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Hou T, Chen L. Sulfonylurea receptor 2 (SUR2), intricate sensors for intracellular Mg-nucleotides. Bioessays 2024; 46:e2300151. [PMID: 38227376 DOI: 10.1002/bies.202300151] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2023] [Revised: 12/19/2023] [Accepted: 12/21/2023] [Indexed: 01/17/2024]
Abstract
SUR2, similar to SUR1, is a regulatory subunit of the ATP-sensitive potassium channel (KATP), which plays a key role in numerous important physiological processes and is implicated in various diseases. Recent structural studies have revealed that, like SUR1, SUR2 can undergo ligand-dependent dynamic conformational changes, transitioning between an inhibitory inward-facing conformation and an activating occluded conformation. In addition, SUR2 possesses a unique inhibitory Regulatory helix (R helix) that is absent in SUR1. The binding of the activating Mg-ADP to NBD2 of SUR2 competes with the inhibitory Mg-ATP, thereby promoting the release of the R helix and initiating the activation process. Moreover, the signal generated by Mg-ADP binding to NBD2 might be directly transmitted to the TMD of SUR2, prior to NBD dimerization. Furthermore, the C-terminal 42 residues (C42) of SUR2 might allosterically regulate the kinetics of Mg-nucleotide binding on NBD2. These distinctive properties render SUR2 intricate sensors for intracellular Mg-nucleotides.
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Affiliation(s)
- Tianyi Hou
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Beijing, China
| | - Lei Chen
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, Beijing, Beijing, China
- National Biomedical Imaging Center, Peking University, Beijing, Beijing, China
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2
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Ding D, Hou T, Wei M, Wu JX, Chen L. The inhibition mechanism of the SUR2A-containing K ATP channel by a regulatory helix. Nat Commun 2023; 14:3608. [PMID: 37330603 PMCID: PMC10276813 DOI: 10.1038/s41467-023-39379-4] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2022] [Accepted: 06/10/2023] [Indexed: 06/19/2023] Open
Abstract
KATP channels are metabolic sensors for intracellular ATP/ADP ratios, play essential roles in many physiological processes, and are implicated in a spectrum of pathological conditions. SUR2A-containing KATP channels differ from other subtypes in their sensitivity to Mg-ADP activation. However, the underlying structural mechanism remains poorly understood. Here we present a series of cryo-EM structures of SUR2A in the presence of different combinations of Mg-nucleotides and the allosteric inhibitor repaglinide. These structures uncover regulatory helix (R helix) on the NBD1-TMD2 linker, which wedges between NBD1 and NBD2. R helix stabilizes SUR2A in the NBD-separated conformation to inhibit channel activation. The competitive binding of Mg-ADP with Mg-ATP to NBD2 mobilizes the R helix to relieve such inhibition, allowing channel activation. The structures of SUR2B in similar conditions suggest that the C-terminal 42 residues of SUR2B enhance the structural dynamics of NBD2 and facilitate the dissociation of the R helix and the binding of Mg-ADP to NBD2, promoting NBD dimerization and subsequent channel activation.
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Affiliation(s)
- Dian Ding
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Peking University, 100871, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, 100871, Beijing, China
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Tianyi Hou
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China
- Peking-Tsinghua Center for Life Sciences, Peking University, 100871, Beijing, China
- Academy for Advanced Interdisciplinary Studies, Peking University, 100871, Beijing, China
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Miao Wei
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Jing-Xiang Wu
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China
| | - Lei Chen
- State Key Laboratory of Membrane Biology, College of Future Technology, Institute of Molecular Medicine, Peking University, Beijing Key Laboratory of Cardiometabolic Molecular Medicine, 100871, Beijing, China.
- Peking-Tsinghua Center for Life Sciences, Peking University, 100871, Beijing, China.
- National Biomedical Imaging Center, Peking University, 100871, Beijing, China.
