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Hosy E, Dérand R, Revilloud J, Vivaudou M. Remodelling of the SUR-Kir6.2 interface of the KATP channel upon ATP binding revealed by the conformational blocker rhodamine 123. J Physiol 2007; 582:27-39. [PMID: 17510180 PMCID: PMC2075286 DOI: 10.1113/jphysiol.2007.134288] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
ATP-sensitive K+ channels (K(ATP) channels) are metabolic sensors formed by association of a K+ channel, Kir6, and an ATP-binding cassette (ABC) protein, SUR, which allosterically regulates channel gating in response to nucleotides and pharmaceutical openers and blockers. How nucleotide binding to SUR translates into modulation of Kir6 gating remains largely unknown. To address this issue, we have used a novel conformational KATP channel inhibitor, rhodamine 123 (Rho123) which targets the Kir6 subunit in a SUR-dependent manner. Rho123 blocked SUR-less Kir6.2 channels with an affinity of approximately 1 microM, regardless of the presence of nucleotides, but it had no effect on channels formed by the association of Kir6.2 and the N-terminal transmembrane domain TMD0 of SUR. Rho123 blocked SUR + Kir6.2 channels with the same affinity as Kir6.2 but this effect was antagonized by ATP. Protection from Rho123 block by ATP was due to direct binding of ATP to SUR and did not entail hydrolysis because it was not mimicked by AMP, did not require Mg2+ and was reduced by mutations in the nucleotide-binding domains of SUR. These results suggest that Rho123 binds at the TMD0-Kir6.2 interface and that binding of ATP to SUR triggers a change in the structure of the contact zone between Kir6.2 and domain TMD0 of SUR that causes masking of the Rho123 site on Kir6.2.
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MESH Headings
- ATP-Binding Cassette Transporters/chemistry
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/metabolism
- Adenosine Triphosphate/metabolism
- Allosteric Regulation/drug effects
- Animals
- Binding, Competitive
- Cloning, Molecular
- Cricetinae
- Female
- Fluorescent Dyes/metabolism
- Fluorescent Dyes/pharmacology
- Ion Channel Gating/drug effects
- Membrane Potentials/drug effects
- Mice
- Mutation
- Oocytes
- Patch-Clamp Techniques
- Potassium Channel Blockers/metabolism
- Potassium Channel Blockers/pharmacology
- Potassium Channels/chemistry
- Potassium Channels/genetics
- Potassium Channels/metabolism
- Potassium Channels, Inwardly Rectifying/antagonists & inhibitors
- Potassium Channels, Inwardly Rectifying/chemistry
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/metabolism
- Protein Conformation/drug effects
- Protein Structure, Tertiary
- Rats
- Receptors, Drug/chemistry
- Receptors, Drug/genetics
- Receptors, Drug/metabolism
- Rhodamine 123/metabolism
- Rhodamine 123/pharmacology
- Sulfonylurea Receptors
- Time Factors
- Xenopus laevis
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Affiliation(s)
- Eric Hosy
- Institute of Structural Biology, UMR5075 CEA-CNRS-University J. Fourier, 41, rue Jules Horowitz, 38027 Grenoble, France
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52
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Carosati E, Mannhold R, Wahl P, Hansen JB, Fremming T, Zamora I, Cianchetta G, Baroni M. Virtual Screening for Novel Openers of Pancreatic KATPChannels. J Med Chem 2007; 50:2117-26. [PMID: 17425298 DOI: 10.1021/jm061440p] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ligand-based virtual screening approaches were applied to search for new chemotype KCOs activating Kir6.2/SUR1 KATP channels. A total of 65 208 commercially available compounds, extracted from the ZINC archive, served as database for screening. In a first step, pharmacokinetic filtering via VolSurf reduced the initial database to 1913 compounds. Afterward, six molecules were selected as templates for similarity searches: similarity scores, obtained toward these templates, were calculated with the GRIND, FLAP, and TOPP approaches, which differently encode structural information into potential pharmacophores. In this way, we obtained 32 hit candidates, 16 via GRIND and eight each via FLAP and TOPP. For biological testing of the hit candidates, their effects on membrane potentials in HEK 293 cells expressing Kir6.2/SUR1 were studied. GRIND, FLAP, and TOPP all yielded hits, but no method top-ranked all the actives. Thus, parallel application of different approaches probably improves hit detection.
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Affiliation(s)
- Emanuele Carosati
- Laboratory for Chemometrics and Cheminformatics, Chemistry Department, University of Perugia, Via Elce di Sotto, 10, I-06123 Perugia, Italy.
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53
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Schulze K, Duschek C, Lasley RD, Bünger R. Adenosine enhances cytosolic phosphorylation potential and ventricular contractility in stunned guinea pig heart: receptor-mediated and metabolic protection. J Appl Physiol (1985) 2007; 102:1202-13. [PMID: 17341737 DOI: 10.1152/japplphysiol.00245.2006] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Mechanisms of adenosine (ADO) protection of reperfused myocardium are not fully understood. We tested the hypothesis that ADO (0.1 mM) alleviates ventricular stunning by ADO A(1)-receptor stimulation combined with purine metabolic enhancements. Langendorff guinea pig hearts were stunned at constant left ventricular end-diastolic pressure by low-flow ischemia. Myocardial phosphate metabolites were measured by (31)P-NMR, with phosphorylation potential {[ATP]/([ADP].[P(i)]), where brackets indicate concentration} estimated from creatine kinase equilibrium. Creatine and IMP, glycolytic intermediates, were measured enzymatically and glycolytic flux and extracellular spaces were measured by radiotracers. All treatment interventions started after a 10-min normoxic stabilization period. At 30 min reperfusion, ventricular contractility (dP/dt, left ventricular pressure) was reduced 17-26%, ventricular power (rate-pressure product) by 37%, and [ATP]/([ADP].[P(i)]) by 53%. The selective A(1) agonist 2-chloro-N(6)-cyclo-pentyladenosine marginally preserved [ATP]/([ADP].[P(i)]) and ventricular contractility but not rate-pressure product. Purine salvage precursor inosine (0.1 mM) substantially raised [ATP]/([ADP].[P(i)]) but weakly affected contractility. The ATP-sensitive potassium channel blocker glibenclamide (50 microM) abolished ADO protection of [ATP]/([ADP].[P(i)]) and contractility. ADO raised myocardial IMP and glucose-6-phosphate, demonstrating increased purine salvage and pentose phosphate pathway flux potential. Coronary hyperemia alone (papaverine) was not cardioprotective. We found that ADO protected energy metabolism and contractility in stunned myocardium more effectively than both the A(1)-receptor agonist 2-chloro-N(6)-cyclo-pentyladenosine and the purine salvage precursor inosine. Because ADO failed to stimulate glycolytic flux, the enhancement of reperfusion, [ATP]/([ADP].[P(i)]), indicates protection of mitochondrial function. Reduced ventricular dysfunction at enhanced [ATP]/([ADP].[P(i)]) argues against opening of mitochondrial ATP-sensitive potassium channel. The results establish a multifactorial mechanism of ADO antistunning, which appears to combine ADO A(1)-receptor signaling with metabolic adenylate and antioxidant enhancements.
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Affiliation(s)
- Karsten Schulze
- Abteilung für Kardiologie und Pneumologie, Campus Benjamin Franklin, Charité Berlin, 12200 Berlin, Germany.
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54
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Brambilla A, Tarroni P. The GeneTrawler®: mapping potential drug targets in human and rat tissues. Expert Opin Ther Targets 2007; 11:567-80. [PMID: 17373885 DOI: 10.1517/14728222.11.4.567] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Expression data are an important element of target identification and validation. The authors have established an automated high-throughput method based on real time quantitative polymerase chain reaction, called the GeneTrawler, for the characterization of pharmaceutical targets on an annotated collection of human tissues. The authors have conducted a variability analysis of the system, which demonstrates that the majority of the variability between expression levels determined is due to biologic variation between samples, rather than technical variation due to imprecision of the method. Gene expression maps, generated with this carefully controlled system provide a large, reliable, consistent data set. The authors have used this system to characterize the expression of > 100 genes, and here they show the expression profile of SUR1 in order to illustrate its use. The authors were able to confirm SUR1 expression in the lung, which was suggested on the basis of pharmacologic experiments but has not previously been confirmed by mRNA detection. The data also show SUR1 expression in tissues that have been associated with some of the side effects seen with SUR1 modulators. This and other examples demonstrate that the GeneTrawler is useful to gauge the suitability of a prospective therapeutic target, to fully exploit a known drug target, or to identify and help validate new hypothetical druggable targets to fuel drug discovery pipelines.
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Affiliation(s)
- Andrea Brambilla
- Axxam, San Raffaele Biomedical Science Park, Via Olgettina 58, 20132 Milan, Italy
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55
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Fujita R, Kimura S, Kawasaki S, Watanabe S, Watanabe N, Hirano H, Matsumoto M, Sasaki K. Electrophysiological and pharmacological characterization of the K(ATP) channel involved in the K+-current responses to FSH and adenosine in the follicular cells of Xenopus oocyte. J Physiol Sci 2007; 57:51-61. [PMID: 17239259 DOI: 10.2170/physiolsci.rp010006] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2006] [Accepted: 01/21/2007] [Indexed: 11/05/2022]
Abstract
The follicular cells surrounding Xenopus oocyte under voltage clamp produce K(+)-current responses to follicle-stimulating hormone (FSH), adenosine (Ade), and intracellularly applied cAMP. We previously reported that these responses are suppressed by the stimulation of P2Y receptor through phosphorylation by PKC presumably of the ATP-sensitive K(+) (K(ATP)) channel. This channel comprises sulfonylurea receptors (SURs) and K(+) ionophores (Kirs) having differential sensitivities to K(+) channel openers (KCOs) depending on the SURs. To characterize the K(+) channels involved in the FSH- and Ade-induced responses, we investigated the effects of various KCOs and SUR blockers on the agonist-induced responses. The applications of PCO400, cromakalim (Cro), and pinacidil, but not diazoxide, produced K(+)-current responses similar to the FSH- and Ade-induced responses in the magnitude order of PCO400 > Cro >> pinacidil in favor of SUR2A. The application of glibenclamide, phentolamine, and tolbutamide suppressed all the K(+)-current responses to FSH, Ade, cAMP, and KCOs. Furthermore, both the FSH- and Ade-induced responses were markedly augmented during the KCO-induced responses, or vice versa. The I-V curves for the K(+)-current responses induced by Cro, Ade, and FSH showed outward rectification in normal [K(+)](o), but weak inward rectification in 122 mM [K(+)](o). Also, stimulations of P2Y receptor by UTP or PKC by PDBu markedly depressed the K(+)-current response to KCOs in favor of Kir6.1, as previously observed with the responses to FSH and Ade. These results suggest that the K(+)-current responses to FSH and Ade may be produced by the opening of a novel type of K(ATP) channel comprising SUR2A and Kir6.1.
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Affiliation(s)
- Reiko Fujita
- Department of Chemistry, School of Liberal Arts & Sciences, Iwate Medical University, Morioka, Japan.
