeutic targets for preventing I/R-induced cardiac diseases.
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8
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Wu Y, Zhao X, Chen L, Wang J, Duan Y, Li H, Lu L. Transcriptomic Analyses of the Hypothalamic-Pituitary-Gonadal Axis Identify Candidate Genes Related to Egg Production in Xinjiang Yili Geese. Animals (Basel) 2020; 10:E90. [PMID: 31935822 PMCID: PMC7023467 DOI: 10.3390/ani10010090] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2019] [Revised: 12/26/2019] [Accepted: 01/02/2020] [Indexed: 12/22/2022] Open
Abstract
The study was conducted to investigate the transcriptomic differences of the hypothalamic-pituitary-gonadal axis between Xinjiang Yili geese with high and low egg production and to find candidate genes regulating the egg production of Xinjiang Yili geese. The 8 selected Xinjiang Yili Geese with high or low egg production (4 for each group) were 3 years old, with good health, and under the same feeding condition. High-throughput sequencing technology was used to sequence cDNA libraries of the hypothalami, pituitary glands, and ovaries. The sequencing data were compared and analyzed, and the transcripts with significant differences were identified and analyzed with bioinformatics. The study showed that the transcriptome sequencing data of the 24 samples contained a total of 1,176,496,146 valid reads and 176.47 gigabase data. Differential expression analyses identified 135, 56, and 331 genes in the hypothalami, pituitary glands, and ovaries of Xinjiang Yili geese with high and low egg production. Further annotation of these differentially expressed genes in the non-redundant protein sequence database (Nr) revealed that 98, 52, and 309 genes were annotated, respectively. Through the annotations of GO (Gene Ontology) and KEGG (Kyoto Encyclopedia of Genes and Genomes) databases, 30 candidate genes related to the egg production of Xinjiang Yili geese were preliminarily selected. The gap junction, focal adhesion, and ECM-receptor interaction signaling pathways were enriched with the hypothalamic, pituitary, and ovarian differentially expressed genes, and the calcium signaling pathway was enriched with the pituitary and ovarian differentially expressed genes. Thus, these pathways in the hypothalamic-pituitary-gonadal axis may play an important role in regulating egg production of Xinjiang Yili geese. The results provided the transcriptomic information of the hypothalamic-pituitary-gonadal axis of Xinjiang Yili geese and laid the theoretical basis for revealing the molecular mechanisms regulating the egg-laying traits of Xinjiang Yili geese.
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Affiliation(s)
- Yingping Wu
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Xiaoyu Zhao
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Li Chen
- Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China;
| | - Junhua Wang
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Yuqing Duan
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Haiying Li
- College of Animal Science, Xinjiang Agricultural University, Urumqi 830000, China; (Y.W.); (X.Z.); (J.W.); (Y.D.)
| | - Lizhi Lu
- Institute of Animal Husbandry and Veterinary Science, Zhejiang Academy of Agricultural Sciences, Hangzhou 310021, China;
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Salerno EE, Patel SP, Marshall A, Marshall J, Alsufayan T, Mballo CSA, Quade BN, Parker MD. Extrarenal Signs of Proximal Renal Tubular Acidosis Persist in Nonacidemic Nbce1b/c-Null Mice. J Am Soc Nephrol 2019; 30:979-989. [PMID: 31040187 DOI: 10.1681/asn.2018050545] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2018] [Accepted: 03/05/2019] [Indexed: 12/12/2022] Open
Abstract
BACKGROUND The SLC4A4 gene encodes electrogenic sodium bicarbonate cotransporter 1 (NBCe1). Inheritance of recessive mutations in SLC4A4 causes proximal renal tubular acidosis (pRTA), a disease characterized by metabolic acidosis, growth retardation, ocular abnormalities, and often dental abnormalities. Mouse models of pRTA exhibit acidemia, corneal edema, weak dental enamel, impacted colons, nutritional defects, and a general failure to thrive, rarely surviving beyond weaning. Alkali therapy remains the preferred treatment for pRTA, but it is unclear which nonrenal signs are secondary to acidemia and which are a direct consequence of NBCe1 loss from nonrenal sites (such as the eye and enamel organ) and therefore require separate therapy. SLC4A4 encodes three major NBCe1 variants: NBCe1-A, NBCe1-B, and NBCe1-C. NBCe1-A is expressed in proximal tubule epithelia; its dysfunction causes the plasma bicarbonate insufficiency that underlies acidemia. NBCe1-B and NBCe1-C exhibit a broad extra-proximal-tubular distribution. METHODS To explore the consequences of Nbce1b/c loss in the absence of acidemia, we engineered a novel strain of Nbce1b/c-null mice and assessed them for signs of pRTA. RESULTS Nbce1b/c-null mice have normal blood pH, but exhibit increased mortality, growth retardation, corneal edema, and tooth enamel defects. CONCLUSIONS The correction of pRTA-related acidemia should not be considered a panacea for all signs of pRTA. The phenotype of Nbce1b/c-null mice highlights the physiologic importance of NBCe1 variants expressed beyond the proximal tubular epithelia and potential limitations of pH correction by alkali therapy in pRTA. It also suggests a novel genetic locus for corneal dystrophy and enamel hypomineralization without acidemia.
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Affiliation(s)
| | - Sangita P Patel
- Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and.,Research and Ophthalmology Services, VA Western New York Healthcare System, Buffalo, New York
| | | | | | | | | | | | - Mark D Parker
- Departments of Physiology and Biophysics and .,Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo, The State University of New York, Buffalo, New York.,State University of New York Eye Institute, Buffalo, New York; and
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10
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Simon MJ, Murchison C, Iliff JJ. A transcriptome-based assessment of the astrocytic dystrophin-associated complex in the developing human brain. J Neurosci Res 2018; 96:180-193. [PMID: 28509351 PMCID: PMC5995340 DOI: 10.1002/jnr.24082] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/05/2017] [Revised: 03/23/2017] [Accepted: 04/20/2017] [Indexed: 11/10/2022]
Abstract
Astrocytes play a critical role in regulating the interface between the cerebral vasculature and the central nervous system. Contributing to this is the astrocytic endfoot domain, a specialized structure that ensheathes the entirety of the vasculature and mediates signaling between endothelial cells, pericytes, and neurons. The astrocytic endfoot has been implicated as a critical element of the glymphatic pathway, and changes in protein expression profiles in this cellular domain are linked to Alzheimer's disease pathology. Despite this, basic physiological properties of this structure remain poorly understood including the developmental timing of its formation, and the protein components that localize there to mediate its functions. Here we use human transcriptome data from male and female subjects across several developmental stages and brain regions to characterize the gene expression profile of the dystrophin-associated complex (DAC), a known structural component of the astrocytic endfoot that supports perivascular localization of the astroglial water channel aquaporin-4. Transcriptomic profiling is also used to define genes exhibiting parallel expression profiles to DAC elements, generating a pool of candidate genes that encode gene products that may contribute to the physiological function of the perivascular astrocytic endfoot domain. We found that several genes encoding transporter proteins are transcriptionally associated with DAC genes.