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Alquisiras-Burgos I, Franco-Pérez J, Rubio-Osornio M, Aguilera P. The short form of the SUR1 and its functional implications in the damaged brain. Neural Regen Res 2022; 17:488-496. [PMID: 34380876 PMCID: PMC8504400 DOI: 10.4103/1673-5374.320967] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
Abstract
Sulfonylurea receptor (SUR) belongs to the adenosine 5′-triphosphate (ATP)-binding cassette (ABC) transporter family; however, SUR is associated with ion channels and acts as a regulatory subunit determining the opening or closing of the pore. Abcc8 and Abcc9 genes code for the proteins SUR1 and SUR2, respectively. The SUR1 transcript encodes a protein of 1582 amino acids with a mass around 140–177 kDa expressed in the pancreas, brain, heart, and other tissues. It is well known that SUR1 assembles with Kir6.2 and TRPM4 to establish KATP channels and non-selective cation channels, respectively. Abbc8 and 9 are alternatively spliced, and the resulting transcripts encode different isoforms of SUR1 and SUR2, which have been detected by different experimental strategies. Interestingly, the use of binding assays to sulfonylureas and Western blotting has allowed the detection of shorter forms of SUR (~65 kDa). Identity of the SUR1 variants has not been clarified, and some authors have suggested that the shorter forms are unspecific. However, immunoprecipitation assays have shown that SUR2 short forms are part of a functional channel even coexisting with the typical forms of the receptor in the heart. This evidence confirms that the structure of the short forms of the SURs is fully functional and does not lose the ability to interact with the channels. Since structural changes in short forms of SUR modify its affinity to ATP, regulation of its expression might represent an advantage in pathologies where ATP concentrations decrease and a therapeutic target to induce neuroprotection. Remarkably, the expression of SUR1 variants might be induced by conditions associated to the decrease of energetic substrates in the brain (e.g. during stroke and epilepsy). In this review, we want to contribute to the knowledge of SUR1 complexity by analyzing evidence that shows the existence of short SUR1 variants and its possible implications in brain function.
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Affiliation(s)
- Iván Alquisiras-Burgos
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Javier Franco-Pérez
- Laboratorio de Formación Reticular, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Moisés Rubio-Osornio
- Laboratorio Experimental de Enfermedades Neurodegenerativas, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
| | - Penélope Aguilera
- Laboratorio de Patología Vascular Cerebral, Instituto Nacional de Neurología y Neurocirugía "Manuel Velasco Suárez", CDMX, Mexico
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Kim JE, Hwang SD, Lee SW, Song JH, Kim K. Potassium Channel Syndrome Caused by Nicorandil in Chronic Kidney Disease: A Case Report and Literature Review. Electrolyte Blood Press 2022; 20:17-20. [DOI: 10.5049/ebp.2022.20.1.17] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2022] [Revised: 04/27/2022] [Accepted: 04/28/2022] [Indexed: 11/25/2022] Open
Affiliation(s)
- Ji-Eun Kim
- Department of Internal Medicine, Inha University Hospital, Incheon, Republic of Korea
| | - Seun Deuk Hwang
- Division of Nephrology and Hypertension, Department of Internal Medicine, Inha University College of Medicine, Incheon, Republic of Korea
| | - Seoung Woo Lee
- Division of Nephrology and Hypertension, Department of Internal Medicine, Inha University College of Medicine, Incheon, Republic of Korea
| | - Joon Ho Song
- Division of Nephrology and Hypertension, Department of Internal Medicine, Inha University College of Medicine, Incheon, Republic of Korea
| | - Kipyo Kim
- Division of Nephrology and Hypertension, Department of Internal Medicine, Inha University College of Medicine, Incheon, Republic of Korea
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Abstract
KATP channels are integral to the functions of many cells and tissues. The use of electrophysiological methods has allowed for a detailed characterization of KATP channels in terms of their biophysical properties, nucleotide sensitivities, and modification by pharmacological compounds. However, even though they were first described almost 25 years ago (Noma 1983, Trube and Hescheler 1984), the physiological and pathophysiological roles of these channels, and their regulation by complex biological systems, are only now emerging for many tissues. Even in tissues where their roles have been best defined, there are still many unanswered questions. This review aims to summarize the properties, molecular composition, and pharmacology of KATP channels in various cardiovascular components (atria, specialized conduction system, ventricles, smooth muscle, endothelium, and mitochondria). We will summarize the lessons learned from available genetic mouse models and address the known roles of KATP channels in cardiovascular pathologies and how genetic variation in KATP channel genes contribute to human disease.
