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Alquisiras-Burgos I, Franco-Pérez J, Rubio-Osornio M, Aguilera P. The short form of the SUR1 and its functional implications in the damaged brain. Neural Regen Res 2022; 17:488-496. [PMID: 34380876 PMCID: PMC8504400 DOI: 10.4103/1673-5374.320967] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Sulfonylurea receptor (SUR) belongs to the adenosine 5′-triphosphate (ATP)-binding cassette (ABC) transporter family; however, SUR is associated with ion channels and acts as a regulatory subunit determining the opening or closing of the pore. Abcc8 and Abcc9 genes code for the proteins SUR1 and SUR2, respectively. The SUR1 transcript encodes a protein of 1582 amino acids with a mass around 140–177 kDa expressed in the pancreas, brain, heart, and other tissues. It is well known that SUR1 assembles with Kir6.2 and TRPM4 to establish KATP channels and non-selective cation channels, respectively. Abbc8 and 9 are alternatively spliced, and the resulting transcripts encode different isoforms of SUR1 and SUR2, which have been detected by different experimental strategies. Interestingly, the use of binding assays to sulfonylureas and Western blotting has allowed the detection of shorter forms of SUR (~65 kDa). Identity of the SUR1 variants has not been clarified, and some authors have suggested that the shorter forms are unspecific. However, immunoprecipitation assays have shown that SUR2 short forms are part of a functional channel even coexisting with the typical forms of the receptor in the heart. This evidence confirms that the structure of the short forms of the SURs is fully functional and does not lose the ability to interact with the channels. Since structural changes in short forms of SUR modify its affinity to ATP, regulation of its expression might represent an advantage in pathologies where ATP concentrations decrease and a therapeutic target to induce neuroprotection. Remarkably, the expression of SUR1 variants might be induced by conditions associated to the decrease of energetic substrates in the brain (e.g. during stroke and epilepsy). In this review, we want to contribute to the knowledge of SUR1 complexity by analyzing evidence that shows the existence of short SUR1 variants and its possible implications in brain function.
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Affiliation(s)
- Iván Alquisiras-Burgos
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Javier Franco-Pérez
- Laboratorio de Formación Reticular, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Moisés Rubio-Osornio
- Laboratorio Experimental de Enfermedades Neurodegenerativas, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Penélope Aguilera
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
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2
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Huang Y, Hu D, Huang C, Nichols CG. Genetic Discovery of ATP-Sensitive K + Channels in Cardiovascular Diseases. Circ Arrhythm Electrophysiol 2020; 12:e007322. [PMID: 31030551 DOI: 10.1161/circep.119.007322] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The ATP-sensitive K+ (KATP) channels are hetero-octameric protein complexes comprising 4 pore-forming (Kir6.x) subunits and 4 regulatory sulfonylurea receptor (SURx) subunits. They are prominent in myocytes, pancreatic β cells, and neurons and link cellular metabolism with membrane excitability. Using genetically modified animals and genomic analysis in patients, recent studies have implicated certain ATP-sensitive K+ channel subtypes in physiological and pathological processes in a variety of cardiovascular diseases. In this review, we focus on the causal relationship between ATP-sensitive K+ channel activity and pathophysiology in the cardiovascular system, particularly from the perspective of genetic changes in human and animal models.
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Affiliation(s)
- Yan Huang
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Dan Hu
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Congxin Huang
- Department of Cardiology, Renmin Hospital of Wuhan University; Cardiovascular Research Institute, Wuhan University, PR China (Y.H., D.H., C.H.).,Hubei Key Laboratory of Cardiology, Wuhan, PR China (Y.H., D.H., C.H.)
| | - Colin G Nichols
- Center for the Investigation of Membrane Excitability Diseases and Department of Cell Biology and Physiology, Washington University School of Medicine, Saint Louis, MO (C.G.N.)
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Tinker A, Aziz Q, Li Y, Specterman M. ATP‐Sensitive Potassium Channels and Their Physiological and Pathophysiological Roles. Compr Physiol 2018; 8:1463-1511. [DOI: 10.1002/cphy.c170048] [Citation(s) in RCA: 72] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
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4
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Flanagan SE, Dũng VC, Houghton JAL, De Franco E, Ngoc CTB, Damhuis A, Ashcroft FM, Harries LW, Ellard S. An ABCC8 Nonsense Mutation Causing Neonatal Diabetes Through Altered Transcript Expression. J Clin Res Pediatr Endocrinol 2017; 9:260-264. [PMID: 28663158 PMCID: PMC5596808 DOI: 10.4274/jcrpe.4624] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The pancreatic ATP-sensitive K+ (K-ATP) channel is a key regulator of insulin secretion. Gain-of-function mutations in the genes encoding the Kir6.2 (KCNJ11) and SUR1 (ABCC8) subunits of the channel cause neonatal diabetes, whilst loss-of-function mutations in these genes result in congenital hyperinsulinism. We report two patients with neonatal diabetes in whom we unexpectedly identified recessively inherited loss-of-function mutations. The aim of this study was to investigate how a homozygous nonsense mutation in ABCC8 could result in neonatal diabetes. The ABCC8 p.Glu747* was identified in two unrelated Vietnamese patients. This mutation is located within the in-frame exon 17 and RNA studies confirmed (a) the absence of full length SUR1 mRNA and (b) the presence of the alternatively spliced transcript lacking exon 17. Successful transfer of both patients to sulphonylurea treatment suggests that the altered transcript expression enhances the sensitivity of the K-ATP channel to Mg-ADP/ATP. This is the first report of an ABCC8 nonsense mutation causing a gain-of-channel function and these findings extend the spectrum of K-ATP channel mutations observed in patients with neonatal diabetes.