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56
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Hambrock A, de Oliveira Franz CB, Hiller S, Grenz A, Ackermann S, Schulze DU, Drews G, Osswald H. Resveratrol binds to the sulfonylurea receptor (SUR) and induces apoptosis in a SUR subtype-specific manner. J Biol Chem 2006; 282:3347-56. [PMID: 17138562 DOI: 10.1074/jbc.m608216200] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptors (SURs) constitute the regulatory subunits of ATP-sensitive K+ channels (K(ATP) channels). SUR binds nucleotides and synthetic K(ATP) channel modulators, e.g. the antidiabetic sulfonylurea glibenclamide, which acts as a channel blocker. However, knowledge about naturally occurring ligands of SUR is very limited. In this study, we show that the plant phenolic compound trans-resveratrol can bind to SUR and displace binding of glibenclamide. Electrophysiological measurements revealed that resveratrol is a blocker of pancreatic SUR1/K(IR)6.2 K(ATP) channels. We further demonstrate that, like glibenclamide, resveratrol induces enhanced apoptosis. This was shown by analyzing different apoptotic parameters (cell detachment, nuclear condensation and fragmentation, and activities of different caspase enzymes). The observed apoptotic effect was specific to cells expressing the SUR1 isoform and was not mediated by the electrical activity of K(ATP) channels, as it was observed in human embryonic kidney 293 cells expressing SUR1 alone. Enhanced susceptibility to resveratrol was not observed in pancreatic beta-cells from SUR1 knock-out mice or in cells expressing the isoform SUR2A or SUR2B or the mutant SUR1(M1289T). Resveratrol was much more potent than glibenclamide in inducing SUR1-specific apoptosis. Treatment with etoposide, a classical inducer of apoptosis, did not result in SUR isoform-specific apoptosis. In conclusion, resveratrol is a natural SUR ligand that can induce apoptosis in a SUR isoform-specific manner. Considering the tissue-specific expression patterns of SUR isoforms and the possible effects of SUR mutations on susceptibility to apoptosis, these observations could be important for diabetes and/or cancer research.
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MESH Headings
- ATP-Binding Cassette Transporters/drug effects
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/physiology
- Animals
- Apoptosis/drug effects
- Apoptosis/physiology
- Caspases/drug effects
- Caspases/metabolism
- Cell Adhesion/drug effects
- Cell Line
- Etoposide/pharmacology
- Female
- Humans
- Hypoglycemic Agents/pharmacology
- Islets of Langerhans/cytology
- Islets of Langerhans/drug effects
- Islets of Langerhans/metabolism
- Islets of Langerhans/physiology
- Kidney
- Male
- Mice
- Mice, Inbred C57BL
- Mice, Knockout
- Potassium Channels/deficiency
- Potassium Channels/drug effects
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/deficiency
- Potassium Channels, Inwardly Rectifying/drug effects
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Receptors, Drug/deficiency
- Receptors, Drug/drug effects
- Receptors, Drug/genetics
- Receptors, Drug/physiology
- Recombinant Proteins/drug effects
- Recombinant Proteins/metabolism
- Resveratrol
- Stilbenes/pharmacokinetics
- Stilbenes/pharmacology
- Sulfonylurea Receptors
- Transfection
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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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57
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Khan AU, Gilani AH. Selective bronchodilatory effect of Rooibos tea (Aspalathus linearis) and its flavonoid, chrysoeriol. Eur J Nutr 2006; 45:463-9. [PMID: 17080260 DOI: 10.1007/s00394-006-0620-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2006] [Accepted: 08/17/2006] [Indexed: 10/24/2022]
Abstract
BACKGROUND Rooibos tea (Aspalathus linearis) is commonly used for hyperactive gastrointestinal, respiratory and cardiovascular disorders. AIM OF STUDY The aqueous extract of Rooibos tea (RT) was studied for the possible bronchodilator, antispasmodic and blood pressure lowering activities in an attempt to rationalize some of its medicinal uses. METHODS Isolated tissue preparations, such as rabbit jejunum, aorta and guinea-pig trachea and atria were set up in appropriate physiological salt solutions and aerated with carbogen. For in vivo studies rats were anesthetized with pentothal sodium and blood pressure was measured through carotid artery cannulation. RESULTS In jejunum, RT caused a concentration-dependent relaxation of low K(+) (25 mM)-induced contractions, with mild effect on the contractions induced by high K(+) (80 mM). In presence of glibenclamide, the relaxation of low K(+)-induced contractions was prevented. Similarly, cromakalim caused glibenclamide-sensitive inhibition of low K(+), but not of high K(+), while verapamil did not differentiate in its inhibitory effect on contractions produced by the two concentrations of K(+). Like in jejunum, RT caused glibenclamide-sensitive relaxation of low K(+)-induced contractions in trachea and aorta, but with a 20 times higher potency in trachea. In atria, RT was least potent with weak inhibitory effect on atrial force and rate of contractions. RT caused a dose-dependent fall in arterial blood pressure in rats under anesthesia. Among the tested pure compounds of Rooibos, chrysoeriol showed selective bronchodilator effect. Chrysoeriol (luteolin 3'-methyl ether) is a bioactive flavonoid known for antioxidant, antiinflammatory, antitumor, antimicrobial, antiviral, and free radical scavenging activities. CONCLUSION These results indicate that the bronchodilator, antispasmodic and blood pressure lowering effects of Rooibos tea are mediated predominantly through K(ATP) channel activation with the selective bronchodilatory effect. This study provides a sound mechanistic basis for the wide medicinal use of Rooibos tea, with the therapeutic potential to be developed for congestive respiratory ailments.
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Affiliation(s)
- Arif-ullah Khan
- Dept. of Biological and Biomedical Sciences, The Aga Khan University Medical College, Karachi, 74800, Pakistan
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58
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Rolland JF, Tricarico D, Laghezza A, Loiodice F, Tortorella V, Camerino DC. A new benzoxazine compound blocks KATP channels in pancreatic beta cells: molecular basis for tissue selectivity in vitro and hypoglycaemic action in vivo. Br J Pharmacol 2006; 149:870-9. [PMID: 17057758 PMCID: PMC2014689 DOI: 10.1038/sj.bjp.0706895] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022] Open
Abstract
BACKGROUND AND PURPOSE The 2-propyl-1,4 benzoxazine (AM10) shows a peculiar behaviour in skeletal muscle, inhibiting or opening the ATP-sensitive K(+) (KATP) channel in the absence and presence of ATP, respectively. We focused on tissue selectivity and mechanism of action of AM10 by testing its effects on pancreatic KATP channels by means of both in vitro and in vivo investigations. EXPERIMENTAL APPROACH In vitro, patch-clamp recordings were performed in native pancreatic beta cells and in tsA201 cells expressing the Kir6.2 Delta C36 channel. In vivo, an intraperitoneal glucose tolerance test was performed in normal mice. KEY RESULTS In contrast with what observed in the skeletal muscle, AM10, in whole cell perforated mode, did not augment KATP current (I(KATP)) of native beta cells but it inhibited it in a concentration-dependent manner (IC(50): 11.5 nM; maximal block: 60%). Accordingly, in current clamp recordings, a concentration-dependent membrane depolarization was observed. On excised patches, AM10 reduced the open-time probability of KATP channels without altering their single channel conductance; the same effect was observed in the presence of trypsin in the bath solution. Moreover, AM10 inhibited, in an ATP-independent manner, the K(+) current resulting from expressed Kir6.2 Delta C36 (maximal block: 60% at 100 microM; IC(50): 12.7 nM) corroborating an interaction with Kir. In vivo, AM10 attenuated the glycemia increase following a glucose bolus in a dose-dependent manner, without, at the dose tested, inducing fasting hypoglycaemia. CONCLUSION AND IMPLICATIONS Altogether, these results help to gain insight into a new class of tissue specific KATP channel modulators.
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Affiliation(s)
- J-F Rolland
- Department of Pharmacobiology, Unit of Pharmacology, Faculty of Pharmacy, University of Bari Bari, Italy
| | - D Tricarico
- Department of Pharmacobiology, Unit of Pharmacology, Faculty of Pharmacy, University of Bari Bari, Italy
| | - A Laghezza
- Department of Medicinal Chemistry, Faculty of Pharmacy, University of Bari Bari, Italy
| | - F Loiodice
- Department of Medicinal Chemistry, Faculty of Pharmacy, University of Bari Bari, Italy
| | - V Tortorella
- Department of Medicinal Chemistry, Faculty of Pharmacy, University of Bari Bari, Italy
| | - D Conte Camerino
- Department of Pharmacobiology, Unit of Pharmacology, Faculty of Pharmacy, University of Bari Bari, Italy
- Author for correspondence:
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59
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Stephan D, Salamon E, Weber H, Russ U, Lemoine H, Quast U. KATP channel openers of the benzopyran type reach their binding site via the cytosol. Br J Pharmacol 2006; 149:199-205. [PMID: 16921394 PMCID: PMC2013803 DOI: 10.1038/sj.bjp.0706858] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE ATP-sensitive K+ (KATP) channels are composed of pore-forming subunits (Kir6.x) and of sulphonylurea receptors (SUR). Both sulphonylureas and K(ATP) channel openers act by binding to SUR. Sulphonylureas reach their binding site from the cytosol but it remains unknown whether this holds for openers too. EXPERIMENTAL APPROACH A poorly membrane-permeant sulphonic acid derivative of the benzopyran-type opener, bimakalim, was synthesized, descyano-bimakalim-6-sulphonic acid (BMSA). Binding of BMSA and bimakalim was compared in membranes and intact cells expressing the Kir6.2/SUR2B channel and channel opening was compared in inside-out patches and whole cells. KEY RESULTS In membranes, bimakalim and BMSA bound to Kir6.2/SUR2B with Ki values of 61 nM and 4.3 microM, showing that the negative charge decreased affinity 69-fold. In intact cells, however, binding of BMSA was much weaker than in membranes (75-fold) whereas that of bimakalim was unchanged. The Ki value of BMSA decreased with increasing incubation time. In inside-out patches, bimakalim (1 microM) and BMSA (100 microM) opened the Kir6.2/SUR2B channel closed by MgATP to a similar degree whereas in whole-cell experiments, only bimakalim was effective. CONCLUSIONS AND IMPLICATIONS Despite its negative charge, BMSA is an effective channel opener. The fact that BMSA binds and acts more effectively when applied to the inner side of the cell membrane shows that benzopyran openers reach their binding site at SUR from the cytosol. This suggests that the binding pocket of SUR is only open on the cytoplasmic side.
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Affiliation(s)
- D Stephan
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany
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60
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Bryan J, Muñoz A, Zhang X, Düfer M, Drews G, Krippeit-Drews P, Aguilar-Bryan L. ABCC8 and ABCC9: ABC transporters that regulate K+ channels. Pflugers Arch 2006; 453:703-18. [PMID: 16897043 DOI: 10.1007/s00424-006-0116-z] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Accepted: 06/08/2006] [Indexed: 11/28/2022]
Abstract
The sulfonylurea receptors (SURs) ABCC8/SUR1 and ABCC9/SUR2 are members of the C-branch of the transport adenosine triphosphatase superfamily. Unlike their brethren, the SURs have no identified transport function; instead, evolution has matched these molecules with K(+) selective pores, either K(IR)6.1/KCNJ8 or K(IR)6.2/KCNJ11, to assemble adenosine triphosphate (ATP)-sensitive K(+) channels found in endocrine cells, neurons, and both smooth and striated muscle. Adenine nucleotides, the major regulators of ATP-sensitive K(+) (K(ATP)) channel activity, exert a dual action. Nucleotide binding to the pore reduces the activity or channel open probability, whereas Mg-nucleotide binding and/or hydrolysis in the nucleotide-binding domains of SUR antagonize this inhibitory action to stimulate channel openings. Mutations in either subunit can alter this balance and, in the case of the SUR1/KIR6.2 channels found in neurons and insulin-secreting pancreatic beta cells, are the cause of monogenic forms of hyperinsulinemic hypoglycemia and neonatal diabetes. Additionally, the subtle dysregulation of K(ATP) channel activity by a K(IR)6.2 polymorphism has been suggested as a predisposing factor in type 2 diabetes mellitus. Studies on K(ATP) channel null mice are clarifying the roles of these metabolically sensitive channels in a variety of tissues.