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Affiliation(s)
- Monique N Foster
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
| | - William A Coetzee
- Departments of Pediatrics, Physiology & Neuroscience, and Biochemistry and Molecular Pharmacology, NYU School of Medicine, New York, New York
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Sensitivity of KATP channels to cellular metabolic disorders and the underlying structural basis. Acta Pharmacol Sin 2016; 37:134-42. [PMID: 26725741 DOI: 10.1038/aps.2015.134] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2015] [Accepted: 11/25/2015] [Indexed: 11/08/2022] Open
Abstract
AIM ATP-sensitive potassium (KATP) channels formed by a combination of SUR/Kir6.x subunits play a crucial role in protection against hypoxic or ischemic injuries resulting from cell metabolic disorders. In this study we investigated the effects of Na-azide, a metabolic inhibitor, on KATP channels expressed in Xenopus oocytes, and explored the structure basis for their sensitivity to cell metabolic disorders. METHODS Six subtypes of KATP channels (wild SUR1/Kir6.2, SUR2B/Kir6.2, SUR1/Kir6.1, SUR2B/Kir6.1, SUR2A/Kir6.2 and SUR2A/Kir6.1), as well as eleven subtypes of KATP channels with mutant subunits were expressed in Xenopus oocytes. KATP currents were recorded using a two-electrode voltage clamp recording technique. The drugs were applied through bath. RESULTS Except SUR2A/Kir6.1, five subtypes of KATP channels were activated by Na-azide (3 mmol/L) with an order of the responses: SUR1/Kir6.2>SUR2B/Kir6.2>SUR1/Kir6.1>SUR2B/Kir6.1>SUR2A/Kir6.2, and the opening rate (t1/2) was SUR1/Kir6.x>SUR2B/Kir6.x>SUR2A/Kir6.2. Furthermore, Kir6.2, rather than Kir6.1, had intrinsic sensitivity to Na-azide, and the residues involved in ATP-binding (R50 and K185) or pH-sensing (H175) were associated with the sensitivity of the Kir6.2 subunit to Na-azide. Moreover, the residues (K707 and K1348) within the Walker A (WA) motifs of two nucleotide-binding domains (NBDs) were essential for SUR2B/Kir6.x (especially SUR2B/Kir6.1) channel activation by Na-azide, suggesting a key role for Mg-adenine nucleotide binding and/or hydrolysis in the SUR2B subunit. CONCLUSION Among the six subtypes of KATP channels, SUR1/Kir6.2 is the most sensitive, whereas SUR2A/Kir6.1 is insensitive, to cell metabolic disorders. The Kir6.2 subunit, rather than the Kir6.1 subunit, has intrinsic sensitivity to cell metabolic disorders. The residues (K707 and K1348) within the WA motifs of SUR2B are important for the sensitivity of SUR2B/Kir6.x channels to cell metabolic disorders.
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Chuang CY, Chen LY, Fu RH, Chen SM, Ho MH, Huang JM, Hsu CC, Wang CC, Chen MS, Tsai RT. Involvement of the carboxyl-terminal region of the yeast peroxisomal half ABC transporter Pxa2p in its interaction with Pxa1p and in transporter function. PLoS One 2014; 9:e104892. [PMID: 25118695 PMCID: PMC4132065 DOI: 10.1371/journal.pone.0104892] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2014] [Accepted: 07/17/2014] [Indexed: 11/18/2022] Open
Abstract
BACKGROUND The peroxisome is a single membrane-bound organelle in eukaryotic cells involved in lipid metabolism, including β-oxidation of fatty acids. The human genetic disorder X-linked adrenoleukodystrophy (X-ALD) is caused by mutations in the ABCD1 gene (encoding ALDP, a peroxisomal half ATP-binding cassette [ABC] transporter). This disease is characterized by defective peroxisomal β-oxidation and a large accumulation of very long-chain fatty acids in brain white matter, adrenal cortex, and testis. ALDP forms a homodimer proposed to be the functional transporter, whereas the peroxisomal transporter in yeast is a heterodimer comprising two half ABC transporters, Pxa1p and Pxa2p, both orthologs of human ALDP. While the carboxyl-terminal domain of ALDP is engaged in dimerization, it remains unknown whether the same region is involved in the interaction between Pxa1p and Pxa2p. METHODS/PRINCIPAL FINDINGS Using a yeast two-hybrid assay, we found that the carboxyl-terminal region (CT) of Pxa2p, but not of Pxa1p, is required for their interaction. Further analysis indicated that the central part of the CT (designated CT2) of Pxa2p was indispensable for its interaction with the carboxyl terminally truncated Pxa1_NBD. An interaction between the CT of Pxa2p and Pxa1_NBD was not detected, but could be identified in the presence of Pxa2_NBD-CT1. A single mutation of two conserved residues (aligned with X-ALD-associated mutations at the same positions in ALDP) in the CT2 of the Pxa2_NBD-CT protein impaired its interaction with Pxa1_NBD or Pxa1_NBD-CT, resulting in a mutant protein that exhibited a proteinase K digestion profile different from that of the wild-type protein. Functional analysis of these mutant proteins on oleate plates indicated that they were defective in transporter function. CONCLUSIONS/SIGNIFICANCE The CT of Pxa2p is involved in its interaction with Pxa1p and in transporter function. This concept may be applied to human ALDP studies, helping to establish the pathological mechanism for CT-related X-ALD disease.
