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Kokoti L, Al-Karagholi MAM, Waldorff Nielsen CA, Ashina M. Glibenclamide Posttreatment Does Not Inhibit Levcromakalim Induced Headache in Healthy Participants: A Randomized Clinical Trial. Neurotherapeutics 2023; 20:389-398. [PMID: 36763326 PMCID: PMC10121935 DOI: 10.1007/s13311-023-01350-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/29/2023] [Indexed: 02/11/2023] Open
Abstract
Intravenous infusion of ATP-sensitive potassium channel (KATP) opener levcromakalim causes headache in humans and implicates KATP channels in headache pathophysiology. Whether KATP channel blocker glibenclamide inhibits levcromakalim-induced headache has not yet been elucidated. We aimed to investigate the effect of posttreatment with glibenclamide on levcromakalim-induced headache in healthy participants. In a double blind, randomized, three-arm, placebo-controlled, crossover study, 20 healthy participants were randomized to receive 20 mL of levcromakalim (0.05 mg/min (50 mg/mL)) or 20 mL placebo (isotonic saline) intravenously over 20 min followed by oral administration of 10 mg glibenclamide or placebo. Fifteen participants completed all three study days. The primary endpoint was the difference in incidence of headache (0-12 h) between glibenclamide and placebo. More participants developed headache on levcromakalim-placebo day (15/15, 100%) (P = 0.013) and levcromakalim-glibenclamide day (13/15, 86%) compared to placebo-placebo day (7/15, 46%) (P = 0.041). We found no difference in headache incidence between levcromakalim-placebo day and levcromakalim-glibenclamide day (P = 0.479). The AUC0-12 h for headache intensity was significantly larger in levcromakalim-placebo day and levcromakalim-glibenclamide day compared to placebo-placebo day (106.3 ± 215.8) (P < 0.01). There was no difference in the AUC0-12 h for headache intensity between the levcromakalim-placebo day (494 ± 336.6) and the levcromakalim-glibenclamide day (417 ± 371.6) (P = 0.836). We conclude that non-specific KATP channel inhibitor glibenclamide did not attenuate levcromakalim-induced headache in healthy volunteers. Future studies should clarify the involvement of the distinct isoforms of sulfonylurea receptor subunits of KATP channels in the pathogenesis of headache and migraine.
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Affiliation(s)
- Lili Kokoti
- Danish Headache Center, Department of Neurology, Rigshospitalet – Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Valdemar Hansen Vej 5, 2600 Glostrup, Denmark
| | - Mohammad Al-Mahdi Al-Karagholi
- Danish Headache Center, Department of Neurology, Rigshospitalet – Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Valdemar Hansen Vej 5, 2600 Glostrup, Denmark
| | - Cherie Amalie Waldorff Nielsen
- Danish Headache Center, Department of Neurology, Rigshospitalet – Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Valdemar Hansen Vej 5, 2600 Glostrup, Denmark
| | - Messoud Ashina
- Danish Headache Center, Department of Neurology, Rigshospitalet – Glostrup, Faculty of Health and Medical Sciences, University of Copenhagen, Valdemar Hansen Vej 5, 2600 Glostrup, Denmark
- Danish Headache Knowledge Center, Rigshospitalet – Glostrup, Glostrup, Denmark
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Pirotte B, Florence X, Goffin E, Leleux F, Lebrun P. Research Advancements on Fluorinated and Non-Fluorinated 4-Phenyl(thio)ureido-Substituted 2,2-Dimethylchromans Acting as Inhibitors of Insulin Release and Smooth Muscle Relaxants. Med Chem 2022; 18:884-894. [PMID: 35189799 DOI: 10.2174/1573406418666220221145500] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2021] [Revised: 11/29/2021] [Accepted: 12/21/2021] [Indexed: 11/22/2022]
Abstract
AIMS The present study aimed at characterizing the impact of the presence or absence of fluorine atoms on the phenyl and benzopyran rings of 4-phenyl(thio)ureido-substituted 2,2-dimethylchromans on their ability to inhibit insulin release from pancreatic -cells or to relax vascular smooth muscle cells. METHODS Most compounds were found to inhibit insulin secretion and to provoke a marked myorelaxant activity. RESULTS The lack of a fluorine or a chlorine atom at the 6-position of the 2,2-dimethylchroman core structure reduced the inhibitory activity on the pancreatic endocrine tissue. One of the most active compounds on both tissues, compound 11h (BPDZ 678), was selected for further pharmacological investigations. CONCLUSION The biological data suggested that 11h mainly expressed the profile of a KATP channel opener on pancreatic -cells, although a calcium entry blockade effect was also observed. On vascular smooth muscle cells, 11h behaved as a calcium entry blocker.
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Affiliation(s)
- Bernard Pirotte
- Laboratoire de Chimie Pharmaceutique, Center for Interdisciplinary Research on Medicines (CIRM), Université de Liège, Quartier Hôpital, Avenue Hippocrate 15, B-4000 Liège, Belgium
| | - Xavier Florence
- Laboratoire de Chimie Pharmaceutique, Center for Interdisciplinary Research on Medicines (CIRM), Université de Liège, Quartier Hôpital, Avenue Hippocrate 15, B-4000 Liège, Belgium
- Laboratoire de Physiologie et Pharmacologie, Université Libre de Bruxelles, Faculté de Médecine, 808 Route de Lennik, B-1070 Bruxelles, Belgium
| | - Eric Goffin
- Laboratoire de Chimie Pharmaceutique, Center for Interdisciplinary Research on Medicines (CIRM), Université de Liège, Quartier Hôpital, Avenue Hippocrate 15, B-4000 Liège, Belgium
| | - Fabienne Leleux
- Laboratoire de Physiologie et Pharmacologie, Université Libre de Bruxelles, Faculté de Médecine, 808 Route de Lennik, B-1070 Bruxelles, Belgium
| | - Philippe Lebrun
- Laboratoire de Physiologie et Pharmacologie, Université Libre de Bruxelles, Faculté de Médecine, 808 Route de Lennik, B-1070 Bruxelles, Belgium
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Zhao S, Wang M, Ma Z. Therapeutic potential of ATP-sensitive potassium channels in Parkinson's disease. Brain Res Bull 2021; 169:1-7. [PMID: 33434622 DOI: 10.1016/j.brainresbull.2021.01.003] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/06/2020] [Revised: 12/19/2020] [Accepted: 01/04/2021] [Indexed: 11/19/2022]
Abstract
In the past decade, there was an increasing interest in the therapeutic potential targeting ATP-sensitive potassium (KATP) channels for an effective treatment of Parkinson's disease (PD). KATP channels are widely expressed in the central nervous system and were reported to mediate the degeneration and death of nigral dopamine neurons in the pathogenesis of PD. This review aims to address the pivotal roles of KATP channels played in the mechanisms underlying PD pathogenesis, and provide possible directions for further research from different perspectives, such as the vulnerability of dopamine neurons in the substantia nigra, neurotransmitter releasing, iron metabolism in the brain, α-synuclein secretion and mitochondrial dysfunction, which are off critical importance in the investigation of KATP channels-targeted precise therapeutic interventions for PD.
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Affiliation(s)
- Sha Zhao
- Department of Physiology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - MengZhen Wang
- Department of Physiology, School of Basic Medicine, Qingdao University, Qingdao, China
| | - ZeGang Ma
- Department of Physiology, School of Basic Medicine, Qingdao University, Qingdao, China; Institute of Brain Science and Disorders, Qingdao University, Qingdao, China.
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Latest Insights into the Pathophysiology of Migraine: the ATP-Sensitive Potassium Channels. Curr Pain Headache Rep 2020; 24:77. [DOI: 10.1007/s11916-020-00911-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/15/2020] [Indexed: 12/15/2022]
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Zhou M, Yoshikawa K, Akashi H, Miura M, Suzuki R, Li TS, Abe H, Bando Y. Localization of ATP-sensitive K + channel subunits in rat liver. World J Exp Med 2019; 9:14-31. [PMID: 31938690 PMCID: PMC6955576 DOI: 10.5493/wjem.v9.i2.14] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/17/2019] [Revised: 09/05/2019] [Accepted: 11/21/2019] [Indexed: 02/06/2023] Open
Abstract
BACKGROUND ATP-sensitive K+ (KATP) channels were originally found in cardiac myocytes by Noma in 1983. KATP channels were formed by potassium ion-passing pore-forming subunits (Kir6.1, Kir6.2) and regulatory subunits SUR1, SU2A and SUR2B. A number of cells and tissues have been revealed to contain these channels including hepatocytes, but detailed localization of these subunits in different types of liver cells was still uncertain.
