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William A. Catterall - One of the best experts on this subject based on the ideXlab platform.
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structure and Function of voltage gated Sodium Channels at atomic resolution
Experimental Physiology, 2014Co-Authors: William A. CatterallAbstract:New Findings • What is the topic of this review?The central goal of the research reviewed here is to understand the Functional properties of voltage-gated Sodium Channels at the level of high-resolution structure of the Channel protein. • What advances does it highlight?The key Functional properties of voltage-gated Sodium Channels, including voltage-dependent activation. Sodium conductance and selectivity, block by local anesthetics and related drugs, and both fast and slow inactivation, are now understood at the level of protein structure with high resolution. These emerging high-resolution structural models may lead to development of safer and more efficacious drugs for treatment of epilepsy, chronic pain, and cardiac arrhythmia through structure-based drug design. Voltage-gated Sodium Channels initiate action potentials in nerve, muscle and other excitable cells. Early physiological studies described Sodium selectivity, voltage-dependent activation and fast inactivation, and developed conceptual models for Sodium Channel Function. This review article follows the topics of my 2013 Sharpey-Schafer Prize Lecture and gives an overview of research using a combination of biochemical, molecular biological, physiological and structural biological approaches that have elucidated the structure and Function of Sodium Channels at the atomic level. Structural models for voltage-dependent activation, Sodium selectivity and conductance, drug block and both fast and slow inactivation are discussed. A perspective for the future envisions new advances in understanding the structural basis for Sodium Channel Function and the opportunity for structure-based discovery of novel therapeutics.
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Structure and Function of voltage‐gated Sodium Channels at atomic resolution
Experimental physiology, 2013Co-Authors: William A. CatterallAbstract:New Findings • What is the topic of this review?The central goal of the research reviewed here is to understand the Functional properties of voltage-gated Sodium Channels at the level of high-resolution structure of the Channel protein. • What advances does it highlight?The key Functional properties of voltage-gated Sodium Channels, including voltage-dependent activation. Sodium conductance and selectivity, block by local anesthetics and related drugs, and both fast and slow inactivation, are now understood at the level of protein structure with high resolution. These emerging high-resolution structural models may lead to development of safer and more efficacious drugs for treatment of epilepsy, chronic pain, and cardiac arrhythmia through structure-based drug design. Voltage-gated Sodium Channels initiate action potentials in nerve, muscle and other excitable cells. Early physiological studies described Sodium selectivity, voltage-dependent activation and fast inactivation, and developed conceptual models for Sodium Channel Function. This review article follows the topics of my 2013 Sharpey-Schafer Prize Lecture and gives an overview of research using a combination of biochemical, molecular biological, physiological and structural biological approaches that have elucidated the structure and Function of Sodium Channels at the atomic level. Structural models for voltage-dependent activation, Sodium selectivity and conductance, drug block and both fast and slow inactivation are discussed. A perspective for the future envisions new advances in understanding the structural basis for Sodium Channel Function and the opportunity for structure-based discovery of novel therapeutics.
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Voltage-gated Sodium Channels at 60
The Journal of physiology, 2012Co-Authors: William A. CatterallAbstract:Voltage-gated Sodium Channels initiate action potentials in nerve, muscle and other excitable cells. The Sodium current that initiates the nerve action potential was discovered by Hodgkin and Huxley using the voltage clamp technique in their landmark series of papers in The Journal of Physiology in 1952. They described Sodium selectivity, voltage-dependent activation and fast inactivation, and they developed a quantitative model for action potential generation that has endured for many decades. This article gives an overview of the legacy that has evolved from their work, including development of conceptual models of Sodium Channel Function, discovery of the Sodium Channel protein, analysis of its structure and Function, determination of its structure at high resolution, definition of the mechanism and structural basis for drug block, and exploration of the role of the Sodium Channel as a target for disease mutations. Structural models for Sodium selectivity and conductance, voltage-dependent activation, fast inactivation and drug block are discussed. A perspective for the future envisions new advances in understanding the structural basis for Sodium Channel Function, the role of Sodium Channels in disease and the opportunity for discovery of novel therapeutics.