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Affiliation(s)
- Cheng-Yi Chuang
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Ling-Yun Chen
- Department of Biochemistry, School of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Ru-Huei Fu
- Graduate Institute of Immunology, China Medical University, Taichung, Taiwan
| | - Shih-Ming Chen
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Ming-Hua Ho
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Jie-Mau Huang
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Chia-Chi Hsu
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Chien-Cheng Wang
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Meng-Shian Chen
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan
| | - Rong-Tzong Tsai
- Institute of Biochemistry and Biotechnology, College of Medicine, Chung Shan Medical University, Taichung, Taiwan; Department of Biochemistry, School of Medicine, Chung Shan Medical University, Taichung, Taiwan
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Ohba T, Sawada E, Suzuki Y, Yamamura H, Ohya S, Tsuda H, Imaizumi Y. Enhancement of Ca(2+) influx and ciliary beating by membrane hyperpolarization due to ATP-sensitive K(+) channel opening in mouse airway epithelial cells. J Pharmacol Exp Ther 2013; 347:145-53. [PMID: 23922448 DOI: 10.1124/jpet.113.205138] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Among the several types of cells composing the airway epithelium, the ciliary cells are responsible for one of the most important defense mechanisms of the airway epithelium: the transport of inhaled particles back up into the throat by coordinated ciliary movement. Changes in the cytoplasmic Ca(2+) concentration ([Ca(2+)]i) are the main driving force controlling the ciliary activity. In mouse ciliary cells, membrane hyperpolarization from -20 to -60 mV under whole-cell voltage-clamp induced a slow but significant [Ca(2+)]i rise in a reversible manner. This rise was completely inhibited by the removal of Ca(2+) from the extracellular solution. Application of diazoxide, an ATP-dependent K(+) channel opener, dose-dependently induced a membrane hyperpolarization (EC50 = 2.3 μM), which was prevented by the addition of 5 μM glibenclamide. An inwardly rectifying current was elicited by the application of 10 μM diazoxide and suppressed by subsequent addition of 5 μM glibenclamide. Moreover, the application of 10 μM diazoxide induced a significant [Ca(2+)]i rise and facilitated ciliary movement. Multi-cell reverse-transcription polymerase chain reaction analyses and immunocytochemical staining suggested that the subunit combination of Kir6.2/SUR2B and possibly also Kir6.1/SUR2B is expressed in ciliary cells. The confocal Ca(2+) imaging analyses suggested that the [Ca(2+)]i rise induced by diazoxide occurred preferentially in the apical submembrane region. In conclusion, the application of a KATP channel opener to airway ciliary cells induces membrane hyperpolarization and thereby induces a [Ca(2+)]i rise via the facilitation of Ca(2+) influx through the non-voltage-dependent Ca(2+) permeable channels. Therefore, a KATP opener may be beneficial in facilitating ciliary movement.
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Affiliation(s)
- Teruya Ohba
- Department of Molecular and Cellular Pharmacology, Graduate School of Pharmaceutical Sciences (T.O., E.S., Y.S., H.Y., Y.I.) and Nanomaterial Toxicology Project (H.T.), Nagoya City University, Nagoya, Japan; and Department of Pharmacology, Division of Pathological Sciences, Kyoto Pharmaceutical University, Kyoto, Japan (S.O.)