AIM To investigate the expression of KATP channel subunits in rat liver and their localization in different cells of the liver.
METHODS Rabbit anti-rat SUR1 peptide antibody was raised and purified by antigen immunoaffinity column chromatography. Four of Sprague-Dawley rats were used for liver protein extraction for immunoblot analysis, seven of them were used for immunohistochemistry both for the ABC method and immunofluorescence staining. Four of Wistar rats were used for the isolation of hepatic stellate cells (HSCs) and Kupffer cells for both primary culture and immunocytochemistry.
RESULTS Immunoblot analysis showed that the five kinds of KATP channel subunits, i.e. Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B, were detected in liver. Immunohistochemical staining showed that Kir6.1 and Kir6.2 were weakly to moderately expressed in parenchymal cells and sinusoidal lining cells, while SUR1, SUR2A, and SUR2B were mainly localized to sinusoidal lining cells, such as HSCs, Kupffer cells, and sinusoidal endothelial cells. Immunoreactivity for SUR2A and SUR2B was expressed in the hepatocyte membrane. Double immunofluorescence staining further showed that the pore-forming subunits Kir6.1 and/or Kir6.2 colocalized with GFAP in rat liver sections and primary cultured HSCs. These KATP channel subunits also colocalized with CD68 in liver sections and primary cultured Kupffer cells. The SUR subunits colocalized with GFAP in liver sections and colocalized with CD68 both in liver sections and primary cultured Kupffer cells. In addition, five KATP channel subunits colocalized with SE-1 in sinusoidal endothelial cells.
CONCLUSION Observations from the present study indicated that KATP channel subunits expressed in rat liver and the diversity of KATP channel subunit composition might form different types of KATP channels. This is applicable to hepatocytes, HSCs, various types of Kupffer cells and sinusoidal endothelial cells.
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Affiliation(s)
- Ming Zhou
- Department of Anatomy, Akita University Graduate School of Medicine, Akita 010-8543, Japan
| | - Kiwamu Yoshikawa
- Department of Cell Biology and Morphology, Akita University Graduate School of Medicine, Akita 010-8543, Japan
| | - Hideo Akashi
- Department of Anatomy, Akita University Graduate School of Medicine, Akita 010-8543, Japan
| | - Mitsutaka Miura
- Department of Cell Biology and Morphology, Akita University Graduate School of Medicine, Akita 010-8543, Japan
| | - Ryoji Suzuki
- Department of Anatomy, Akita University Graduate School of Medicine, Akita 010-8543, Japan
| | - Tao-Sheng Li
- Department of Stem Cell Biology, Atomic Bomb Disease Institute, Nagasaki University, Nagasaki 852-8523, Japan
| | - Hiroshi Abe
- TRUST, A Long-Term Care Health Facility, Sendai 980-0011, Japan
| | - Yoshio Bando
- Department of Anatomy, Akita University Graduate School of Medicine, Akita 010-8543, Japan
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Pirotte B, Florence X, Goffin E, Lebrun P. 2,2-Dimethyl-3,4-dihydro-2 H-1,4-benzoxazines as isosteres of 2,2-dimethylchromans acting as inhibitors of insulin release and vascular smooth muscle relaxants. MEDCHEMCOMM 2019; 10:431-438. [PMID: 31015906 DOI: 10.1039/c8md00593a] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 02/01/2019] [Indexed: 11/21/2022]
Abstract
The present study describes the synthesis and biological evaluation of 4-phenylureido/thioureido-substituted 2,2-dimethyl-3,4-dihydro-2H-1,4-benzoxazines as isosteres of corresponding 2,2-dimethylchromans reported to be pancreatic β-cell KATP channel openers. The benzoxazines were found to be less active as inhibitors of the glucose-induced insulin release than their corresponding chromans, while the myorelaxant activity of some 4-arylureido-substituted benzoxazines was more pronounced than that exhibited by their chroman counterparts. The myorelaxant activity of the most potent benzoxazine 8e was further characterized on rat aortic rings precontracted by 30 mM KCl in the presence of glibenclamide (10 μM) or precontracted by 80 mM extracellular KCl. Our findings indicate that, on vascular smooth muscle cells, the benzoxazine 8e mainly behaved as a calcium entry blocker.
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Affiliation(s)
- Bernard Pirotte
- Laboratoire de Chimie Pharmaceutique , Center for Interdisciplinary Research on Medicines (CIRM) , Université de Liège , Quartier Hôpital , Avenue Hippocrate 15 , B-4000 Liège , Belgium .
| | - Xavier Florence
- Laboratoire de Chimie Pharmaceutique , Center for Interdisciplinary Research on Medicines (CIRM) , Université de Liège , Quartier Hôpital , Avenue Hippocrate 15 , B-4000 Liège , Belgium . .,Laboratoire de Physiologie et Pharmacologie , Université Libre de Bruxelles , Faculté de Médecine , 808 Route de Lennik , B-1070 Bruxelles , Belgium
| | - Eric Goffin
- Laboratoire de Chimie Pharmaceutique , Center for Interdisciplinary Research on Medicines (CIRM) , Université de Liège , Quartier Hôpital , Avenue Hippocrate 15 , B-4000 Liège , Belgium .
| | - Philippe Lebrun
- Laboratoire de Physiologie et Pharmacologie , Université Libre de Bruxelles , Faculté de Médecine , 808 Route de Lennik , B-1070 Bruxelles , Belgium
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Pirotte B, Florence X, Goffin E, Lebrun P. Deciphering Structure-Activity Relationships in a Series of 2,2-Dimethylchromans Acting as Inhibitors of Insulin Release and Smooth Muscle Relaxants. ChemMedChem 2017; 12:1810-1817. [DOI: 10.1002/cmdc.201700409] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 09/20/2017] [Indexed: 11/09/2022]
Affiliation(s)
- Bernard Pirotte
- Laboratoire de Chimie Pharmaceutique; Center for Interdisciplinary Research on Medicines (CIRM); Université de Liège; Quartier Hôpital, Avenue Hippocrate 15 4000 Liège Belgium
| | - Xavier Florence
- Laboratoire de Chimie Pharmaceutique; Center for Interdisciplinary Research on Medicines (CIRM); Université de Liège; Quartier Hôpital, Avenue Hippocrate 15 4000 Liège Belgium
- Laboratoire de Physiologie et Pharmacologie; Université Libre de Bruxelles; Faculté de Médecine; 808 Route de Lennik 1070 Bruxelles Belgium
| | - Eric Goffin
- Laboratoire de Chimie Pharmaceutique; Center for Interdisciplinary Research on Medicines (CIRM); Université de Liège; Quartier Hôpital, Avenue Hippocrate 15 4000 Liège Belgium
| | - Philippe Lebrun
- Laboratoire de Physiologie et Pharmacologie; Université Libre de Bruxelles; Faculté de Médecine; 808 Route de Lennik 1070 Bruxelles Belgium
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Roy Chowdhury U, Bahler CK, Holman BH, Fautsch MP. ATP-sensitive potassium (KATP) channel openers diazoxide and nicorandil lower intraocular pressure by activating the Erk1/2 signaling pathway. PLoS One 2017; 12:e0179345. [PMID: 28594895 PMCID: PMC5464668 DOI: 10.1371/journal.pone.0179345] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2017] [Accepted: 05/26/2017] [Indexed: 01/17/2023] Open
Abstract
Elevated intraocular pressure is the most prevalent and only treatable risk factor for glaucoma, a degenerative disease of the optic nerve. While treatment options to slow disease progression are available, all current therapeutic and surgical treatments have unwanted side effects or limited efficacy, resulting in the need to identify new options. Previous reports from our laboratory have established a novel ocular hypotensive effect of ATP-sensitive potassium channel (KATP) openers including diazoxide (DZ) and nicorandil (NCD). In the current study, we evaluated the role of Erk1/2 signaling pathway in KATP channel opener mediated reduction of intraocular pressure (IOP). Western blot analysis of DZ and NCD treated primary normal trabecular meshwork (NTM) cells, human TM (isolated from perfusion cultures of human anterior segments) and mouse eyes showed increased phosphorylation of Erk1/2 when compared to vehicle treated controls. DZ and NCD mediated pressure reduction (p<0.02) in human anterior segments (n = 7 for DZ, n = 4 for NCD) was abrogated by U0126 (DZ + U0126: -9.7 ± 11.5%, p = 0.11; NCD + U0126: -0.1 ± 11.5%, p = 1.0). In contrast, U0126 had no effect on latanoprostfree acid-induced pressure reduction (-52.5 ± 6.8%, n = 4, p = 0.001). In mice, DZ and NCD reduced IOP (DZ, 14.9 ± 3.8%, NCD, 16.9 ± 2.5%, n = 10, p<0.001), but the pressure reduction was inhibited by U0126 (DZ + U0126, 0.7 ± 3.0%; NCD + U0126, 0.9 ± 2.2%, n = 10, p>0.1). Histologic evaluation of transmission electron micrographs from DZ + U0126 and NCD + U0126 treated eyes revealed no observable morphological changes in the ultrastructure of the conventional outflow pathway. Taken together, the results indicate that the Erk1/2 pathway is necessary for IOP reduction by KATP channel openers DZ and NCD.