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Overview of the voltage-gated Sodium Channel family
Genome biology, 2003Co-Authors: William A. CatterallAbstract:Selective permeation of Sodium ions through voltage-dependent Sodium Channels is fundamental to the generation of action potentials in excitable cells such as neurons. These Channels are large integral membrane proteins and are encoded by at least ten genes in mammals. The different Sodium Channels have remarkably similar Functional properties, but small changes in Sodium-Channel Function are biologically relevant, as underscored by mutations that cause several human diseases of hyperexcitability.
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Detection of marine toxins using reconstituted Sodium Channels.
Journal of AOAC International, 1995Co-Authors: Vera L. Trainer, Daniel G Baden, William A. CatterallAbstract:Specific binding of the marine toxins saxitoxin, tetrodotoxin, and brevetoxin to the rat brain Sodium Channel is demonstrated using purified Sodium Channels reconstituted into phospholipid vesicles. Restoration of Sodium Channel Function and binding activity by incorporation into phospholipid vesicles provides the only rigorous proof that the purified protein contains the neurotoxin receptor sites. In addition, reconstitution provides a valuable experimental preparation for biochemical analysis of neurotoxin binding sites and may facilitate the development of a specific toxin detection system
Carol Ann Remme - One of the best experts on this subject based on the ideXlab platform.
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Heritable arrhythmia syndromes associated with abnormal cardiac Sodium Channel Function: ionic and non-ionic mechanisms.
Cardiovascular research, 2020Co-Authors: Mathilde R Rivaud, Mario Delmar, Carol Ann RemmeAbstract:The cardiac Sodium Channel NaV1.5, encoded by the SCN5A gene, is responsible for the fast upstroke of the action potential. Mutations in SCN5A may cause Sodium Channel dysFunction by decreasing peak Sodium current, which slows conduction and facilitates reentry-based arrhythmias, and by enhancing late Sodium current, which prolongs the action potential and sets the stage for early afterdepolarization and arrhythmias. Yet, some NaV1.5-related disorders, in particular structural abnormalities, cannot be directly or solely explained on the basis of defective NaV1.5 expression or biophysics. An emerging concept that may explain the large disease spectrum associated with SCN5A mutations centres around the multiFunctionality of the NaV1.5 complex. In this alternative view, alterations in NaV1.5 affect processes that are independent of its canonical ion-conducting role. We here propose a novel classification of NaV1.5 (dys)Function, categorized into (i) direct ionic effects of Sodium influx through NaV1.5 on membrane potential and consequent action potential generation, (ii) indirect ionic effects of Sodium influx on intracellular homeostasis and signalling, and (iii) non-ionic effects of NaV1.5, independent of Sodium influx, through interactions with macromolecular complexes within the different microdomains of the cardiomyocyte. These indirect ionic and non-ionic processes may, acting alone or in concert, contribute significantly to arrhythmogenesis. Hence, further exploration of these multiFunctional effects of NaV1.5 is essential for the development of novel preventive and therapeutic strategies.
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cardiac Sodium Channel dys Function and inherited arrhythmia syndromes
2018Co-Authors: Carol Ann RemmeAbstract:Normal cardiac Sodium Channel Function is essential for ensuring excitability of myocardial cells and proper conduction of the electrical impulse within the heart. Cardiac Sodium Channel dysFunction is associated with an increased risk of arrhythmias and sudden cardiac death. Over the last 20 years, (combined) genetic, electrophysiological, and molecular studies have provided insight into the (dys)Function and (dys)regulation of the cardiac Sodium Channel under physiological circumstances and in the setting of SCN5A mutations identified in patients with inherited arrhythmia syndromes. Although our understanding of these Sodium Channelopathies has increased substantially, important issues remain incompletely understood. It has become increasingly clear that Sodium Channel distribution, Function, and regulation are more complicated than traditionally assumed. Moreover, recent evidence suggests that the Sodium Channel may play additional, as of yet unrecognized, roles in cardiomyocyte Function, which in turn may ultimately also impact on arrhythmogenesis. In this chapter, an overview is provided of the structure and Function of the cardiac Sodium Channel and the clinical and biophysical characteristics of inherited Sodium Channel dysFunction. In addition, more recent insights into the electrophysiological and molecular aspects of Sodium Channel dysregulation and dysFunction in the setting of SCN5A mutations are discussed.