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Affiliation(s)
- Matthew J. Simon
- Neuroscience Graduate Program, Oregon Health & Science University, Portland, OR, USA
- Department of Anesthesiology and Perioperative Medicine, Oregon Health & Science University, Portland, OR, USA
| | - Charles Murchison
- Department of Neurology, Oregon Health & Science University, Portland, OR, USA
| | - Jeffrey J. Iliff
- Department of Anesthesiology and Perioperative Medicine, Oregon Health & Science University, Portland, OR, USA
- Knight Cardiovascular Institute. Oregon Health & Science University, Portland, OR, USA
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11
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MacVicar BA, Choi HB. Astrocytes Provide Metabolic Support for Neuronal Synaptic Function in Response to Extracellular K . Neurochem Res 2017; 42:2588-2594. [PMID: 28664400 DOI: 10.1007/s11064-017-2315-8] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Revised: 05/19/2017] [Accepted: 05/26/2017] [Indexed: 01/07/2023]
Abstract
It is an honour to have this opportunity write an article in recognition of the immense contributions of Bruce Ransom to the field of glial research. For me (BAM) personally there are many highlights both as a colleague and a friend that come to mind when I reflect on the many years that I have known Bruce. My own entry into the glial field was inspired by the early work by Ransom and his lab showing the sensitivity of astrocytes to neuronal activity. During my PhD and postdoctoral research I read these early papers and was inspired to ask the question when I first set up my independent lab in 1983: what if astrocytes also express some of the multitude of ion channels or transmitter receptors that were beginning to be described in neurons? Could they modify neuronal excitability during seizures or behaviour? As it turned out this was not only true but glial-neuronal interactions continues to be a growing and exciting field that I am still working in. I first met Bruce at the 1984 Society for Neuroscience meeting in Anaheim at my poster describing voltage gated calcium channels in astrocytes in cell culture. That was the start of a great friendship and years of discussions and collaborations. This review describes recent work from my lab led by Hyun Beom Choi that followed and was inspired by the groundbreaking studies by Bruce on electrophysiological and pH recordings from astrocytes and on glycogen mobilization in astrocytes to protect white matter axons.
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Affiliation(s)
- Brian A MacVicar
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, V6T 1Z3, Canada.
| | - Hyun Beom Choi
- Djavad Mowafaghian Centre for Brain Health, University of British Columbia, Vancouver, V6T 1Z3, Canada
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12
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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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13
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Yao H, Azad P, Zhao HW, Wang J, Poulsen O, Freitas BC, Muotri AR, Haddad GG. The Na +/HCO 3- co-transporter is protective during ischemia in astrocytes. Neuroscience 2016; 339:329-337. [PMID: 27717805 DOI: 10.1016/j.neuroscience.2016.09.050] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Revised: 09/24/2016] [Accepted: 09/29/2016] [Indexed: 02/03/2023]
Abstract
The sodium bicarbonate co-transporter (NBC) is the major bicarbonate-dependent acid-base transporter in mammalian astrocytes and has been implicated in ischemic brain injury. A malfunction of astrocytes could have great impact on the outcome of stroke due to their participation in the formation of blood-brain barrier, synaptic transmission, and electrolyte balance in the human brain. Nevertheless, the role of NBC in the ischemic astrocyte death has not been well understood. In this work, we obtained skin biopsies from healthy human subjects and had their fibroblasts grown in culture and reprogrammed into human-induced pluripotent stem cells (hiPSCs). These hiPSCs were further differentiated into neuroprogenitor cells (NPCs) and then into human astrocytes. These astrocytes express GFAP and S100β and readily propagate calcium waves upon mechanical stimulation. Using pH-sensitive dye BCECF [2',7'-bis-(carboxyethyl)-5-(and-6)-carboxyfluorescein] and qPCR technique, we have confirmed that these astrocytes express functional NBC including electrogenic NBC (NBCe). In addition, astrocytes exposed to an ischemic solution (IS) that mimics the ischemic penumbral environment enhanced both mRNA and protein expression level of NBCe1 in astrocytes. Using IS and a generic NBC blocker S0859, we have studied the involvement of NBC in IS-induced human astrocytes death. Our results show that a 30μM S0859 induced a 97.5±1.6% (n=10) cell death in IS-treated astrocytes, which is significantly higher than 43.6±4.5%, (n=10) in the control group treated with IS alone. In summary, a NBC blocker exaggerates IS-induced cell death, suggesting that NBC activity is essential for astrocyte survival when exposed to ischemic penumbral environment.
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Affiliation(s)
- Hang Yao
- Departments of Pediatrics, University of California San Diego, La Jolla, CA 92093, United States
| | - Priti Azad
- Departments of Pediatrics, University of California San Diego, La Jolla, CA 92093, United States
| | - Huiwen W Zhao
- Departments of Pediatrics, University of California San Diego, La Jolla, CA 92093, United States
| | - Juan Wang
- Departments of Pediatrics, University of California San Diego, La Jolla, CA 92093, United States
| | - Orit Poulsen
- Departments of Pediatrics, University of California San Diego, La Jolla, CA 92093, United States
| | - Beatriz C Freitas
- Department of Pediatrics/Rady Children's Hospital San Diego, Department of Cellular & Molecular Medicine, Stem Cell Program, La Jolla, CA 92093, United States
| | - Alysson R Muotri
- Department of Pediatrics/Rady Children's Hospital San Diego, Department of Cellular & Molecular Medicine, Stem Cell Program, La Jolla, CA 92093, United States
| | - Gabriel G Haddad
- Departments of Pediatrics & Neuroscience, University of California-San Diego, La Jolla, CA 92093, United States; Rady Children's Hospital-San Diego, San Diego, CA 92123, United States.