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Affiliation(s)
- Uttio Roy Chowdhury
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Cindy K. Bahler
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Bradley H. Holman
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, United States of America
| | - Michael P. Fautsch
- Department of Ophthalmology, Mayo Clinic, Rochester, Minnesota, United States of America
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Lin Z, Huang H, Gu Y, Huang K, Hu Y, Ji Z, Wu Y, Wang S, Yang T, Pan S. Glibenclamide ameliorates cerebral edema and improves outcomes in a rat model of status epilepticus. Neuropharmacology 2017; 121:1-11. [PMID: 28412320 DOI: 10.1016/j.neuropharm.2017.04.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2016] [Revised: 04/06/2017] [Accepted: 04/09/2017] [Indexed: 12/30/2022]
Abstract
Glibenclamide (GBC), a sulfonylurea receptor 1 blocker, emerges recently as a promising neuron protectant in various neurological disorders. This study aimed to determine whether GBC improves survival and neurological outcome of status epilepticus (SE). Male Sprague-Dawley rats successfully undergoing SE for 2.5 h (n = 134) were randomly assigned to GBC or vehicle group. Rats in the GBC group received a loading dose of 10 μg/kg of GBC, followed by 1.2 μg/6 h for 3 days, while same dose of vehicle was used as control. The 28-day survival rate in the GBC group (11/23) was significantly higher than that in the vehicle group (8/36). In addition, the frequency and duration of spontaneous recurrent seizures in SE rats were profoundly reduced by GBC but not by vehicle treatment. Moreover, cognitive impairment was observed in the SE rats at day 28, which was reversed by GBC treatment. Meanwhile, cerebral edema, as well as neuronal loss, was decreased in several brain areas in the GBC group. Additionally, on the molecular basis, the subunits of sulfonylurea receptor 1/transient receptor potential M4 (SUR1-TRPM4) heterodimer were both strongly upregulated after SE but partly suppressed by GBC treatment. Furthermore, gene knockdown of Trpm4 in SE rats reduced BBB disruption and neuronal loss, similar to the inhibitory effects with GBC treatment. Taken together, GBC treatment markedly improved survival and neurologic outcomes after SE. The salutary effects of GBC were correlated to the alleviation of cerebral edema and reduction in neurological injury via down-regulation of SUR1-TRPM4 channel.
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Affiliation(s)
- Zhenzhou Lin
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Hua Huang
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Yong Gu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Kaibin Huang
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Yafang Hu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Zhong Ji
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Yongming Wu
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Shengnan Wang
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Tingting Yang
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China
| | - Suyue Pan
- Department of Neurology, Nanfang Hospital, Southern Medical University, Guangzhou, China.
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Pirotte B, Florence X, Goffin E, Medeiros MB, de Tullio P, Lebrun P. 4-Phenylureido/thioureido-substituted 2,2-dimethylchroman analogs of cromakalim bearing a bulky ‘carbamate’ moiety at the 6-position as potent inhibitors of glucose-sensitive insulin secretion. Eur J Med Chem 2016; 121:338-351. [DOI: 10.1016/j.ejmech.2016.05.042] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2015] [Revised: 05/19/2016] [Accepted: 05/20/2016] [Indexed: 11/25/2022]
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Roy Chowdhury U, Bahler CK, Holman BH, Dosa PI, Fautsch MP. Ocular Hypotensive Effects of the ATP-Sensitive Potassium Channel Opener Cromakalim in Human and Murine Experimental Model Systems. PLoS One 2015; 10:e0141783. [PMID: 26535899 PMCID: PMC4633217 DOI: 10.1371/journal.pone.0141783] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Accepted: 10/13/2015] [Indexed: 11/17/2022] Open
Abstract
Elevated intraocular pressure (IOP) is the most prevalent and only treatable risk factor for glaucoma, a leading cause of irreversible blindness worldwide. Unfortunately, all current therapeutics used to treat elevated IOP and glaucoma have significant and sometimes irreversible side effects necessitating the development of novel compounds. We evaluated the IOP lowering ability of the broad spectrum KATP channel opener cromakalim. Cultured human anterior segments when treated with 2 μM cromakalim showed a decrease in pressure (19.33 ± 2.78 mmHg at 0 hours to 13.22 ± 2.64 mmHg at 24 hours; p<0.001) when compared to vehicle treated controls (15.89 ± 5.33 mmHg at 0 h to 15.56 ± 4.88 mmHg at 24 hours; p = 0.89). In wild-type C57BL/6 mice, cromakalim reduced IOP by 18.75 ± 2.22% compared to vehicle treated contralateral eyes (17.01 ± 0.32 mmHg at 0 hours to 13.82 ± 0.37 mmHg at 24 hours; n = 10, p = 0.002). Cromakalim demonstrated an additive effect when used in conjunction with latanoprost free acid, a common ocular hypotensive drug prescribed to patients with elevated IOP. To examine KATP channel subunit specificity, Kir6.2(-/-) mice were treated with cromakalim, but unlike wild-type animals, no change in IOP was noted. Histologic analysis of treated and control eyes in cultured human anterior segments and in mice showed similar cell numbers and extracellular matrix integrity within the trabecular meshwork, with no disruptions in the inner and outer walls of Schlemm's canal. Together, these studies suggest that cromakalim is a potent ocular hypotensive agent that lowers IOP via activation of Kir6.2 containing KATP channels, its effect is additive when used in combination with the commonly used glaucoma drug latanoprost, and is not toxic to cells and tissues of the aqueous humor outflow pathway, making it a candidate for future therapeutic development.
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Affiliation(s)
- Uttio Roy Chowdhury
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, United States of America
| | - Cindy K Bahler
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, United States of America
| | - Bradley H Holman
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, United States of America
| | - Peter I Dosa
- Institute for Therapeutics Discovery and Development, University of Minnesota, Minneapolis, MN, United States of America
| | - Michael P Fautsch
- Department of Ophthalmology, Mayo Clinic, Rochester, MN, United States of America
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Florence X, Desvaux V, Goffin E, de Tullio P, Pirotte B, Lebrun P. Influence of the alkylsulfonylamino substituent located at the 6-position of 2,2-dimethylchromans structurally related to cromakalim: from potassium channel openers to calcium entry blockers? Eur J Med Chem 2014; 80:36-46. [PMID: 24763361 DOI: 10.1016/j.ejmech.2014.04.024] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 03/28/2014] [Accepted: 04/05/2014] [Indexed: 10/25/2022]
Abstract
The present study described the synthesis of original R/S-6-alkylsulfonylamino-3,4-dihydro-2,2-dimethyl-2H-1-benzopyrans bearing a 3- or 4-substituted phenylthiourea or phenylurea moiety at the 4-position. Their biological effects were evaluated both on insulin-secreting and smooth muscle cells and were compared to those of reference KATP channel activators such as (±)-cromakalim, diazoxide and previously synthesized cromakalim analogues. The study aimed at exploring the influence of the introduction of an alkylsulfonylamino substituent at the 6-position of 2,2-dimethylchromans in order to improve biological activity, tissue selectivity but also hydrophilicity of dihydrobenzopyran derivatives. Several compounds were found to be equipotent or even more potent than (±)-cromakalim and diazoxide at inhibiting the insulin releasing process. Most of the newly synthesized and more hydrophilic dihydrobenzopyrans also exhibited a marked vasorelaxant activity although they were less potent than (±)-cromakalim. Additional pharmacological and radioisotopic investigations suggested that R/S-N-3-chlorophenyl-N'-(3,4-dihydro-6-methylsulfonylamino-2,2-dimethyl-2H-1-benzopyran-4-yl)thiourea (21) did not act as a potassium channel opener but rather as a Ca(2+) entry blocker.
