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Moral-Sanz J, Mahmoud AD, Ross FA, Eldstrom J, Fedida D, Hardie DG, Evans AM. AMP-activated protein kinase inhibits Kv 1.5 channel currents of pulmonary arterial myocytes in response to hypoxia and inhibition of mitochondrial oxidative phosphorylation. J Physiol 2016; 594:4901-15. [PMID: 27062501 PMCID: PMC5009768 DOI: 10.1113/jp272032] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2015] [Accepted: 03/26/2016] [Indexed: 12/29/2022] Open
Abstract
KEY POINTS Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage-gated potassium channels (Kv ) in pulmonary arterial smooth muscle by hypoxia, although the precise molecular mechanisms have been unclear. AMP-activated protein kinase (AMPK) has been proposed to couple inhibition of mitochondrial metabolism by hypoxia to acute hypoxic pulmonary vasoconstriction and progression of pulmonary hypertension. Inhibition of complex I of the mitochondrial electron transport chain activated AMPK and inhibited Kv 1.5 channels in pulmonary arterial myocytes. AMPK activation by 5-aminoimidazole-4-carboxamide riboside, A769662 or C13 attenuated Kv 1.5 currents in pulmonary arterial myocytes, and this effect was non-additive with respect to Kv 1.5 inhibition by hypoxia and mitochondrial poisons. Recombinant AMPK phosphorylated recombinant human Kv 1.5 channels in cell-free assays, and inhibited K(+) currents when introduced into HEK 293 cells stably expressing Kv 1.5. These results suggest that AMPK is the primary mediator of reductions in Kv 1.5 channels following inhibition of mitochondrial oxidative phosphorylation during hypoxia and by mitochondrial poisons. ABSTRACT Progression of hypoxic pulmonary hypertension is thought to be due, in part, to suppression of voltage-gated potassium channels (Kv ) in pulmonary arterial smooth muscle cells that is mediated by the inhibition of mitochondrial oxidative phosphorylation. We sought to determine the role in this process of the AMP-activated protein kinase (AMPK), which is intimately coupled to mitochondrial function due to its activation by LKB1-dependent phosphorylation in response to increases in the cellular AMP:ATP and/or ADP:ATP ratios. Inhibition of complex I of the mitochondrial electron transport chain using phenformin activated AMPK and inhibited Kv currents in pulmonary arterial myocytes, consistent with previously reported effects of mitochondrial inhibitors. Myocyte Kv currents were also markedly inhibited upon AMPK activation by A769662, 5-aminoimidazole-4-carboxamide riboside and C13 and by intracellular dialysis from a patch-pipette of activated (thiophosphorylated) recombinant AMPK heterotrimers (α2β2γ1 or α1β1γ1). Hypoxia and inhibitors of mitochondrial oxidative phosphorylation reduced AMPK-sensitive K(+) currents, which were also blocked by the selective Kv 1.5 channel inhibitor diphenyl phosphine oxide-1 but unaffected by the presence of the BKCa channel blocker paxilline. Moreover, recombinant human Kv 1.5 channels were phosphorylated by AMPK in cell-free assays, and K(+) currents carried by Kv 1.5 stably expressed in HEK 293 cells were inhibited by intracellular dialysis of AMPK heterotrimers and by A769662, the effects of which were blocked by compound C. We conclude that AMPK mediates Kv channel inhibition by hypoxia in pulmonary arterial myocytes, at least in part, through phosphorylation of Kv 1.5 and/or an associated protein.