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Affiliation(s)
- Sarah E. Flanagan
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
,* Address for Correspondence: University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom E-mail:
| | - Vũ Chí Dũng
- National Children’s Hospital, Department of Endocrinology, Metabolism and Genetics, Hanoi, Vietnam
| | - Jayne A. L. Houghton
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Elisa De Franco
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Can Thi Bich Ngoc
- National Children’s Hospital, Department of Endocrinology, Metabolism and Genetics, Hanoi, Vietnam
| | - Annet Damhuis
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Frances M. Ashcroft
- University of Oxford, Henry Wellcome Centre for Gene Function, Department of Physiology, Anatomy and Genetics, Oxford, United Kingdom
| | - Lorna W. Harries
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
| | - Sian Ellard
- University of Exeter Medical School, Institute of Biomedical and Clinical Science, Department of Molecular Genetics, Exeter, United Kingdom
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5
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Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
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Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
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Abstract
The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.
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Burley DS, Cox CD, Zhang J, Wann KT, Baxter GF. Natriuretic peptides modulate ATP-sensitive K(+) channels in rat ventricular cardiomyocytes. Basic Res Cardiol 2014; 109:402. [PMID: 24477916 PMCID: PMC3951884 DOI: 10.1007/s00395-014-0402-4] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 12/10/2013] [Accepted: 01/10/2014] [Indexed: 11/28/2022]
Abstract
B-type natriuretic peptide (BNP) and C-type natriuretic peptide (CNP), and (Cys-18)-atrial natriuretic factor (4–23) amide (C-ANF), are cytoprotective under conditions of ischemia–reperfusion, limiting infarct size. ATP-sensitive K+ channel (KATP) opening is also cardioprotective, and although the KATP activation is implicated in the regulation of cardiac natriuretic peptide release, no studies have directly examined the effects of natriuretic peptides on cardiac KATP activity. Normoxic cardiomyocytes were patch clamped in the cell-attached configuration to examine sarcolemmal KATP (sKATP) activity. The KATP opener pinacidil (200 μM) increased the open probability of the patch (NPo; values normalized to control) at least twofold above basal value, and this effect was abolished by HMR1098 10 μM, a selective KATP blocker (5.23 ± 1.20 versus 0.89 ± 0.18; P < 0.001). We then examined the effects of BNP, CNP, C-ANF and 8Br-cGMP on the sKATP current. Bath application of BNP (≥10 nM) or CNP (≥0.01 nM) suppressed basal NPo (BNP: 1.00 versus 0.56 ± 0.09 at 10 nM, P < 0.001; CNP: 1.0 versus 0.45 ± 0.16, at 0.01 nM, P < 0.05) and also abolished the pinacidil-activated current at concentrations ≥10 nM. C-ANF (≥10 nM) enhanced KATP activity (1.00 versus 3.85 ± 1.13, at 100 nM, P < 0.05). The cGMP analog 8Br-cGMP 10 nM dampened the pinacidil-activated current (2.92 ± 0.60 versus 1.53 ± 0.32; P < 0.05). Natriuretic peptides modulate sKATP current in ventricular cardiomyocytes. This may be at least partially associated with their ability to augment intracellular cGMP concentrations via NPR-A/B, or their ability to bind NPR-C with high affinity. Although the mechanism of modulation requires elucidation, these preliminary data give new insights into the relationship between natriuretic peptide signaling and sKATP in the myocardium.
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Affiliation(s)
- Dwaine S Burley
- Cardiff School of Pharmacy and Pharmaceutical Sciences, Cardiff University, King Edward VII Avenue, Cardiff, CF10 3NB, UK,
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8
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Schmid D, Stolzlechner M, Sorgner A, Bentele C, Assinger A, Chiba P, Moeslinger T. An abundant, truncated human sulfonylurea receptor 1 splice variant has prodiabetic properties and impairs sulfonylurea action. Cell Mol Life Sci 2012; 69:129-48. [PMID: 21671119 PMCID: PMC11114697 DOI: 10.1007/s00018-011-0739-x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2010] [Revised: 05/20/2011] [Accepted: 05/23/2011] [Indexed: 12/20/2022]
Abstract
An alternatively spliced form of human sulfonylurea receptor (SUR) 1 mRNA lacking exon 2 (SUR1Δ2) has been identified. The omission of exon 2 caused a frame shift and an immediate stop codon in exon 3 leading to translation of a 5.6-kDa peptide that comprises the N-terminal extracellular domain and the first transmembrane helix of SUR1. Based on a weak first splice acceptor site in the human SUR1 gene (ABCC8), RT-PCR revealed a concurrent expression of SUR1Δ2 and SUR1. The SUR1Δ2/(SUR1 + SUR1Δ2) mRNA ratio differed between tissues, and was lowest in pancreas (46%), highest in heart (88%) and negatively correlated with alternative splice factor/splicing factor 2 (ASF/SF2) expression. In COS-7 cells triple transfected with SUR1Δ2/SUR1/Kir6.2, the SUR1Δ2 peptide co-immunoprecipitated with Kir6.2, thereby displacing two of four SUR1 subunits on the cell surface. The ATP sensitivity of these hybrid ATP-sensitive potassium channels (K(ATP)) channels was reduced by about sixfold, as shown with single-channel recordings. RINm5f rat insulinoma cells, which genuinely express SUR1 but not SUR1Δ2, exhibited a strongly increased K(ATP) channel current upon transfection with SUR1Δ2. This led to inhibition of glucose-induced depolarization, calcium flux, insulin release and glibenclamide action. A non-mutagenic SNP on nucleotide position 333 (Pro69Pro) added another exonic splicing enhancer sequence detected by ASF/SF2, reduced relative abundance of SUR1Δ2 and slightly protected from non-insulin dependent diabetes in homozygotic individuals. Thus, SUR1Δ2 represents an endogenous K(ATP)-channel modulator with prodiabetic properties in islet cells. Its predominance in heart may explain why high-affinity sulfonylurea receptors are not found in human cardiac tissue.