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Affiliation(s)
- Xavier Florence
- Laboratoire de Pharmacodynamie et de Thérapeutique, Université Libre de Bruxelles, Faculté de Médecine, 808 Route de Lennik, B-1070 Bruxelles, Belgium.
| | - Vincent Desvaux
- Centre de Recherches du Cyclotron, Université de Liège, 8 Allée du 6 Août, B-4000 Liège, Belgium
| | - Eric Goffin
- Laboratoire de Chimie Pharmaceutique, Centre Interfacultaire de Recherche du Médicament (C.I.R.M.), Université de Liège, C.H.U., 1 Avenue de l'Hôpital, B-4000 Liège, Belgium
| | - Pascal de Tullio
- Laboratoire de Chimie Pharmaceutique, Centre Interfacultaire de Recherche du Médicament (C.I.R.M.), Université de Liège, C.H.U., 1 Avenue de l'Hôpital, B-4000 Liège, Belgium
| | - Bernard Pirotte
- Laboratoire de Chimie Pharmaceutique, Centre Interfacultaire de Recherche du Médicament (C.I.R.M.), Université de Liège, C.H.U., 1 Avenue de l'Hôpital, B-4000 Liège, Belgium
| | - Philippe Lebrun
- Laboratoire de Pharmacodynamie et de Thérapeutique, Université Libre de Bruxelles, Faculté de Médecine, 808 Route de Lennik, B-1070 Bruxelles, Belgium
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Tanaka T, Nagashima K, Inagaki N, Kioka H, Takashima S, Fukuoka H, Noji H, Kakizuka A, Imamura H. Glucose-stimulated single pancreatic islets sustain increased cytosolic ATP levels during initial Ca2+ influx and subsequent Ca2+ oscillations. J Biol Chem 2013; 289:2205-16. [PMID: 24302735 DOI: 10.1074/jbc.m113.499111] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
In pancreatic islets, insulin secretion occurs via synchronous elevation of Ca(2+) levels throughout the islets during high glucose conditions. This Ca(2+) elevation has two phases: a quick increase, observed after the glucose stimulus, followed by prolonged oscillations. In these processes, the elevation of intracellular ATP levels generated from glucose is assumed to inhibit ATP-sensitive K(+) channels, leading to the depolarization of membranes, which in turn induces Ca(2+) elevation in the islets. However, little is known about the dynamics of intracellular ATP levels and their correlation with Ca(2+) levels in the islets in response to changing glucose levels. In this study, a genetically encoded fluorescent biosensor for ATP and a fluorescent Ca(2+) dye were employed to simultaneously monitor the dynamics of intracellular ATP and Ca(2+) levels, respectively, inside single isolated islets. We observed rapid increases in cytosolic and mitochondrial ATP levels after stimulation with glucose, as well as with methyl pyruvate or leucine/glutamine. High ATP levels were sustained as long as high glucose levels persisted. Inhibition of ATP production suppressed the initial Ca(2+) increase, suggesting that enhanced energy metabolism triggers the initial phase of Ca(2+) influx. On the other hand, cytosolic ATP levels did not fluctuate significantly with the Ca(2+) level in the subsequent oscillation phases. Importantly, Ca(2+) oscillations stopped immediately before ATP levels decreased significantly. These results might explain how food or glucose intake evokes insulin secretion and how the resulting decrease in plasma glucose levels leads to cessation of secretion.
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Rufino AT, Rosa SC, Judas F, Mobasheri A, Lopes MC, Mendes AF. Expression and function of K(ATP) channels in normal and osteoarthritic human chondrocytes: possible role in glucose sensing. J Cell Biochem 2013; 114:1879-89. [PMID: 23494827 PMCID: PMC3736163 DOI: 10.1002/jcb.24532] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2013] [Accepted: 02/27/2013] [Indexed: 12/20/2022]
Abstract
ATP-sensitive potassium [K(ATP)] channels sense intracellular ATP/ADP levels, being essential components of a glucose-sensing apparatus in various cells that couples glucose metabolism, intracellular ATP/ADP levels and membrane potential. These channels are present in human chondrocytes, but their subunit composition and functions are unknown. This study aimed at elucidating the subunit composition of K(ATP) channels expressed in human chondrocytes and determining whether they play a role in regulating the abundance of major glucose transporters, GLUT-1 and GLUT-3, and glucose transport capacity. The results obtained show that human chondrocytes express the pore forming subunits, Kir6.1 and Kir6.2, at the mRNA and protein levels and the regulatory sulfonylurea receptor (SUR) subunits, SUR2A and SUR2B, but not SUR1. The expression of these subunits was no affected by culture under hyperglycemia-like conditions. Functional impairment of the channel activity, using a SUR blocker (glibenclamide 10 or 20 nM), reduced the protein levels of GLUT-1 and GLUT-3 by approximately 30% in normal chondrocytes, while in cells from cartilage with increasing osteoarthritic (OA) grade no changes were observed. Glucose transport capacity, however, was not affected in normal or OA chondrocytes. These results show that K(ATP) channel activity regulates the abundance of GLUT-1 and GLUT-3, although other mechanisms are involved in regulating the overall glucose transport capacity of human chondrocytes. Therefore, K(ATP) channels are potential components of a broad glucose sensing apparatus that modulates glucose transporters and allows human chondrocytes to adjust to varying extracellular glucose concentrations. This function of K(ATP) channels seems to be impaired in OA chondrocytes.
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Affiliation(s)
- Ana T Rufino
- Center for Neuroscience and Cell Biology, University of Coimbra, 3004-517 Coimbra, Portugal
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15
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16
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Florence X, Dilly S, de Tullio P, Pirotte B, Lebrun P. Modulation of the 6-position of benzopyran derivatives and inhibitory effects on the insulin releasing process. Bioorg Med Chem 2011; 19:3919-28. [DOI: 10.1016/j.bmc.2011.05.040] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 04/26/2011] [Accepted: 05/19/2011] [Indexed: 11/26/2022]
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Lovasz N, Ducza E, Gaspar R, Falkay G. Ontogeny of sulfonylurea-binding regulatory subunits of K(ATP) channels in the pregnant rat myometrium. Reproduction 2011; 142:175-81. [PMID: 21527399 DOI: 10.1530/rep-10-0492] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
ATP-sensitive potassium channels (K(ATP) channels) are composed of sulfonylurea receptors (SURs) and potassium inward rectifiers (Kir(6.x)) that assemble to form a large octameric channel. This study was designed to examine the expression and role of sulfonylurea-binding regulatory subunits 1 (SUR1 (ABCC8)) and 2 (SUR2 (ABCC9)) of the K(ATP) channels in the pregnant rat myometrium with particular regard to the contractility. RT-PCR and western blot analyses were performed to detect the presence of SUR1 and SUR2. The SUR1 levels were markedly increased in the early stages of pregnancy. The highest level was detected on day 6 of pregnancy, whereas in the late stages, the levels of SUR1 were significantly decreased. The SUR2 level remained unchanged throughout pregnancy. The SUR non-selective diazoxide and the SUR2-selective pinacidil inhibited oxytocin-induced contractions. Glibenclamide, a K(ATP) channel blocker, antagonized both pinacidil- and diazoxide-induced relaxations. It was established that SURs are responsible for pharmacological reactivity of K(ATP) channel openers. We conclude that both SURs are involved in the K(ATP) channel in the pregnant rat myometrium. It may further be concluded that 'pinacidil-like' K(ATP) channel openers may be of therapeutic relevance as tocolytic agents in the future.
