1
|
Büyükgüzel K, Büyükgüzel E, Chudzińska E, Lewandowska-Wosik A, Gaj R, Adamski Z. Drosophila melanogaster Response to Feeding with Neomycin-Based Medium Expressed in Fluctuating Asymmetry. INSECTS 2020; 11:E378. [PMID: 32570778 PMCID: PMC7348700 DOI: 10.3390/insects11060378] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/18/2020] [Revised: 06/08/2020] [Accepted: 06/15/2020] [Indexed: 11/16/2022]
Abstract
The fruit fly Drosophila melanogaster is a model species used for a wide range of studies. Contamination of Drosophila cultures with bacterial infection is common and is readily eradicated by antibiotics. Neomycin antibiotics can cause stress to D. melanogaster's larvae and imagoes, which may affect the interpretation of the results of research using culture from neomycin-based medium. In the present study, fluctuating asymmetry (FA), one of the important bioindicators of stress, was measured. Larvae and imagoes of a wild-type D. melanogaster strain were exposed to various concentrations of neomycin. The size of anal papillae and selected wing veins were measured using scanning electron and light microscopy, respectively. Next, the FA was checked. The values obtained for larval anal papillae appeared to be concentration-dependant; the FA indices increased with the concentration of neomycin. The wing FA presented a large but variable correlation, depending on the measured vein. However, the mean length of veins was the highest for the control group, with neomycin-exposed groups showing lower values. The research showed that neomycin may cause sublethal stress in D. melanogaster, which manifests in increased FA indices. This suggests that neomycin can cause physiological and developmental stress in insects, which should be taken into account when interpreting the results of studies using these model organisms.
Collapse
Affiliation(s)
- Kemal Büyükgüzel
- Department of Biology, Faculty of Arts and Science, Zonguldak Bülent Ecevit University, 67100 Zonguldak, Turkey;
| | - Ender Büyükgüzel
- Department of Molecular Biology and Genetics, Faculty of Arts and Science, Zonguldak Bülent Ecevit University, 67100 Zonguldak, Turkey;
| | - Ewa Chudzińska
- Department of Genetics, Faculty of Biology, Adam Mickiewicz University, 61-614 Poznań, Poland; (E.C.); (A.L.-W.)
| | - Anetta Lewandowska-Wosik
- Department of Genetics, Faculty of Biology, Adam Mickiewicz University, 61-614 Poznań, Poland; (E.C.); (A.L.-W.)
| | - Renata Gaj
- Department of Agricultural Chemistry & Environmental Biogeochemistry, Poznan University of Life Science, 60-637 Poznań, Poland;
| | - Zbigniew Adamski
- Electron and Confocal Microscope Laboratory, Faculty of Biology, Adam Mickiewicz University, 61-614 Poznań, Poland
- Department of Animal Physiology and Development, Faculty of Biology, Adam Mickiewicz University, 61-614 Poznań, Poland
| |
Collapse
|
2
|
Woods Acevedo MA, Erickson AK, Pfeiffer JK. The Antibiotic Neomycin Enhances Coxsackievirus Plaque Formation. mSphere 2019; 4:e00632-18. [PMID: 30787120 PMCID: PMC6382971 DOI: 10.1128/msphere.00632-18] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 01/31/2019] [Indexed: 01/06/2023] Open
Abstract
Coxsackievirus typically infects humans via the gastrointestinal tract, which has a large number of microorganisms collectively referred to as the microbiota. To study how the intestinal microbiota influences enteric virus infection, several groups have used an antibiotic regimen in mice to deplete bacteria. These studies have shown that bacteria promote infection with several enteric viruses. However, very little is known about whether antibiotics influence viruses in a microbiota-independent manner. In this study, we sought to determine the effects of antibiotics on coxsackievirus B3 (CVB3) using an in vitro cell culture model in the absence of bacteria. We determined that an aminoglycoside antibiotic, neomycin, enhanced the plaque size of CVB3 strain Nancy. Neomycin treatment did not alter viral attachment, translation, or replication. However, we found that the positive charge of neomycin and other positively charged compounds enhanced viral diffusion by overcoming the negative inhibitory effect of sulfated polysaccharides present in agar overlays. Neomycin and the positively charged compound protamine also enhanced plaque formation of reovirus. Overall, these data provide further evidence that antibiotics can play noncanonical roles in viral infections and that this should be considered when studying enteric virus-microbiota interactions.IMPORTANCE Coxsackieviruses primarily infect the gastrointestinal tract of humans, but they can disseminate systemically and cause severe disease. Using antibiotic treatment regimens to deplete intestinal microbes in mice, several groups have shown the bacteria promote infection with a variety of enteric viruses. However, it is possible that antibiotics have microbiota-independent effects on viruses. Here we show that an aminoglycoside antibiotic, neomycin, can influence quantification of coxsackievirus in cultured cells in the absence of bacteria.