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Myers EJ, Yuan L, Felmlee MA, Lin YY, Jiang Y, Pei Y, Wang O, Li M, Xing XP, Marshall A, Xia WB, Parker MD. A novel mutant Na + /HCO3 - cotransporter NBCe1 in a case of compound-heterozygous inheritance of proximal renal tubular acidosis. J Physiol 2016; 594:6267-6286. [PMID: 27338124 DOI: 10.1113/jp272252] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/29/2016] [Accepted: 06/08/2016] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS The inheritance of two defective alleles of SLC4A4, the gene that encodes the widely-expressed electrogenic sodium bicarbonate cotransporter NBCe1, results in the bicarbonate-wasting disease proximal renal tubular acidosis (pRTA). In the present study, we report the first case of compound-heterozygous inheritance of pRTA (p.Arg510His/p.Gln913Arg) in an individual with low blood pH, blindness and neurological signs that resemble transient ischaemic attacks. We employ fluorescence microscopy on non-polarized (human embryonic kidney) and polarized (Madin-Darby canine kidney) renal cell lines and electrophysiology on Xenopus oocytes to characterize the mutant transporters (R510H and Q913R). Both mutant transporters exhibit enhanced intracellular retention in renal cells, an observation that probably explains the HCO3- transport deficit in the individual. Both mutants retain a close-to-normal per molecule Na+ /HCO3- cotransport activity in Xenopus oocytes, suggesting that they are suitable candidates for folding-correction therapy. However, Q913R expression is uniquely associated with a depolarizing, HCO3- independent, Cl- -conductance in oocytes that could have pathological consequences if expressed in the cells of patients. ABSTRACT Proximal renal tubular acidosis (pRTA) is a rare, recessively-inherited disease characterized by abnormally acidic blood, blindness, as well as below average height and weight. pRTA is typically associated with homozygous mutation of the solute carrier 4 family gene SLC4A4. SLC4A4 encodes the electrogenic sodium bicarbonate cotransporter NBCe1, a membrane protein that acts to maintain intracellular and plasma pH. We present the first description of a case of compound-heterozygous inheritance of pRTA. The individual has inherited two mutations in NBCe1: p.Arg510His (R510H) and p.Gln913Arg (Q913R), one from each parent. In addition to the usual features of pRTA, the patient exhibits unusual signs, such as muscle spasms and fever. We have recreated these mutant transporters for expression in model systems. We find that both of the mutant proteins exhibit substantial intracellular retention when expressed in mammalian renal cell lines. When expressed in Xenopus oocytes, we find that the R510H and Q913R-mutant NBCe1 molecules exhibit apparently normal Na+ /HCO3- cotransport activity but that Q913R is associated with an unusual HCO3- independent anion-leak. We conclude that a reduced accumulation of NBCe1 protein in the basolateral membrane of proximal-tubule epithelia is the most probable cause of pRTA in this case. We further note that the Q913R-associated anion-leak could itself be pathogenic if expressed in the plasma membrane of mammalian cells, compromising the benefit of strategies aiming to enhance mutant NBCe1 accumulation in the plasma membrane.
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Affiliation(s)
- Evan J Myers
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Lu Yuan
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Melanie A Felmlee
- Department of Pharmaceutical Sciences, School of Pharmacy and Pharmaceutical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.,Department of Pharmaceutics and Medicinal Chemistry, Thomas J. Long School of Pharmacy and Health Sciences, University of the Pacific, Stockton, California, USA
| | - Yuan-Yuan Lin
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yan Jiang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Yu Pei
- Department of Endocrinology, Chinese People's Army General Hospital, Beijing, China
| | - Ou Wang
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Mei Li
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Xiao-Ping Xing
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China
| | - Aniko Marshall
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA
| | - Wei-Bo Xia
- Department of Endocrinology, Key Laboratory of Endocrinology of Ministry of Health, Peking Union Medical College Hospital, Peking Union Medical College, Chinese Academy of Medical Sciences, Beijing, China.
| | - Mark D Parker
- Department of Physiology and Biophysics, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,Department of Ophthalmology, Jacobs School of Medicine and Biomedical Sciences, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA. .,State University of New York Eye Institutes, University at Buffalo: The State University of New York, Buffalo, New York, NY, USA.
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15
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Cannabinoid Type 2 Receptors Mediate a Cell Type-Specific Plasticity in the Hippocampus. Neuron 2016; 90:795-809. [PMID: 27133464 DOI: 10.1016/j.neuron.2016.03.034] [Citation(s) in RCA: 203] [Impact Index Per Article: 25.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2014] [Revised: 01/20/2016] [Accepted: 03/18/2016] [Indexed: 02/07/2023]
Abstract
Endocannabinoids (eCBs) exert major control over neuronal activity by activating cannabinoid receptors (CBRs). The functionality of the eCB system is primarily ascribed to the well-documented retrograde activation of presynaptic CB1Rs. We find that action potential-driven eCB release leads to a long-lasting membrane potential hyperpolarization in hippocampal principal cells that is independent of CB1Rs. The hyperpolarization, which is specific to CA3 and CA2 pyramidal cells (PCs), depends on the activation of neuronal CB2Rs, as shown by a combined pharmacogenetic and immunohistochemical approach. Upon activation, they modulate the activity of the sodium-bicarbonate co-transporter, leading to a hyperpolarization of the neuron. CB2R activation occurred in a purely self-regulatory manner, robustly altered the input/output function of CA3 PCs, and modulated gamma oscillations in vivo. To conclude, we describe a cell type-specific plasticity mechanism in the hippocampus that provides evidence for the neuronal expression of CB2Rs and emphasizes their importance in basic neuronal transmission.
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16
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Zhao H, Carney KE, Falgoust L, Pan JW, Sun D, Zhang Z. Emerging roles of Na⁺/H⁺ exchangers in epilepsy and developmental brain disorders. Prog Neurobiol 2016; 138-140:19-35. [PMID: 26965387 DOI: 10.1016/j.pneurobio.2016.02.002] [Citation(s) in RCA: 49] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2015] [Revised: 02/03/2016] [Accepted: 02/27/2016] [Indexed: 12/15/2022]
Abstract
Epilepsy is a common central nervous system (CNS) disease characterized by recurrent transient neurological events occurring due to abnormally excessive or synchronous neuronal activity in the brain. The CNS is affected by systemic acid-base disorders, and epileptic seizures are sensitive indicators of underlying imbalances in cellular pH regulation. Na(+)/H(+) exchangers (NHEs) are a family of membrane transporter proteins actively involved in regulating intracellular and organellar pH by extruding H(+) in exchange for Na(+) influx. Altering NHE function significantly influences neuronal excitability and plays a role in epilepsy. This review gives an overview of pH regulatory mechanisms in the brain with a special focus on the NHE family and the relationship between epilepsy and dysfunction of NHE isoforms. We first discuss how cells translocate acids and bases across the membrane and establish pH homeostasis as a result of the concerted effort of enzymes and ion transporters. We focus on the specific roles of the NHE family by detailing how the loss of NHE1 in two NHE mutant mice results in enhanced neuronal excitability in these animals. Furthermore, we highlight new findings on the link between mutations of NHE6 and NHE9 and developmental brain disorders including epilepsy, autism, and attention deficit hyperactivity disorder (ADHD). These studies demonstrate the importance of NHE proteins in maintaining H(+) homeostasis and their intricate roles in the regulation of neuronal function. A better understanding of the mechanisms underlying NHE1, 6, and 9 dysfunctions in epilepsy formation may advance the development of new epilepsy treatment strategies.