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Affiliation(s)
- N Lovasz
- Department of Pharmacodynamics and Biopharmacy, Faculty of Pharmacy, University of Szeged, Szeged, Hungary
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18
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Andrade F, Trujillo X, Sánchez-Pastor E, Montoya-Pérez R, Saavedra-Molina A, Ortiz-Mesina M, Huerta M. Glibenclamide increases post-fatigue tension in slow skeletal muscle fibers of the chicken. J Comp Physiol B 2010; 181:403-12. [PMID: 21079972 PMCID: PMC3058534 DOI: 10.1007/s00360-010-0527-1] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2010] [Revised: 10/08/2010] [Accepted: 10/25/2010] [Indexed: 01/18/2023]
Abstract
In contrast to fast-twitch skeletal muscle fibers of the chicken, slow-twitch fibers are fatigue-resistant. In fast fibers, the fatigue process has been related to K(ATP) channels. In the present study, we investigated the action of glibenclamide (an anti-diabetic sulphonylurea that acts on K(ATP) channels) on fatigued slow skeletal muscle, studying twitch and tetanus tension after inducing the muscle to fatigue by continuous electrical stimulation. Our results showed that glibenclamide (150 μM) increased post-fatigue twitch tension by about 25% with respect to the fatigued condition (P < 0.05). In addition, glibenclamide (150 μM) increased post-fatigue tetanic tension (83.61 ± 15.7% in peak tension, and 85.0 ± 19.0% in tension-time integral, P = 0.02, and 0.04, respectively; n = 3). Moreover, after exposing the muscle to a condition that inhibits mitochondrial ATP formation in order to activate K(ATP) channels with cyanide (10 mM), tension also diminished, but in the presence of glibenclamide the effect produced by cyanide was abolished. To determine a possible increase in intracellular calcium concentration, the effects of glibenclamide on caffeine-evoked contractures were explored. After muscle pre-incubation with glibenclamide (150 μM), tension of caffeine-evoked contractures increased (6.5 ± 1.5% in maximal tension, and 5.9 ± 3.8% in tension-time integral, P < 0.05). These results suggest a possible role of K(ATP) channels in the fatigue process, since glibenclamide increases twitch and tetanus tension in fatigued slow muscle of the chicken and during metabolic inhibition, possibly by increasing intracellular calcium.
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Affiliation(s)
- Felipa Andrade
- Instituto Tecnológico de Colima, Avenida Tecnológico No. 1, C.P. 28976, Villa de Álvarez, Colima, México
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19
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Vascular control in humans: focus on the coronary microcirculation. Basic Res Cardiol 2009; 104:211-27. [PMID: 19190954 DOI: 10.1007/s00395-009-0775-y] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/14/2008] [Accepted: 12/15/2008] [Indexed: 12/27/2022]
Abstract
Myocardial perfusion is regulated by a variety of factors that influence arteriolar vasomotor tone. An understanding of the physiological and pathophysiological factors that modulate coronary blood flow provides the basis for the judicious use of medications for the treatment of patients with coronary artery disease. Vasomotor properties of the coronary circulation vary among species. This review highlights the results of recent studies that examine the mechanisms by which the human coronary microcirculation is regulated in normal and disease states, focusing on diabetes. Multiple pathways responsible for myogenic constriction and flow-mediated dilation in human coronary arterioles are addressed. The important role of endothelium-derived hyperpolarizing factors, their interactions in mediating dilation, as well as speculation regarding the clinical significance are emphasized. Unique properties of coronary arterioles in human vs. other species are discussed.
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Namekata I, Yamaguchi Y, Moriguchi S, Yamazaki S, Terasawa A, Yamagishi R, Aikawa T, Saito T, Kurashima K, Seri K, Imamura Y, Akita H, Shigenobu K, Tanaka H. (R)-ACX, a pancreatic β-cell selective sulfonylurea, does not aggravate myocardial ischemia-reperfusion damage. Eur J Pharmacol 2007; 577:211-8. [DOI: 10.1016/j.ejphar.2007.09.012] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2007] [Revised: 09/12/2007] [Accepted: 09/19/2007] [Indexed: 11/26/2022]
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21
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Rajasekaran SA, Beyenbach KW, Rajasekaran AK. Interactions of tight junctions with membrane channels and transporters. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2007; 1778:757-69. [PMID: 18086552 DOI: 10.1016/j.bbamem.2007.11.007] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2007] [Revised: 11/02/2007] [Accepted: 11/09/2007] [Indexed: 12/22/2022]
Abstract
Tight junctions are unique organelles in epithelial cells. They are localized to the apico-lateral region and essential for the epithelial cell transport functions. The paracellular transport process that occurs via tight junctions is extensively studied and is intricately regulated by various extracellular and intracellular signals. Fine regulation of this transport pathway is crucial for normal epithelial cell functions. Among factors that control tight junction permeability are ions and their transporters. However, this area of research is still in its infancy and much more needs to be learned about how these molecules regulate tight junction structure and functions. In this review we have attempted to compile literature on ion transporters and channels involved in the regulation of tight junctions.
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Affiliation(s)
- Sigrid A Rajasekaran
- The Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, University of California, Los Angeles, CA 90095, USA
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22
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Greer RM, Shah J, Jeske YW, Brown D, Walker RM, Cowley D, Bowling FG, Liaskou D, Harris M, Thomsett MJ, Choong C, Bell JR, Jack MM, Cotterill AM. Genotype-phenotype associations in patients with severe hyperinsulinism of infancy. Pediatr Dev Pathol 2007; 10:25-34. [PMID: 17378627 DOI: 10.2350/06-04-0083.1] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/28/2006] [Accepted: 07/01/2006] [Indexed: 11/20/2022]
Abstract
In hyperinsulinism of infancy (HI), unregulated insulin secretion causes hypoglycemia. Pancreatectomy may be required in severe cases, most of which result from a defect in the beta-cell KATP channel, encoded by ABCC8 and KCNJ11. Pancreatic histology may be classified as diffuse or focal disease (the latter associated with single paternal ABCC8 mutations), indicated by the presence of islet cell nuclear enlargement in areas of diffuse abnormality. We investigated genotype-phenotype associations in a heterogeneous Australian cohort. ABCC8 and KCNJ11 genes were sequenced and case histology was reviewed in 21 infants who had pancreatectomy. Ninety-eight control DNA samples were tested by single nucleotide polymorphism analysis. Eighteen ABCC8 mutations were identified, 10 novel. Eleven patients (4 compound heterozygote, 4 single mutation, 3 no mutation detected) had diffuse hyperinsulinism. Nine patients had focal hyperinsulinism (6 single paternal mutation, 2 single mutation of undetermined parental origin, 1 none found) with absence of islet cell nuclear enlargement outside the focal area, although centroacinar cell proliferation and/or nesidiodysplasia was present in 7 cases. Regeneration after near-total pancreatectomy was documented in 4 patients, with aggregates of endocrine tissue observed at subsequent operations in 3. Although the absence of enlarged islet cell nuclei is a useful discriminant of focal hyperinsulinism associated with a paternal ABCC8 mutation, further research is needed to understand the pathophysiology of other histological abnormalities in patients with HI, which may have implications for mechanisms of ductal and islet cell proliferation. Previous surgery should be taken into account when interpreting pancreatic histology.
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Affiliation(s)
- Ristan M Greer
- Department of Paediatrics and Child Health, University of Queensland, Brisbane, and Department of Endocrinology and Diabetes, Princess Margaret Hospital for Children, Western Australia, Australia.
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23
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Jöns T, Wittschieber D, Beyer A, Meier C, Brune A, Thomzig A, Ahnert-Hilger G, Veh RW. K+-ATP-channel-related protein complexes: potential transducers in the regulation of epithelial tight junction permeability. J Cell Sci 2006; 119:3087-97. [PMID: 16820413 DOI: 10.1242/jcs.03041] [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] [Indexed: 01/10/2023] Open
Abstract
K+-ATP channels are composed of an inwardly rectifying Kir6 subunit and an auxiliary sulfonylurea receptor (SUR) protein. The SUR subunits of Kir6 channels have been recognized as an ATPase, which appears to work as a mechanochemical device like other members of the ABC protein family. Thus, in spite of just gating ions, Kir6/Sur might, in addition, regulate completely different cellular systems. However, so far no model system was available to directly investigate this possibility. Using highly specific antibodies against Kir6.1-SUR2A and an in vitro model system of the rat small intestine, we describe a new function of the Kir6.1-SUR2A complex, namely the regulation of paracellular permeability. The Kir6.1-SUR2A complex localizes to regulated tight junctions in a variety of gastrointestinal, renal and liver tissues of rat, pig and human, whereas it is absent in the urothelium. Changes in paracellular permeability following food intake was investigated by incubating the lumen of morphological well-defined segments of rat small intestine with various amounts of glucose. Variations in the lumenal glucose concentrations and regulators of Kir6.1/SUR2A activity, such as tolbutamide or diazoxide, specifically modulate paracellular permeability. The data presented here shed new light on the physiological and pathophysiological role K+-ATP channels might have for the regulation of tight junctions.