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Affiliation(s)
- Joseph Bryan
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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61
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Kurachi Y, Yamada M. [Relationship between function and structure of ATP-sensitive K+ (KATP) channels]. Nihon Yakurigaku Zasshi 2006; 126:311-6. [PMID: 16394574 DOI: 10.1254/fpj.126.311] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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62
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Hambrock A, de Oliveira Franz CB, Hiller S, Osswald H. Glibenclamide-induced apoptosis is specifically enhanced by expression of the sulfonylurea receptor isoform SUR1 but not by expression of SUR2B or the mutant SUR1(M1289T). J Pharmacol Exp Ther 2005; 316:1031-7. [PMID: 16306272 DOI: 10.1124/jpet.105.097501] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Sulfonylurea receptor 1 (SUR1) is the regulatory subunit of the pancreatic ATP-sensitive K+ channel (K(ATP) channel), which is essential for triggering insulin secretion via membrane depolarization. Sulfonylureas, such as glibenclamide and tolbutamide, act as K(ATP) channel blockers and are widely used in diabetes treatment. These antidiabetic substances are known to induce apoptosis in pancreatic beta-cells or beta-cell lines under certain conditions. However, the precise molecular mechanisms of this sulfonylurea-induced apoptosis are still unidentified. To investigate the role of SUR in apoptosis induction, we tested the effect of glibenclamide on recombinant human embryonic kidney 293 cells expressing either SUR1, the smooth muscular isoform SUR2B, or the mutant SUR1(M1289T) at which a single amino acid in transmembrane helix 17 (TM17) was exchanged by the corresponding amino acid of SUR2. By analyzing cell detachment, nuclear condensation, DNA fragmentation, and caspase-3-like activity, we observed a SUR1-specific enhancement of glibenclamide-induced apoptosis that was not seen in SUR2B, SUR1(M1289T), or control cells. Coexpression with the pore-forming Kir6.2 subunit did not significantly alter the apoptotic effect of glibenclamide on SUR1 cells. In conclusion, expression of SUR1, but not of SUR2B or SUR1(M1289T), renders cells more susceptible to glibenclamide-induced apoptosis. Therefore, SUR1 as a pancreatic protein could be involved in specific variation of beta-cell mass and might also contribute to the regulation of insulin secretion at this level. According to our results, TM17 is essentially involved in SUR1-mediated apoptosis. This effect does not require the presence of functional Kir6.2-containing K(ATP) channels, which points to additional, so far unknown functions of SUR.
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Affiliation(s)
- Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Tübingen, Germany.
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63
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Jahangir A, Terzic A. K(ATP) channel therapeutics at the bedside. J Mol Cell Cardiol 2005; 39:99-112. [PMID: 15953614 PMCID: PMC2743392 DOI: 10.1016/j.yjmcc.2005.04.006] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Revised: 03/17/2005] [Accepted: 04/26/2005] [Indexed: 11/22/2022]
Abstract
The family of potassium channel openers regroups drugs that share the property of activating adenosine triphosphate-sensitive potassium (K(ATP)) channels, metabolic sensors responsible for adjusting membrane potential-dependent functions to match cellular energetic demands. K(ATP) channels, widely represented in metabolically-active tissue, are heteromultimers composed of an inwardly rectifying potassium channel pore and a regulatory sulfonylurea receptor subunit, the site of action of potassium channel opening drugs that promote channel activity by antagonizing ATP-induced pore inhibition. The activity of K(ATP) channels is critical in the cardiovascular adaptive response to stress, maintenance of neuronal electrical stability, and hormonal homeostasis. Thereby, K(ATP) channel openers have a unique therapeutic spectrum, ranging from applications in myopreservation and vasodilatation in patients with heart or vascular disease to potential clinical use as bronchodilators, bladder relaxants, islet cell protector, antiepileptics and promoters of hair growth. While the current experience in practice with potassium channel openers remains limited, multitude of ongoing investigations aims at defining the benefit of this emerging family of therapeutics in diverse disease conditions associated with metabolic distress.
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Affiliation(s)
- A Jahangir
- Division of Cardiovascular Diseases, Departmentof Medicine, Mayo Clinic College of Medicine, Guggenheim 7, Mayo Clinic, 200 First Street SW, Rochester, MN 55905, USA.
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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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Fokunang C, . KW, . LS, . AP, . CB. Molecular Cloning of the Nucleotide Binding Domain of Sulphonylurea Receptor 1, a Component of the ATP-sensitive K-channel. JOURNAL OF MEDICAL SCIENCES 2005. [DOI: 10.3923/jms.2005.141.152] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
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Alekseev AE, Hodgson DM, Karger AB, Park S, Zingman LV, Terzic A. ATP-sensitive K+ channel channel/enzyme multimer: metabolic gating in the heart. J Mol Cell Cardiol 2005; 38:895-905. [PMID: 15910874 PMCID: PMC2736952 DOI: 10.1016/j.yjmcc.2005.02.022] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/01/2005] [Accepted: 02/16/2005] [Indexed: 10/25/2022]
Abstract
Cardiac ATP-sensitive K(+) (K(ATP)) channels, gated by cellular metabolism, are formed by association of the inwardly rectifying potassium channel Kir6.2, the potassium conducting subunit, and SUR2A, the ATP-binding cassette protein that serves as the regulatory subunit. Kir6.2 is the principal site of ATP-induced channel inhibition, while SUR2A regulates K(+) flux through adenine nucleotide binding and catalysis. The ATPase-driven conformations within the regulatory SUR2A subunit of the K(ATP) channel complex have determinate linkage with the states of the channel's pore. The probability and life-time of ATPase-induced SUR2A intermediates, rather than competitive nucleotide binding alone, defines nucleotide-dependent K(ATP) channel gating. Cooperative interaction, instead of independent contribution of individual nucleotide binding domains within the SUR2A subunit, serves a decisive role in defining K(ATP) channel behavior. Integration of K(ATP) channels with the cellular energetic network renders these channel/enzyme heteromultimers high-fidelity metabolic sensors. This vital function is facilitated through phosphotransfer enzyme-mediated transmission of controllable energetic signals. By virtue of coupling with cellular energetic networks and the ability to decode metabolic signals, K(ATP) channels set membrane excitability to match demand for homeostatic maintenance. This new paradigm in the operation of an ion channel multimer is essential in providing the basis for K(ATP) channel function in the cardiac cell, and for understanding genetic defects associated with life-threatening diseases that result from the inability of the channel complex to optimally fulfill its physiological role.
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Affiliation(s)
- Alexey E Alekseev
- Division of Cardiovascular Diseases, Department of Medicine, Mayo Clinic College of Medicine, Rochester, MN 55905, USA.
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Yamada M, Kurachi Y. A functional role of the C-terminal 42 amino acids of SUR2A and SUR2B in the physiology and pharmacology of cardiovascular ATP-sensitive K(+) channels. J Mol Cell Cardiol 2005; 39:1-6. [PMID: 15978900 DOI: 10.1016/j.yjmcc.2004.11.022] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2004] [Revised: 07/19/2004] [Accepted: 11/12/2004] [Indexed: 11/16/2022]
Abstract
The ATP-sensitive K(+) (K(ATP)) channel is composed of four pore-forming Kir6.2 subunits and four sulfonylurea receptors (SUR). Intracellular ATP inhibits K(ATP) channels through Kir6.2. SUR is an ABC protein bearing transmembrane domains and two nucleotide-binding domains (NBD1 and NBD2). SUR increases the open probability of K(ATP) channels by interacting with ATP and ADP through NBDs and with K(+) channel openers such as nicorandil through its transmembrane domain. Because NBDs and the drug receptor allosterically interact with each other, nucleotides and drugs probably activate K(ATP) channels by causing the same conformational change of SUR. SUR2A and SUR2B have the identical drug receptor and NBDs and differ only in the C-terminal 42 amino acids (C42). Nonetheless, nicorandil ~100 times more potently activates SUR2B/Kir6.2 than SUR2A/Kir6.2 channels. Based on our allosteric model, we have analyzed the interaction between NBDs and the drug receptor in SUR2A and SUR2B and found that both nucleotide-bound NBD1 and NBD2 more strongly induce the conformational change in SUR2B than SUR2A. Therefore, C42 modulates the function of not only NBD2 which is close to C42 in a primary structure but NBD1 which is more than 630 amino acid N-terminal to C42. This raises the possibility that in the presence of nucleotides, NBD1 and NBD2 dimerize to induce the conformational change and that the dimerization enables C42 to gain access to both NBDs. Modulation of the nucleotide-NBD1 and -NBD2 interactions by C42 would determine the stability of the nucleotide-dependent dimer and thus, the physiological and pharmacological properties of K(ATP) channels.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine, Faculty of Medicine, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan
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68
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Conseil G, Deeley RG, Cole SPC. Role of two adjacent cytoplasmic tyrosine residues in MRP1 (ABCC1) transport activity and sensitivity to sulfonylureas. Biochem Pharmacol 2005; 69:451-61. [PMID: 15652236 DOI: 10.1016/j.bcp.2004.10.014] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2004] [Accepted: 10/22/2004] [Indexed: 11/22/2022]
Abstract
The human ATP-binding cassette (ABC) protein MRP1 causes resistance to many anticancer drugs and is also a primary active transporter of conjugated metabolites and endogenous organic anions, including leukotriene C(4) (LTC(4)) and glutathione (GSH). The sulfonylurea receptors SUR1 and SUR2 are related ABC proteins with the same domain structure as MRP1, but serve as regulators of the K(+) channel Kir6.2. Despite their functional differences, the activity of both SUR1/2 and MRP1 can be blocked by glibenclamide, a sulfonylurea used to treat diabetes. Residues in the cytoplasmic loop connecting transmembrane helices 15 and 16 of the SUR proteins have been implicated as molecular determinants of their sensitivity to glibenclamide and other sulfonylureas. We have now investigated the effect of mutating Tyr(1189) and Tyr(1190) in the comparable region of MRP1 on its transport activity and sulfonylurea sensitivity. Ala and Ser substitutions of Tyr(1189) and Tyr(1190) caused a > or =50% decrease in the ability of MRP1 to transport different organic anions, and a decrease in LTC(4) photolabeling. Kinetic analyses showed the decrease in GSH transport was attributable primarily to a 10-fold increase in K(m). In contrast, mutations of these Tyr residues had no major effect on the catalytic activity of MRP1. Furthermore, the mutant proteins showed no substantial differences in their sensitivity to glibenclamide and tolbutamide. We conclude that MRP1 Tyr(1189) and Tyr(1190), unlike the corresponding residues in SUR1, are not involved in its differential sensitivity to sulfonylureas, but nevertheless, may be involved in the transport activity of MRP1, especially with respect to GSH.
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Affiliation(s)
- Gwenaëlle Conseil
- Divison of Cancer Biology and Genetics, Cancer Research Institute, Queen's University, Kingston, Ont., K7L 3N6, Canada
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69
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Yamasaki K, Takemura S, Minamiyama Y, Hai S, Yamamoto S, Kodai S, Hirohashi K, Suehiro S. Minoxidil, a K(ATP) channel opener, accelerates DNA synthesis following partial hepatectomy in rats. Biofactors 2005; 23:15-23. [PMID: 15817995 DOI: 10.1002/biof.5520230103] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
A large number of studies have reported the action of K(ATP) channel openers in accelerating the proliferation of hepatocytes and many other cell types in vitro. Few studies, however, have examined the proliferative effect of K(ATP) channel openers in vivo. The aim of this study was to determine whether the K(ATP) channel opener minoxidil accelerates liver regeneration after partial hepatectomy (PH) in vivo. Male Wistar rats underwent a 70% partial hepatectomy (PH) after receiving a subcutaneous injection of minoxidil (0.01 mg/kg or 0.03 mg/kg). Some of the rats were intravenously treated with 5-hydroxydecanoic acid (5-HD, 10 mg/kg) just before the minoxidil injection. Seventy-two hours after PH, DNA synthesis was immunohistochemically assessed by bromodeoxyuridine (BrdU) incorporation into the nuclei. Minoxidil induced significant and dose-dependent increase in the BrdU labeling index after PH, and 5-HD reversed this minoxidil-induced change. Minoxidil did not significantly affect the changes in liver weight and liver function after PH. The hepatic levels of prealbumin decreased by about 60% after PH and minoxidil inhibited the decrease. In conclusion, the K(ATP) channel opener minoxidil enhanced DNA synthesis after PH without affecting the liver function.