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Fedida D, Macdonald L. hERG long QT syndrome type 2 mutants need more than a chaperone to dance. J Physiol 2016; 594:4095-4096. [PMID: 27477605 PMCID: PMC4967728 DOI: 10.1113/jp272417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/01/2024] Open
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Rezazadeh S, Hesketh JC, Fedida D. Rb+ Flux through hERG Channels Affects the Potency of Channel Blocking Drugs: Correlation with Data Obtained Using a High-Throughput Rb+ Efflux Assay. ACTA ACUST UNITED AC 2016; 9:588-97. [PMID: 15475478 DOI: 10.1177/1087057104264798] [Citation(s) in RCA: 47] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The nonradioactive Rb+ efflux assay has become a reliable and efficient high-throughput hERG screening method, but it is limited by its low sensitivity for potent hERG blockers. Using the patch clamp technique, the authors found that the low sensitivity is due in part to the use of Rb+ as the permeating cation in the assay. The affinities of the drugs measured by patch clamp technique in the presence of Rb+ were 3- to 10-fold lower than when measured by the same method in the presence of K+ ions. The apparent affinity of the drugs decreased even further when monitored bytheRb+ efflux assay. It was also observed that Rb+ had minimal effects on the activation properties of channels while there was a significant change in the half-inactivation potential. This voltage shift reduces hERG channel inactivation at efflux assay potentials, and will reduce the affinity of hERG-blocking drugs that bind to inactivated states of the channel. In combination with the effects of elevated extracellular ion concentrations, it is likely that Rb+ modulation of hERG channel inactivation is largely responsible for the reduced drug potencies observed in the Rb+ efflux assay.
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Jalily PH, Eldstrom J, Miller SC, Kwan DC, Tai SSH, Chou D, Niikura M, Tietjen I, Fedida D. Mechanisms of Action of Novel Influenza A/M2 Viroporin Inhibitors Derived from Hexamethylene Amiloride. Mol Pharmacol 2016; 90:80-95. [PMID: 27193582 DOI: 10.1124/mol.115.102731] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/07/2015] [Accepted: 05/12/2016] [Indexed: 01/09/2023] Open
Abstract
The increasing prevalence of influenza viruses with resistance to approved antivirals highlights the need for new anti-influenza therapeutics. Here we describe the functional properties of hexamethylene amiloride (HMA)-derived compounds that inhibit the wild-type and adamantane-resistant forms of the influenza A M2 ion channel. For example, 6-(azepan-1-yl)-N-carbamimidoylnicotinamide ( 9: ) inhibits amantadine-sensitive M2 currents with 3- to 6-fold greater potency than amantadine or HMA (IC50 = 0.2 vs. 0.6 and 1.3 µM, respectively). Compound 9: competes with amantadine for M2 inhibition, and molecular docking simulations suggest that 9: binds at site(s) that overlap with amantadine binding. In addition, tert-butyl 4'-(carbamimidoylcarbamoyl)-2',3-dinitro-[1,1'-biphenyl]-4-carboxylate ( 27: ) acts both on adamantane-sensitive and a resistant M2 variant encoding a serine to asparagine 31 mutation (S31N) with improved efficacy over amantadine and HMA (IC50 = 0.6 µM and 4.4 µM, respectively). Whereas 9: inhibited in vitro replication of influenza virus encoding wild-type M2 (EC50 = 2.3 µM), both 27: and tert-butyl 4'-(carbamimidoylcarbamoyl)-2',3-dinitro-[1,1'-biphenyl]-4-carboxylate ( 26: ) preferentially inhibited viruses encoding M2(S31N) (respective EC50 = 18.0 and 1.5 µM). This finding indicates that HMA derivatives can be designed to inhibit viruses with resistance to amantadine. Our study highlights the potential of HMA derivatives as inhibitors of drug-resistant influenza M2 ion channels.
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Goodchild SJ, Macdonald LC, Fedida D. Sequence of gating charge movement and pore gating in HERG activation and deactivation pathways. Biophys J 2016; 108:1435-1447. [PMID: 25809256 DOI: 10.1016/j.bpj.2015.02.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2014] [Revised: 02/08/2015] [Accepted: 02/18/2015] [Indexed: 12/26/2022] Open
Abstract
KV11.1 voltage-gated K(+) channels are noted for unusually slow activation, fast inactivation, and slow deactivation kinetics, which tune channel activity to provide vital repolarizing current during later stages of the cardiac action potential. The bulk of charge movement in human ether-a-go-go-related gene (hERG) is slow, as is return of charge upon repolarization, suggesting that the rates of hERG channel opening and, critically, that of deactivation might be determined by slow voltage sensor movement, and also by a mode-shift after activation. To test these ideas, we compared the kinetics and voltage dependence of ionic activation and deactivation with gating charge movement. At 0 mV, gating charge moved ∼threefold faster than ionic current, which suggests the presence of additional slow transitions downstream of charge movement in the physiological activation pathway. A significant voltage sensor mode-shift was apparent by 24 ms at +60 mV in gating currents, and return of charge closely tracked pore closure after pulses of 100 and 300 ms duration. A deletion of the N-terminus PAS domain, mutation R4AR5A or the LQT2-causing mutation R56Q gave faster-deactivating channels that displayed an attenuated mode-shift of charge. This indicates that charge movement is perturbed by N- and C-terminus interactions, and that these domain interactions stabilize the open state and limit the rate of charge return. We conclude that slow on-gating charge movement can only partly account for slow hERG ionic activation, and that the rate of pore closure has a limiting role in the slow return of gating charges.