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Affiliation(s)
- Hanshu Zhao
- Department of Neurology, The First Affiliated Hospital of the Harbin Medical University, Harbin, China.,Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Karen E Carney
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Lindsay Falgoust
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Jullie W Pan
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Dandan Sun
- Department of Neurology, University of Pittsburgh, Pittsburgh, PA 15213, USA.,Veterans Affairs Pittsburgh Health Care System, Geriatric Research, Educational and Clinical Center, Pittsburgh, PA 15213, USA
| | - Zhongling Zhang
- Department of Neurology, The First Affiliated Hospital of the Harbin Medical University, Harbin, China
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17
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Abstract
The human exocrine pancreas consists of 2 main cell types: acinar and ductal cells. These exocrine cells interact closely to contribute to the secretion of pancreatic juice. The most important ion in terms of the pancreatic ductal secretion is HCO3. In fact, duct cells produce an alkaline fluid that may contain up to 140 mM NaHCO3, which is essential for normal digestion. This article provides an overview of the basics of pancreatic ductal physiology and pathophysiology. In the first part of the article, we discuss the ductal electrolyte and fluid transporters and their regulation. The central role of cystic fibrosis transmembrane conductance regulator (CFTR) is highlighted, which is much more than just a Cl channel. We also review the role of pancreatic ducts in severe debilitating diseases such as cystic fibrosis (caused by various genetic defects of cftr), pancreatitis, and diabetes mellitus. Stimulation of ductal secretion in cystic fibrosis and pancreatitis may have beneficial effects in their treatment.
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18
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Ando H, Hirose M, Gainche L, Kawaai K, Bonneau B, Ijuin T, Itoh T, Takenawa T, Mikoshiba K. IRBIT Interacts with the Catalytic Core of Phosphatidylinositol Phosphate Kinase Type Iα and IIα through Conserved Catalytic Aspartate Residues. PLoS One 2015; 10:e0141569. [PMID: 26509711 PMCID: PMC4624786 DOI: 10.1371/journal.pone.0141569] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2015] [Accepted: 10/10/2015] [Indexed: 11/18/2022] Open
Abstract
Phosphatidylinositol phosphate kinases (PIPKs) are lipid kinases that generate phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2), a critical lipid signaling molecule that regulates diverse cellular functions, including the activities of membrane channels and transporters. IRBIT (IP3R-binding protein released with inositol 1,4,5-trisphosphate) is a multifunctional protein that regulates diverse target proteins. Here, we report that IRBIT forms signaling complexes with members of the PIPK family. IRBIT bound to all PIPK isoforms in heterologous expression systems and specifically interacted with PIPK type Iα (PIPKIα) and type IIα (PIPKIIα) in mouse cerebellum. Site-directed mutagenesis revealed that two conserved catalytic aspartate residues of PIPKIα and PIPKIIα are involved in the interaction with IRBIT. Furthermore, phosphatidylinositol 4-phosphate, Mg2+, and/or ATP interfered with the interaction, suggesting that IRBIT interacts with catalytic cores of PIPKs. Mutations of phosphorylation sites in the serine-rich region of IRBIT affected the selectivity of its interaction with PIPKIα and PIPKIIα. The structural flexibility of the serine-rich region, located in the intrinsically disordered protein region, is assumed to underlie the mechanism of this interaction. Furthermore, in vitro binding experiments and immunocytochemistry suggest that IRBIT and PIPKIα interact with the Na+/HCO3− cotransporter NBCe1-B. These results suggest that IRBIT forms signaling complexes with PIPKIα and NBCe1-B, whose activity is regulated by PI(4,5)P2.
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Affiliation(s)
- Hideaki Ando
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
- * E-mail: (HA); (KM)
| | - Matsumi Hirose
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Laura Gainche
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Katsuhiro Kawaai
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Benjamin Bonneau
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
| | - Takeshi Ijuin
- Division of Biochemistry, Kobe University Graduate School of Medicine, Kobe, Hyogo, Japan
| | - Toshiki Itoh
- Biosignal Research Center, Organization of Advanced Science and Technology, Kobe University, Kobe, Hyogo, Japan
| | - Tadaomi Takenawa
- Biosignal Research Center, Organization of Advanced Science and Technology, Kobe University, Kobe, Hyogo, Japan
| | - Katsuhiko Mikoshiba
- Laboratory for Developmental Neurobiology, RIKEN Brain Science Institute, Wako, Saitama, Japan
- * E-mail: (HA); (KM)
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19
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Abstract
Cation-coupled HCO3(-) transport was initially identified in the mid-1970s when pioneering studies showed that acid extrusion from cells is stimulated by CO2/HCO3(-) and associated with Na(+) and Cl(-) movement. The first Na(+)-coupled bicarbonate transporter (NCBT) was expression-cloned in the late 1990s. There are currently five mammalian NCBTs in the SLC4-family: the electrogenic Na,HCO3-cotransporters NBCe1 and NBCe2 (SLC4A4 and SLC4A5 gene products); the electroneutral Na,HCO3-cotransporter NBCn1 (SLC4A7 gene product); the Na(+)-driven Cl,HCO3-exchanger NDCBE (SLC4A8 gene product); and NBCn2/NCBE (SLC4A10 gene product), which has been characterized as an electroneutral Na,HCO3-cotransporter or a Na(+)-driven Cl,HCO3-exchanger. Despite the similarity in amino acid sequence and predicted structure among the NCBTs of the SLC4-family, they exhibit distinct differences in ion dependency, transport function, pharmacological properties, and interactions with other proteins. In epithelia, NCBTs are involved in transcellular movement of acid-base equivalents and intracellular pH control. In nonepithelial tissues, NCBTs contribute to intracellular pH regulation; and hence, they are crucial for diverse tissue functions including neuronal discharge, sensory neuron development, performance of the heart, and vascular tone regulation. The function and expression levels of the NCBTs are generally sensitive to intracellular and systemic pH. Animal models have revealed pathophysiological roles of the transporters in disease states including metabolic acidosis, hypertension, visual defects, and epileptic seizures. Studies are being conducted to understand the physiological consequences of genetic polymorphisms in the SLC4-members, which are associated with cancer, hypertension, and drug addiction. Here, we describe the current knowledge regarding the function, structure, and regulation of the mammalian cation-coupled HCO3(-) transporters of the SLC4-family.
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Affiliation(s)
- Christian Aalkjaer
- Department of Biomedicine, and the Water and Salt Research Center, Aarhus University, Aarhus, Denmark; Department of Physiology, Emory University School of Medicine, Atlanta, USA
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20
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Bernardino RL, Martins AD, Jesus TT, Sá R, Sousa M, Alves MG, Oliveira PF. Estrogenic regulation of bicarbonate transporters from SLC4 family in rat Sertoli cells. Mol Cell Biochem 2015; 408:47-54. [DOI: 10.1007/s11010-015-2481-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2015] [Accepted: 06/13/2015] [Indexed: 11/30/2022]
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21
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Liu Y, Chen LM. Towards bridging the gap between acid-base transporters and neuronal excitability modulation. INTERNATIONAL JOURNAL OF PHYSIOLOGY, PATHOPHYSIOLOGY AND PHARMACOLOGY 2014; 6:221-225. [PMID: 25755844 PMCID: PMC4348708] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 11/30/2014] [Accepted: 12/14/2014] [Indexed: 06/04/2023]
Abstract
pH homeostasis is a fundamental regulator of the function of the central nervous system. Dysfunction of acid-base transporters often results in disturbance of neuronal excitability. In a latest issue of Journal of Neuroscience, Jones et al. report that increasing intracellular bicarbonate concentration substantially stimulates the excitability of pyramidal neurons from mouse hippocampus by inhibiting KCNQ potassium channel. The finding shed important new light in understanding the molecular mechanism underlying the regulation of neuronal excitability by acid-base transporters.