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Targeting Sodium Channels in cardiac arrhythmia.
Current opinion in pharmacology, 2013Co-Authors: Carol Ann Remme, Arthur A.m. WildeAbstract:Cardiac voltage-gated Sodium Channels are responsible for proper electrical conduction in the heart. During acquired pathological conditions and inherited Sodium Channelopathies, altered Sodium Channel Function causes conduction disturbances and ventricular arrhythmias. Although the clinical, genetic and biophysical characteristics of cardiac Sodium Channel disease have been extensively studied, limited progress has been made in the development of treatment strategies targeting Sodium Channels. Classical non-selective Sodium Channel blockers have only limited clinical applicability, while more selective inhibitors of the late Sodium current constitute a more promising treatment option. Because of our insufficient understanding of their complexity and subcellular diversity, other specific therapeutic targets for modulating Sodium Channels remain elusive. The current status and future potential of targeting Sodium Channels in cardiac arrhythmias are discussed.
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reduced Sodium Channel Function unmasks residual embryonic slow conduction in the adult right ventricular outflow tract
Circulation Research, 2013Co-Authors: Bastiaan J Boukens, Marc Sylva, Corrie De Gierde Vries, Carol Ann Remme, Connie R Bezzina, Vincent M Christoffels, Ruben CoronelAbstract:Rationale: In patients with Brugada syndrome, arrhythmias typically originate in the right ventricular outflow tract (RVOT). The RVOT develops from the slowly conducting embryonic outflow tract. Objective: We hypothesize that this embryonic phenotype is maintained in the fetal and adult RVOT and leads to conduction slowing, especially after Sodium current reduction. Methods and Results: We determined expression patterns in the embryonic myocardium and performed activation mapping in fetal and adult hearts, including hearts from adult mice heterozygous for a mutation associated with Brugada syndrome ( Scn5a 1798insD/+ ). The embryonic RVOT was characterized by expression of Tbx2 , a repressor of differentiation, and absence of expression of both Hey2 , a ventricular transcription factor, and Gja1 , encoding the principal gap-junction subunit for ventricular fast conduction. Also, conduction velocity was lower in the RVOT than in the right ventricular free wall. Later in the development, Gja1 and Scn5a expression remained lower in the subepicardial myocardium of the RVOT than in RV myocardium. Nevertheless, conduction velocity in the adult RVOT was similar to that of the right ventricular free wall. However, in hearts of Scn5a 1798insD/+ mice and in normal hearts treated with ajmaline, conduction was slower in the RVOT than in the right ventricular wall. Conclusions: The slowly conducting embryonic phenotype is maintained in the fetal and adult RVOT and is unmasked when cardiac Sodium Channel Function is reduced.
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review Sodium Channel dys Function and cardiac arrhythmias
Cardiovascular Therapeutics, 2010Co-Authors: Carol Ann Remme, Connie R BezzinaAbstract:SUMMARY Cardiac voltage-gated Sodium Channels are transmembrane proteins located in the cell membrane of cardiomyocytes. Influx of Sodium ions through these ion Channels is responsible for the initial fast upstroke of the cardiac action potential. This inward Sodium current thus triggers the initiation and propagation of action potentials throughout the myocardium and consequently plays a central role in excitability of myocardial cells and proper conduction of the electrical impulse within the heart. The importance of Sodium Channels for normal cardiac electrical activity is emphasized by the occurrence of potentially lethal arrhythmias in the setting of inherited and acquired Sodium Channel disease. During common pathological conditions such as myocardial ischemia and heart failure, altered Sodium Channel Function causes conduction disturbances and ventricular arrhythmias. In addition, Sodium Channel dysFunction caused by mutations in the SCN5A gene, encoding the major Sodium Channel in heart, is associated with a number of arrhythmia syndromes. Here, we provide an overview of the structure and Function of the cardiac Sodium Channel, the clinical and biophysical characteristics of inherited and acquired Sodium Channel dysFunction, and the (limited) therapeutic options for the treatment of cardiac Sodium Channel disease.