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Affiliation(s)
- Keiichi Yamasaki
- Department of Hepato-Biliary-Pancreatic Surgery, Osaka City University Graduate School of Medicine, Abeno, Osaka 545-8585, Japan
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Moreau C, Gally F, Jacquet-Bouix H, Vivaudou M. The size of a single residue of the sulfonylurea receptor dictates the effectiveness of K ATP channel openers. Mol Pharmacol 2004; 67:1026-33. [PMID: 15615694 DOI: 10.1124/mol.104.008698] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
K(ATP) channel openers are a diverse group of molecules able to activate ATP-sensitive K(+) channels in a tissue-dependent manner by binding to the channel regulatory subunit, the sulfonylurea receptor (SUR), an ATP-binding cassette protein. Residues crucial to this action were previously identified in the last transmembrane helix of SUR, transmembrane helix 17. This study examined the residue at the most important position, 1253 in the muscle isoform SUR2A and the matching 1290 in the pancreatic/neuronal isoform SUR1 (rat numbering). At this position in either isoform, a threonine enables action of openers, whereas a methionine prohibits it. Using single-point mutagenesis, we have examined the physicochemical basis of this phenomenon and discovered that it relied uniquely on side chain volume and not on shape, polarity, or hydrogen-bonding capacity of the residue. Moreover, the aromatic nature of neighboring residues conserved in SUR1 and SUR2A was found necessary for SUR2A to sustain the wild-type levels of channel activation by the openers tested, the cromakalim analog SR47063 [4-(2-cyanimino-1,2-dihydro-1-pyridyl)-2,2-dimethyl-6-nitrochromene] and the pinacidil analog P1075 [N-cyano-N'-(1,1-dimethylpropyl)-N'-3-pyridylguanidine]. These observations suggest that these residues can interact with openers via nonspecific stacking interactions provided that the adjacent 1253/1290 residue does not obstruct access. The smaller Thr1253 of SUR2A would permit activation, whereas the bulky Met1290 of SUR1 would not. This hypothesis is discussed in the context of a simple molecular model of transmembrane helix 17.
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Affiliation(s)
- Christophe Moreau
- Biophysique Moléculaire et Cellulaire, Centre National de la Recherche Scientifique Unité Mixte de Recherche 5090, DRDC-BMC, 17 rue des Martyrs, 38054 Grenoble, France
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71
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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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Bryan J, Vila-Carriles WH, Zhao G, Babenko AP, Aguilar-Bryan L. Toward linking structure with function in ATP-sensitive K+ channels. Diabetes 2004; 53 Suppl 3:S104-12. [PMID: 15561897 DOI: 10.2337/diabetes.53.suppl_3.s104] [Citation(s) in RCA: 87] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Advances in understanding the overall structural features of inward rectifiers and ATP-binding cassette (ABC) transporters are providing novel insight into the architecture of ATP-sensitive K+ channels (KATP channels) (KIR6.0/SUR)4. The structure of the K(IR) pore has been modeled on bacterial K+ channels, while the lipid-A exporter, MsbA, provides a template for the MDR-like core of sulfonylurea receptor (SUR)-1. TMD0, an NH2-terminal bundle of five alpha-helices found in SURs, binds to and activates KIR6.0. The adjacent cytoplasmic L0 linker serves a dual function, acting as a tether to link the MDR-like core to the KIR6.2/TMD0 complex and exerting bidirectional control over channel gating via interactions with the NH2-terminus of the KIR. Homology modeling of the SUR1 core offers the possibility of defining the glibenclamide/sulfonylurea binding pocket. Consistent with 30-year-old studies on the pharmacology of hypoglycemic agents, the pocket is bipartite. Elements of the COOH-terminal half of the core recognize a hydrophobic group in glibenclamide, adjacent to the sulfonylurea moiety, to provide selectivity for SUR1, while the benzamido group appears to be in proximity to L0 and the KIR NH2-terminus.
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Affiliation(s)
- Joseph Bryan
- Department of Molecular and Cellular Biology, Baylor College of Medicine, Houston, TX 77030, USA.
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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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Yamada M, Ishii M, Hibino H, Kurachi Y. Mutation in nucleotide-binding domains of sulfonylurea receptor 2 evokes Na-ATP-dependent activation of ATP-sensitive K+ channels: implication for dimerization of nucleotide-binding domains to induce channel opening. Mol Pharmacol 2004; 66:807-16. [PMID: 15258252 DOI: 10.1124/mol.104.002717] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
The ATP-sensitive K+ (KATP) channel is composed of a sulfonylurea receptor (SUR) and a pore-forming subunit, Kir6.2. SUR is an ATP-binding cassette (ABC) protein with two nucleotide-binding domains (NBD1 and NBD2). Intracellular ATP inhibits KATP channels through Kir6.2 and activates them through NBDs. However, it is still unknown how ATP-bound NBDs activate KATP channels. A prokaryotic ABC protein, MJ0796, which is entirely NBD, forms a dimer in the presence of Na-ATP when its glutamate at position 171 is substituted with glutamine. Mg2+ or K+ destabilizes the dimer. We made the corresponding mutation in the NBD1 (D834N) and/or NBD2 (E1471Q) of SUR2A and SUR2B. As measured in the inside-out configuration of the patch-clamp method, SUR2x(D834N, E1471)/Kir6.2 channels mediated significantly larger currents in the presence of internal 1 mM Na-ATP than K-ATP alone or Mg-ATP. The response to Na-ATP resulted from an increase in the open probability but not single-channel amplitude of the channels and was abolished by glibenclamide (10(-5) M). In the presence of 1 mM Mg2+ -free ATP, Na+ increased the activity of the channels in a concentration-dependent manner. The Na-ATP-dependent activation was never observed with KATP channels including either the wild-type SUR2x, SUR2x(D834N), or SUR2x(E1471). Nicorandil activated SUR2x(D834N, E1471Q)/Kir6.2 channels more strongly in the presence of Na-ATP than K-ATP alone, whereas the reverse was true for wild-type SUR2x/Kir6.2 channels. Therefore, it is likely that NBDs of SUR2x dimerize in response to ATP and nicorandil. The dimerization induces the opening of the KATP channel, probably by causing a conformational change of SUR2x.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine Osaka University, 2-2 Yamada-oka, Suita, 565-0871, Japan
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Prost AL, Bloc A, Hussy N, Derand R, Vivaudou M. Zinc is both an intracellular and extracellular regulator of KATP channel function. J Physiol 2004; 559:157-67. [PMID: 15218066 PMCID: PMC1665068 DOI: 10.1113/jphysiol.2004.065094] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Extracellular Zn(2+) has been identified as an activator of pancreatic K(ATP) channels. We further examined the action of Zn(2+) on recombinant K(ATP) channels formed with the inward rectifier K(+) channel subunit Kir6.2 associated with either the pancreatic/neuronal sulphonylurea receptor 1 (SUR1) subunit or the cardiac SUR2A subunit. Zn(2+), applied at either the extracellular or intracellular side of the membrane appeared as a potent, reversible activator of K(ATP) channels. External Zn(2+), at micromolar concentrations, activated SUR1/Kir6.2 but induced a small inhibition of SUR2A/Kir6.2 channels. Cytosolic Zn(2+) dose-dependently stimulated both SUR1/Kir6.2 and SUR2A/Kir6.2 channels, with half-maximal effects at 1.8 and 60 microm, respectively, but it did not affect the Kir6.2 subunit expressed alone. These observations point to an action of both external and internal Zn(2+) on the SUR subunit. Effects of internal Zn(2+) were not due to Zn(2+) leaking out, since they were unaffected by the presence of a Zn(2+) chelator on the external side. Similarly, internal chelators did not affect activation by external Zn(2+). Therefore, Zn(2+) is an endogenous K(ATP) channel opener being active on both sides of the membrane, with potentially distinct sites of action located on the SUR subunit. These findings uncover a novel regulatory pathway targeting K(ATP) channels, and suggest a new role for Zn(2+) as an intracellular signalling molecule.
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Affiliation(s)
- Anne-Lise Prost
- Biophysique Moléculaire & Cellulaire, CNRS UMR5090, CEA/DRDC, 17 rue des Martyrs, 38054 Grenoble, France
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Mannhold R. KATP channel openers: structure-activity relationships and therapeutic potential. Med Res Rev 2004; 24:213-66. [PMID: 14705169 DOI: 10.1002/med.10060] [Citation(s) in RCA: 132] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
ATP-sensitive potassium channels (K(ATP) channels) are heteromeric complexes of pore-forming inwardly rectifying potassium channel subunits and regulatory sulfonylurea receptor subunits. K(ATP) channels were identified in a variety of tissues including muscle cells, pancreatic beta-cells, and various neurons. They are regulated by the intracellular ATP/ADP ratio; ATP induces channel inhibition and MgADP induces channel opening. Functionally, K(ATP) channels provide a means of linking the electrical activity of a cell to its metabolic state. Shortening of the cardiac action potential, smooth muscle relaxation, inhibition of both insulin secretion, and neurotransmitter release are mediated via K(ATP) channels. Given their many physiological functions, K(ATP) channels represent promising drug targets. Sulfonylureas like glibenclamide block K(ATP) channels; they are used in the therapy of type 2 diabetes. Openers of K(ATP) channels (KCOs), for example, relax smooth muscle and induce hypotension. KCOs are chemically heterogeneous and include as different classes as the benzopyrans, cyanoguanidines, thioformamides, thiadiazines, and pyridyl nitrates. Examples for new chemical entities more recently developed as KCOs include cyclobutenediones, dihydropyridine related structures, and tertiary carbinols.
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Affiliation(s)
- Raimund Mannhold
- Department of Laser Medicine, Molecular Drug Research Group, Heinrich-Heine-Universität, Universitätsstrasse 1, 40225 Düsseldorf, Germany.
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77
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Yamada M, Kurachi Y. The nucleotide-binding domains of sulfonylurea receptor 2A and 2B play different functional roles in nicorandil-induced activation of ATP-sensitive K+ channels. Mol Pharmacol 2004; 65:1198-207. [PMID: 15102948 DOI: 10.1124/mol.65.5.1198] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Nicorandil activates ATP-sensitive K(+) channels composed of Kir6.2 and either sulfonylurea receptor (SUR) 2A or 2B. Although SUR2A and SUR2B differ only in their C-terminal 42 amino acids (C42) and possess identical drug receptors and nucleotide-binding domains (NBDs), nicorandil more potently activates SUR2B/Kir6.2 than SUR2A/Kir6.2 channels. Here, we analyzed the roles of NBDs in these channels' response to nicorandil with the inside-out configuration of the patch-clamp method. Binding and hydrolysis of nucleotides by NBDs were impaired by mutations in the Walker A motif of NBD1 (K708A) and NBD2 (K1349A) and in the Walker B motif of NBD2 (D1470N). Experiments were done with internal ATP (1 mM). In SUR2A/Kir6.2 channels, the K708A mutation abolished, and the K1349A but not D1470N mutation reduced the sensitivity to nicorandil. ADP (100 microM) significantly increased the wild-type channels' sensitivity to nicorandil, which was abolished by the K1349A or D1470N mutation. Thus, the SUR2A/Kir6.2 channels' response to nicorandil critically depends on ATP-NBD1 interaction and is facilitated by interactions of ATP or ADP with NBD2. In SUR2B/Kir6.2 channels, either the K708A or K1349A mutation partially suppressed the response to nicorandil, and double mutations abolished it. The D1470N mutation also significantly impaired the response. ADP did not sensitize the channels. Thus, NBD2 hydrolyzes ATP, and NBD1 and NBD2 equally contribute to the response by interacting with ATP and ADP, accounting for the higher nicorandil sensitivity of SUR2B/Kir6.2 than SUR2A/Kir6.2 channels in the presence of ATP alone. Thus, C42 modulates the interaction of both NBDs with intracellular nucleotides.