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Affiliation(s)
- Ying Liu
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology 1037 Luoyu Rd, Wuhan, Hubei Province, 430074, P.R. China
| | - Li-Ming Chen
- Department of Biophysics and Molecular Physiology, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology 1037 Luoyu Rd, Wuhan, Hubei Province, 430074, P.R. China
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22
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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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23
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Kurtz I. NBCe1 as a model carrier for understanding the structure-function properties of Na⁺ -coupled SLC4 transporters in health and disease. Pflugers Arch 2014; 466:1501-16. [PMID: 24515290 DOI: 10.1007/s00424-014-1448-8] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2013] [Revised: 01/07/2014] [Accepted: 01/08/2014] [Indexed: 01/17/2023]
Abstract
SLC4 transporters are membrane proteins that in general mediate the coupled transport of bicarbonate (carbonate) and share amino acid sequence homology. These proteins differ as to whether they also transport Na(+) and/or Cl(-), in addition to their charge transport stoichiometry, membrane targeting, substrate affinities, developmental expression, regulatory motifs, and protein-protein interactions. These differences account in part for the fact that functionally, SLC4 transporters have various physiological roles in mammals including transepithelial bicarbonate transport, intracellular pH regulation, transport of Na(+) and/or Cl(-), and possibly water. Bicarbonate transport is not unique to the SLC4 family since the structurally unrelated SLC26 family has at least three proteins that mediate anion exchange. The present review focuses on the first of the sodium-dependent SLC4 transporters that was identified whose structure has been most extensively studied: the electrogenic Na(+)-base cotransporter NBCe1. Mutations in NBCe1 cause proximal renal tubular acidosis (pRTA) with neurologic and ophthalmologic extrarenal manifestations. Recent studies have characterized the important structure-function properties of the transporter and how they are perturbed as a result of mutations that cause pRTA. It has become increasingly apparent that the structure of NBCe1 differs in several key features from the SLC4 Cl(-)-HCO3 (-) exchanger AE1 whose structural properties have been well-studied. In this review, the structure-function properties and regulation of NBCe1 will be highlighted, and its role in health and disease will be reviewed in detail.
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Affiliation(s)
- Ira Kurtz
- Division of Nephrology, David Geffen School of Medicine, and Brain Research Institute, UCLA, Los Angeles, CA, USA,
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Boedtkjer E, Aalkjaer C. Disturbed acid-base transport: an emerging cause of hypertension. Front Physiol 2013; 4:388. [PMID: 24399970 PMCID: PMC3870919 DOI: 10.3389/fphys.2013.00388] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 12/09/2013] [Indexed: 11/26/2022] Open
Abstract
Genome-wide association studies and physiological investigations have linked alterations in acid-base transporters to hypertension. Accordingly, Na+-coupled HCO−3-transporters, Na+/H+-exchangers, and anion-exchangers have emerged as putative mechanistic components in blood pressure disturbances. Even though hypertension has been studied extensively over the last several decades, the cause of the high blood pressure has in most cases not been identified. Renal, cardiovascular, and neuronal dysfunctions all seem to play a role in hypertension development but their relative importance and mutual interdependency are still being debated. Multiple functional and structural alterations have been described in patients and animals with hypertension but it is typically unclear whether they are causes or consequences of hypertension or represent mechanistically unrelated associations. Perturbed blood pressure regulation has been demonstrated in several animal models with disrupted expression of acid-base transporters; and reciprocally, disturbed acid-base transport function has been described in hypertensive individuals. In addition to regulating intracellular and extracellular pH, Na+-coupled HCO−3-transport, Na+/H+-exchange, and anion-exchange also contribute to water and electrolyte balance in cells and systemically. Since acid-base transporters are widely expressed, alterations in transport activities likely affect multiple cell and organ functions, and it is a significant challenge to determine the mechanisms linking perturbed acid-base transport function to hypertension. It is the purpose of this review to evaluate the current evidence for involvement of acid-base transporters in hypertension development and discuss the cellular and integrative mechanisms, which may link changes in acid-base transport to blood pressure disturbances.
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Affiliation(s)
- Ebbe Boedtkjer
- Department of Biomedicine, Aarhus University Aarhus, Denmark
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Song D, Man Y, Li B, Xu J, Hertz L, Peng L. Comparison between drug-induced and K+-induced changes in molar acid extrusion fluxes (JH +) and in energy consumption rates in astrocytes. Neurochem Res 2013; 38:2364-74. [DOI: 10.1007/s11064-013-1149-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2013] [Revised: 08/08/2013] [Accepted: 08/31/2013] [Indexed: 10/26/2022]
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Oehlke O, Speer JM, Roussa E. Variants of the electrogenic sodium bicarbonate cotransporter 1 (NBCe1) in mouse hippocampal neurons are regulated by extracellular pH changes: evidence for a Rab8a-dependent mechanism. Int J Biochem Cell Biol 2013; 45:1427-38. [PMID: 23583738 DOI: 10.1016/j.biocel.2013.04.008] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2012] [Revised: 03/25/2013] [Accepted: 04/03/2013] [Indexed: 11/24/2022]
Abstract
Changes in extracellular pH are common events in both pathological conditions and during normal brain function. In organs other than the brain, cells may respond to pH changes by trafficking of acid-base transporters. However, regulation of neuronal acid-base transporters during pH shifts is not understood. The aim of this study was to investigate regulatory mechanisms of the variants of the electrogenic sodium/bicarbonate cotransporter 1, NBCe1-A and NBCe1-B/C, in neurons following changes of extracellular pH. Therefore, primary mouse hippocampal neurons were exposed to extracellular acidosis or alkalosis. We show that acid-base changes regulated trafficking and membrane expression of neuronal NBCe1 but the underlying molecular cues were distinct for individual NBCe1 variants. Following extracellular acidosis NBCe1-A was recruited from intracellular pools to the plasma membrane, followed by increased membrane expression, whereas NBCe1-B/C was retrieved from the membrane. Extracellular alkalosis had no impact on NBCe1-A, but caused translocation of NBCe1-B/C toward the dendrites. We also show that acidosis-induced NBCe1-A, but not NBCe1-B/C, trafficking is mediated by Rab8a. Rab8a is expressed in hippocampal neurons, co-localizes, and interacts with NBCe1-A. Loss-of-function of Rab8a using specific siRNA prevented acidosis-induced redistribution of NBCe1-A. These data propose opposite recruitment pattern for NBCe1 variants in neurons following extracellular acid-base changes, implicating distinct physiological functions of individual NBCe1 variants, and introduce Rab8a as a novel molecular determinant and crucial mediator of acidosis-induced NBCe1 trafficking in neurons.
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Affiliation(s)
- Oliver Oehlke
- Institute of Anatomy and Cell Biology, Department of Molecular Embryology, Albert-Ludwigs University Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany.