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Zhou M, He HJ, Tanaka O, Sekiguchi M, Kawahara K, Abe H. Localization of the ATP-sensitive K(+) channel regulatory subunits SUR2A and SUR2B in the rat brain. Neurosci Res 2012; 74:91-105. [PMID: 22960600 DOI: 10.1016/j.neures.2012.08.005] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/2012] [Revised: 08/22/2012] [Accepted: 08/23/2012] [Indexed: 01/11/2023]
Abstract
ATP-sensitive K(+) (K(ATP)) channel subunits SUR2A and SUR2B in the rat brain were investigated by RT-PCR assay, western blot analysis, in situ hybridization histochemistry, and immunohistochemical staining. The results show that the mRNA and protein of SUR2A and SUR2B are expressed in whole rat brain extracts and selected regions. SUR2 mRNA is widely expressed in many neurons and glial cells as revealed by in situ hybridization histochemistry. Immunohistochemical staining shows SUR2A to be widely expressed in neurons of the brain, especially in the large pyramidal neurons and their main dendrites in the neocortex and in the Purkinje cells of the cerebellar cortex. In contrast to SUR2A, SUR2B is potently expressed in small cells in the corpus callosum and cerebellar white matter, but is also weakly expressed in some neurons. Double immunostaining shows SUR2B to be localized in astrocytes and oligodendrocytes, while SUR2A is only localized in oligodendrocytes. These results suggest that SUR2A might be mainly a regulatory subunit of the K(ATP) channel in most neurons and part of oligodendrocytes, while SUR2B might be mainly a regulatory subunit of the K(ATP) channel in astrocytes, oligodendrocytes, and some neurons.
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Affiliation(s)
- Ming Zhou
- Department of Anatomy, Akita University Graduate School of Medicine and Faculty of Medicine, 1-1-1 Hondo, Akita 010-8543, Japan.
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Tanabe K, Lanaspa MA, Kitagawa W, Rivard CJ, Miyazaki M, Klawitter J, Schreiner GF, Saleem MA, Mathieson PW, Makino H, Johnson RJ, Nakagawa T. Nicorandil as a novel therapy for advanced diabetic nephropathy in the eNOS-deficient mouse. Am J Physiol Renal Physiol 2012; 302:F1151-60. [PMID: 22338086 DOI: 10.1152/ajprenal.00596.2011] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023] Open
Abstract
Nicorandil is an orally available drug that can act as a nitric oxide donor, an antioxidant, and an ATP-dependent K channel activator. We hypothesized that it may have a beneficial role in treating diabetic nephropathy. We administered nicorandil to a model of advanced diabetic nephropathy (the streptozotocin-induced diabetes in mice lacking endothelial nitric oxide synthase, eNOSKO); controls included diabetic eNOS KO mice without nicorandil and nondiabetic eNOS KO mice treated with either nicorandil or vehicle. Mice were treated for 8 wk. Histology, blood pressure, and renal function were determined. Additional studies involved examining the effects of nicorandil on cultured human podocytes. Here, we found that nicorandil did not affect blood glucose levels, blood pressure, or systemic endothelial function, but significantly reduced proteinuria and glomerular injury (mesangiolysis and glomerulosclerosis). Nicorandil protected against podocyte loss and podocyte oxidative stress. Studies in cultured podocytes showed that nicorandil likely protects against glucose-mediated oxidant stress via the ATP-dependent K channel as opposed to its NO-stimulating effects. In conclusion, nicorandil may be beneficial in diabetic nephropathy by preserving podocyte function. We recommend clinical trials to determine whether nicorandil may benefit diabetic nephropathy or other conditions associated with podocyte dysfunction.