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MESH Headings
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Alternative Splicing/physiology
- Animals
- COS Cells
- Calcium/metabolism
- Chlorocebus aethiops
- Diabetes Mellitus, Type 2/genetics
- Diabetes Mellitus, Type 2/metabolism
- Diabetes Mellitus, Type 2/physiopathology
- Exons/physiology
- Glyburide/pharmacology
- Humans
- Hypoglycemic Agents/pharmacology
- Insulin/metabolism
- Islets of Langerhans/metabolism
- KATP Channels/drug effects
- KATP Channels/metabolism
- Myocardium/metabolism
- Organ Specificity/genetics
- Pancreas/metabolism
- Polymorphism, Single Nucleotide
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- Rats
- Receptors, Drug/genetics
- Receptors, Drug/metabolism
- Species Specificity
- Sulfonylurea Receptors
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Affiliation(s)
- Diethart Schmid
- Institute of Physiology, Center for Physiology and Pharmacology, Medical University of Vienna, Vienna, Austria.
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9
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Flagg TP, Enkvetchakul D, Koster JC, Nichols CG. Muscle KATP channels: recent insights to energy sensing and myoprotection. Physiol Rev 2010; 90:799-829. [PMID: 20664073 DOI: 10.1152/physrev.00027.2009] [Citation(s) in RCA: 202] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are present in the surface and internal membranes of cardiac, skeletal, and smooth muscle cells and provide a unique feedback between muscle cell metabolism and electrical activity. In so doing, they can play an important role in the control of contractility, particularly when cellular energetics are compromised, protecting the tissue against calcium overload and fiber damage, but the cost of this protection may be enhanced arrhythmic activity. Generated as complexes of Kir6.1 or Kir6.2 pore-forming subunits with regulatory sulfonylurea receptor subunits, SUR1 or SUR2, the differential assembly of K(ATP) channels in different tissues gives rise to tissue-specific physiological and pharmacological regulation, and hence to the tissue-specific pharmacological control of contractility. The last 10 years have provided insights into the regulation and role of muscle K(ATP) channels, in large part driven by studies of mice in which the protein determinants of channel activity have been deleted or modified. As yet, few human diseases have been correlated with altered muscle K(ATP) activity, but genetically modified animals give important insights to likely pathological roles of aberrant channel activity in different muscle types.
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Affiliation(s)
- Thomas P Flagg
- Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
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10
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Stoller DA, Fahrenbach JP, Chalupsky K, Tan BH, Aggarwal N, Metcalfe J, Hadhazy M, Shi NQ, Makielski JC, McNally EM. Cardiomyocyte sulfonylurea receptor 2-KATP channel mediates cardioprotection and ST segment elevation. Am J Physiol Heart Circ Physiol 2010; 299:H1100-8. [PMID: 20656890 DOI: 10.1152/ajpheart.00084.2010] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Sulfonylurea receptor-containing ATP-sensitive potassium (K(ATP)) channels have been implicated in cardioprotection, but the cell type and constitution of channels responsible for this protection have not been clear. Mice deleted for the first nucleotide binding region of sulfonylurea receptor 2 (SUR2) are referred to as SUR2 null since they lack full-length SUR2 and glibenclamide-responsive K(ATP) channels in cardiac, skeletal, and smooth muscle. As previously reported, SUR2 null mice develop electrocardiographic changes of ST segment elevation that were shown to correlate with coronary artery vasospasm. Here we restored expression of the cardiomyocyte SUR2-K(ATP) channel in SUR2 null mice by generating transgenic mice with ventricular cardiomyocyte-restricted expression of SUR2A. Introduction of the cardiomyocyte SUR2A transgene into the SUR2 null background restored functional cardiac K(ATP) channels. Hearts isolated from rescued mice, referred to as MLC2A, had significantly reduced infarct size (27 ± 3% of area at risk) compared with SUR2 null mice (36 ± 3% of area at risk). Compared with SUR2 null hearts, MLC2A hearts exhibited significantly improved cardiac function during the postischemia reperfusion period primarily because of preservation of low diastolic pressures. Additionally, restoration of cardiac SUR2-K(ATP) channels significantly reduced the degree and frequency of ST segment elevation episodes in MLC2A mice. Therefore, cardioprotective mechanisms both dependent and independent of SUR2-K(ATP) channels contribute to cardiac function.
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Affiliation(s)
- Douglas A Stoller
- Committee on Cellular and Molecular Physiology, University of Chicago, Chicago, IL 60637, USA
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11
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Lefer DJ, Nichols CG, Coetzee WA. Sulfonylurea receptor 1 subunits of ATP-sensitive potassium channels and myocardial ischemia/reperfusion injury. Trends Cardiovasc Med 2009; 19:61-7. [PMID: 19577714 DOI: 10.1016/j.tcm.2009.04.008] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
K(ATP) channels are generally cardioprotective under conditions of metabolic impairment, consisting of pore-forming (Kir6.1 and/or Kir6.2) and sulphonylurea-binding, modulatory subunits [sulfonylurea receptor (SUR) 1, 2A, or 2B]. Cardiovascular K(ATP) channels are generally thought to consist of Kir6.2/SUR2A subunits (in the case of heart muscle) or Kir6.1/SUR2B subunits (smooth muscle), whereas SUR1-containing channels have well-documented roles in pancreatic insulin release. Recent data, however, demonstrated the presence of SUR1 subunits in mouse cardiac tissue (particularly in atria) and a surprising protection from myocardial ischemia/reperfusion in SUR1-null mice. Here, we review some of the extra-pancreatic roles assigned to SUR1 subunits and consider whether these might be involved in the sequelae of ischemia/reperfusion.