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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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Liu Y, Xu JY, Wang DK, Wang L, Chen LM. Cloning and identification of two novel NBCe1 splice variants from mouse reproductive tract tissues: a comparative study of NCBT genes. Genomics 2011; 98:112-9. [PMID: 21600280 DOI: 10.1016/j.ygeno.2011.04.010] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2011] [Revised: 04/18/2011] [Accepted: 04/27/2011] [Indexed: 12/26/2022]
Abstract
Na(+)-coupled HCO(3)(-) transporters (NCBTs) of the SLC4 family play critical roles in pH regulation as well as transepithelial HCO(3)(-) transport. We systematically examined, in the mouse reproductive tract tissues, the mRNA expression of five NCBTs as well as the five NBCe1 (Slc4a4) variants NBCe1-A through -E, of which NBCe1-D and NBCe1-E are novel. Cloning of NBCe1-D and NBCe1-E, both lacking a 27-nucleotide cassette I, reveals a novel alternative splicing unit in the mouse Slc4a4 gene. Transcripts of Slc4a4 lacking cassette I are expressed in diverse murine tissues as shown by RT-PCR analysis and in diverse tissues of other vertebrate species as shown by blast against GenBank database. Genomic sequence analysis indicates that cassette I of SLC4A4 is conserved in all NCBT genes except for SLC4A5, which presumably lost cassette I during its evolution. Our present study represents an important step towards understanding the molecular physiology of NBCe1, and presumably other NCBTs.
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Affiliation(s)
- Ying Liu
- Department of Biological Sciences, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science & Technology School of Life Science & Technology,Wuhan, Hubei Province 430074, China
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Lee HJ, Park HJ, Lee S, Kim YH, Choi I. The sodium-driven chloride/bicarbonate exchanger NDCBE in rat brain is upregulated by chronic metabolic acidosis. Brain Res 2011; 1377:13-20. [DOI: 10.1016/j.brainres.2010.12.062] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2010] [Revised: 11/30/2010] [Accepted: 12/20/2010] [Indexed: 11/27/2022]
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Chen LM, Liu Y, Boron WF. Role of an extracellular loop in determining the stoichiometry of Na+-HCO₃⁻ cotransporters. J Physiol 2011; 589:877-90. [PMID: 21224233 DOI: 10.1113/jphysiol.2010.198713] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The Na+–HCO₃⁻ cotransporters (NBCs) of the solute carrier 4 family (SLC4) are critical for regulating pH in cells as well as in fluids such as blood and cerebrospinal fluid. Moreover, mutations and gene disruptions in NBC are linked to a wide range of pathologies. NBCe1 (SLC4A4) is electrogenic because it has an apparent Na+:HCO₃⁻ stoichiometry of 1:2 or 1:3, whereas NBCn1 (SLC4A7) is electroneutral because it has an apparent stoichiometry of 1:1. Because stoichiometry influences the effect of transport on membrane potential and vice versa, a central question is what structural features underlie electrogenicity versus electroneutrality. A previous study on rat NBCe1/n1 chimeras demonstrated that the structural elements determining the electrogenicity of NBCe1-A are located within the transmembrane domain, excluding the large third extracellular loop. In the present study we generated a series of chimeras of human NBCe1-A and human NBCn1-A. We found that replacing merely the predicted fourth extracellular loop (EL4) – containing 32 amino acid residues that include 7 prolines – of human NBCe1-A with EL4 of NBCn1-A creates an electroneutral NBC. The opposite switch converts an electroneutral construct to one with electrogenic properties. The introduction of an N-glycosylation site into EL4 confirms that at least a part of it is exposed to the extracellular fluid. We hypothesize that putative EL4 either contributes to the substrate-binding vestibule or indirectly influences substrate binding by interacting with one or more transmembrane segments, thereby controlling the nature of transport.
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Affiliation(s)
- Li-Ming Chen
- Department of Biological Science, Key Laboratory of Molecular Biophysics of Ministry of Education, Huazhong University of Science and Technology School of Life Science and Technology, 1037 Luoyu Road, Wuhan, Hubei Province 430074, P.R. China.
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Kimelberg HK, Nedergaard M. Functions of astrocytes and their potential as therapeutic targets. Neurotherapeutics 2010; 7:338-53. [PMID: 20880499 PMCID: PMC2982258 DOI: 10.1016/j.nurt.2010.07.006] [Citation(s) in RCA: 278] [Impact Index Per Article: 19.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2010] [Accepted: 07/27/2010] [Indexed: 12/28/2022] Open
Abstract
Astrocytes are often referred to, and historically have been regarded as, support cells of the mammalian CNS. Work over the last decade suggests otherwise-that astrocytes may in fact play a more active role in higher neural processing than previously recognized. Because astrocytes can potentially serve as novel therapeutic targets, it is critical to understand how astrocytes execute their diverse supportive tasks while maintaining neuronal health. To that end, this review focuses on the supportive roles of astrocytes, a line of study relevant to essentially all acute and chronic neurological diseases, and critically re-evaluates our concepts of the functional properties of astrocytes and relates these functions and properties to the intricate morphology of these cells.
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Affiliation(s)
| | - Maiken Nedergaard
- grid.16416.340000000419369174Center for Translational Neuromedicine, Department of Neurosurgery, University of Prochester Medical School, 601 Elmwood Avenue, 114642 Rochester, New York
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Majumdar D, Bevensee MO. Na-coupled bicarbonate transporters of the solute carrier 4 family in the nervous system: function, localization, and relevance to neurologic function. Neuroscience 2010; 171:951-72. [PMID: 20884330 DOI: 10.1016/j.neuroscience.2010.09.037] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2010] [Revised: 09/03/2010] [Accepted: 09/14/2010] [Indexed: 12/26/2022]
Abstract
Many cellular processes including neuronal activity are sensitive to changes in intracellular and/or extracellular pH-both of which are regulated by acid-base transporter activity. HCO(3)(-)-dependent transporters are particularly potent regulators of intracellular pH in neurons and astrocytes, and also contribute to the composition of the cerebrospinal fluid (CSF). The molecular physiology of HCO(3)(-) transporters has advanced considerably over the past ∼14 years as investigators have cloned and characterized the function and localization of many Na-Coupled Bicarbonate Transporters of the solute carrier 4 (Slc4) family (NCBTs). In this review, we provide an updated overview of the function and localization of NCBTs in the nervous system. Multiple NCBTs are expressed in neurons and astrocytes in various brain regions, as well as in epithelial cells of the choroid plexus. Characteristics of human patients with SLC4 gene mutations/deletions and results from recent studies on mice with Slc4 gene disruptions highlight the functional importance of NCBTs in neuronal activity, somatosensory function, and CSF production. Furthermore, energy-deficient states (e.g., hypoxia and ischemia) lead to altered expression and activity of NCBTs. Thus, recent studies expand our understanding of the role of NCBTs in regulating the pH and ionic composition of the nervous system that can modulate neuronal activity.