Collapse
Affiliation(s)
- Mikal A Woods Acevedo
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Andrea K Erickson
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| | - Julie K Pfeiffer
- Department of Microbiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA
| |
Collapse
|
3
|
Murayama T, Kurebayashi N, Ishigami-Yuasa M, Mori S, Suzuki Y, Akima R, Ogawa H, Suzuki J, Kanemaru K, Oyamada H, Kiuchi Y, Iino M, Kagechika H, Sakurai T. Efficient High-Throughput Screening by Endoplasmic Reticulum Ca2+ Measurement to Identify Inhibitors of Ryanodine Receptor Ca2+-Release Channels. Mol Pharmacol 2018; 94:722-730. [DOI: 10.1124/mol.117.111468] [Citation(s) in RCA: 37] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2017] [Accepted: 04/12/2018] [Indexed: 11/22/2022] Open
|
4
|
Bannister ML, Alvarez-Laviada A, Thomas NL, Mason SA, Coleman S, du Plessis CL, Moran AT, Neill-Hall D, Osman H, Bagley MC, MacLeod KT, George CH, Williams AJ. Effect of flecainide derivatives on sarcoplasmic reticulum calcium release suggests a lack of direct action on the cardiac ryanodine receptor. Br J Pharmacol 2016; 173:2446-59. [PMID: 27237957 PMCID: PMC4945764 DOI: 10.1111/bph.13521] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/10/2016] [Revised: 05/16/2016] [Accepted: 05/17/2016] [Indexed: 11/29/2022] Open
Abstract
BACKGROUND AND PURPOSE Flecainide is a use-dependent blocker of cardiac Na(+) channels. Mechanistic analysis of this block showed that the cationic form of flecainide enters the cytosolic vestibule of the open Na(+) channel. Flecainide is also effective in the treatment of catecholaminergic polymorphic ventricular tachycardia but, in this condition, its mechanism of action is contentious. We investigated how flecainide derivatives influence Ca(2) (+) -release from the sarcoplasmic reticulum through the ryanodine receptor channel (RyR2) and whether this correlates with their effectiveness as blockers of Na(+) and/or RyR2 channels. EXPERIMENTAL APPROACH We compared the ability of fully charged (QX-FL) and neutral (NU-FL) derivatives of flecainide to block individual recombinant human RyR2 channels incorporated into planar phospholipid bilayers, and their effects on the properties of Ca(2) (+) sparks in intact adult rat cardiac myocytes. KEY RESULTS Both QX-FL and NU-FL were partial blockers of the non-physiological cytosolic to luminal flux of cations through RyR2 channels but were significantly less effective than flecainide. None of the compounds influenced the physiologically relevant luminal to cytosol cation flux through RyR2 channels. Intracellular flecainide or QX-FL, but not NU-FL, reduced Ca(2) (+) spark frequency. CONCLUSIONS AND IMPLICATIONS Given its inability to block physiologically relevant cation flux through RyR2 channels, and its lack of efficacy in blocking the cytosolic-to-luminal current, the effect of QX-FL on Ca(2) (+) sparks is likely, by analogy with flecainide, to result from Na(+) channel block. Our data reveal important differences in the interaction of flecainide with sites in the cytosolic vestibules of Na(+) and RyR2 channels.