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Affiliation(s)
- David J Lefer
- Department of Surgery, Division of Cardiothoracic Surgery, Emory University School of Medicine, Atlanta, GA, USA
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12
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Elrod JW, Harrell M, Flagg TP, Gundewar S, Magnuson MA, Nichols CG, Coetzee WA, Lefer DJ. Role of sulfonylurea receptor type 1 subunits of ATP-sensitive potassium channels in myocardial ischemia/reperfusion injury. Circulation 2008; 117:1405-13. [PMID: 18316485 DOI: 10.1161/circulationaha.107.745539] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Opening of cardiac ATP-sensitive potassium channels (K(ATP) channels) is a well-characterized protective mechanism against ischemia and reperfusion injury. Evidence exists for an involvement of both sarcolemmal and mitochondrial K(ATP) channels in such protection. Classically, cardiac sarcolemmal K(ATP) channels are thought to be composed of Kir6.2 (inward-rectifier potassium channel 6.2) and SUR2A (sulfonylurea receptor type 2A) subunits; however, the evidence is strong that SUR1 (sulfonylurea receptor type 1) subunits are also expressed in the heart and that they may have a functional role. The aim of this study, therefore, was to examine the role of SUR1 in myocardial infarction. METHODS AND RESULTS We subjected mice lacking SUR1 subunits to in vivo myocardial ischemia/reperfusion injury. Interestingly, the SUR1-null mice were markedly protected against the ischemic insult, displaying a reduced infarct size and preservation of left ventricular function, which suggests a role for this K(ATP) channel subunit in cardiovascular function during conditions of stress. CONCLUSIONS SUR1 subunits have a high sensitivity toward many sulfonylureas and certain K(ATP) channel-opening drugs. Their potential role during ischemic events should therefore be considered both in the interpretation of experimental data with pharmacological agents and in the clinical arena when the cardiovascular outcome of patients treated with antidiabetic sulfonylureas is being considered.
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Affiliation(s)
- John W Elrod
- Department of Medicine and Pathology, Albert Einstein College of Medicine, New York, NY, USA
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13
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Cardiac sulfonylurea receptor short form-based channels confer a glibenclamide-insensitive KATP activity. J Mol Cell Cardiol 2007; 44:188-200. [PMID: 18001767 DOI: 10.1016/j.yjmcc.2007.09.010] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/28/2007] [Revised: 08/16/2007] [Accepted: 09/07/2007] [Indexed: 11/23/2022]
Abstract
The cardiac sarcolemmal ATP-sensitive potassium channel (K(ATP)) consists of a Kir6.2 pore and an SUR2 regulatory subunit, which is an ATP-binding cassette (ABC) transporter. K(ATP) channels have been proposed to play protective roles during ischemic preconditioning. An SUR2 mutant mouse was previously generated by disrupting the first nucleotide-binding domain (NBD1), where a glibenclamide action site was located. In the mutant ventricular myocytes, a non-conventional glibenclamide-insensitive (10 microM), ATP-sensitive current (I(KATPn)) was detected in 33% of single-channel recordings with an average amplitude of 12.3+/-5.4 pA per patch, an IC(50) to ATP inhibition at 10 microM and a mean burst duration at 20.6+/-1.8 ms. Newly designed SUR2 isoform- or variant-specific antibodies identified novel SUR2 short forms in the sizes of 28 and 68 kDa in addition to a 150-kDa long form in the sarcolemmal membrane of wild-type (WT) heart. We hypothesized that channels constituted by these short forms that lack NBD1 confer I(KATPn). The absence of the long form in the mutant corresponded to loss of the conventional glibenclamide-sensitive K(ATP) currents (I(KATP)) in isolated cardiomyocytes and vascular smooth muscle cells but the SUR2 short forms remained intact. Nested exonic RT-PCR in the mutant indicated that the short forms lacked NBD1 but contained NBD2. The SUR2 short forms co-immunoprecipitated with Kir6.1 or Kir6.2 suggesting that the short forms may function as hemi-transporters reported in other eukaryotic ABC transporter subgroups. Our results indicate that different K(ATP) compositions may co-exist in cardiac sarcolemmal membrane.
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14
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Ordög B, Brutyó E, Puskás LG, Papp JG, Varró A, Szabad J, Boldogkoi Z. Gene expression profiling of human cardiac potassium and sodium channels. Int J Cardiol 2006; 111:386-93. [PMID: 16257073 DOI: 10.1016/j.ijcard.2005.07.063] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2005] [Revised: 07/26/2005] [Accepted: 07/30/2005] [Indexed: 11/24/2022]
Abstract
BACKGROUND The native cardiac ion currents and the action potential itself are the results of the concerted action of several different ion channels. The electrophysiological properties of cardiac cells are determined by the composition of ion channels and by their absolute abundance and proportional ratio. METHODS Our aim in this study was to compare the gene expression level of a representative panel of cardiac ion channels with each other and to compare the same channels in the atrium and ventricle of the human heart using quantitative real-time PCR analysis. RESULTS We obtained a significant difference in the gene expression levels in 21 of 35 channels between atrium and ventricle of healthy human hearts. Further, we found that the expression levels of Kv1.5 and Kv2.1 transcripts in the ventricle were very high, and that mRNAs for Kv1.7 and Kv3.4 are highly abundant in both the atrium and ventricle, which might indicate a functional role of these ion channel subunits in the formation of action potential in the human ventricle and both in the atrium and ventricle, respectively. CONCLUSIONS This is the first report on the expression of several ion channel subunits, such as Kv1.7, Kv3.3 or Kv3.4 in human cardiomyocytes. The expression levels of these genes are comparable with that of well known ion channel subunits. Therefore, it is reasonable to assume, that these ion channel subunits may contribute to native currents in the human myocardium.