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Affiliation(s)
- D Majumdar
- Department of Physiology and Biophysics, University of Alabama at Birmingham, Birmingham, AL 35294, USA
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Defective membrane expression of the Na(+)-HCO(3)(-) cotransporter NBCe1 is associated with familial migraine. Proc Natl Acad Sci U S A 2010; 107:15963-8. [PMID: 20798035 DOI: 10.1073/pnas.1008705107] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Homozygous mutations in SLC4A4, encoding the electrogenic Na(+)-HCO(3)(-) cotransporter NBCe1, have been known to cause proximal renal tubular acidosis (pRTA) and ocular abnormalities. In this study, we report two sisters with pRTA, ocular abnormalities, and hemiplegic migraine. Genetic analysis ruled out pathological mutations in the known genes for familial hemiplegic migraine, but identified a homozygous 65-bp deletion (Delta65bp) in the C terminus of NBCe1, corresponding to the codon change S982NfsX4. Several heterozygous members of this family also presented glaucoma and migraine with or without aura. Despite the normal electrogenic activity in Xenopus oocytes, the Delta65bp mutant showed almost no transport activity due to a predominant cytosolic retention in mammalian cells. Furthermore, coexpression experiments uncovered a dominant negative effect of the mutant through hetero-oligomer formation with wild-type NBCe1. Among other pRTA pedigrees with different NBCe1 mutations, we identified four additional homozygous patients with migraine. The immunohistological and functional analyses of these mutants demonstrate that the near total loss of NBCe1 activity in astrocytes can cause migraine potentially through dysregulation of synaptic pH.
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34
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Abstract
Before the roles of normal, mature astrocytes in the mammalian CNS can be discussed, we first need to define these cells. A definition proposed here is that such a class is best defined as consisting of the protoplasmic and fibrous astrocytes of the gray and white matter, respectively, the Bergmann glia of the molecular layer of the cerebellum, and the Muller cells of the retina. It is concluded that the established properties and functions of these mature astrocytes are essential support for neuronal activity, in the sense of Claude Bernard's principle of maintaining "la fixité du milieu intérieur." This milieu would be the extracellular space common to astrocytes and neurons. More specialized roles, such as the recently described "light guides" for retinal Muller cells can also be viewed as support and facilitation. The ECS is also, of course, common to all other neural cells, but here, I limit the discussion to perturbations of the ECS caused only by neuronal activities and the resolution of these perturbations by astrocytes, such as control of increases in extracellular K(+), uptake of excitatory amino acids, and alterations in blood vessel diameter and therefore blood flow. It is also proposed how this fits into the current morphological picture for the protoplasmic astrocytes as having small cell bodies with up to 100,000 process endings that occupy separate territories on which the processes of neighboring astrocytes scarcely intrude.
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35
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Erlichman JS, Leiter JC. Glia modulation of the extracellular milieu as a factor in central CO2 chemosensitivity and respiratory control. J Appl Physiol (1985) 2010; 108:1803-11. [PMID: 20110540 DOI: 10.1152/japplphysiol.01321.2009] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
We discuss the influence of astrocytes on respiratory function, particularly central CO2 chemosensitivity. Fluorocitrate (FC) poisons astrocytes, and studies in intact animals using FC provide strong evidence that disrupting astrocytic function can influence CO2 chemosensitivity and ventilation. Gap junctions interconnect astrocytes and contribute to K+ homeostasis in the extracellular fluid (ECF). Blocking gap junctions alters respiratory control, but proof that this is truly an astrocytic effect is lacking. Intracellular pH regulation of astrocytes has reciprocal effects on extracellular pH. Electrogenic sodium-bicarbonate transport (NBCe) is present in astrocytes. The activity of NBCe alkalinizes intracellular pH and acidifies extracellular pH when activated by depolarization (and a subset of astrocytes are depolarized by hypercapnia). Thus, to the extent that astrocytic intracellular pH regulation during hypercapnia lowers extracellular pH, astrocytes will amplify the hypercapnic stimulus and may influence central chemosensitivity. However, the data so far provide only inferential support for this hypothesis. A lactate shuttle from astrocytes to neurons seems to be active in the retrotrapezoid nucleus (RTN) and important in setting the chemosensory stimulus in the RTN (and possibly other chemosensory nuclei). Thus astrocytic processes, so vital in controlling the constituents of the ECF in the central nervous system, may profoundly influence central CO2 chemosensitivity and respiratory control.
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Affiliation(s)
- Joseph S Erlichman
- Department of Biology, St. Lawrence University, Canton, NY 13617-1475, USA.
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Boron WF, Chen L, Parker MD. Modular structure of sodium-coupled bicarbonate transporters. ACTA ACUST UNITED AC 2009; 212:1697-706. [PMID: 19448079 DOI: 10.1242/jeb.028563] [Citation(s) in RCA: 103] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Mammalian genomes contain 10 SLC4 genes that, between them, encode three Cl-HCO(3) exchangers, five Na(+)-coupled HCO(3) transporters (NCBTs), one reported borate transporter, and what is reported to be a fourth Cl-HCO(3) exchanger. The NCBTs are expressed throughout the body and play important roles in maintaining intracellular and whole-body pH, as well as contributing to transepithelial transport processes. The importance of NCBTs is underscored by the genetic association of dysfunctional NCBT genes with blindness, deafness, epilepsy, hypertension and metal retardation. Key to understanding the action and regulation of NCBTs is an appreciation of the diversity of NCBT gene products. The transmembrane domains of human NCBT paralogs are 50-84% identical to each other at the amino acid level, and are capable of a diverse range of actions, including electrogenic Na/HCO(3) cotransport (i.e. NBCe1 and NBCe2) and electroneutral Na/HCO(3) cotransport (i.e. NBCn1 and NBCn2), as well as Na(+)-dependent Cl-HCO(3) exchange (i.e. NDCBE). Furthermore, by the use of alternative promoters and alternative-splicing events, individual SLC4 genes have the potential to generate multiple splice variants (as many as 16 in the case of NBCn1), each of which could have unique temporal and spatial patterns of distribution, unitary transporter activity (i.e. flux mediated by one molecule), array of protein-binding partners, and complement of regulatory stimuli. In the first section of this review, we summarize our present knowledge of the function and distribution of mammalian NCBTs and their multiple variants. In the second section of this review we consider the molecular consequences of NCBT variation.