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Capmas P, Pourcelot AG, Giral E, Fedida D, Fernandez H. Office hysteroscopy: A report of 2402 cases. ACTA ACUST UNITED AC 2016; 45:445-50. [DOI: 10.1016/j.jgyn.2016.02.007] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2015] [Revised: 02/08/2016] [Accepted: 02/24/2016] [Indexed: 11/15/2022]
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Macdonald L, Kim RY, Kurata HT, Ahern C, Fedida D. Using Unnatural Amino Acids to Probe the Molecular Basis for Herg Drug Block. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.2817] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022] Open
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Westhoff MF, Murray CI, Thompson E, Emes R, Eldstrom J, Fedida D. Insertion of Crosslinkable Amino Acids into the IKS Channel Complex Demonstrates a Variable KCNQ1:KCNE1 Stoichiometry of up to 4:4. Biophys J 2016. [DOI: 10.1016/j.bpj.2015.11.634] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
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Murray CI, Westhoff M, Eldstrom J, Thompson E, Emes R, Fedida D. Unnatural amino acid photo-crosslinking of the IKs channel complex demonstrates a KCNE1:KCNQ1 stoichiometry of up to 4:4. eLife 2016; 5. [PMID: 26802629 PMCID: PMC4807126 DOI: 10.7554/elife.11815] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2015] [Accepted: 01/22/2016] [Indexed: 12/20/2022] Open
Abstract
Cardiac repolarization is determined in part by the slow delayed rectifier current (IKs), through the tetrameric voltage-gated ion channel, KCNQ1, and its β-subunit, KCNE1. The stoichiometry between α and β-subunits has been controversial with studies reporting either a strict 2 KCNE1:4 KCNQ1 or a variable ratio up to 4:4. We used IKs fusion proteins linking KCNE1 to one (EQ), two (EQQ) or four (EQQQQ) KCNQ1 subunits, to reproduce compulsory 4:4, 2:4 or 1:4 stoichiometries. Whole cell and single-channel recordings showed EQQ and EQQQQ to have increasingly hyperpolarized activation, reduced conductance, and shorter first latency of opening compared to EQ - all abolished by the addition of KCNE1. As well, using a UV-crosslinking unnatural amino acid in KCNE1, we found EQQQQ and EQQ crosslinking rates to be progressively slowed compared to KCNQ1, which demonstrates that no intrinsic mechanism limits the association of up to four β-subunits within the IKs complex. DOI:http://dx.doi.org/10.7554/eLife.11815.001 The membrane that surrounds heart muscle cells contains specialized channels that can open and close to control the movements of charged ions into and out of the cell. This ion flow generates the electrical signals that stimulate the heart muscle to contract for each heart beat. Different ion channels influence different steps in the initiation and termination of each electrical signal. For example, the IKs ion channel complex helps to return the cell to a resting state so the heart muscle can relax. This allows chambers of the heart to fill with blood before the next beat pumps blood throughout the body. Mutations that affect IKs cause serious heart conditions that affect heart rhythm, such as Long QT Syndrome. The IKs complex consists of channels that are each made of four copies of a protein called KCNQ1, through which potassium ions exit the cell. This channel opens in response to changes in the voltage across the cell membrane (known as the “membrane potential”). A small protein subunit called KCNE1 also makes up part of the complex, but it was not clear how many KCNE1 molecules combine with KCNQ1 to form a working channel complex. Several previous studies have reported two different results: that the KCNQ1 channel complex only exists with two KCNE1 molecules, or that