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Affiliation(s)
- Balázs Ordög
- Department of Biology, Faculty of Medicine, University of Szeged, Somogyi B. 4. H-6720, Szeged, Hungary
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15
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Stephan D, Stauß E, Lange U, Felsch H, Löffler-Walz C, Hambrock A, Russ U, Quast U. The mutation Y1206S increases the affinity of the sulphonylurea receptor SUR2A for glibenclamide and enhances the effects of coexpression with Kir6.2. Br J Pharmacol 2005; 144:1078-88. [PMID: 15711591 PMCID: PMC1576091 DOI: 10.1038/sj.bjp.0706142] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
1. ATP-sensitive K(+) channels (K(ATP) channels) are tetradimeric complexes of inwardly rectifying K(+) channels (Kir6.x) and sulphonylurea receptors (SURs). The SURs SUR2A (cardiac) and SUR2B (smooth muscle) differ only in the last 42 amino acids. In SUR2B, the mutation Y1206S, located at intracellular loop 8, increases the affinity for glibenclamide (GBC) about 10-fold. Here, we examined whether the mutation Y1206S in SUR2A had effects similar to those in SUR2B.2. GBC bound to SUR2A with K(D)=20 nM; the mutation increased affinity approximately 5 x. 3. In cells, coexpression of SUR2A with Kir6.2 increased the affinity for GBC approximately 3 x; with the mutant, the increase was 9 x. 4. The mutation did not affect the affinity of SUR2A for openers; coexpression with Kir6.2 reduced opener affinity of wild-type and mutant SUR2A by about 2 x. 5. The negative allosteric interaction between the opener, P1075, and GBC at wild-type and mutant SUR2A was markedly affected by the presence of MgATP and by coexpression with Kir6.2. 6. In inside-out patches, GBC inhibited the wild-type Kir6.2/SUR2A and 2B channels with IC(50) values of 27 nM; the mutation shifted the IC(50) values to approximately 1 nM. 7. The data show that the mutation Y1206S increased the affinity of SUR2A for GBC and modulated the effects of coexpression. Overall, the changes were similar to those observed with SUR2B(Y1206S), suggesting that the differences in the last 42 carboxy-terminal amino acids of SUR2A and 2B are of limited influence on the binding of GBC and P1075 to the SUR2 isoforms.
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Affiliation(s)
- Damian Stephan
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Eva Stauß
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulf Lange
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Holger Felsch
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Cornelia Löffler-Walz
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulrich Russ
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
| | - Ulrich Quast
- Department of Pharmacology and Toxicology, Medical Faculty, Pharmakologisches Institut/Abt. Molekularpharmakologie, University of Tübingen, Wilhelmstr. 56, Tübingen, D-72074 Germany
- Author for correspondence:
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16
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Arun KHS, Kaul CL, Ramarao P. Green fluorescent proteins in receptor research: An emerging tool for drug discovery. J Pharmacol Toxicol Methods 2005; 51:1-23. [PMID: 15596111 DOI: 10.1016/j.vascn.2004.07.006] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2003] [Accepted: 07/27/2004] [Indexed: 01/20/2023]
Abstract
In the last five years, green fluorescent protein (GFP) has emerged from being a mere curiosity to become a reliable tool for molecular pharmacological research. GFP produces an intense and stable green fluorescence noncatalytically by absorbing blue light maximally at 395 nm and emitting green light with a peak at 509 nm. It consists of 238 amino acids and its molecular mass is 27-30 kDa. GFP fluorescence occurs without cofactors and this property allows GFP fluorescence to be utilised in nonnative organisms, wherein it can be used as a reporter. This use of GFP permits real-time analysis of receptor dynamics. The emitted fluorescence can be used as a nontoxic marker and detected using fluorescence-activated cell sorting (FACS), thus avoiding any staining procedure, expensive mRNA analysis or hazardous radiolabeled binding assays. The potential value of GFP has also been recognized in orphan receptor research, where various GFP-tagged therapeutic proteins have been constructed in an attempt to identify the endogenous ligand(s). These chimeric proteins have been used to determine the site and time course of receptor expression and to relate receptor dynamics with therapeutic outcome. The preparation of new GFP constructs for identifying germ layer cells (endodermal, ectodermal, and mesodermal), as well as neuronal, haematopoietic, endothelial, and cartilage cells, has provided a useful battery of tissue/receptor-specific screening assays for new chemical entities. Genetically engineered cells with GFP expression have provided a valuable tool for automated analysis, and can be adapted for high-throughput systems. GFP is being increasingly utilised for the study of receptor dynamics, where, having already proved beneficial, it will likely continue to contribute towards the search for new classes of drugs, as well as to "de-orphaning" orphan receptors.