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Affiliation(s)
- Walter F Boron
- Department of Physiology, Case Western Reserve University Medical School, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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Wang Y, Han TZ. Prenatal exposure to heroin in mice elicits memory deficits that can be attributed to neuronal apoptosis. Neuroscience 2009; 160:330-8. [DOI: 10.1016/j.neuroscience.2009.02.058] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2009] [Revised: 02/16/2009] [Accepted: 02/26/2009] [Indexed: 10/21/2022]
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Cooper DS, Yang HS, He P, Kim E, Rajbhandari I, Yun CC, Choi I. Sodium/bicarbonate cotransporter NBCn1/slc4a7 increases cytotoxicity in magnesium depletion in primary cultures of hippocampal neurons. Eur J Neurosci 2008; 29:437-46. [PMID: 19170751 DOI: 10.1111/j.1460-9568.2008.06611.x] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Growing evidence suggests that pharmacological inhibition of Na/H exchange and Na/HCO(3) transport provides protection against damage or injury in cardiac ischemia. In this study, we examined the contribution of the sodium/bicarbonate cotransporter NBCn1 (slc4a7) to cytotoxicity in cultured hippocampal neurons of rats. In neurons exposed to extracellular pH (pH(o)) ranging from 6.2 to 8.3, NBCn1 protein expression increased by fivefold at pH < 6.5 compared to the expression at pH(o) 7.4. At pH(o) 6.5, the intracellular pH of neurons was approximately 1 unit lower than that at pH 7.4. Immunochemistry showed a marked increase in NBCn1 immunofluorescence in plasma membranes and cytosol of the soma as well as in dendrites, at pH(o) 6.5. NBCn1 expression also increased by 40% in a prolonged Mg(2+)-free incubation at normal pH(o). Knockdown of NBCn1 in neurons had negligible effect on cell viability. The effect of NBCn1 knockdown on cytotoxicity was then determined by exposing neurons to 0.5 mm glutamate for 10 min and measuring lactate dehydrogenase (LDH) release from neurons. Compared to normal incubation (pH(o) 7.2 for 6 h) after glutamate exposure, acidic incubation (pH(o) 6.3 for 6 h) reduced cytotoxicity by 75% for control neurons and 78% for NBCn1-knockdown neurons. Thus, both controls and knockdown neurons showed acidic protection from cytotoxicity. However, in Mg(2+)-free incubation after glutamate exposure, NBCn1 knockdown progressively attenuated cytotoxicity. This attenuation was unaffected by acidic preincubation before glutamate exposure. We conclude that NBCn1 has a dynamic upregulation in low pH(o) and Mg(2+) depletion. NBCn1 is not required for acidic protection, but increases cytotoxicity in Mg(2+)-free conditions.
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Affiliation(s)
- Deborah S Cooper
- Department of Physiology, Emory University School of Medicine, Atlanta, GA 30322, USA
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Majumdar D, Maunsbach AB, Shacka JJ, Williams JB, Berger UV, Schultz KP, Harkins LE, Boron WF, Roth KA, Bevensee MO. Localization of electrogenic Na/bicarbonate cotransporter NBCe1 variants in rat brain. Neuroscience 2008; 155:818-32. [PMID: 18582537 DOI: 10.1016/j.neuroscience.2008.05.037] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2008] [Revised: 05/16/2008] [Accepted: 05/20/2008] [Indexed: 10/22/2022]
Abstract
The activity of HCO(3)(-) transporters contributes to the acid-base environment of the nervous system. In the present study, we used in situ hybridization, immunoblotting, immunohistochemistry, and immunogold electron microscopy to localize electrogenic Na/bicarbonate cotransporter NBCe1 splice variants (-A, -B, and -C) in rat brain. The in situ hybridization data are consistent with NBCe1-B and -C, but not -A, being the predominant NBCe1 variants in brain, particularly in the cerebellum, hippocampus, piriform cortex, and olfactory bulb. An antisense probe to the B and C variants strongly labeled granule neurons in the dentate gyrus of the hippocampus, and cells in the granule layer and Purkinje layer (e.g. Bergmann glia) of the cerebellum. Weaker labeling was observed in the pyramidal layer of the hippocampus and in astrocytes throughout the brain. Similar, but weaker labeling was obtained with an antisense probe to the A and B variants. In immunoblot studies, antibodies to the A and B variants (alphaA/B) and C variant (alphaC) labeled approximately 130-kDa proteins in various brain regions. From immunohistochemistry data, both alphaA/B and alphaC exhibited diffuse labeling throughout brain, but alphaA/B labeling was more intracellular and punctate. Based on co-localization studies with antibodies to neuronal or astrocytic markers, alphaA/B labeled neurons in the pyramidal layer and dentate gyrus of the hippocampus, as well as cortex. alphaC labeled glia surrounding neurons (and possibly neurons) in the neuropil of the Purkinje cell layer of the cerebellum, the pyramidal cell layer and dentate gyrus of the hippocampus, and the cortex. According to electron microscopy data from the cerebellum, alphaA/B primarily labeled neurons intracellularly and alphaC labeled astrocytes at the plasma membrane. In summary, the B and C variants are the predominant NBCe1 variants in rat brain and exhibit different localization profiles.
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Affiliation(s)
- D Majumdar
- Department of Physiology and Biophysics, University of Alabama at Birmingham, 1918 University Boulevard, 812 MCLM, Birmingham, AL 35294, USA
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Bevensee MO, Boron WF. Effects of acute hypoxia on intracellular-pH regulation in astrocytes cultured from rat hippocampus. Brain Res 2007; 1193:143-52. [PMID: 18190894 DOI: 10.1016/j.brainres.2007.12.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2007] [Revised: 12/03/2007] [Accepted: 12/03/2007] [Indexed: 11/28/2022]
Abstract
We used the pH-sensitive dye BCECF to evaluate the effect of acute (5-10 min) hypoxia (approximately 3% O(2)) on the regulation of intracellular pH (pH(i)) in astrocyte populations cultured from rat hippocampus. For cells in the nominal absence of CO(2)/HCO(3)(-) at an extracellular pH of 7.40 (37 degrees C), acute hypoxia caused a small (0.05) decrease in steady-state pH(i), but increased the pH(i) recovery rate from an acid load during all but the late phase of the pH(i) recovery. During such pH(i) recoveries, the total acid extrusion rate (phi(E), the product of dpH(i)/dt and proton buffering power) decreased with increasing pH(i). Hypoxia alkali shifted the plot of phi(E) vs. pH(i); over the upper approximately 85% of the phi(E) range, this shift was 0.15-0.30. Hypoxia also stimulated the pH(i) recovery rate from an alkali load. Under normoxic conditions, switching the extracellular buffer to 5% CO(2)/22 mM HCO(-)(3) also alkali shifted the phi(E)-pH(i) plot (upper approximately 85%) by 0.4-0.5. Superimposing hypoxia on CO(2)/HCO(-)(3) further alkali shifted the phi(E)-pH(i) plot (upper approximately 85% of the phi(E) range) by 0.05-0.15. The SITS-insensitive component of phi(E) was alkali shifted by 0.20-0.30, whereas the SITS-sensitive component of phi(E) was depressed in the low pH(i) range. Thus, in the nominal absence of CO(2)/HCO(3)(-), acute hypoxia has little effect on steady-state pH(i) but stimulates acid extrusion and acid loading, whereas in the presence of CO(2)/HCO(-)(3), hypoxia stimulates the SITS-insensitive but inhibits the SITS-sensitive acid extrusion.
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Affiliation(s)
- Mark O Bevensee
- Department of Cellular and Molecular Physiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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