Collapse
Affiliation(s)
- Mark L Bannister
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| | - Anita Alvarez-Laviada
- Myocardial Function Section, National Heart and Lung Institute, Imperial College London, London, UK
| | - N Lowri Thomas
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| | - Sammy A Mason
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| | - Sharon Coleman
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| | - Christo L du Plessis
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton, UK
| | - Abbygail T Moran
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton, UK
| | - David Neill-Hall
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton, UK
| | - Hasnah Osman
- School of Chemical Sciences, Universiti Sains Malaysia, Penang, Malaysia
| | - Mark C Bagley
- Department of Chemistry, School of Life Sciences, University of Sussex, Brighton, UK
| | - Kenneth T MacLeod
- Myocardial Function Section, National Heart and Lung Institute, Imperial College London, London, UK
| | - Christopher H George
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| | - Alan J Williams
- Wales Heart Research Institute, Cardiff University School of Medicine, Cardiff, UK
| |
Collapse
|
5
|
Padilla IMG, Burgos L. Aminoglycoside antibiotics: structure, functions and effects on in vitro plant culture and genetic transformation protocols. PLANT CELL REPORTS 2010; 29:1203-13. [PMID: 20644935 DOI: 10.1007/s00299-010-0900-2] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Revised: 07/06/2010] [Accepted: 07/06/2010] [Indexed: 05/12/2023]
Abstract
Plant transformation protocols generally involve the use of selectable marker genes for the screening of transgenic material. The bacterial gene nptII, coding for a neomycin phosphotransferase, and the hpt gene, coding for a hygromycin phosphotransferase, are frequently used. These enzymes detoxify aminoglycoside antibiotics by phosphorylation, thereby permitting cell growth in the presence of antibiotics. Nevertheless, the screening for transgenic regenerated shoots is often partial and difficult due to regeneration of escapes and chimeras. These difficulties can be caused, in part, by an incorrect assumption about the mode of action of antibiotics in bacterial and eukaryotic cells and in in vitro tissue culture. The information contained in this review could be useful to establish better selection strategies by taking into account factors such as explant complexity, transformation and selection protocols that allow better accessibility to cells of Agrobacterium and antibiotics, and faster regeneration methods that avoid collateral effects of antibiotics on recovered, putative transgenic shoots.
Collapse
Affiliation(s)
- I M G Padilla
- Grupo de Biotecnología de Frutales, Departamento de Mejora, CEBAS-CSIC, Campus Universitario de Espinardo, Apartado de correos 164, 30100, Murcia, Spain.
| | | |
Collapse
|
6
|
Vaithianathan T, Narayanan D, Asuncion-Chin MT, Jeyakumar LH, Liu J, Fleischer S, Jaggar JH, Dopico AM. Subtype identification and functional characterization of ryanodine receptors in rat cerebral artery myocytes. Am J Physiol Cell Physiol 2010; 299:C264-78. [PMID: 20445169 PMCID: PMC2928634 DOI: 10.1152/ajpcell.00318.2009] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2009] [Accepted: 05/04/2010] [Indexed: 11/22/2022]
Abstract
Ryanodine receptors (RyRs) regulate contractility in resistance-size cerebral artery smooth muscle, yet their molecular identity, subcellular location, and phenotype in this tissue remain unknown. Following rat resistance-size cerebral artery myocyte sarcoplasmic reticulum (SR) purification and incorporation into POPE-POPS-POPC (5:3:2; wt/wt) bilayers, unitary conductances of 110 +/- 8, 334 +/- 15, and 441 +/- 27 pS in symmetric 300 mM Cs(+) were usually detected. The most frequent (34/40 bilayers) conductance (334 pS) decreased to
Collapse
Affiliation(s)
- Thirumalini Vaithianathan
- Department Pharmacology, University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA
| | | | | | | | | | | | | | | |
Collapse
|
7
|
Diaz-Sylvester PL, Copello JA. Voltage-dependent modulation of cardiac ryanodine receptors (RyR2) by protamine. PLoS One 2009; 4:e8315. [PMID: 20016815 PMCID: PMC2789381 DOI: 10.1371/journal.pone.0008315] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2009] [Accepted: 11/19/2009] [Indexed: 11/18/2022] Open
Abstract
It has been reported that protamine (>10 µg/ml) blocks single skeletal RyR1 channels and inhibits RyR1-mediated Ca2+ release from sarcoplasmic reticulum microsomes. We extended these studies to cardiac RyR2 reconstituted into planar lipid bilayers. We found that protamine (0.02–20 µg/ml) added to the cytosolic surface of fully activated RyR2 affected channel activity in a voltage-dependent manner. At membrane voltage (Vm; SR lumen - cytosol) = 0 mV, protamine induced conductance transitions to several intermediate states (substates) as well as full block of RyR2. At Vm>10 mV, the substate with the highest level of conductance was predominant. Increasing Vm from 0 to +80 mV, decreased the number of transitions and residence of the channel in this substate. The drop in current amplitude (full opening to substate) had the same magnitude at 0 and +80 mV despite the ∼3-fold increase in amplitude of the full opening. This is more similar to rectification of channel conductance induced by other polycations than to the action of selective conductance modifiers (ryanoids, imperatoxin). A distinctive effect of protamine (which might be shared with polylysines and histones but not with non-peptidic polycations) is the activation of RyR2 in the presence of nanomolar cytosolic Ca2+ and millimolar Mg2+ levels. Our results suggest that RyRs would be subject to dual modulation (activation and block) by polycationic domains of neighboring proteins via electrostatic interactions. Understanding these interactions could be important as such anomalies may be associated with the increased RyR2-mediated Ca2+ leak observed in cardiac diseases.