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Affiliation(s)
- K H S Arun
- Cardiovascular and Receptorology Laboratory, Department of Pharmacology and Toxicology, National Institute of Pharmaceutical Education and Research, Phase-X, Sector 67, S.A.S. Nagar (Mohali)-160 062, Punjab, India
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17
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Hambrock A, Kayar T, Stumpp D, Osswald H. Effect of two amino acids in TM17 of Sulfonylurea receptor SUR1 on the binding of ATP-sensitive K+ channel modulators. Diabetes 2004; 53 Suppl 3:S128-34. [PMID: 15561900 DOI: 10.2337/diabetes.53.suppl_3.s128] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The sulfonylurea receptor (SUR) is the important regulatory subunit of ATP-sensitive K+ channels. It is an ATP-binding cassette protein comprising 17 transmembrane helices. SUR is endowed with binding sites for channel blockers like the antidiabetic sulfonylurea glibenclamide and for the chemically very heterogeneous channel openers. SUR1, the typical pancreatic SUR isoform, shows much higher affinity for glibenclamide but considerably lower affinity for most openers than SUR2. In radioligand binding assays, we investigated the role of two amino acids, T1285 and M1289, located in transmembrane helix (TM)-17, in opener binding to SUR1. These amino acids were exchanged for the corresponding amino acids of SUR2. In competition experiments using [3H]glibenclamide as radioligand, SUR1(T1285L, M1289T) showed much higher affinity toward the cyanoguanidine openers pinacidil and P1075 than SUR1 wild type. The affinity for the thioformamide aprikalim was also markedly increased. In contrast, the affinity for the benzopyrans rilmakalim and levcromakalim was unaffected; however, the amount of displaced [3H]glibenclamide binding was nearly doubled. The binding properties of the opener diazoxide and the blocker glibenclamide were unchanged. In conclusion, mutation of two amino acids in TM17 of SUR1, especially of M1289, leads to class-specific effects on opener binding by increasing opener affinity or by changing allosteric coupling between opener and glibenclamide binding.
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstrasse 56, D-72074 Tübingen, Germany.
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18
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Scott VE, Davis-Taber RA, Silvia C, Hoogenboom L, Choi W, Kroeger P, Whiteaker KL, Gopalakrishnan M. Characterization of human urinary bladder KATP channels containing SUR2B splice variants expressed in L-cells. Eur J Pharmacol 2004; 483:195-205. [PMID: 14729107 DOI: 10.1016/j.ejphar.2003.10.034] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
The molecular properties of the sulfonylurea receptor 2 (SUR2) subunits of K(ATP) channels expressed in urinary bladder were assessed by polymerase chain reaction (PCR). This showed that SUR2B exon 17- mRNA (72%) was predominant over the SUR2B exon 17+ splice variant (28%). The pharmacological properties of both of these isoforms stably expressed in mouse Ltk(-)cells (L-cells) with K(IR) 6.2 were determined by measuring changes in membrane potential responses evoked by K(+) channel openers using bis-(1,3-dibutylbarbituric acid) trimethine oxonol (DiBAC(4)(3)) fluorescence. The rank order potency of a variety of structurally distinct K(+) channel openers was found to be the same in both stable cell lines and compared well with guinea pig bladder cells. The potency of these compounds in the SUR2B exon 17- cells more closely resembled the potency measured in guinea pig bladder unlike the cell line containing the SUR2B exon 17+ subtype. Analysis of the displacement of [125I]A-312110 binding with the same K(+) channel openers to the SUR2B exon 17- cells showed excellent correlation to those measured in guinea pig bladder. This study supports the notion that K(ATP) channels containing SUR2B exon 17- represent a major splice variant expressed in urinary bladder smooth muscle.
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Affiliation(s)
- Victoria E Scott
- Neuroscience Disease Research AP9A, Rm. 218, Abbott Laboratories, 100 Abbott Park Rd.,Abbott Park, IL 60064-6125, USA.
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19
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Gopalakrishnan M, Buckner SA, Shieh CC, Fey T, Fabiyi A, Whiteaker KL, Davis-Taber R, Milicic I, Daza AV, Scott VES, Castle NA, Printzenhoff D, London B, Turner SC, Carroll WA, Sullivan JP, Coghlan MJ, Brune ME. In vitro and in vivo characterization of a novel naphthylamide ATP-sensitive K+ channel opener, A-151892. Br J Pharmacol 2004; 143:81-90. [PMID: 15302680 PMCID: PMC1575269 DOI: 10.1038/sj.bjp.0705908] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2004] [Revised: 06/03/2004] [Accepted: 06/09/2004] [Indexed: 11/08/2022] Open
Abstract
1. Openers of ATP-sensitive K(+) channels are of interest in several therapeutic indications including overactive bladder and other lower urinary tract disorders. This study reports on the in vitro and in vivo characterization of a structurally novel naphthylamide N-[2-(2,2,2-trifluoro-1-hydroxy-1-trifluoromethyl-ethyl)-naphthalen-1-yl]-acetamide (A-151892), as an opener of the ATP-sensitive potassium channels. 2. A-151892 was found to be a potent and efficacious potassium channel opener (KCO) as assessed by glibenclamide-sensitive whole-cell current and fluorescence-based membrane potential responses (-log EC(50)=7.63) in guinea-pig bladder smooth muscle cells. 3. Evidence for direct interaction with KCO binding sites was derived from displacement of binding of the 1,4-dihydropyridine opener [(125)I]A-312110. A-151892 displaced [(125)I]A-312110 binding to bladder membranes with a -log Ki value of 7.45, but lacked affinity against over 70 neurotransmitter receptor and ion channel binding sites. 4. In pig bladder strips, A-151892 suppressed phasic, carbachol-evoked and electrical field stimulus-evoked contractility in a glibenclamide-reversible manner with -log IC(50) values of 8.07, 7.33 and 7.02 respectively, comparable to that of the potencies of the prototypical cyanoguanidine KCO, P1075. The potencies to suppress contractions in thoracic aorta (-log IC(50)=7.81) and portal vein (-log IC(50)=7.98) were not substantially different from those observed for suppression of phasic contractility of the bladder smooth muscle. 5. In vivo, A-151892 was found to potently suppress unstable bladder contractions in obstructed models of unstable contractions in both pigs and rats with pED(35%) values of 8.05 and 7.43, respectively. 6. These results demonstrate that naphthylamide analogs exemplified by A-151892 are novel K(ATP) channel openers and may serve as chemotypes to exploit additional analogs with potential for the treatment of overactive bladder and lower urinary tract symptoms.