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Affiliation(s)
- Katsuyuki Tanabe
- Division of Renal Diseases and Hypertension, University of Colorado Denver, C281, 12900E 19th Ave., Aurora, CO 80045, USA
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Chowdhury UR, Bahler CK, Hann CR, Chang M, Resch ZT, Romero MF, Fautsch MP. ATP-sensitive potassium (KATP) channel activation decreases intraocular pressure in the anterior chamber of the eye. Invest Ophthalmol Vis Sci 2011; 52:6435-42. [PMID: 21743021 DOI: 10.1167/iovs.11-7523] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
PURPOSE. ATP-sensitive potassium channel (K(ATP)) openers target key cellular events, many of which have been implicated in glaucoma. The authors sought to determine whether K(ATP) channel openers influence outflow facility in human anterior segment culture and intraocular pressure (IOP) in vivo. METHODS. Anterior segments from human eyes were placed in perfusion organ culture and treated with the K(ATP) channel openers diazoxide, nicorandil, and P1075 or the K(ATP) channel closer glyburide (glibenclamide). The presence, functionality, and specificity of K(ATP) channels were determined by RT-PCR, immunohistochemistry, and inside-out patch clamp in human trabecular meshwork (TM) tissue or primary cultures of normal human trabecular meshwork (NTM) cells. The effect of diazoxide on IOP in anesthetized Brown Norway rats was measured with a rebound tonometer. RESULTS. K(ATP) channel openers increased outflow facility in human anterior segments (0.14 ± 0.02 to 0.26 ± 0.09 μL/min/mm Hg; P < 0.001) compared with fellow control eyes (0.22 ± 0.11 to 0.21 ± 0.11 μL/min/mm Hg; P > 0.5). The effect was reversible, with outflow facility returning to baseline after drug removal. The addition of glyburide inhibited diazoxide from increasing outflow facility. Electrophysiology confirmed the presence and specificity of functional K(ATP) channels. K(ATP) channel subunits K(ir)6.1, K(ir)6.2, SUR2A, and SUR2B were expressed in TM and NTM cells. In vivo, diazoxide significantly lowered IOP in Brown Norway rats. CONCLUSIONS. Functional K(ATP) channels are present in the trabecular meshwork. When activated by K(ATP) channel openers, these channels increase outflow facility through the trabecular outflow pathway in human anterior segment organ culture and decrease IOP in Brown Norway rat eyes.
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Hibino H, Inanobe A, Furutani K, Murakami S, Findlay I, Kurachi Y. Inwardly rectifying potassium channels: their structure, function, and physiological roles. Physiol Rev 2010; 90:291-366. [PMID: 20086079 DOI: 10.1152/physrev.00021.2009] [Citation(s) in RCA: 1070] [Impact Index Per Article: 76.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Inwardly rectifying K(+) (Kir) channels allow K(+) to move more easily into rather than out of the cell. They have diverse physiological functions depending on their type and their location. There are seven Kir channel subfamilies that can be classified into four functional groups: classical Kir channels (Kir2.x) are constitutively active, G protein-gated Kir channels (Kir3.x) are regulated by G protein-coupled receptors, ATP-sensitive K(+) channels (Kir6.x) are tightly linked to cellular metabolism, and K(+) transport channels (Kir1.x, Kir4.x, Kir5.x, and Kir7.x). Inward rectification results from pore block by intracellular substances such as Mg(2+) and polyamines. Kir channel activity can be modulated by ions, phospholipids, and binding proteins. The basic building block of a Kir channel is made up of two transmembrane helices with cytoplasmic NH(2) and COOH termini and an extracellular loop which folds back to form the pore-lining ion selectivity filter. In vivo, functional Kir channels are composed of four such subunits which are either homo- or heterotetramers. Gene targeting and genetic analysis have linked Kir channel dysfunction to diverse pathologies. The crystal structure of different Kir channels is opening the way to understanding the structure-function relationships of this simple but diverse ion channel family.
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Affiliation(s)
- Hiroshi Hibino
- Department of Pharmacology, Graduate School of Medicine and The Center for Advanced Medical Engineering and Informatics, Osaka University, Osaka 565-0871, Japan
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13
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Park S, Terzic A. Quaternary structure of KATP channel SUR2A nucleotide binding domains resolved by synchrotron radiation X-ray scattering. J Struct Biol 2010; 169:243-51. [PMID: 19919849 PMCID: PMC2818519 DOI: 10.1016/j.jsb.2009.11.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2009] [Revised: 10/11/2009] [Accepted: 11/10/2009] [Indexed: 01/03/2023]
Abstract
Heterodimeric nucleotide binding domains NBD1/NBD2 distinguish the ATP-binding cassette protein SUR2A, a recognized regulatory subunit of cardiac ATP-sensitive K(+) (K(ATP)) channels. The tandem function of these core domains ensures metabolism-dependent gating of the Kir6.2 channel pore, yet their structural arrangement has not been resolved. Here, purified monodisperse and interference-free recombinant particles were subjected to synchrotron radiation small-angle X-ray scattering (SAXS) in solution. Intensity function analysis of SAXS profiles resolved NBD1 and NBD2 as octamers. Implemented by ab initio simulated annealing, shape determination prioritized an oblong envelope wrapping NBD1 and NBD2 with respective dimensions of 168x80x37A(3) and 175x81x37A(3) based on symmetry constraints, validated by atomic force microscopy. Docking crystal structure homology models against SAXS data reconstructed the NBD ensemble surrounding an inner cleft suitable for Kir6.2 insertion. Human heart disease-associated mutations introduced in silico verified the criticality of the mapped protein-protein interface. The resolved quaternary structure delineates thereby a macromolecular arrangement of K(ATP) channel SUR2A regulatory domains.