Collapse
Affiliation(s)
- Paula L. Diaz-Sylvester
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
| | - Julio A. Copello
- Department of Pharmacology, Southern Illinois University School of Medicine, Springfield, Illinois, United States of America
- * E-mail:
| |
Collapse
|
8
|
Hilliard FA, Steele DS, Laver D, Yang Z, Le Marchand SJ, Chopra N, Piston DW, Huke S, Knollmann BC. Flecainide inhibits arrhythmogenic Ca2+ waves by open state block of ryanodine receptor Ca2+ release channels and reduction of Ca2+ spark mass. J Mol Cell Cardiol 2009; 48:293-301. [PMID: 19835880 DOI: 10.1016/j.yjmcc.2009.10.005] [Citation(s) in RCA: 185] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/18/2009] [Revised: 09/09/2009] [Accepted: 10/05/2009] [Indexed: 01/11/2023]
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is linked to mutations in the cardiac ryanodine receptor (RyR2) or calsequestrin. We recently found that the drug flecainide inhibits RyR2 channels and prevents CPVT in mice and humans. Here we compared the effects of flecainide and tetracaine, a known RyR2 inhibitor ineffective in CPVT myocytes, on arrhythmogenic Ca(2+) waves and elementary sarcoplasmic reticulum (SR) Ca(2+) release events, Ca(2+) sparks. In ventricular myocytes isolated from a CPVT mouse model, flecainide significantly reduced spark amplitude and spark width, resulting in a 40% reduction in spark mass. Surprisingly, flecainide significantly increased spark frequency. As a result, flecainide had no significant effect on spark-mediated SR Ca(2+) leak or SR Ca(2+) content. In contrast, tetracaine decreased spark frequency and spark-mediated SR Ca(2+) leak, resulting in a significantly increased SR Ca(2+) content. Measurements in permeabilized rat ventricular myocytes confirmed the different effects of flecainide and tetracaine on spark frequency and Ca(2+) waves. In lipid bilayers, flecainide inhibited RyR2 channels by open state block, whereas tetracaine primarily prolonged RyR2 closed times. The differential effects of flecainide and tetracaine on sparks and RyR2 gating can explain why flecainide, unlike tetracaine, does not change the balance of SR Ca(2+) fluxes. We suggest that the smaller spark mass contributes to flecainide's antiarrhythmic action by reducing the probability of saltatory wave propagation between adjacent Ca(2+) release units. Our results indicate that inhibition of the RyR2 open state provides a new therapeutic strategy to prevent diastolic Ca(2+) waves resulting in triggered arrhythmias, such as CPVT.