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Affiliation(s)
- Murali Gopalakrishnan
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, IL 60064, USA.
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20
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Abstract
We tested the hypothesis that cyclooxygenase (COX), thromboxane A
2
synthase (TxA
2
-S), thromboxane prostanoid receptors (TP-Rs), or superoxide anion (O
2
−
) mediates enhanced contractions of renal afferent arterioles (Aff) of angiotensin II (Ang II)-infused rabbits. Rabbits were infused with vehicle (sham), Ang II 60 ng·kg
−1
·min
−1
(Ang II 60) or 200 ng·kg
−1
·min
−1
(Ang II 200). There was a selective enhanced vasoconstriction of Affs from Ang II 60 rabbits to Ang II (Δdiameter−78±8% versus −43±9%;
P
<0.01) that was normalized by a TP-R antagonist but not by a superoxide dismutase (SOD) mimetic. Affs from Ang II 200 rabbits had increased (
P
<0.01) mRNA for COX-2 and enhanced vasoconstriction to Ang II, U-46 619 (TP-R mimetic), and endothelin-1 that was normalized by ifetroban plus tempol together. Endothelium removal enhanced Ang II responses of Affs from sham rabbits but blunted responses from Ang II 200 rabbits and abolished responses to ifetroban. Affs from Ang II 200 rabbits had an endothelium-dependent contraction factor (EDCF) response to that was blunted (
P
<0.001) by a SOD mimetic or antagonists of COX-1 or TxA
2
-S but normalized by antagonists of COX-2 or TP-R. Thus, enhanced Ang II responses in Affs from rabbits infused with slow pressor Ang II are mediated independently by O
2
−
in the vascular smooth muscle cells and by an EDCF that is principally a vasoconstrictor prostaglandin generated by COX-2 >−1 activating TP-Rs, whereas enhanced responses in rabbits infused with a lower Ang II dose are dependent on TP-R but not O
2
−
.
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MESH Headings
- 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid/pharmacology
- 8,11,14-Eicosatrienoic Acid/analogs & derivatives
- 8,11,14-Eicosatrienoic Acid/pharmacology
- Angiotensin II/administration & dosage
- Angiotensin II/pharmacology
- Animals
- Arterioles/drug effects
- Arterioles/physiopathology
- Bridged Bicyclo Compounds, Heterocyclic/pharmacology
- Cyclic N-Oxides/pharmacology
- Cyclooxygenase 2
- Dose-Response Relationship, Drug
- Endothelin-1/pharmacology
- Endothelins/metabolism
- Endothelium, Vascular/drug effects
- Endothelium, Vascular/metabolism
- Endothelium, Vascular/physiology
- Isoenzymes/physiology
- Kidney/blood supply
- Male
- Nitroarginine/pharmacology
- Norepinephrine/pharmacology
- Oxazoles/pharmacology
- Oxidative Stress
- Prostaglandin-Endoperoxide Synthases/physiology
- Pyrazoles/pharmacology
- RNA, Messenger/biosynthesis
- Rabbits
- Receptors, Thromboxane/antagonists & inhibitors
- Receptors, Thromboxane/physiology
- Spin Labels
- Superoxides/metabolism
- Vascular Resistance/drug effects
- Vasoconstriction/drug effects
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Affiliation(s)
- Dan Wang
- Division of Nephrology and Hypertension and the Cardiovascular-Kidney Institute, Georgetown University, Washington, DC 20007-2197, USA
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21
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Kocks MJA, Gschwend S, de Zeeuw D, Navis G, Buikema H. Low Sodium Modifies the Vascular Effects of Angiotensin-Converting Enzyme Inhibitor Therapy in Healthy Rats. J Pharmacol Exp Ther 2004; 310:1183-9. [PMID: 15175418 DOI: 10.1124/jpet.104.067272] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Low dietary sodium (LS) increases the effect of angiotensin-converting enzyme (ACE) inhibitor therapy in patients and experimental models, but mechanisms underlying this enhanced efficacy are largely unknown. Because the benefits of ACE inhibition are mediated to a considerable extent by their effect on the vasculature, we studied whether low sodium alters the vascular effects of ACE inhibition. Baseline functional and morphological characteristics, and endothelium-dependent and -independent dilatory responses were studied in isolated perfused small intrarenal and mesenteric arteries obtained from control rats (CON), rats on LS, lisinopril-treated rats (CON-LIS), or rats treated with lisinopril during LS (LS-LIS). We found, first, that LS-LIS compared with CON-LIS enhances blood pressure reduction. Second, interlobar renal arteries had increased lumen diameter and reduced adrenergic contractility in CON-LIS compared with CON, without additional effects of LS. In contrast, mesenteric arteries were not altered in CON-LIS compared with CON, but became triggered for increased myogenic and adrenergic constriction in LS-LIS. Third, LS-LIS decreased acetylcholine (ACh)-induced vasodilation in both mesenteric and renal arteries compared with CON-LIS. During the latter condition, opposite prostaglandins are involved in the endothelial function of the two different vascular beds, i.e., increased involvement of contractile prostaglandins in ACh-induced vasodilatation in renal arteries, versus dilatory prostaglandins in mesenteric arteries. Whether cause or consequence of the enhanced blood pressure response, our data demonstrate a modifying effect of dietary sodium on vascular effects of ACE inhibition. These findings provide a rationale for further studies addressing the mechanism-of-actions of our therapies to find additional strategies to improve therapy response.
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Affiliation(s)
- Menno J A Kocks
- Department of Clinical Pharmacology, University of Groningen, Antonius Deusinglaan 1, 9713 AV Groningen, The Netherlands.