the association is flexible, allowing the complex to contain up to four KCNE1 subunits. Murray et al. have now constructed IKs fusion channels out of different numbers of KCNQ1 and KCNE1 molecules to investigate how different KCNQ1:KCNE1 ratios affect how the channel works. Measuring the responses of these modified channels in mammalian cells revealed that channels with four KCNE1 subunits conducted ions better than channels with one or two KCNE1s. The channels containing fewer KCNE1s also opened at lower membrane potentials and after a shorter delay following a change in the membrane potential. Further experiments also supported the theory that up to four independent KCNE1 subunits may be easily added to the IKs ion channel complex. Murray et al. suggest that by being able to form channel complexes containing different numbers of KCNE1 subunits, cells can more flexibly control the rate at which ions flow out of the heart cells to tune the electrical signals that trigger each heart beat. The next challenges will be to determine the composition of the IKs channel complex in adult heart cells and to investigate how the complex might change with disease. DOI:http://dx.doi.org/10.7554/eLife.11815.002
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Wang L, Meng X, Yuchi Z, Zhao Z, Xu D, Fedida D, Wang Z, Huang C. De Novo Mutation in the SCN5A Gene Associated with Brugada Syndrome. Cell Physiol Biochem 2015; 36:2250-62. [PMID: 26279430 DOI: 10.1159/000430189] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/12/2015] [Indexed: 11/19/2022] Open
Abstract
BACKGROUND Brugada syndrome (BrS) is a genetically determined cardiac electrical disorder, characterized by typical electrocardiography (ECG) alterations, and it is an arrhythmogenic syndrome that may lead to sudden cardiac death. The most common genotype found among BrS patients is caused by mutations in the SCN5A gene, which lead to a loss of function of the cardiac sodium (Na(+)) channel (Nav1.5) by different mechanisms. METHODS The assay of confocal laser microscopy and western blot were used to identify the expression and location of L812Q at the cell surface. Characterization of Nav1.5 L812Q mutant Na(+) channels was text by patch-clamp recordings, and the PHYRE2 server was used to build a model for human Nav1.5 channel. RESULTS Here, we report that a novel missense SCN5A mutation, L812Q, localized in the DII-S4 transmembrane region of the Nav1.5 channel protein, was identified in an index patient who showed a typical BrS type-1 ECG phenotype. The mutation was absent in the patient's parents and brother. Heterologous expression of the wild-type (WT) and L812Q mutant Nav1.5 channels in human embryonic kidney cells (HEK293 cells) reveals that the mutation results in a reduction of Na(+) current density as well as ∼20 mV hyperpolarizing shift of the voltage dependence of inactivation. The voltage dependence of activation and the time course for recovery from inactivation are not affected by the mutation. The hyperpolarizing shift of the voltage dependence of inactivation caused a reduction of the Na(+) window current as well. In addition, western blot and confocal laser microscopy imaging experiments showed that the mutation causes fewer channel to be expressed at the membrane than WT channel. A large proportion of the mutant channels are retained in the cytoplasm, probably in the endoplasmic reticulum. CONCLUSION The decrease of channel expression, hyperpolarizing shift of voltage dependence of inactivation, and a decline of Na(+) window current caused by L812Q mutation lead to a reduction of Na(+) current during the upstroke and the repolarization phases of cardiac action potential, which contribute to the development of BrS.