Collapse
Affiliation(s)
- Fredrick A Hilliard
- Division of Clinical Pharmacology, Oates Institute for Experimental Therapeutics, Vanderbilt University School of Medicine, Nashville, TN 37232-0575, USA
| | | | | | | | | | | | | | | | | |
Collapse
|
9
|
Mead-Savery FC, Wang R, Tanna-Topan B, Chen SRW, Welch W, Williams AJ. Changes in negative charge at the luminal mouth of the pore alter ion handling and gating in the cardiac ryanodine-receptor. Biophys J 2009; 96:1374-87. [PMID: 19217855 DOI: 10.1016/j.bpj.2008.10.054] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2007] [Accepted: 10/28/2008] [Indexed: 12/20/2022] Open
Abstract
We have tested the hypothesis that a high density of negative charge at the luminal mouth of the RyR2 pore plays a pivotal role in the high cation conductance and limited selectivity observed in this channel by introducing into each monomer a double point mutation to neutralize acidic residues in this region of the mouse RyR2 channel. The resultant channel, ED4832AA, is capable of functioning as a calcium-release channel in situ. Consistent with our hypothesis, the ED4832AA mutation altered the ion handling characteristics of single RyR2 channels. The mutant channel retains the ability to discriminate between cations and anions but cation conductance is altered significantly. Unitary K+ conductance is reduced at low levels of activity but increases dramatically as activity is raised and shows little sign of saturation. ED4832AA no longer discriminates between divalent and monovalent cations. In addition, the gating characteristics of single RyR2 channels are altered markedly by residue neutralization. Open probability in the ED4832AA channel is substantially higher than that of the wild-type channel. Moreover, at holding potentials in excess of +/-50 mV several subconductance states become apparent in ED4832AA and are more prevalent at very high holding potentials. These observations are discussed within the structural framework provided by a previously developed model of the RyR2 pore. Our data indicates that neutralization of acidic residues in the luminal mouth of the pore produces wide-ranging changes in the electric field in the pore, the interaction energies of permeant ions in the pore and the stability of the selectivity filter region of the pore, which together contribute to the observed changes ion handling and gating.
Collapse
Affiliation(s)
- Fiona C Mead-Savery
- Cardiac Medicine, National Heart and Lung Institute, Faculty of Medicine, Imperial College London, London SW3 6LY, United Kingdom
| | | | | | | | | | | |
Collapse
|
10
|
Wang X, Jia S, Currall B, Yang S, He DZ. Streptomycin and gentamicin have no immediate effect on outer hair cell electromotility. Hear Res 2007; 234:52-8. [DOI: 10.1016/j.heares.2007.09.001] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/13/2007] [Revised: 08/02/2007] [Accepted: 09/14/2007] [Indexed: 10/22/2022]
|
11
|
Laver DR, Hamada T, Fessenden JD, Ikemoto N. The ryanodine receptor pore blocker neomycin also inhibits channel activity via a previously undescribed high-affinity Ca(2+) binding site. J Membr Biol 2007; 220:11-20. [PMID: 17879109 DOI: 10.1007/s00232-007-9067-3] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2006] [Accepted: 07/21/2007] [Indexed: 10/22/2022]
Abstract
In this study, we present evidence for the mechanism of neomycin inhibition of skeletal ryanodine receptors (RyRs). In single-channel recordings, neomycin produced monophasic inhibition of RyR open probability and biphasic inhibition of [(3)H]ryanodine binding. The half-maximal inhibitory concentration (IC(50)) for channel blockade by neomycin was dependent on membrane potential and cytoplasmic [Ca(2+)], suggesting that neomycin acts both as a pore plug and as a competitive antagonist at a cytoplasmic Ca(2+) binding site that causes allosteric inhibition. This novel Ca(2+)/neomycin binding site had a neomycin affinity of 100 nM: and a Ca(2+) affinity of 35 nM,: which is 30-fold higher than that of the well-described cytoplasmic Ca(2+) activation site. Therefore, a new high-affinity class of Ca(2+) binding site(s) on the RyR exists that mediates neomycin inhibition. Neomycin plugging of the channel pore induced brief (1-2 ms) conductance substates at 30% of the fully open conductance, whereas allosteric inhibition caused complete channel closure with durations that depended on the neomycin concentration. We quantitatively account for these results using a dual inhibition model for neomycin that incorporates voltage-dependent pore plugging and Ca(2+)-dependent allosteric inhibition.