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Affiliation(s)
- Mitsuhiko Yamada
- Department of Pharmacology II, Graduate School of Medicine, Osaka University, Suita, Japan
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78
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Nakaya H, Miki T, Seino S, Yamada K, Inagaki N, Suzuki M, Sato T, Yamada M, Matsushita K, Kurachi Y, Arita M. [Molecular and functional diversity of ATP-sensitive K+ channels: the pathophysiological roles and potential drug targets]. Nihon Yakurigaku Zasshi 2003; 122:243-50. [PMID: 12939542 DOI: 10.1254/fpj.122.243] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022]
Abstract
ATP-sensitive K(+) (K(ATP)) channels comprise the pore-forming subunit (Kir6.1 or Kir6.2) and the regulatory subunit sulfonylurea receptors (SUR1 or SUR2). K(ATP) channels with different combinations of these subunits are present in various tissues and regulate cellular functions. From the analysis of mouse models with targeted deletion of the gene encoding the pore-forming subunit Kir6.1 or Kir6.2, functional roles of K(ATP) channels in various organs have been clarified. Kir6.1(-/-) mice showed sudden death associated with ST elevation and atrioventricular block in ECG, a phenotype resembling Prinzmetal angina in humans. Kir6.2(-/-) mice were more susceptible to generalized seizure during hypoxia than wild-type (WT) mice, suggesting that neuronal K(ATP) channels, probably composed of Kir6.2 and SUR1, play a crucial role for the protection of the brain against lethal damage due to seizure. In Kir6.2(-/-) mice lacking the sarcolemmal K(ATP) channel activity in cardiac cells, ischemic preconditioning failed to reduce the infarct size, suggesting that sarcolemmal K(ATP) channels play an important role in cardioprotection against ischemia/reperfusion injuries in the heart. Mitochondrial K(ATP) channels have been also proposed to play a crucial role in cardioprotection, although the molecular identity of the channel has not been established. Nicorandil and minoxidil, K(+) channel openers activating mitochondrial K(ATP) channels, decreased the mitochondrial membrane potential, thereby preventing the Ca(2+) overload in the mitochondria of guinea-pig ventricular cells. SURs are the receptors for K(+) channel openers and the activating effects on sarcolemmal K(ATP) channels in cardiovascular tissues could be modulated by the interaction of nucleotides. Due to the molecular diversity of the accessory and pore subunits of K(ATP) channels, there would be considerable differences in the tissue selectivity of K(ATP) channel-acting drugs. Studies of Kir6.1 and Kir6.2 knockout mice indicate that K(ATP) channels are involved in the mechanisms of the protection against metabolic stress. Further clarification of physiological as well as pathophysiological roles of K(ATP) channels may lead to a new therapeutic strategy to improve the quality of life.
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Affiliation(s)
- Haruaki Nakaya
- Department of Pharmacology, Chiba University Graduate School of Medicine, Japan.
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79
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Prost AL, Dérand R, Gros L, Becq F, Vivaudou M. Inhibition of ATP-sensitive K+ channels by substituted benzo[c]quinolizinium CFTR activators. Biochem Pharmacol 2003; 66:425-30. [PMID: 12907241 DOI: 10.1016/s0006-2952(03)00289-2] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
The substituted benzo[c]quinolizinium compounds MPB-07 and MPB-91 are novel activators of the cystic fibrosis transmembrane conductance regulator (CFTR) chloride channel. High homologies between CFTR and the sulfonylurea receptor (SUR), which associates with the potassium channel Kir6.2 to form the ATP-sensitive K(+) (K(ATP)) channel, prompted us to examine possible effects of these compounds on K(ATP) channels using electrophysiological recordings and binding assays. Activity of recombinant K(ATP) channels expressed in Xenopus oocytes was recorded in the inside-out configuration of the patch-clamp technique. Channels were practically unaffected by MPB-07 but were fully blocked by MPB-91 with half-inhibition achieved at approximately 20 microM MPB-91. These effects were similar on channels formed by Kir6.2, and either the SUR1 or SUR2A isoforms were independent of the presence of nucleotides. They were not influenced by SUR mutations known to interfere with its nucleotide-binding capacity. MPB-91, but not MPB-07, was able to displace binding of glibenclamide to HEK cells expressing recombinant SUR1/Kir6.2 channels. Glibenclamide binding to native channels from pancreatic MIN6 cells was also displaced by MPB-91. A Kir6.2 mutant able to form channels without SUR was also blocked by MPB-91, but not by MPB-07. These observations demonstrate that neither MPB-07 nor MPB-91 interact with SUR, in spite of its high homology with CFTR, and that MPB-91 blocks K(ATP) channels by binding to the Kir6.2 subunit. Thus, caution should be exercised when planning to use MPB compounds in cystic fibrosis therapy, specially MPB-91 which could nonetheless find interesting applications as the precursor of a new class of K channel blockers.
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Affiliation(s)
- Ann- Lise Prost
- CEA, DRDC, Laboratoire de Biophysique Moléculaire et Cellulaire (UMR 5090), 17 rue des Martyrs, 38054 Grenoble, France
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80
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Chan KW, Zhang H, Logothetis DE. N-terminal transmembrane domain of the SUR controls trafficking and gating of Kir6 channel subunits. EMBO J 2003; 22:3833-43. [PMID: 12881418 PMCID: PMC169049 DOI: 10.1093/emboj/cdg376] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
The sulfonylurea receptor (SUR), an ATP-binding cassette (ABC) protein, assembles with a potassium channel subunit (Kir6) to form the ATP-sensitive potassium channel (K(ATP)) complex. Although SUR is an important regulator of Kir6, the specific SUR domain that associates with Kir6 is still unknown. All functional ABC proteins contain two transmembrane domains but some, including SUR and MRP1 (multidrug resistance protein 1), contain an extra N-terminal transmembrane domain called TMD0. The functions of any TMD0s are largely unclear. Using Xenopus oocytes to coexpress truncated SUR constructs with Kir6, we demonstrated by immunoprecipitation, single-oocyte chemiluminescence and electrophysiological measurements that the TMD0 of SUR1 strongly associated with Kir6.2 and modulated its trafficking and gating. Two TMD0 mutations, A116P and V187D, previously correlated with persistent hyperinsulinemic hypoglycemia of infancy, were found to disrupt the association between TMD0 and Kir6.2. These results underscore the importance of TMD0 in K(ATP) channel function, explaining how specific mutations within this domain result in disease, and suggest how an ABC protein has evolved to regulate a potassium channel.
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Affiliation(s)
- Kim W Chan
- Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York University, New York, NY 10029, USA.
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81
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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: 214] [Impact Index Per Article: 10.2] [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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82
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Davis-Taber R, Molinari EJ, Altenbach RJ, Whiteaker KL, Shieh CC, Rotert G, Buckner SA, Malysz J, Milicic I, McDermott JS, Gintant GA, Coghlan MJ, Carroll WA, Scott VE, Gopalakrishnan M. [125I]A-312110, a novel high-affinity 1,4-dihydropyridine ATP-sensitive K+ channel opener: characterization and pharmacology of binding. Mol Pharmacol 2003; 64:143-53. [PMID: 12815170 DOI: 10.1124/mol.64.1.143] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Although ATP-sensitive K+ channels continue to be explored for their therapeutic potential, developments in high-affinity radioligands to investigate native and recombinant KATP channels have been less forthcoming. This study reports the identification and pharmacological characterization of a novel iodinated 1,4-dihydropyridine KATP channel opener, [125I]A-312110 [(9R)-9-(4-fluoro-3-125iodophenyl)-2,3,5,9-tetrahydro-4H-pyrano[3,4-b]thieno[2,3-e]pyridin-8(7H)-one-1,1-dioxide]. Binding of [125I]A-312110 to guinea pig cardiac (KD = 5.8 nM) and urinary bladder (KD = 4.9 nM) membranes were of high affinity, saturable, and to a single set of binding sites. Displacement of [125I]A-312110 by structurally diverse potassium channel openers (KCOs) indicated a similar rank order of potency in both guinea pig cardiac and bladder membranes (Ki, heart): A-312110 (4.3 nM) > N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine (P1075) > (-)-N-(2-ethoxyphenyl)-N'-(1,2,3-trimethylpropyl)-2-nitroethene-1,1-diamine (Bay X 9228) > pinacidil > (-)-cromakalim > N-(4-benzoyl phenyl)-3,3,3-trifluro-2-hydroxy-2-methylpropionamine (ZD6169) > 9-(3-cyanophenyl)-3,4,6,7,9,10-hexahydro-1,8-(2H,5H)-acridinedione (ZM244085) >> diazoxide (16.7 microM). Displacement by KATP channel blockers, the sulfonylurea glyburide, and the cyanoguanidine N-[1-(3-chlorophenyl)cyclobutyl]-N'-cyano-N"-3-pyridinyl-guanidine (PNU-99963) were biphasic in the heart but monophasic in bladder with about a 100- to 500-fold difference in Ki values between high- and low-affinity sites. Good correlations were observed between cardiac or bladder-binding affinities of KCOs with functional activation as assessed by their respective potencies to either suppress action potential duration (APD) in Purkinje fibers or to relax electrical field-stimulated bladder contractions. Collectively, these results demonstrate that [125I]A-312110 binds with high affinity and has an improved activity profile compared with other radiolabeled KCOs. [125I]A-312110 is a useful tool for investigation of the molecular and functional properties of the KATP channel complex and for the identification, in a high throughput manner, of both novel channel blockers and openers that interact with cardiac/smooth muscle-type KATP channels.
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Affiliation(s)
- Rachel Davis-Taber
- Neuroscience Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Abbott Park, Illinois, USA
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83
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Tricarico D, Barbieri M, Antonio L, Tortorella P, Loiodice F, Camerino DC. Dualistic actions of cromakalim and new potent 2H-1,4-benzoxazine derivatives on the native skeletal muscle K ATP channel. Br J Pharmacol 2003; 139:255-62. [PMID: 12770930 PMCID: PMC1573836 DOI: 10.1038/sj.bjp.0705233] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1 New 2H-1,4-benzoxazine derivatives were synthesized and tested for their agonist properties on the ATP-sensitive K(+) channels (K(ATP)) of native rat skeletal muscle fibres by using the patch-clamp technique. The novel modifications involved the introduction at position 2 of the benzoxazine ring of alkyl substituents such as methyl (-CH(3)), ethyl (-C(2)H(5)) or propyl (-C(3)H(7)) groups, while maintaining pharmacophore groups critical for conferring agonist properties. 2 The effects of these molecules were compared with those of cromakalim in the presence or absence of internal ATP (10(-4) M). In the presence of internal ATP, all the compounds increased the macropatch K(ATP) currents. The order of potency of the molecules as agonists was -C(3)H(7) (DE(50)=1.63 x 10(-8) M) >-C(2)H(5) (DE(50)=1.11 x 10(-7) M)>-CH(3) (DE(50)=2.81 x 10(-7) M)>cromak-slim (DE(50)= 1.42 x 10(-5) M). Bell-shaped dose-response curves were observed for these compounds and cromakalim indicating a downturn in response when a certain dose was exceeded. 3 In contrast, in the absence of internal ATP, all molecules including cromakalim inhibited the K(ATP) currents. The order of increasing potency as antagonists was cromakalim (IC(50)=1.15 x 10(-8) M)> or =-CH(3) (IC(50)=2.6 x 10(-8) M)>-C(2)H(5) (IC(50)=4.4 x 10(-8) M)>-C(3)H(7) (IC(50)=1.68 x 10(-7) M) derivatives. 4 These results suggest that the newly synthesized molecules and cromakalim act on muscle K(ATP) channel by binding on two receptor sites that have opposite actions. Alternatively, a more simple explanation is to consider the existence of a single site for potassium channel openers regulated by ATP which favours the transduction of the channel opening. The alkyl chains at position 2 of the 2H-1,4-benzoxazine nucleus is pivotal in determining the potency of benzoxazine derivatives as agonists or antagonists.