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Tietjen I, Ntie-Kang F, Mwimanzi P, Onguéné PA, Scull MA, Idowu TO, Ogundaini AO, Meva’a LM, Abegaz BM, Rice CM, Andrae-Marobela K, Brockman MA, Brumme ZL, Fedida D. Screening of the Pan-African natural product library identifies ixoratannin A-2 and boldine as novel HIV-1 inhibitors. PLoS One 2015; 10:e0121099. [PMID: 25830320 PMCID: PMC4382154 DOI: 10.1371/journal.pone.0121099] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2014] [Accepted: 02/09/2015] [Indexed: 11/29/2022] Open
Abstract
The continued burden of HIV in resource-limited regions such as parts of sub-Saharan Africa, combined with adverse effects and potential risks of resistance to existing antiretroviral therapies, emphasize the need to identify new HIV inhibitors. Here we performed a virtual screen of molecules from the pan-African Natural Product Library, the largest collection of medicinal plant-derived pure compounds on the African continent. We identified eight molecules with structural similarity to reported interactors of Vpu, an HIV-1 accessory protein with reported ion channel activity. Using in vitro HIV-1 replication assays with a CD4+ T cell line and peripheral blood mononuclear cells, we confirmed antiviral activity and minimal cytotoxicity for two compounds, ixoratannin A-2 and boldine. Notably, ixoratannin A-2 retained inhibitory activity against recombinant HIV-1 strains encoding patient-derived mutations that confer resistance to protease, non-nucleoside reverse transcriptase, or integrase inhibitors. Moreover, ixoratannin A-2 was less effective at inhibiting replication of HIV-1 lacking Vpu, supporting this protein as a possible direct or indirect target. In contrast, boldine was less effective against a protease inhibitor-resistant HIV-1 strain. Both ixoratannin A-2 and boldine also inhibited in vitro replication of hepatitis C virus (HCV). However, BIT-225, a previously-reported Vpu inhibitor, demonstrated antiviral activity but also cytotoxicity in HIV-1 and HCV replication assays. Our work identifies pure compounds derived from African plants with potential novel activities against viruses that disproportionately afflict resource-limited regions of the world.
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Eldstrom J, Wang Z, Werry D, Wong N, Fedida D. Microscopic mechanisms for long QT syndrome type 1 revealed by single-channel analysis of I(Ks) with S3 domain mutations in KCNQ1. Heart Rhythm 2014; 12:386-94. [PMID: 25444851 DOI: 10.1016/j.hrthm.2014.10.029] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/16/2014] [Indexed: 10/24/2022]
Abstract
BACKGROUND The slowly activating delayed rectifier current IKs participates in cardiac repolarization, particularly at high heart rates, and mutations in this K(+) channel complex underlie long QT syndrome (LQTS) types 1 and 5. OBJECTIVE The purpose of this study was to determine biophysical mechanisms of LQT1 through single-channel kinetic analysis of IKs carrying LQT1 mutations in the S3 transmembrane region of the pore-forming subunit KCNQ1. METHODS We analyzed cell-attached recordings from mammalian cells in which a single active KCNQ1 (wild type or mutant) and KCNE1 complex could be detected. RESULTS The S3 mutants of KCNQ1 studied (D202H, I204F, V205M, and S209F), with the exception of S209F, all led to a reduction in channel activity through distinct kinetic mechanisms. D202H, I204F, and V205M showed decreased open probability (Po) compared with wild type (0.07, 0.04, and 0.12 vs 0.2); increased first latency from 1.66 to >2 seconds at +60 mV (I204F, V205M); variable-to-severe reductions in open dwell times (≥50% in V205M); stabilization of closed states (D202H); and an inability of channels to reach full conductance levels (V205M, I204F). S209F is a kinetic gain-of-function mutation with a high Po (0.40) and long open-state dwell times. CONCLUSION S3 mutations in KCNQ1 cause diverse kinetic defects in I(Ks), affecting opening and closing properties, and can account for LQT1 phenotypes.