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Affiliation(s)
- Sungjo Park
- Marriott Heart Disease Research Program, Division of Cardiovascular Diseases, Departments of Medicine, Molecular Pharmacology and Experimental Therapeutics, and Medical Genetics, Mayo Clinic, Rochester, MN 55905, USA
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Abstract
OBJECTIVE Proteinuria is an important risk factor for cardiovascular and renal morbidity and mortality. The effect of nicorandil on proteinuria in hypertensive patients well controlled by antihypertensive agents containing a low dose of valsartan has not been studied. PATIENTS AND METHODS A total of 136 proteinuric (300-3000 mg/day), valsartan-treated hypertensive patients with blood pressure less than 140/90 mmHg were randomized into three groups to receive placebo, isosorbide dinitrate (30 mg/day), or nicorandil (15 mg/day) for 6 months. RESULTS The average dose of valsartan given to the patients was similar in the three groups. Creatinine clearance remained stable throughout the study in the three groups. Nicorandil, but not isosorbide dinitrate, significantly reduced proteinuria by 44% after 6 months (P < 0.0001). Urinary endothelin-1 levels significantly decreased after administration of nicorandil (P = 0.002), whereas placebo and isosorbide dinitrate had no effect. Urinary excretion of endothelin-1 was significantly correlated with improvement in urinary protein excretion in nicorandil-treated patients (r = 0.69, P < 0.0001). The urinary excretion of retinol-binding protein decreased after nicorandil administration, probably reflecting an improvement in tubular function. In contrast, the urinary excretion of immunoglobulin G did not change significantly throughout the study in the three groups. Multivariate analysis revealed that proteinuria was only significantly correlated with the use of nicorandil (model adjusted r = 0.35, P < 0.0001). CONCLUSION The addition of nicorandil to treatment for patients with well controlled hypertension may have an additive effect on reducing proteinuria independent of hemodynamics and nitric oxide effects, possibly through inhibiting renal endothelin-1 synthesis and improving tubular function.
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15
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Kajioka S, Nakayama S, Asano H, Seki N, Naito S, Brading AF. Levcromakalim and MgGDP activate small conductance ATP-sensitive K+ channels of K+ channel pore 6.1/sulfonylurea receptor 2A in pig detrusor smooth muscle cells: uncoupling of cAMP signal pathways. J Pharmacol Exp Ther 2008; 327:114-23. [PMID: 18596222 DOI: 10.1124/jpet.108.140269] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Pharmacological studies have suggested the existence of ATP-sensitive K(+) (K(ATP)) channel as a therapeutic target in urinary bladders; however, electrical properties have not yet been shown. Patch-clamp techniques were applied to investigate the properties of K(ATP) channels in pig detrusor cells. In whole-cell configuration, levcromakalim, a K(ATP) channel opener, induced a long-lasting outward current in a concentration-dependent manner. The current-voltage curve of the levcromakalim-induced membrane current intersected at approximately -80 mV. This current was abolished by glibenclamide. Intracellular application of 0.1 mM GDP significantly enhanced the levcromakalim-induced membrane current, whereas cAMP did not. Furthermore, neurotransmitters related to cAMP signaling, such as calcitonin gene-related peptide, vasointestinal peptide, adenosine, and somatostatin, had little effect on the membrane current. In cell-attached configuration, levcromakalim activated K(+) channels with a unitary conductance of approximately 12 pS. When the patch configuration was changed to inside-out mode, the K(+) channel activity ran down. Subsequent application of 1 mM GDP reactivated the channels. The openings of the approximately 12 pS K(+) channels in the presence of 1 mM GDP was suppressed by ATP and glibenclamide. In reverse transcription-polymerase chain reaction, K(+) channel pore 6.1 and sulfonylurea receptor (SUR)2A were predominant in pig detrusor cells. The 12 pS K(+) channel activated by levcromakalim in pig detrusor smooth muscle cells is a K(ATP) channel. The predominant expression of SUR2A can account for the lack of effect of neurotransmitters related to cAMP.