Collapse
Affiliation(s)
- Derek R Laver
- School of Biomedical Sciences, University of Newcastle and Hunter Medical Research Institute, Callaghan, NSW 2308, Australia.
| | | | | | | |
Collapse
|
12
|
Scholz-Starke J, Carpaneto A, Gambale F. On the interaction of neomycin with the slow vacuolar channel of Arabidopsis thaliana. ACTA ACUST UNITED AC 2006; 127:329-40. [PMID: 16505151 PMCID: PMC2151498 DOI: 10.1085/jgp.200509402] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
This study investigates the interaction of the aminoglycoside antibiotic neomycin with the slow vacuolar (SV) channel in vacuoles from Arabidopsis thaliana mesophyll cells. Patch-clamp experiments in the excised patch configuration revealed a complex pattern of neomycin effects on the channel: applied at concentrations in the submicromolar to millimolar range neomycin (a) blocked macroscopic SV currents in a voltage- and concentration-dependent manner, (b) slowed down activation and deactivation kinetics of the channel, and most interestingly, (c) at concentrations above 10 μM, neomycin shifted the SV activation threshold towards negative membrane potentials, causing a two-phasic activation at high concentrations. Single channel experiments showed that neomycin causes these macroscopic effects by combining a decrease of the single channel conductance with a concomitant increase of the channel's open probability. Our results clearly demonstrate that the SV channel can be activated at physiologically relevant tonoplast potentials in the presence of an organic effector molecule. We therefore propose the existence of a cellular equivalent regulating the activity of the SV channel in vivo.
Collapse
|
13
|
Pugh N, Mead-Savery FC, Coadwell WJ, Rossi D, Sorrentino V, Williams AJ. Probing luminal negative charge in the type 3 ryanodine receptor. Biochem Biophys Res Commun 2005; 337:1072-9. [PMID: 16225847 DOI: 10.1016/j.bbrc.2005.09.163] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2005] [Accepted: 09/26/2005] [Indexed: 11/25/2022]
Abstract
In this study, we have investigated block of potassium (K(+)) current by neomycin, a large polycation, from the luminal face of the type 3 ryanodine receptor (RyR3). Previous studies have shown that neomycin is an open channel blocker of RyR2 that interacts with negatively charged residues in the mouth of the conduction pathway to partially occlude it. In the current study, we have used neomycin as a probe to investigate proposed negatively charged regions in the luminal pore mouth of RyR3. Luminal neomycin induces concentration- and voltage-dependent partial block to a subconductance state in RyR3. Blocking parameters calculated in this study show that neomycin has a higher affinity for RyR3 than RyR2, but block may occur at the same site within the pore mouth. The change in affinity may be due to altered negative charge density at the site of interaction.
Collapse
Affiliation(s)
- Nicholas Pugh
- The Laboratory of Functional Immunogenetics, The Babraham Institute, Cambridge CB2 4AT, UK
| | | | | | | | | | | |
Collapse
|
14
|
Xu L, Wang Y, Gillespie D, Meissner G. Two rings of negative charges in the cytosolic vestibule of type-1 ryanodine receptor modulate ion fluxes. Biophys J 2005; 90:443-53. [PMID: 16239337 PMCID: PMC1367051 DOI: 10.1529/biophysj.105.072538] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The tetrameric ryanodine receptor calcium release channels (RyRs) are cation-selective channels that have pore architecture similar to that of K+ channels. We recently identified, in close proximity to the selectivity filter motif GGGIG, a conserved lumenal DE motif that has a critical role in RyR ion permeation and selectivity. Here, we substituted three aspartate residues (D4938, D4945, D4953) with asparagine and four glutamate residues (E4942, E4948, E4952, E4955) with glutamine hypothesized to line the cytosolic vestibule of the skeletal muscle RyR (RyR1). Mutant single channel properties were determined using the planar lipid bilayer method. Two mutants (D4938N, D4945N) showed a reduced K+ ion conductance, with D4938N also exhibiting a reduced selectivity for Ca2+ compared to K+. The cytosolic location of D4938 and D4945 was confirmed using the polycation neomycin. Both D4938N and D4945N exhibited an attenuated block by neomycin to a greater extent from the cytosolic than lumenal side. By comparison, charge neutralization of lumenal loop residues (D4899Q, E4900N) eliminated the block from the lumenal but not the cytosolic side. The results suggest that, in addition to negatively charged residues on the lumenal side, rings of four negative charges formed by D4938 and D4945 in the cytosolic vestibule determine RyR ion fluxes.
Collapse
Affiliation(s)
- Le Xu
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599, USA
| | | | | | | |
Collapse
|