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Affiliation(s)
- Domenico Tricarico
- Department of Pharmacobiology, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
| | - Mariagrazia Barbieri
- Department of Pharmacobiology, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
| | - Laghezza Antonio
- Department of Medicinal Chemistry, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
| | - Paolo Tortorella
- Department of Medicinal Chemistry, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
| | - Fulvio Loiodice
- Department of Medicinal Chemistry, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
| | - Diana Conte Camerino
- Department of Pharmacobiology, Faculty of Pharmacy, via Orabona no. 4, University of Bari, I-70126 Bari, Italy
- Author for correspondence:
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84
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Russ U, Lange U, Löffler-Walz C, Hambrock A, Quast U. Binding and effect of K ATP channel openers in the absence of Mg2+. Br J Pharmacol 2003; 139:368-80. [PMID: 12770942 PMCID: PMC1573839 DOI: 10.1038/sj.bjp.0705238] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
1 Openers of ATP-sensitive K(+) channels (K(ATP) channels) are thought to act by enhancing the ATPase activity of sulphonylurea receptors (SURs), the regulatory channel subunits. At higher concentrations, some openers activate K(ATP) channels also in the absence of MgATP. Here, we describe binding and effect of structurally diverse openers in the absence of Mg(2+) and presence of EDTA. 2 Binding of openers to SUR2B was measured using a mutant with high affinity for [(3)H]glibenclamide ([(3)H]GBC). In the absence of Mg(2+), 'typical' openers (benzopyrans, cyanoguanidines and aprikalim) inhibited [(3)H]GBC binding with K(i) values approximately 200 x higher than in the presence of MgATP. Minoxidil sulphate and nicorandil were inactive, whereas binding of diazoxide was unaffected by MgATP. 3 In the absence/presence of MgATP, N-cyano-N'-(1,1-dimethylpropyl)-N"-3-pyridylguanidine (P1075) activated the Kir6.2/SUR2B channel in inside-out patches with EC(50)=2000/67nM and E(max)=32/134%. In the absence of Mg(2+), responses were variable with only a small part of the variability being explained by a decrease in channel responsiveness with time after patch excision and to differences in the ATP sensitivity between patches. 4 The rank order of efficacy of the openers was P1075>rilmakalim approximately nicorandil>diazoxide>minoxidil sulphate. 5 The data show that structurally diverse openers are able to bind to, and to activate the Kir6.2/SUR2B channel by a pathway independent of ATP hydrolysis. These effects are observed at concentrations used to define the biochemical mechanism of the openers in the presence of MgATP and allow the openers to be classified into 'typical' and 'atypical' KCOs with diazoxide standing apart.
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Affiliation(s)
- Ulrich Russ
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, Tübingen D-72074, Germany
| | - Ulf Lange
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, Tübingen D-72074, Germany
| | - Cornelia Löffler-Walz
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, Tübingen D-72074, Germany
| | - Annette Hambrock
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, Tübingen D-72074, Germany
| | - Ulrich Quast
- Department of Pharmacology and Toxicology, Medical Faculty, University of Tübingen, Wilhelmstr. 56, Tübingen D-72074, Germany
- Author for correspondence:
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85
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Hodgson DM, Zingman LV, Kane GC, Perez-Terzic C, Bienengraeber M, Ozcan C, Gumina RJ, Pucar D, O'Coclain F, Mann DL, Alekseev AE, Terzic A. Cellular remodeling in heart failure disrupts K(ATP) channel-dependent stress tolerance. EMBO J 2003; 22:1732-42. [PMID: 12682006 PMCID: PMC154482 DOI: 10.1093/emboj/cdg192] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
ATP-sensitive potassium (K(ATP)) channels are required for maintenance of homeostasis during the metabolically demanding adaptive response to stress. However, in disease, the effect of cellular remodeling on K(ATP) channel behavior and associated tolerance to metabolic insult is unknown. Here, transgenic expression of tumor necrosis factor alpha induced heart failure with typical cardiac structural and energetic alterations. In this paradigm of disease remodeling, K(ATP) channels responded aberrantly to metabolic signals despite intact intrinsic channel properties, implicating defects proximal to the channel. Indeed, cardiomyocytes from failing hearts exhibited mitochondrial and creatine kinase deficits, and thus a reduced potential for metabolic signal generation and transmission. Consequently, K(ATP) channels failed to properly translate cellular distress under metabolic challenge into a protective membrane response. Failing hearts were excessively vulnerable to metabolic insult, demonstrating cardiomyocyte calcium loading and myofibrillar contraction banding, with tolerance improved by K(ATP) channel openers. Thus, disease-induced K(ATP) channel metabolic dysregulation is a contributor to the pathobiology of heart failure, illustrating a mechanism for acquired channelopathy.
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Affiliation(s)
- Denice M Hodgson
- Department of Medicine, Mayo Clinic, Mayo Foundation, Rochester, MN 55905, USA
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86
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Dzeja PP, Bast P, Ozcan C, Valverde A, Holmuhamedov EL, Van Wylen DGL, Terzic A. Targeting nucleotide-requiring enzymes: implications for diazoxide-induced cardioprotection. Am J Physiol Heart Circ Physiol 2003; 284:H1048-56. [PMID: 12666660 DOI: 10.1152/ajpheart.00847.2002] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Modulation of mitochondrial respiratory chain, dehydrogenase, and nucleotide-metabolizing enzyme activities is fundamental to cellular protection. Here, we demonstrate that the potassium channel opener diazoxide, within its cardioprotective concentration range, modulated the activity of flavin adenine dinucleotide-dependent succinate dehydrogenase with an IC50 of 32 microM and reduced the rate of succinate-supported generation of reactive oxygen species (ROS) in heart mitochondria. 5-Hydroxydecanoic fatty acid circumvented diazoxide-inhibited succinate dehydrogenase-driven electron flow, indicating a metabolism-dependent supply of redox equivalents to the respiratory chain. In perfused rat hearts, diazoxide diminished the generation of malondialdehyde, a marker of oxidative stress, which, however, increased on diazoxide washout. This effect of diazoxide mimicked ischemic preconditioning and was associated with reduced oxidative damage on ischemia-reperfusion. Diazoxide reduced cellular and mitochondrial ATPase activities, along with nucleotide degradation, contributing to preservation of myocardial ATP levels during ischemia. Thus, by targeting nucleotide-requiring enzymes, particularly mitochondrial succinate dehydrogenase and cellular ATPases, diazoxide reduces ROS generation and nucleotide degradation, resulting in preservation of myocardial energetics under stress.
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Affiliation(s)
- Petras P Dzeja
- Department of Medicine, Mayo Clinic, Mayo Foundation, Rochester, MN 55905, USA
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87
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Gribble FM, Reimann F. Differential selectivity of insulin secretagogues: mechanisms, clinical implications, and drug interactions. J Diabetes Complications 2003; 17:11-5. [PMID: 12623163 DOI: 10.1016/s1056-8727(02)00272-6] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The sulphonylurea receptor (SUR) subunits of K(ATP) channels are the targets for several classes of therapeutic drugs. Sulphonylureas close K(ATP) channels in pancreatic beta-cells and are used to stimulate insulin release in type 2 diabetes, whereas the K(ATP) channel opener nicorandil acts as an antianginal agent by opening K(ATP) channels in cardiac and vascular smooth muscle. The predominant type of SUR varies between tissues: SUR1 in beta-cells, SUR2A in cardiac muscle, and SUR2B in smooth muscle. Sulphonylureas and related drugs exhibit differences in tissue specificity, as the drugs interact to varying degrees with different types of SUR. Gliclazide and tolbutamide are beta-cell selective and reversible. Glimepiride, glibenclamide, and repaglinide, however, inhibit cardiac and smooth muscle K(ATP) channels in addition to those in beta-cells and are only slowly reversible. Similar properties have been observed by recording K(ATP) channel activity in intact cells and in Xenopus oocytes expressing cloned K(ATP) channel subunits. While K(ATP) channels in cardiac and smooth muscle are largely closed under physiological conditions (but open during ischaemia), they are activated by antianginal agents such as nicorandil. Under these conditions, they may be inhibited by sulphonylureas that block SUR2-type K(ATP) channels (e.g., glibenclamide). Care should, therefore, be taken when choosing a sulphonylurea if potential interactions with cardiac and smooth muscle K(ATP) channels are to be avoided.
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Affiliation(s)
- Fiona M Gribble
- Department of Clinical Biochemistry, University of Cambridge, Addenbrookes Hospital, Box 232, Hills Road, CB2 2QR, Cambridge, UK
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88
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Cartier EA, Shen S, Shyng SL. Modulation of the trafficking efficiency and functional properties of ATP-sensitive potassium channels through a single amino acid in the sulfonylurea receptor. J Biol Chem 2003; 278:7081-90. [PMID: 12496311 DOI: 10.1074/jbc.m211395200] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mutations in the sulfonylurea receptor 1 (SUR1), a subunit of ATP-sensitive potassium (K(ATP)) channels, cause familial hyperinsulinism. One such mutation, deletion of phenylalanine 1388 (DeltaPhe-1388), leads to defects in both trafficking and MgADP response of K(ATP) channels. Here we investigated the biochemical features of Phe-1388 that control the proper trafficking and function of K(ATP) channels by substituting the residue with all other 19 amino acids. Whereas surface expression is largely dependent on hydrophobicity, channel response to MgADP is governed by multiple factors and involves the detailed architecture of the amino acid side chain. Thus, structural features in SUR1 required for proper channel function are distinct from those required for correct protein trafficking. Remarkably, replacing Phe-1388 by leucine profoundly alters the physiological and pharmacological properties of the channel. The F1388L-SUR1 channel has increased sensitivity to MgADP and metabolic inhibition, decreased sensitivity to glibenclamide, and responds to both diazoxide and pinacidil. Because this conservative amino acid substitution occurs in the SUR2A and SUR2B isoforms, the mutation provides a mechanism by which functional diversities in K(ATP) channels are generated.