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16
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Burke MA, Mutharasan RK, Ardehali H. The Sulfonylurea Receptor, an Atypical ATP-Binding Cassette Protein, and Its Regulation of the KATPChannel. Circ Res 2008; 102:164-76. [DOI: 10.1161/circresaha.107.165324] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Affiliation(s)
- Michael A. Burke
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
| | - R. Kannan Mutharasan
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
| | - Hossein Ardehali
- From the Division of Cardiology, Feinberg Cardiovascular Institute, Northwestern University, Chicago, Ill
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17
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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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18
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Fujita H, Ogura T, Tamagawa M, Uemura H, Sato T, Ishida A, Imamaki M, Kimura F, Miyazaki M, Nakaya H. A key role for the subunit SUR2B in the preferential activation of vascular KATP channels by isoflurane. Br J Pharmacol 2006; 149:573-80. [PMID: 17001304 PMCID: PMC2014679 DOI: 10.1038/sj.bjp.0706891] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
BACKGROUND AND PURPOSE It has been postulated that isoflurane, a volatile anaesthetic, produces vasodilatation through activation of ATP-sensitive K+ (KATP) channels. However, there is no direct evidence for the activation of vascular KATP channels by isoflurane. This study was conducted to examine the effect of isoflurane on vascular KATP channels and compare it with that on cardiac KATP channels. EXPERIMENTAL APPROACH Effects of isoflurane on KATP channels were examined in aortic smooth muscle cells and cardiomyocytes of the mouse using patch clamp techniques. Effects of the anaesthetic on the KATP channels with different combinations of the inward rectifier pore subunits (Kir6.1 and Kir6.2) and sulphonylurea receptor subunits (SUR2A and SUR2B) reconstituted in a heterologous expression system were also examined. KEY RESULTS Isoflurane increased the coronary flow in Langendorff-perfused mouse hearts in a concentration-dependent manner, which was abolished by 10 microM glibenclamide. In enzymically-dissociated aortic smooth muscle cells, isoflurane evoked a glibenclamide-sensitive current (i.e. KATP current). In isolated mouse ventricular cells, however, isoflurane failed to evoke the KATP current unless the KATP current was preactivated by the K+ channel opener pinacidil. Although isoflurane readily activated the Kir6.1/SUR2B channels (vascular type), the volatile anesthetic could not activate the Kir6.2/SUR2A channels (cardiac type) expressed in HEK293 cells. Isoflurane activated a glibenclamide-sensitive current in HEK293 cells expressing Kir6.2/SUR2B channels. CONCLUSION AND IMPLICATIONS Isoflurane activates KATP channels in vascular smooth muscle cells and produces coronary vasodilation in mouse hearts. SUR2B may be important for the activation of vascular-type KATP channels by isoflurane.
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MESH Headings
- ATP-Binding Cassette Transporters/genetics
- ATP-Binding Cassette Transporters/physiology
- Anesthetics, Inhalation/pharmacology
- Animals
- Aorta, Thoracic/drug effects
- Aorta, Thoracic/physiology
- Cell Line
- Cells, Cultured
- Coronary Circulation/drug effects
- Dose-Response Relationship, Drug
- G Protein-Coupled Inwardly-Rectifying Potassium Channels/genetics
- G Protein-Coupled Inwardly-Rectifying Potassium Channels/physiology
- Glyburide/pharmacology
- Humans
- In Vitro Techniques
- Isoflurane/pharmacology
- Membrane Potentials/drug effects
- Membrane Potentials/physiology
- Mice
- Mice, Inbred C57BL
- Myocytes, Cardiac/cytology
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/physiology
- Patch-Clamp Techniques/methods
- Pinacidil/pharmacology
- Potassium Channels/genetics
- Potassium Channels/physiology
- Potassium Channels, Inwardly Rectifying/genetics
- Potassium Channels, Inwardly Rectifying/physiology
- Receptors, Drug/genetics
- Receptors, Drug/physiology
- Sulfonylurea Receptors
- Theophylline/pharmacology
- Transfection/methods
- Vasodilation/drug effects
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Affiliation(s)
- H Fujita
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
- Department of General Surgery, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - T Ogura
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - M Tamagawa
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - H Uemura
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - T Sato
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - A Ishida
- Department of General Surgery, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - M Imamaki
- Department of General Surgery, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - F Kimura
- Department of General Surgery, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - M Miyazaki
- Department of General Surgery, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
| | - H Nakaya
- Department of Pharmacology, Chiba University Graduate School of Medicine Chuo-ku, Chiba, Japan
- Author for correspondence:
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19
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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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