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Affiliation(s)
- Thomas Jöns
- Charité-Universitätsmedizin Berlin, Centrum für Anatomie, Institut für Integrative Neuroanatomie, Philippstr. 12, 10115 Berlin, Germany.
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24
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Dhar-Chowdhury P, Harrell MD, Han SY, Jankowska D, Parachuru L, Morrissey A, Srivastava S, Liu W, Malester B, Yoshida H, Coetzee WA. The glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase, triose-phosphate isomerase, and pyruvate kinase are components of the K(ATP) channel macromolecular complex and regulate its function. J Biol Chem 2005; 280:38464-70. [PMID: 16170200 PMCID: PMC4667781 DOI: 10.1074/jbc.m508744200] [Citation(s) in RCA: 98] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The regulation of ATP-sensitive potassium (K(ATP)) channel activity is complex and a multitude of factors determine their open probability. Physiologically and pathophysiologically, the most important of these are intracellular nucleotides, with a long-recognized role for glycolytically derived ATP in regulating channel activity. To identify novel regulatory subunits of the K(ATP) channel complex, we performed a two-hybrid protein-protein interaction screen, using as bait the mouse Kir6.2 C terminus. Screening a rat heart cDNA library, we identified two potential interacting proteins to be the glycolytic enzymes, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and triose-phosphate isomerase. The veracity of interaction was verified by co-immunoprecipitation techniques in transfected mammalian cells. We additionally demonstrated that pyruvate kinase also interacts with Kir6.2 subunits. The physiological relevance of these interactions is illustrated by the demonstration that native Kir6.2 protein similarly interact with GAPDH and pyruvate kinase in rat heart membrane fractions and that Kir6.2 protein co-localize with these glycolytic enzymes in rat ventricular myocytes. The functional relevance of our findings is demonstrated by the ability of GAPDH or pyruvate kinase substrates to directly block the K(ATP) channel under patch clamp recording conditions. Taken together, our data provide direct evidence for the concept that key enzymes involved in glycolytic ATP production are part of a multisubunit K(ATP) channel protein complex. Our data are consistent with the concept that the activity of these enzymes (possibly by ATP formation in the immediate intracellular microenvironment of this macromolecular K(ATP) channel complex) causes channel closure.
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Affiliation(s)
- Piyali Dhar-Chowdhury
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Maddison D. Harrell
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Sandra Y. Han
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Danuta Jankowska
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Lavanya Parachuru
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Alison Morrissey
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Shekhar Srivastava
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Weixia Liu
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Brian Malester
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - Hidetada Yoshida
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
| | - William A. Coetzee
- Department of Pediatrics, New York University School of Medicine, New York, New York 10016
- Department of Physiology & Neuroscience, New York University School of Medicine, New York, New York 10016
- Department of Pharmacology, New York University School of Medicine, New York, New York 10016
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25
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Nakayama S, Ohya S, Liu HN, Watanabe T, Furuzono S, Wang J, Nishizawa Y, Aoyama M, Murase N, Matsubara T, Ito Y, Imaizumi Y, Kajioka S. Sulphonylurea receptors differently modulate ICC pacemaker Ca2+ activity and smooth muscle contractility. J Cell Sci 2005; 118:4163-73. [PMID: 16141235 DOI: 10.1242/jcs.02540] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Appropriate gastrointestinal motility is essential to properly control the body energy level. Intracellular Ca2+ ([Ca2+]i) oscillations in interstitial cells of Cajal (ICCs; identified with c-Kit immunoreactivity) are considered to be the primary mechanism for the pacemaker activity in gastrointestinal motility. In the present study, RT-PCR examinations revealed predominant expression of the type 1 isoform of sulphonylurea receptors (SUR1) in ICCs of the mouse ileum, but expression of SUR2 was predominant in smooth muscle. In cell clusters prepared from the same tissue, smooth muscle contractility and pacemaker [Ca2+]i activity in ICCs were found to be differentially modulated by K(ATP) channel openers and sulphonylurea compounds, in accordance with the expression of SUR isoforms. 1 microM cromakalim nearly fully suppressed the mechanical activity in smooth muscle, whereas ICC pacemaker [Ca2+]i oscillations persisted. Greater concentrations (approximately 10 microM) of cromakalim attenuated pacemaker [Ca2+]i oscillations. This effect was not reversed by changing the reversal potential of K+, but was prevented by glibenclamide. Diazoxide at 30 muM terminated ICC pacemaker [Ca2+]i oscillations, but again treatment with high extracellular K+ did not restore them. These results suggest that SUR can modulate pacemaker [Ca2+]i oscillations via voltage-independent mechanism(s), and also that intestinal pacemaking and glucose control are closely associated with SUR.
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Affiliation(s)
- Shinsuke Nakayama
- Department of Cell Physiology, Nagoya University Graduate School of Medicine, Nagoya 466-8550, Japan.
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26
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Hanna ST, Cao K, Wang R. Interaction of acetylcholine with Kir6.1 channels heterologously expressed in human embryonic kidney cells. Eur J Pharmacol 2005; 515:34-42. [PMID: 15894309 DOI: 10.1016/j.ejphar.2005.04.015] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2005] [Revised: 04/05/2005] [Accepted: 04/11/2005] [Indexed: 10/25/2022]
Abstract
Kir6.1 subunit is one of the pore-forming components of K(ATP) channel complex. The endogenous modulation of Kir6.1 subunit function has been largely unknown. Whether acetylcholine modulated the function of Kir6.1 subunit stably expressed in human embryonic kidney (HEK-293) cells was examined in the present study using the whole-cell patch-clamp technique. Acetylcholine from 1-100 microM concentration-dependently stimulated the heteologously expressed and PNU-37883A sensitive Kir6.1 channels (p<0.05). Co-expression of sulphonylurea receptor 1 subunit with Kir6.1 significantly inhibited the stimulatory effect of acetylcholine on K(ATP) currents. Pretreatment of the transfected HEK-293 cells with atropine, alpha-bungarotoxin, mecamylamine, prazocine, propranolol, or dihydro-beta-erythroidine hydrobromide did not alter the stimulatory effect of acetylcholine on Kir6.1 currents. When intracellular ATP was increased from 0.3 mM to 5 mM, acetylcholine at 10 microM still exhibited its stimulatory effect (-16.4+/-2.3 to -25.5+/-3.8 pA/pF, n=8, p<0.05). In conclusion, we have demonstrated an excitatory effect of acetylcholine on Kir6.1 channels, which is mediated neither by an acetylcholine receptor-dependent mechanism, nor by alteration in ATP metabolism.
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Affiliation(s)
- Salma Toma Hanna
- Department of Physiology, University of Saskatchewan, 107 Wiggins Road, Saskatoon, SK, Canada S7N 5E5
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27
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Zhou M, Tanaka O, Sekiguchi M, He HJ, Yasuoka Y, Itoh H, Kawahara K, Abe H. ATP-sensitive K+-channel subunits on the mitochondria and endoplasmic reticulum of rat cardiomyocytes. J Histochem Cytochem 2005; 53:1491-500. [PMID: 15983113 PMCID: PMC3957548 DOI: 10.1369/jhc.5a6736.2005] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
ATP-sensitive K(+) (K(ATP)) channel subunits on the subcellular structures of rat cardiomyocytes were studied with antibodies against Kir6.1 and Kir6.2. According to the results of Western blot analysis, Kir6.1 was strongly expressed in mitochondrial and microsome fractions, and faintly expressed in cell membrane fraction, whereas Kir6.2 was mainly expressed in the microsome fraction and weakly in cell membrane and mitochondrial fractions. Immunohistochemistry showed that Kir6.1 and Kir6.2 were expressed in the endocardium, atrial and ventricular myocardium, and in vascular smooth muscles. Immunoelectron microscopy revealed that Kir6.1 immunoreactivity was mainly localized in the mitochondria, whereas Kir6.2 immunoreactivity was mainly localized in the endoplasmic reticulum and a few in the mitochondria. Both Kir6.1 and Kir6.2 are candidates of mitochondrial K(ATP) channel subunits. The data obtained in this study will be useful for analyzing the composition of K(ATP) channels of cardiomyocytes and help to understanding the cardioprotective role of K(ATP) channels during heart ischemia.