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Affiliation(s)
- Etienne A Cartier
- Center for Research on Occupational and Environmental Toxicology, Oregon Health and Science University, Portland, Oregon 97201, USA
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89
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Seino S, Miki T. Physiological and pathophysiological roles of ATP-sensitive K+ channels. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2003; 81:133-76. [PMID: 12565699 DOI: 10.1016/s0079-6107(02)00053-6] [Citation(s) in RCA: 379] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
ATP-sensitive potassium (K(ATP)) channels are present in many tissues, including pancreatic islet cells, heart, skeletal muscle, vascular smooth muscle, and brain, in which they couple the cell metabolic state to its membrane potential, playing a crucial role in various cellular functions. The K(ATP) channel is a hetero-octamer comprising two subunits: the pore-forming subunit Kir6.x (Kir6.1 or Kir6.2) and the regulatory subunit sulfonylurea receptor SUR (SUR1 or SUR2). Kir6.x belongs to the inward rectifier K(+) channel family; SUR belongs to the ATP-binding cassette protein superfamily. Heterologous expression of differing combinations of Kir6.1 or Kir6.2 and SUR1 or SUR2 variant (SUR2A or SUR2B) reconstitute different types of K(ATP) channels with distinct electrophysiological properties and nucleotide and pharmacological sensitivities corresponding to the various K(ATP) channels in native tissues. The physiological and pathophysiological roles of K(ATP) channels have been studied primarily using K(ATP) channel blockers and K(+) channel openers, but there is no direct evidence on the role of the K(ATP) channels in many important cellular responses. In addition to the analyses of naturally occurring mutations of the genes in humans, determination of the phenotypes of mice generated by genetic manipulation has been successful in clarifying the function of various gene products. Recently, various genetically engineered mice, including mice lacking K(ATP) channels (knockout mice) and mice expressing various mutant K(ATP) channels (transgenic mice), have been generated. In this review, we focus on the physiological and pathophysiological roles of K(ATP) channels learned from genetic manipulation of mice and naturally occurring mutations in humans.
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Affiliation(s)
- Susumu Seino
- Department of Cellular and Molecular Medicine, Graduate School of Medicine, Chiba University, 1-8-1 Inohana Chuo-ku, Chiba 260-8760, Japan.
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90
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Abstract
ATP-sensitive potassium channels (K(ATP)) of vascular smooth muscle cells represent potential therapeutic targets for control of abnormal vascular contractility. The biophysical properties, regulation and pharmacology of these channels have received intense scrutiny during the past twenty years, however, the molecular basis of vascular K(ATP) channels remains ill-defined. This review summarizes the recent advancements made in our understanding of the molecular composition of vascular K(ATP) channels with a focus on the evidence that hetero-octameric complexes of Kir6.1 and SUR2B subunits constitute the vascular K(ATP) subtype responsible for control of arterial diameter by vasoactive agonists.
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Affiliation(s)
- William C Cole
- The Smooth Muscle Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
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91
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Gopalakrishnan M, Miller TR, Buckner SA, Milicic I, Molinari EJ, Whiteaker KL, Davis-Taber R, Scott VE, Cassidy C, Sullivan JP, Carroll WA. Pharmacological characterization of a 1,4-dihydropyridine analogue, 9-(3,4-dichlorophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-1,8(2H,5H)-acridinedione (A-184209) as a novelK(ATP) channel inhibitor. Br J Pharmacol 2003; 138:393-9. [PMID: 12540531 PMCID: PMC1573672 DOI: 10.1038/sj.bjp.0705048] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
1. This study reports on the identification and characterization of a 1,4-dihydropyridine analogue, 9-(3,4-dichlorophenyl)-3,3,6,6-tetramethyl-3,4,6,7,9,10-hexahydro-1,8(2H,5H)-acridinedione (A-184209) as a novel inhibitor of ATP-sensitive K(+) channels. 2. A-184209 inhibited membrane potential changes evoked by the prototypical cyanoguanidine ATP-sensitive K(+) channel opener (KCO) P1075 in both vascular (A10) and urinary bladder smooth muscle cells with IC(50) values of 1.44 and 2.24 micro M respectively. 3. P1075-evoked relaxation of 25 mM K(+) stimulated aortic strips was inhibited by A-184209 in an apparently competitive fashion with a pA(2) value of 6.34. 4. The potencies of A-184209 to inhibit P1075-evoked decreases in membrane potential responses in cardiac myocytes (IC(50)=0.53 micro M) and to inhibit 2-deoxyglucose-evoked cation efflux pancreatic RINm5F cells (IC(50)=0.52 micro M) were comparable to the values for inhibition of smooth muscle K(ATP) channels. 5. On the other hand, a structural analogue of A-184209 that lacked the gem-dimethyl substituent, 9-(3,4-dichlorophenyl)-3,4,6,7,9,10-hexahydro-1,8(2H,5H)-acridinedione (A-184208), was found to be a K(ATP) channel opener, evoking membrane potential responses in A10 smooth muscle cells (EC(50)=385 nM) and relaxing aortic smooth muscle strips (IC(50)=101 nM) in a glyburide-sensitive manner. 6. Radioligand binding studies demonstrated that A-184209 displaced SUR1 binding defined by [(3)H]glyburide binding to RINm5F cell membranes with a K(i) value of 0.11 micro M whereas A-184208 was ineffective. On the other hand, both A-184209 (K(i)=1.34 micro M) and A-184208 (K(i)=1.14 micro M) displaced binding of the KCO radioligand, [(125)I]A-312110 in guinea-pig bladder membranes with similar affinities. 7. These studies demonstrate that A-184209 is a novel and structurally distinct compound that inhibits K(ATP) channels in smooth muscle with potencies comparable to glyburide. The structural overlap between DHP openers and blockers, together with their differential interaction with ligand binding sites, support the notion that both openers and blockers bind to similar or very closely coupled sites on the sulfonylurea receptor and that subtle changes in the pharmacophore itself could switch functional properties from K(ATP) channel activation to inhibition.
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Affiliation(s)
- Murali Gopalakrishnan
- Neuroscience Research, Global Pharmaceutical Research & Development, Abbott Laboratories, 100 Abbott Park Road, Abbott Park, Illinois, IL 60064, U.S.A.
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92
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Giblin JP, Quinn K, Tinker A. The cytoplasmic C-terminus of the sulfonylurea receptor is important for KATP channel function but is not key for complex assembly or trafficking. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:5303-13. [PMID: 12392564 DOI: 10.1046/j.1432-1033.2002.03249.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
ATP-sensitive K+ channels are an octameric assembly of two proteins, a sulfonylurea receptor (SUR1) and an ion conducting subunit (Kir 6.0). We have examined the role of the C-terminus of SUR1 by expressing a series of truncation mutants together with Kir6.2 stably in HEK293 cells. Biochemical analyses using coimmunoprecipitation indicate that SUR1 deletion mutants and Kir6.2 assemble and that a SUR1 deletion mutant binds glibenclamide with high affinity. Electrophysiological recordings indicate that ATP sensitivity is normal but the response of the mutant channel complexes to tolbutamide, MgADP and diazoxide is disturbed. Quantitative immunofluorescence and cell surface biotinylation supports the idea that there is little disturbance in the efficiency of trafficking. Our data show that deletions of the C-terminal most cytoplasmic domain of SUR1, can result in functional channels at the plasma membrane in mammalian cells that have an abnormal response to physiological and pharmacological agents.
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Affiliation(s)
- Jonathan P Giblin
- Centre for Clinical Pharmacology, Department of Medicine, University College London, The Rayne Institute, UK
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93
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Nielsen FE, Bodvarsdottir TB, Worsaae A, MacKay P, Stidsen CE, Boonen HCM, Pridal L, Arkhammar POG, Wahl P, Ynddal L, Junager F, Dragsted N, Tagmose TM, Mogensen JP, Koch A, Treppendahl SP, Hansen JB. 6-Chloro-3-alkylamino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide derivatives potently and selectively activate ATP sensitive potassium channels of pancreatic beta-cells. J Med Chem 2002; 45:4171-87. [PMID: 12213059 DOI: 10.1021/jm0208121] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
6-Chloro-3-alkylamino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide derivatives were synthesized and characterized as activators of adenosine 5'-triphosphate (ATP) sensitive potassium (K(ATP)) channels in the beta-cells by measuring effects on membrane potential and insulin release in vitro. The effects on vascular tissue in vitro were measured on rat aorta and small mesenteric vessels. Selected compounds were characterized as competitive inhibitors of [(3)H]glibenclamide binding to membranes of HEK293 cells expressing human SUR1/Kir6.2 and as potent inhibitors of insulin release in isolated rat islets. 6-Chloro-3-(1-methylcyclobutyl)amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (54) was found to bind and activate the SUR1/Kir6.2 K(ATP) channels in the low nanomolar range and to be at least 1000 times more potent than the reference compound diazoxide with respect to inhibition of insulin release from rat islets. Several compounds, e.g., 3-propylamino- (30), 3-isopropylamino- (34), 3-(S)-sec-butylamino- (37), and 3-(1-methylcyclopropyl)amino-4H-thieno[3,2-e]-1,2,4-thiadiazine 1,1-dioxide (53), which were found to be potent and beta-cell selective activators of K(ATP) channels in vitro, were found to inhibit insulin secretion in rats with minimal effects on blood pressure and to exhibit good oral pharmacokinetic properties.
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Affiliation(s)
- Flemming E Nielsen
- Novo Nordisk Research and Development, Novo Nordisk Park, DK 2760 Måløv, Denmark
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94
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Hambrock A, Preisig-Müller R, Russ U, Piehl A, Hanley PJ, Ray J, Daut J, Quast U, Derst C. Four novel splice variants of sulfonylurea receptor 1. Am J Physiol Cell Physiol 2002; 283:C587-98. [PMID: 12107069 DOI: 10.1152/ajpcell.00083.2002] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
ATP-sensitive K(+) (K(ATP)) channels are composed of pore-forming Kir6.x subunits and regulatory sulfonylurea receptor (SUR) subunits. SURs are ATP-binding cassette proteins with two nucleotide-binding folds (NBFs) and binding sites for sulfonylureas, like glibenclamide, and for channel openers. Here we report the identification and functional characterization of four novel splice forms of guinea pig SUR1. Three splice forms originate from alternative splicing of the region coding for NBF1 and lack exons 17 (SUR1Delta17), 19 (SUR1Delta19), or both (SUR1Delta17Delta19). The fourth (SUR1C) is a COOH-terminal SUR1-fragment formed by exons 31-39 containing the last two transmembrane segments and the COOH terminus of SUR1. RT-PCR analysis showed that these splice forms are expressed in several tissues with strong expression of SUR1C in cardiomyocytes. Confocal microscopy using enhanced green fluorescent protein-tagged SUR or Kir6.x did not provide any evidence for involvement of these splice forms in the mitochondrial K(ATP) channel. Only SUR1 and SUR1Delta17 showed high-affinity binding of glibenclamide (K(d) approximately 2 nM in the presence of 1 mM ATP) and formed functional K(ATP) channels upon coexpression with Kir6.2.
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Affiliation(s)
- Annette Hambrock
- Institute of Pharmacology, Tübingen University, 72074 Tübingen, Germany
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95
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Dabrowski M, Ashcroft FM, Ashfield R, Lebrun P, Pirotte B, Egebjerg J, Bondo Hansen J, Wahl P. The novel diazoxide analog 3-isopropylamino-7-methoxy-4H-1,2,4-benzothiadiazine 1,1-dioxide is a selective Kir6.2/SUR1 channel opener. Diabetes 2002; 51:1896-906. [PMID: 12031979 DOI: 10.2337/diabetes.51.6.1896] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
ATP-sensitive K(+) (K(ATP)) channels are activated by a diverse group of compounds known as potassium channel openers (PCOs). Here, we report functional studies of the Kir6.2/SUR1 Selective PCO 3-isopropylamino-7-methoxy-4H-1,2,4-benzothiadiazine 1,1-dioxide (NNC 55-9216). We recorded cloned K(ATP) channel currents from inside-out patches excised from Xenopus laevis oocytes heterologously expressing Kir6.2/SUR1, Kir6.2/SUR2A, or Kir6.2/SUR2B, corresponding to the beta-cell, cardiac, and smooth muscle types of the K(ATP) channel. NNC 55-9216 reversibly activated Kir6.2/SUR1 currents (EC(50) = 16 micromol/l). This activation was dependent on intracellular MgATP and was abolished by mutation of a single residue in the Walker A motifs of either nucleotide-binding domain of SUR1. The drug had no effect on Kir6.2/SUR2A or Kir6.2/SUR2B currents. We therefore used chimeras of SUR1 and SUR2A to identify regions of SUR1 involved in the response to NNC 55-9216. Activation was completely abolished and significantly reduced by swapping transmembrane domains 8-11. The reverse chimera consisting of SUR2A with transmembrane domains 8-11 and NBD2 consisting SUR1 was activated by NNC 55-9216, indicating that these SUR1 regions are important for drug activation. [(3)H]glibenclamide binding to membranes from HEK293 cells transfected with SUR1 was displaced by NNC 55-9216 (IC(50) = 105 micromol/l), and this effect was impaired when NBD2 of SUR1 was replaced by that of SUR2A. These results suggest NNC 55-9216 is a SUR1-selective PCO that requires structural determinants, which differ from those needed for activation of the K(ATP) channel by pinacidil and cromakalim. The high selectivity of NNC 55-9216 may prove to be useful for studies of the molecular mechanism of PCO action.