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22
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Felsch H, Lange U, Hambrock A, Löffler-Walz C, Russ U, Carroll WA, Gopalakrishnan M, Quast U. Interaction of a novel dihydropyridine K+ channel opener, A-312110, with recombinant sulphonylurea receptors and KATP channels: comparison with the cyanoguanidine P1075. Br J Pharmacol 2004; 141:1098-105. [PMID: 15023854 PMCID: PMC1574886 DOI: 10.1038/sj.bjp.0705718] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
1. ATP-sensitive K(+) channels (K(ATP) channels) are composed of pore-forming subunits (Kir6.x) and of regulatory subunits, the sulphonylurea receptors (SURx). Synthetic openers of K(ATP) channels form a chemically heterogeneous class of compounds that are of interest in several therapeutic areas. We have investigated the interaction of a novel dihydropyridine opener, A-312110 ((9R)-9-(4-fluoro-3-iodophenyl)-2,3,5,9-tetrahydro-4H-pyrano[3,4-b]thieno [2,3-e]pyridin-8(7H)-one-1,1-dioxide), with SURs and Kir6/SUR channels in comparison to the cyanoguanidine opener P1075. 2. In the presence of 1 mM MgATP, A-312110 bound to SUR2A (the SUR in cardiac and skeletal muscle) and to SUR2B (smooth muscle) with K(i) values of 14 and 18 nM; the corresponding values for P1075 were 16 and 9 nM, respectively. Decreasing the MgATP concentration reduced the affinity of A312110 binding to SUR2A significantly more than that to SUR2B; for P1075, the converse was true. At SUR1 (pancreatic beta-cell), both openers showed little binding up to 100 microM. 3. In the presence of MgATP, both openers inhibited [(3)H]glibenclamide binding to the SUR2 subtypes in a biphasic manner. In the absence of MgATP, the high-affinity component of the inhibition curves was absent. 4. In inside-out patches, the two openers activated the Kir6.2/SUR2A and Kir6.2/SUR2B channels with similar potency (approximately 50 nm). Both were almost 2 x more efficacious in opening the Kir6.2/SUR2B than the Kir6.2/SUR2A channel. 5. The results show that the novel dihydropyridine A-312110 is a potent K(ATP) channel opener with binding and channel-opening properties similar to those of P1075.
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MESH Headings
- ATP-Binding Cassette Transporters/drug effects
- ATP-Binding Cassette Transporters/genetics
- Adenosine Triphosphate/chemistry
- Adenosine Triphosphate/metabolism
- Cell Line
- Dihydropyridines/chemistry
- Dihydropyridines/pharmacology
- Drug Interactions/physiology
- Guanidines/chemistry
- Guanidines/pharmacology
- Humans
- Ion Channel Gating
- Kidney/cytology
- Kidney/embryology
- Magnesium/chemistry
- Magnesium/metabolism
- Membrane Proteins/chemistry
- Membrane Proteins/drug effects
- Membrane Proteins/genetics
- Muscle Fibers, Skeletal/cytology
- Muscle Fibers, Skeletal/drug effects
- Muscle Fibers, Skeletal/metabolism
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Patch-Clamp Techniques/methods
- Potassium Channels/drug effects
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/genetics
- Pyridines/chemistry
- Pyridines/pharmacology
- Receptors, Drug/drug effects
- Receptors, Drug/genetics
- Recombinant Proteins/drug effects
- Recombinant Proteins/genetics
- Sulfonylurea Receptors
- Thiophenes/chemistry
- Thiophenes/pharmacology
- Tritium
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Affiliation(s)
- Holger Felsch
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Ulf Lange
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Cornelia Löffler-Walz
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | - Ulrich Russ
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
| | | | | | - Ulrich Quast
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, D-72074 Tübingen, Germany
- Author for correspondence:
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23
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Gribble FM, Reimann F. Sulphonylurea action revisited: the post-cloning era. Diabetologia 2003; 46:875-91. [PMID: 12819907 DOI: 10.1007/s00125-003-1143-3] [Citation(s) in RCA: 211] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2003] [Revised: 04/22/2003] [Indexed: 12/13/2022]
Abstract
Hypoglycaemic agents such as sulphonylureas and the newer group of "glinides" stimulate insulin secretion by closing ATP-sensitive potassium (K(ATP)) channels in pancreatic beta cells, but have varying cross-reactivity with related channels in extrapancreatic tissues such as heart, vascular smooth and skeletal muscle. Experiments on the structure-function relationships of recombinant K(ATP) channels and the phenotypes of mice deficient in different K(ATP) channel subunits have provided important insights into the mechanisms underlying sulphonylurea selectivity, and the potential consequences of K(ATP) channel blockade outside the pancreatic beta cell. The different pharmacological properties of K(ATP) channels from beta cells compared with those from cardiac, smooth and skeletal muscle, are accounted for by the expression of alternative types of sulphonylurea receptor, with non-identical drug binding sites. The sulphonylureas and glinides are found to fall into two groups: one exhibiting selectivity for beta cell sulphonylurea receptors (SUR1), and the other blocking cardiovascular and skeletal muscle sulphonylurea receptors (SUR2) with potencies similar to their action on SUR1. In seeking potential side effects of K(ATP) channel inhibitors in humans, it is essential to take these drug differences into account, along with the probability (suggested by the studies on K(ATP) channel knockout mice) that the effects of extrapancreatic K(ATP) channel inhibition might be either subtle or rare. Further studies are still required before a final decision can be made on whether non-selective agents are appropriate for the therapy of Type 2 diabetes.
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Affiliation(s)
- F M Gribble
- Department of Clinical Biochemistry, Addenbrooke's Hospital, Hills Road, Box 232, Cambridge CB2 2QR, UK.
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