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Affiliation(s)
- Ming Zhou
- Department of Anatomy, Akita University School of Medicine, Japan.
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28
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McCully JD, Levitsky S. Mitochondrial ATP-sensitive potassium channels in surgical cardioprotection. Arch Biochem Biophys 2004; 420:237-45. [PMID: 14654062 DOI: 10.1016/j.abb.2003.06.003] [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: 01/21/2023]
Abstract
ATP-sensitive potassium channels allow for the coupling of membrane potential to cellular metabolic status. Two K(ATP) channel subtypes coexist in the myocardium with one subtype located in the sarcolemma membrane and the other in the inner membrane of the mitochondria. The ATP-sensitive potassium channels can be pharmacologically modulated by a family of structurally diverse agents of varied potency and selectivity, collectively known as potassium channel openers and blockers. Sufficient evidence exists to indicate that the ATP-sensitive potassium channels and in particular the mitochondrial ATP-sensitive potassium channels play an important role both as a trigger and an effector in surgical cardioprotection. In this review, the biochemistry and specificity of the ATP-sensitive potassium channels is examined in relation to surgical cardioprotection.
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Affiliation(s)
- James D McCully
- Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center, Harvard Medical School and the Harvard Institutes of Medicine, Boston, MA, USA.
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29
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Thomzig A, Prüss H, Veh RW. The Kir6.1-protein, a pore-forming subunit of ATP-sensitive potassium channels, is prominently expressed by giant cholinergic interneurons in the striatum of the rat brain. Brain Res 2003; 986:132-8. [PMID: 12965237 DOI: 10.1016/s0006-8993(03)03222-0] [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: 11/26/2022]
Abstract
ATP-sensitive potassium channels comprise a complex of two structurally different proteins: a member of the inwardly rectifying Kir6 family (Kir6.1 or Kir6.2) and a sulfonylurea receptor (SUR1 or SUR2). Their regulation by intracellular ADP/ATP-concentrations and through various pharmacological agents has profound implications for the excitability of cells and, in the case of neurons, for neurotransmitter release. We previously showed that in rat brain, the Kir6.1 subunit is predominantly expressed in astrocytes in contrast to the Kir6.2 subunit, which is exclusively expressed in neurons. In this report we show, that in addition to the astrocytic expression, the Kir6.1 protein is also found in a small subset of neurons in distinct areas of the brain, like the hypothalamic supraoptic and paraventricular nuclei and the striatum. The Kir6.1-positive neurons in the striatum could be characterized as cholinergic interneurones, verified by immunofluorescence double staining. This complete colocalization of the Kir6.1 subunit in cholinergic interneurons is interesting with respect to the pharmacological potential of these channels. A selective modulation of the Kir6.1 subunit in the cholinergic striatal interneurons may eventually be of therapeutic value for the treatment of Parkinson's disease.
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Affiliation(s)
- Achim Thomzig
- Institut für Anatomie, der Charité, Universitätsklinikum der Humboldt-Universität zu Berlin, Philippstrasse 12, D-10115 Berlin, Germany
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Hill RA, Rudra S, Peng B, Roane DS, Bounds JK, Zhang Y, Adloo A, Lu T. Hydroxyl-substituted sulfonylureas as potent inhibitors of specific [3H]glyburide binding to rat brain synaptosomes. Bioorg Med Chem 2003; 11:2099-113. [PMID: 12670661 DOI: 10.1016/s0968-0896(02)00606-5] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
We are seeking to discover potent CNS-active sulfonylureas with structural features that allow for the formation of several types of prodrugs. We report herein the syntheses of compounds comprising an initial series of hydroxyl-substituted analogues of the potent ATP-sensitive potassium channel blockers glyburide (glibenclamide) and gliquidone. Somewhat unexpectedly, several of the compounds were found to be comparably potent to glyburide as inhibitors of specific [(3)H]glyburide binding in rat brain preparations.
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Affiliation(s)
- Ronald A Hill
- Division of Basic Pharmaceutical Sciences, College of Pharmacy, The University of Louisiana at Monroe, Monroe, LA 71209, USA.
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31
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Abstract
Adenosine triphosphate (ATP)-sensitive potassium (K(ATP)) channels allow coupling of membrane potential to cellular metabolic status. Two K(ATP) channel subtypes coexist in the myocardium, with one subtype located in the sarcolemma (sarcK(ATP)) membrane and the other in the inner membrane of the mitochondria (mitoK(ATP)). The K(ATP) channels can be pharmacologically modulated by a family of structurally diverse agents of varied potency and selectivity, collectively known as potassium channel openers and blockers. Sufficient evidence exists to indicate that the K(ATP) channels and, in particular, the mitoK(ATP) channels play an important role both as a trigger and an effector in surgical cardioprotection. In this review, the biochemistry and surgical specificity of the K(ATP) channels are examined.
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Affiliation(s)
- James D McCully
- Division of Cardiothoracic Surgery, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02115, USA.
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Takano M, Kuratomi S. Regulation of cardiac inwardly rectifying potassium channels by membrane lipid metabolism. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2003; 81:67-79. [PMID: 12475570 DOI: 10.1016/s0079-6107(02)00048-2] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Types and distributions of inwardly rectifying potassium (Kir) channels are one of the major determinants of the electrophysiological properties of cardiac myocytes. Kir2.1 (classical inward rectifier K(+) channel), Kir6.2/SUR2A (ATP-sensitive K(+) channel) and Kir3.1/3.4 (muscarinic K(+) channels) in cardiac myocytes are commonly upregulated by a membrane lipid, phosphatidylinositol 4,5-bisphosphates (PIP(2)). PIP(2) interaction sites appear to be conserved by positively charged amino acid residues and the putative alpha-helix in the C-terminals of Kir channels. PIP(2) level in the plasma membrane is regulated by the agonist stimulation. Kir channels in the cardiac myocytes seem to be actively regulated by means of the change in PIP(2) level rather than by downstream signal transduction pathways.
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Affiliation(s)
- Makoto Takano
- Department of Physiology and Biophysics, Graduate School of Medicine, Kyoto University, Japan.
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Cheng SM, Chen I, Levin M. K(ATP) channel activity is required for hatching in Xenopus embryos. Dev Dyn 2002; 225:588-91. [PMID: 12454935 DOI: 10.1002/dvdy.10183] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
A growing body of work suggests that the activity of ion channels and pumps is an important regulatory factor in embryonic development. We are beginning to identify functional roles for proteins suggested by a survey of expression of ion channel and pump genes in Xenopus and chick embryos (Rutenberg et al. [2002] Dev Dyn 225, this issue). Here, we report that the ATP-sensitive K(+) channel protein is present in the hatching gland of Xenopus embryos; moreover, we show that its activity is necessary for hatching in Xenopus. Pharmacologic inhibition of K(ATP) channels not only specifically prevents the hatching process but also greatly reduces the endogenous expression of Connexin-30 in the hatching gland. Based on recent work which showed that gap-junctional communication mediated by Cx30 in the hatching gland was required for secretion of the hatching enzyme, we propose that K(ATP) channel activity is upstream of Cx30 expression and represents a necessary endogenous step in the hatching of the Xenopus embryo.