Connie R Bezzina - One of the best experts on this subject based on the ideXlab platform.
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reduced Sodium Channel Function unmasks residual embryonic slow conduction in the adult right ventricular outflow tract
Circulation Research, 2013Co-Authors: Bastiaan J Boukens, Marc Sylva, Corrie De Gierde Vries, Carol Ann Remme, Connie R Bezzina, Vincent M Christoffels, Ruben CoronelAbstract:Rationale: In patients with Brugada syndrome, arrhythmias typically originate in the right ventricular outflow tract (RVOT). The RVOT develops from the slowly conducting embryonic outflow tract. Objective: We hypothesize that this embryonic phenotype is maintained in the fetal and adult RVOT and leads to conduction slowing, especially after Sodium current reduction. Methods and Results: We determined expression patterns in the embryonic myocardium and performed activation mapping in fetal and adult hearts, including hearts from adult mice heterozygous for a mutation associated with Brugada syndrome ( Scn5a 1798insD/+ ). The embryonic RVOT was characterized by expression of Tbx2 , a repressor of differentiation, and absence of expression of both Hey2 , a ventricular transcription factor, and Gja1 , encoding the principal gap-junction subunit for ventricular fast conduction. Also, conduction velocity was lower in the RVOT than in the right ventricular free wall. Later in the development, Gja1 and Scn5a expression remained lower in the subepicardial myocardium of the RVOT than in RV myocardium. Nevertheless, conduction velocity in the adult RVOT was similar to that of the right ventricular free wall. However, in hearts of Scn5a 1798insD/+ mice and in normal hearts treated with ajmaline, conduction was slower in the RVOT than in the right ventricular wall. Conclusions: The slowly conducting embryonic phenotype is maintained in the fetal and adult RVOT and is unmasked when cardiac Sodium Channel Function is reduced.
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review Sodium Channel dys Function and cardiac arrhythmias
Cardiovascular Therapeutics, 2010Co-Authors: Carol Ann Remme, Connie R BezzinaAbstract:SUMMARY Cardiac voltage-gated Sodium Channels are transmembrane proteins located in the cell membrane of cardiomyocytes. Influx of Sodium ions through these ion Channels is responsible for the initial fast upstroke of the cardiac action potential. This inward Sodium current thus triggers the initiation and propagation of action potentials throughout the myocardium and consequently plays a central role in excitability of myocardial cells and proper conduction of the electrical impulse within the heart. The importance of Sodium Channels for normal cardiac electrical activity is emphasized by the occurrence of potentially lethal arrhythmias in the setting of inherited and acquired Sodium Channel disease. During common pathological conditions such as myocardial ischemia and heart failure, altered Sodium Channel Function causes conduction disturbances and ventricular arrhythmias. In addition, Sodium Channel dysFunction caused by mutations in the SCN5A gene, encoding the major Sodium Channel in heart, is associated with a number of arrhythmia syndromes. Here, we provide an overview of the structure and Function of the cardiac Sodium Channel, the clinical and biophysical characteristics of inherited and acquired Sodium Channel dysFunction, and the (limited) therapeutic options for the treatment of cardiac Sodium Channel disease.
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Sodium Channel dys Function and cardiac arrhythmias
Cardiovascular Therapeutics, 2010Co-Authors: Carol Ann Remme, Connie R BezzinaAbstract:Cardiac voltage-gated Sodium Channels are transmembrane proteins located in the cell membrane of cardiomyocytes. Influx of Sodium ions through these ion Channels is responsible for the initial fast upstroke of the cardiac action potential. This inward Sodium current thus triggers the initiation and propagation of action potentials throughout the myocardium and consequently plays a central role in excitability of myocardial cells and proper conduction of the electrical impulse within the heart. The importance of Sodium Channels for normal cardiac electrical activity is emphasized by the occurrence of potentially lethal arrhythmias in the setting of inherited and acquired Sodium Channel disease. During common pathological conditions such as myocardial ischemia and heart failure, altered Sodium Channel Function causes conduction disturbances and ventricular arrhythmias. In addition, Sodium Channel dysFunction caused by mutations in the SCN5A gene, encoding the major Sodium Channel in heart, is associated with a number of arrhythmia syndromes. Here, we provide an overview of the structure and Function of the cardiac Sodium Channel, the clinical and biophysical characteristics of inherited and acquired Sodium Channel dysFunction, and the (limited) therapeutic options for the treatment of cardiac Sodium Channel disease.