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Peters CJ, Vaid M, Horne AJ, Fedida D, Accili EA. The molecular basis for the actions of KVβ1.2 on the opening and closing of the KV1.2 delayed rectifier channel. Channels (Austin) 2014; 3:314-22. [DOI: 10.4161/chan.3.5.9558] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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Mwimanzi PM, Tietjen I, Shahid A, Miller SC, Fedida D, Brummer Z, Brockman M. Identification of a Novel Acylguanidine-based Inhibitor of HIV-1 Replication. AIDS Res Hum Retroviruses 2014. [DOI: 10.1089/aid.2014.5444.abstract] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
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Pourrier M, Williams S, McAfee D, Belardinelli L, Fedida D. CrossTalk proposal: The late sodium current is an important player in the development of diastolic heart failure (heart failure with a preserved ejection fraction). J Physiol 2014; 592:411-4. [PMID: 24488066 DOI: 10.1113/jphysiol.2013.262261] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
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Kolocouris A, Tzitzoglaki C, Johnson FB, Zell R, Wright AK, Cross TA, Tietjen I, Fedida D, Busath DD. Aminoadamantanes with persistent in vitro efficacy against H1N1 (2009) influenza A. J Med Chem 2014; 57:4629-39. [PMID: 24793875 PMCID: PMC4127532 DOI: 10.1021/jm500598u] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
![]()
A series of 2-adamantanamines with
alkyl adducts of various lengths
were examined for efficacy against strains of influenza A including
those having an S31N mutation in M2 proton channel that confer resistance
to amantadine and rimantadine. The addition of as little as one CH2 group to the methyl adduct of the amantadine/rimantadine
analogue, 2-methyl-2-aminoadamantane, led to activity in vitro against
two M2 S31N viruses A/Calif/07/2009 (H1N1) and A/PR/8/34 (H1N1) but
not to a third A/WS/33 (H1N1). Solid state NMR of the transmembrane
domain (TMD) with a site mutation corresponding to S31N shows evidence
of drug binding. But electrophysiology using the full length S31N
M2 protein in HEK cells showed no blockade. A wild type strain, A/Hong
Kong/1/68 (H3N2) developed resistance to representative drugs within
one passage with mutations in M2 TMD, but A/Calif/07/2009 S31N was
slow (>8 passages) to develop resistance in vitro, and the resistant
virus had no mutations in M2 TMD. The results indicate that 2-alkyl-2-aminoadamantane
derivatives with sufficient adducts can persistently block p2009 influenza
A in vitro through an alternative mechanism. The observations of an
HA1 mutation, N160D, near the sialic acid binding site in both 6-resistant A/Calif/07/2009(H1N1) and the broadly resistant
A/WS/33(H1N1) and of an HA1 mutation, I325S, in the 6-resistant virus at a cell-culture stable site suggest that the drugs
tested here may block infection by direct binding near these critical
sites for virus entry to the host cell.
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Pourrier M, Williams S, McAfee D, Belardinelli L, Fedida D. Rebuttal from Marc Pourrier, Sarah Williams, Donald McAfee, Luiz Belardinelli and David Fedida. J Physiol 2014; 592:419. [DOI: 10.1113/jphysiol.2013.268896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Williams S, Pourrier M, McAfee D, Lin S, Fedida D. Ranolazine improves diastolic function in spontaneously hypertensive rats. Am J Physiol Heart Circ Physiol 2014; 306:H867-81. [PMID: 24464752 DOI: 10.1152/ajpheart.00704.2013] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Diastolic dysfunction can lead to heart failure with preserved ejection fraction, for which there is no effective therapeutic. Ranolazine has been reported to reduce diastolic dysfunction, but the specific mechanisms of action are unclear. The effect of ranolazine on diastolic function was examined in spontaneously hypertensive rats (SHRs), where left ventricular relaxation is impaired and stiffness increased. The objective of this study was to determine whether ranolazine improves diastolic function in SHRs and identify the mechanism(s) by which improvement is achieved. Specifically, to test the hypothesis that ranolazine, by inhibiting late sodium current, reduces Ca(2+) overload and promotes ventricular relaxation and reduction in diastolic stiffness, the effects of ranolazine or vehicle on heart function and the response to dobutamine challenge were evaluated in aged male SHRs and Wistar-Kyoto rats by echocardiography and pressure-volume loop analysis. The effects of ranolazine and the more specific sodium channel inhibitor tetrodotoxin were determined on the late sodium current, sarcomere length, and intracellular calcium in isolated cardiomyocytes. Ranolazine reduced the end-diastolic pressure-volume relationship slope and improved diastolic function during dobutamine challenge in the SHR. Ranolazine and tetrodotoxin also enhanced cardiomyocyte relaxation and reduced myoplasmic free Ca(2+) during diastole at high-stimulus rates in the SHR. The density of the late sodium current was elevated in SHRs. In conclusion, ranolazine was effective in reducing diastolic dysfunction in the SHR. Its mechanism of action, at least in part, is consistent with inhibition of the increased late sodium current in the SHR leading to reduced Ca(2+) overload.