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Affiliation(s)
- Shing-Ming Cheng
- Cytokine Biology Department, Forsyth Institute, and Harvard University Department of Oral and Developmental Biology, Boston, Massachusetts 02115, USA
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Matsumoto N, Komiyama S, Akaike N. Pre- and postsynaptic ATP-sensitive potassium channels during metabolic inhibition of rat hippocampal CA1 neurons. J Physiol 2002; 541:511-20. [PMID: 12042355 PMCID: PMC2290338 DOI: 10.1113/jphysiol.2002.018267] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Presynaptic and postsynaptic membrane activities during experimental metabolic inhibition were analysed in mechanically dissociated rat hippocampal neurons using nystatin-perforated and conventional whole-cell patch clamp recordings. NaCN, an inhibitor of mitochondrial ATP synthesis, induced an outward current across the postsynaptic soma membrane. This current was blocked by tolbutamide, a sulfonylurea, which blocks ATP-sensitive K+ (KATP) channels. The presynaptic effect of metabolic inhibitors such as NaCN, NaN3, or glucose-free solution was to increase the frequency of GABAergic miniature inhibitory postsynaptic currents (mIPSCs). Tolbutamide had no effect on this increase in mIPSC frequency induced by metabolic inhibition. Diazoxide, a KATP channel opener, evoked a similar somatic outward current in a dose-dependent manner. In addition, diazoxide decreased the frequency of mIPSCs in a dose-dependent fashion. Both these pre- and postsynaptic effects of diazoxide were reversed by tolbutamide, suggesting the existence of KATP channels on both pre- and postsynaptic membranes. These results confirm the presence of KATP channels on both the pre- and postsynaptic membranes but indicate that the channels have significantly different sensitivities to metabolic inhibition.
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Affiliation(s)
- Nozomu Matsumoto
- Cellular and System Physiology, Graduate School of Medical Sciences and Department of Otolaryngology, Faculty of Medicine, Kyushu University, Fukuoka 812-8582, Japan
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Ford JW, Stevens EB, Treherne JM, Packer J, Bushfield M. Potassium channels: gene family, therapeutic relevance, high-throughput screening technologies and drug discovery. PROGRESS IN DRUG RESEARCH. FORTSCHRITTE DER ARZNEIMITTELFORSCHUNG. PROGRES DES RECHERCHES PHARMACEUTIQUES 2002; 58:133-68. [PMID: 12079199 DOI: 10.1007/978-3-0348-8183-8_4] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 04/18/2023]
Abstract
Existing drugs that modulate ion channels represent a key class of pharmaceutical agents across many therapeutic areas and there is considerable further potential for potassium channel drug discovery. Potassium channels represent the largest and most diverse sub-group of ion channels and they play a central role in regulating the membrane potential of cells. Recent advances in genomics have greatly added to the number of these potential drug targets, but selecting a suitable potassium channel for drug discovery research is a key step. In particular, the potential therapeutic relevance of a potassium channel should be taken into account when selecting a target for screening. Potassium channel drug discovery is being driven by a need to identify lead compounds that can provide tractable starting points for medicinal chemistry. Furthermore, advances in laboratory automation have brought significant opportunities to increase screening throughput for potassium channel assays, but careful assay configuration to model drug-target interactions in a physiological manner is an essential consideration. Several potassium channel screening platforms are described in this review in order to provide some insight into the variety of formats available for screening, together with some of their inherent advantages and limitations. Particular emphasis is placed on the mechanistic basis of drug-target interaction and those aspects of structure/function that are of prime importance in potassium channel drug discovery.
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Abraham EH, Shrivastav B, Salikhova AY, Sterling KM, Johnston N, Guidotti G, Scala S, Litman T, Chan KC, Arceci RJ, Steiglitz K, Herscher L, Okunieff P. Cellular and biophysical evidence for interactions between adenosine triphosphate and P-glycoprotein substrates: functional implications for adenosine triphosphate/drug cotransport in P-glycoprotein overexpressing tumor cells and in P-glycoprotein low-level expressing erythrocytes. Blood Cells Mol Dis 2001; 27:181-200. [PMID: 11358379 DOI: 10.1006/bcmd.2000.0373] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
P-glycoprotein is involved with the removal of drugs, most of them cations, from the plasma membrane and cytoplasm. Pgp is also associated with movement of ATP, an anion, from the cytoplasm to the extracellular space. The central question of this study is whether drug and ATP transport associated with the expression of Pgp are in any way coupled. We have measured the stoichiometry of transport coupling between drug and ATP release. The drug and ATP transport that is inhibitable by the sulfonylurea compound, glyburide (P. E. Golstein, A. Boom, J. van Geffel, P. Jacobs, B. Masereel, and R. Beauwens, Pfluger's Arch. 437, 652, 1999), permits determination of the transport coupling ratio, which is close to 1:1. In view of this result, we asked whether ATP interacts directly with Pgp substrates. We show by measuring the movement of Pgp substrates in electric fields that ATP and drug movement are coupled. The results are compatible with the view that substrates for Pgp efflux are driven by the movement of ATP through electrostatic interaction and effective ATP-drug complex formation with net anionic character. This mechanism not only pertains to drug efflux from tumor cells overexpressing Pgp, but also provides a framework for understanding the role of erythrocytes in drug resistance. The erythrocyte consists of a membrane surrounding a millimolar pool of ATP. Mammalian RBCs have no nucleus or DNA drug/toxin targets. From the perspective of drug/ATP complex formation, the RBC serves as an important electrochemical sink for toxins. The presence in the erythrocyte membrane of approximately 100 Pgp copies per RBC provides a mechanism for eventual toxin clearance. The RBC transport of toxins permits their removal from sensitive structures and ultimate clearance from the organism via the liver and/or kidneys.
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Affiliation(s)
- E H Abraham
- Department of Medicine, Dartmouth Medical School, Hanover, New Hampshire 03755, USA.
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Abstract
O receptor de sulfoniluréia (SUR1) é uma subunidade dos canais de potássio ATP-dependentes expressos nas células beta pancreáticas, O papel deste receptor nos mecanismos de secreção da insulina foi bem demonstrado após a descrição de que mutações no seu gene codificador são responsáveis pela forma neonatal de hiperinsulinismo. O possível envolvimento de variantes deste gene na predisposição genética ao diabetes mellitus tipo 2 também tem sido estudado. Nesta revisão, discutimos os dados da literatura que abordam o envolvimento de alterações genéticas do SUR1 em patologias como o diabetes tipo 2, assim como nos mecanismos de secreção da insulina.
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Affiliation(s)
- André F. Reis
- Universidade Federal de São Paulo, Brasil; Institut Cochin de Génétique Moléculaire, França
| | - Gilberto Velho
- Universidade Federal de São Paulo, Brasil; Institut Cochin de Génétique Moléculaire, França
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Xie LH, Horie M, Takano M. Phospholipase C-linked receptors regulate the ATP-sensitive potassium channel by means of phosphatidylinositol 4,5-bisphosphate metabolism. Proc Natl Acad Sci U S A 1999; 96:15292-7. [PMID: 10611378 PMCID: PMC24813 DOI: 10.1073/pnas.96.26.15292] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/1999] [Indexed: 11/18/2022] Open
Abstract
In the COS7 cells transfected with cDNAs of the Kir6.2, SUR2A, and M(1) muscarinic receptors, we activated the ATP-sensitive potassium (K(ATP)) channel with a K(+) channel opener and recorded the whole-cell K(ATP) current. The K(ATP) current was reversibly inhibited by the stimulation of the M(1) receptor, which is linked to phospholipase C (PLC) by the G(q) protein. The receptor-mediated inhibition was observed even when protein kinase C (PKC) was inhibited by H-7 or by chelating intracellular Ca(2+) with 10 mM 1, 2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate (BAPTA) included in the pipette solution. However, the receptor-mediated inhibition was blocked by U-73122, a PLC inhibitor. M(1)-receptor stimulation failed to inhibit the K(ATP) current activated by the injection of exogenous phosphatidylinositol 4,5-bisphosphate (PIP(2)) through the whole-cell patch pipette. The receptor-mediated inhibition became irreversible when the replenishment of PIP(2) was blocked by wortmannin (an inhibitor of phosphatidylinositol kinases), or by including adenosine 5'-[beta,gamma-imido]triphosphate (AMPPNP, a nonhydrolyzable ATP analogue) in the pipette solution. In inside-out patch experiments, the ATP sensitivity of the K(ATP) channel was significantly higher when the M(1) receptor in the patch membrane was stimulated by acetylcholine. The stimulatory effect of pinacidil was also attenuated under this condition. We postulate that stimulation of PLC-linked receptors inhibited the K(ATP) channel by increasing the ATP sensitivity, not through PKC activation, but most probably through changing PIP(2) levels.
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Affiliation(s)
- L H Xie
- Department of Physiology, Graduate School of Medicine, Kyoto University, Kyoto 606-8501, Japan
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