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96
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Szamosfalvi B, Cortes P, Alviani R, Asano K, Riser BL, Zasuwa G, Yee J. Putative subunits of the rat mesangial KATP: a type 2B sulfonylurea receptor and an inwardly rectifying K+ channel. Kidney Int 2002; 61:1739-49. [PMID: 11967023 DOI: 10.1046/j.1523-1755.2002.00302.x] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
BACKGROUND Sulfonylurea agents exert their physiological effects in many cell types via binding to specific sulfonylurea receptors (SUR). SUR couple to inwardly-rectifying K+ channel (Kir6.x) to form tetradimeric ATP-sensitive K+ channels (KATP). The SUR subunits confer ATP-sensitivity on KATP and also provide the binding sites for sulfonylureas and other pharmacological agents. Our previous work demonstrated that the exposure of mesangial cells (MC) to sulfonylureas generated profound effects on MC glucose uptake and matrix metabolism and induced heightened cell contractility in association with Ca2+ transients. Because these responses likely resulted from the binding of sulfonylurea to a mesangial SUR2, we subsequently documented [3H]-glibenclamide binding to MC and the gene expression of several mesangial SUR2 transcripts. From these data, we inferred that MC expressed the components of a mesangial KATP and sought to establish their presence in primary MC. METHODS To obtain mesangial SUR2 cDNA sequences, rapid amplification of cDNA ends (RACE) was utilized. DNA sequences were established by the fluorescent dye termination method. Gene expression of mesangial SUR2 and Kir6.1/2 was examined by reverse transcription polymerase chain reaction (RT-PCR) and Northern analysis. SUR2 proteins were identified by immunoblotting of mesangial proteins from membrane-enriched fractions with polyclonal antiserum directed against SUR2. RESULTS RACE cloning yielded two mesangial SUR2 cDNAs of 4.8 and 6.7 kbp whose open reading frames translated proteins of 964 and 1535 aa, respectively. Using probes specific to each cDNA, the presence of a unique, 5.5 kbp serum-regulated mesangial SUR2 splice variant was established. The sequence of this mesangial SUR2 (mcSUR2B) shares identity with the recently cloned rat SUR2B (rSUR2B), but, in comparison to rSUR2B, is truncated by 12 exons at the N-terminus where it contains a unique insert of 16 aa. Immunoblotting studies with anti-SUR2 antiserum demonstrated SUR2 proteins of 108 and 170 kD in membrane-enriched fractions of MC protein extracts. Complementary studies showed abundant gene expression of Kir6.1, thereby establishing gene expression of both components of KATP. CONCLUSIONS Based upon analogy to vascular smooth muscle cells (VSMC), there are at least two putative mesangial KATP that most likely represent hetero-octamers, comprised of either rSUR2B or mcSUR2 in complex with Kir6.1. Our results define the mesangial SUR2B as the possible first link in a chain of cellular events that culminates in MC contraction and altered extracellular matrix metabolism following exposure to sulfonylureas. In addition, our results serve as the basis for the future elucidation of the electrophysiologic characteristics of the mesangial KATP and the study of endogenous regulators of mesangial cell contractility.
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Affiliation(s)
- Balázs Szamosfalvi
- Department of Medicine, Division of Nephrology and Hypertension, Henry Ford Hospital, Detroit, Michigan 48202, USA
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97
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Löffler-Walz C, Hambrock A, Quast U. Interaction of K(ATP) channel modulators with sulfonylurea receptor SUR2B: implication for tetramer formation and allosteric coupling of subunits. Mol Pharmacol 2002; 61:407-14. [PMID: 11809866 DOI: 10.1124/mol.61.2.407] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sulfonylurea receptors (SURs) are subunits of ATP-sensitive K(+) channels (K(ATP) channels); they mediate the channel-closing effect of sulfonylureas such as glibenclamide and the channel-activating effect of K(ATP) channel openers such as the pinacidil analog P1075. We investigated the inhibition by MgATP and P1075 of glibenclamide binding to SUR2B, the SUR subtype in smooth muscle. To increase specific binding, experiments were also performed using SUR2B(Y1206S), a mutant with higher affinity for glibenclamide than for the wild-type (K(D )= 4 versus 22 nM, respectively) but otherwise exhibiting similar pharmacological properties. In the absence of MgATP, [(3)H]glibenclamide binding to both SURs was homogenous. MgATP inhibited [(3)H]glibenclamide binding to both SURs to 25% by reducing the apparent number of glibenclamide binding sites, leaving the affinity unchanged. In the absence of MgATP, P1075 inhibited [(3)H]glibenclamide binding in a monophasic manner with K(i) approximately 1 microM. In the presence of MgATP (1 mM), inhibition was biphasic with one K(i) value resembling the true affinity of P1075 for SUR2B (2-6 nM) and the other resembling K(i) in the absence of MgATP (approximately 1 microM). The data show that (1) MgATP induces heterogeneity in the glibenclamide sites; (2) the high-affinity glibenclamide sites remaining with MgATP are linked to two classes of P1075 sites; and (3) P1075 interacts specifically with SUR2B also in the absence of MgATP. The data are discussed with the assumption that SUR2B, expressed alone, forms tetramers; that MgATP induces allosteric interactions between the subunits; and that mixed SUR2B-glibenclamide-P1075 complexes can exist at equilibrium.
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Affiliation(s)
- Cornelia Löffler-Walz
- Department of Pharmacology, Medical Faculty, University of Tübingen, Tübingen, Germany
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98
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Jahangir A, Terzic A, Shen WK. Potassium channel openers: therapeutic potential in cardiology and medicine. Expert Opin Pharmacother 2001; 2:1995-2010. [PMID: 11825331 DOI: 10.1517/14656566.2.12.1995] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Potassium (K(+)) channel openers (KCOs) define a class of chemically diverse agents that share a common molecular target, the metabolism-regulated ATP-sensitive K(+) (K(ATP)) channel. In view of the unique function that K(ATP) channels play in the maintenance of cellular homeostasis, this novel class of ion channel modulators adds to existent pharmacotherapy with potential in promoting cellular protection under conditions of metabolic stress. Indeed, experimental studies have demonstrated broad therapeutic potential for KCOs, including roles as cardioprotective agents, vasodilators, bronchodilators, bladder relaxants, anti-epileptics, insulin secretagogues and promoters of hair growth. However, clinical experience with these drugs is limited and their place in patient management needs to be fully established.
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Affiliation(s)
- A Jahangir
- Division of Cardiovascular Disease, Department of Medicine, Mayo Clinic, Rochester, MN 55905, USA.
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99
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Conti LR, Radeke CM, Shyng SL, Vandenberg CA. Transmembrane topology of the sulfonylurea receptor SUR1. J Biol Chem 2001; 276:41270-8. [PMID: 11546780 DOI: 10.1074/jbc.m106555200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Sulfonylurea receptors (SURx) are multi-spanning transmembrane proteins of the ATP-binding cassette (ABC) family, which associate with Kir6.x to form ATP-sensitive potassium channels. Two models, with 13-17 transmembrane segments, have been proposed for SURx topologies. Recently, we demonstrated that the amino-terminal region of SUR1 contains 5 transmembrane segments, supporting the 17-transmembrane model. To investigate the topology of the complete full-length SUR1, two strategies were employed. Topology was probed by accessibility of introduced cysteines to a membrane-impermeable biotinylating reagent, biotin maleimide. Amino acid positions 6/26, 99, 159, 337, 567, 1051, and 1274 were accessible, therefore extracellular, whereas many endogenous and some introduced cysteines were inaccessible, thus likely cytoplasmic or intramembrane. These sites correspond to extracellular loops 1-3, 5-6, and 8 and the NH2 terminus, and intracellular loops 3-8 and COOH terminus in the 17-transmembrane model. Immunofluorescence was used to determine accessibility of epitope-tagged SUR1 in intact and permeabilized cells. Epitopes at positions 337 and 1050 (putative external loops 3 and 6) were labeled in intact cells, therefore external, whereas positions 485 and 1119 (putative internal loops 5 and 7) only were accessible after permeabilization and therefore internal. These results are compatible with the 17-transmembrane model with two pairs of transmembrane segments as possible reentrant loops.
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Affiliation(s)
- L R Conti
- Department of Molecular, Cellular, and Developmental Biology and the Neuroscience Research Institute, University of California, Santa Barbara, California 93106, USA
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100
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Ito K, Oleschuk CJ, Westlake C, Vasa MZ, Deeley RG, Cole SP. Mutation of Trp1254 in the multispecific organic anion transporter, multidrug resistance protein 2 (MRP2) (ABCC2), alters substrate specificity and results in loss of methotrexate transport activity. J Biol Chem 2001; 276:38108-14. [PMID: 11500505 DOI: 10.1074/jbc.m105160200] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The ATP-binding cassette (ABC) proteins comprise a large superfamily of transmembrane transporters that utilize the energy of ATP hydrolysis to translocate their substrates across biological membranes. Multidrug resistance protein (MRP) 2 (ABCC2) belongs to subfamily C of the ABC superfamily and, when overexpressed in tumor cells, confers resistance to a wide variety of anticancer chemotherapeutic agents. MRP2 is also an active transporter of organic anions such as methotrexate (MTX), estradiol glucuronide (E217betaG), and leukotriene C4 and is located on the apical membrane of polarized cells including hepatocytes where it acts as a biliary transporter. We recently identified a highly conserved tryptophan residue in the related MRP1 that is critical for the substrate specificity of this protein. In the present study, we have examined the effect of replacing the analogous tryptophan residue at position 1254 of MRP2. We found that only nonconservative substitutions (Ala and Cys) of Trp1254 eliminated [3H]E217betaG transport by MRP2, whereas more conservative substitutions (Phe and Tyr) had no effect. In addition, only the most conservatively substituted mutant (W1254Y) transported [3H]leukotriene C4, whereas all other substitutions eliminated transport of this substrate. On the other hand, all substitutions of Trp1254 eliminated transport of [3H]MTX. Finally, we found that sulfinpyrazone stimulated [3H]E217betaG transport by wild-type MRP2 4-fold, whereas transport by the Trp1254 substituted mutants was enhanced 6-10-fold. In contrast, sulfinpyrazone failed to stimulate [3H]MTX transport by either wild-type MRP2 or the MRP2-Trp1254 mutants. Taken together, our results demonstrate that Trp1254 plays an important role in the ability of MRP2 to transport conjugated organic anions and identify this amino acid in the putative last transmembrane segment (TM17) of this ABC protein as being critical for transport of MTX.
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Affiliation(s)
- K Ito
- Cancer Research Laboratories, Queen's University, Kingston, Ontario K7L 3N6, Canada
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