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Goonasekara CL, Balse E, Hatem S, Steele DF, Fedida D. Cholesterol and cardiac arrhythmias. Expert Rev Cardiovasc Ther 2014; 8:965-79. [DOI: 10.1586/erc.10.79] [Citation(s) in RCA: 34] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
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Wang L, Meng X, Zhao Z, Xu D, Fedida D, Wang Z, Huang C. A Novel Cardiac Nav1.5 Channel Mutation, L812Q, Leads to Brugada Syndrome. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.725] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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Murray CI, Maurice Y, Eldstrom J, Fedida D. State-Dependent Crosslinking in IKS Demonstrates a Closed-State Interaction between KCNE1 at F57 and KCNQ1 that Inhibits Channel Opening. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.141] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
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Wu Y, Dou Y, Fedida D. Role of Charged Residues in the Regulation of Voltage Sensor Movement in Herg K+ Channels. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.4094] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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48
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Peters C, Fedida D, Accili E. Allosteric Coupling of the Inner Activation Gate to the Outer Pore of a Potassium Channel. Biophys J 2014. [DOI: 10.1016/j.bpj.2013.11.2994] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022] Open
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Goodchild SJ, Fedida D. Gating charge movement precedes ionic current activation in hERG channels. Channels (Austin) 2013; 8:84-9. [PMID: 24126078 PMCID: PMC4048346 DOI: 10.4161/chan.26775] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
We recently reported gating currents recorded from hERG channels expressed in mammalian TSA cells and assessed the kinetics at different voltages. We detected 2 distinct components of charge movement with the bulk of the charge being carried by a slower component. Here we compare our findings in TSA cells with recordings made from oocytes using the Cut Open Vaseline Gap clamp (COVG) and go on to directly compare activation of gating charge and ionic currents at 0 and +60 mV. The data show that gating charge saturates and moves more rapidly than ionic current activates suggesting a transition downstream from the movement of the bulk of gating charge is rate limiting for channel opening.
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Dou Y, Goodchild SJ, Velde RV, Wu Y, Fedida D. The neutral, hydrophobic isoleucine at position I521 in the extracellular S4 domain of hERG contributes to channel gating equilibrium. Am J Physiol Cell Physiol 2013; 305:C468-78. [PMID: 23761630 DOI: 10.1152/ajpcell.00147.2013] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The human ether-a-go-go related (hERG) potassium channel has unusual functional characteristics in that the rates of channel activation and deactivation are much slower than inactivation, which is attributed to specific structural elements within the NH2 terminus and the S1-S4 voltage-sensing domains (VSD). Although the charged residues in the VSD have been extensively modified and mutated as a result, the role and importance of specific hydrophobic residues in the S4 has been much less explored in studies of hERG gating. We found that charged, but not neutral or hydrophobic, amino acid substitution of isoleucine 521 at the outer end of the S4 transmembrane domain resulted in channels activating at much more negative voltages associated with a marked hyperpolarization of the conductance-voltage (G-V) relationship. The contributions of different physicochemical properties to this effect were probed by chemical modification of channels substituted with cysteine at position I521. When positively charged reagents including tetramethyl-rhodamine-5-maleimide (TMRM), 1-(2-maleimidylethyl)-4-[5-(4-methoxyphenyl)oxazol-2-yl] pyridinium methane-sulfonate (PyMPO), [2-(trimethylammonium)ethyl] methanethiosulfonate chloride (MTSET), and 2-aminoethyl methanethiosulfonate hydrobromide (MTSEA) were bound to the cysteine, I521C channels activated at more negative membrane potentials. To examine the contributions to hERG gating of other residues at the outer end of S4 (520-528), we performed a cysteine scan combined with MTSET modification. Only L520C, along with I521C, shows a substantial hyperpolarizing shift of the G-V relationship upon MTSET modification. The data indicate that the neutral, hydrophobic residue I521 at the extracellular end of S4 is critical for stabilizing the closed conformation of the hERG channel relative to the open state and by comparison with Shaker supports the alignment of hERG I521 with Shaker L361.
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