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Genetic control of Sodium Channel Function (correction vol 57, pg 961, 2003)
Cardiovascular Research, 2003Co-Authors: Hanno L. Tan, Connie R Bezzina, Jeroen P.p. Smits, Arie O. Verkerk, Arthur A.m. WildeAbstract:In the original article Figs. 2, 3 and 4 were incorrect. The correct figures are shown on the following pages. Fig. 4 (A) Representative electrocardiogram of isolated conduction disease (40 ms/div). Note marked QRS widening and PQ interval prolongation. (B) SCN5A mutations associated with isolated conduction …
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Genetic control of Sodium Channel Function
Cardiovascular research, 2003Co-Authors: Hanno L. Tan, Connie R Bezzina, Jeroen P.p. Smits, Arie O. Verkerk, Arthur A.m. WildeAbstract:Sodium ion (Na) influx through cardiac Na Channels triggers the action potential in cells of the working myocardium and the specialized conduction system. Na Channels thus act as key molecular determinants of cardiac excitability and impulse propagation. Na Channel dysFunction may cause life-threatening arrhythmias. Here, we review the ways in which Na Channel Function can be aberrant due to genetic changes. We discuss how biophysical studies of mutant Na Channels combined with precise clinical phenotyping may improve our understanding of Na Channel Function in health and disease and may be useful as a model from which to derive improved treatment strategies for common disease.
Eric S Bennett - One of the best experts on this subject based on the ideXlab platform.
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the sialic acid component of the β1 subunit modulates voltage gated Sodium Channel Function
Journal of Biological Chemistry, 2004Co-Authors: Daniel T Johnson, Marty L Montpetit, Patrick J Stocker, Eric S BennettAbstract:Abstract Voltage-gated Sodium Channels (Nav) are responsible for initiation and propagation of nerve, skeletal muscle, and cardiac action potentials. Nav are composed of a pore-forming α subunit and often one to several modulating β subunits. Previous work showed that terminal sialic acid residues attached to α subunits affect Channel gating. Here we show that the fully sialylated β1 subunit induces a uniform, hyperpolarizing shift in steady state and kinetic gating of the cardiac and two neuronal α subunit isoforms. Under conditions of reduced sialylation, the β1-induced gating effect was eliminated. Consistent with this, mutation of β1 N-glycosylation sites abolished all effects of β1 on Channel gating. Data also suggest an interaction between the cis effect of α sialic acids and the trans effect of β1 sialic acids on Channel gating. Thus, β1 sialic acids had no effect gating on the of the heavily glycosylated skeletal muscle α subunit. However, when glycosylation of the skeletal muscle α subunit was reduced through chimeragenesis such that α sialic acids did not impact gating, β1 sialic acids caused a significant hyperpolarizing shift in Channel gating. Together, the data indicate that β1 N-linked sialic acids can modulate Nav gating through an apparent saturating electrostatic mechanism. A model is proposed in which a spectrum of differentially sialylated Nav can directly modulate Channel gating, thereby impacting cardiac, skeletal muscle, and neuronal excitability.
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The Sialic Acid Component of the β1 Subunit Modulates Voltage-gated Sodium Channel Function
The Journal of biological chemistry, 2004Co-Authors: Daniel T Johnson, Marty L Montpetit, Patrick J Stocker, Eric S BennettAbstract:Voltage-gated Sodium Channels (Nav) are responsible for initiation and propagation of nerve, skeletal muscle, and cardiac action potentials. Nav are composed of a pore-forming alpha subunit and often one to several modulating beta subunits. Previous work showed that terminal sialic acid residues attached to alpha subunits affect Channel gating. Here we show that the fully sialylated beta1 subunit induces a uniform, hyperpolarizing shift in steady state and kinetic gating of the cardiac and two neuronal alpha subunit isoforms. Under conditions of reduced sialylation, the beta1-induced gating effect was eliminated. Consistent with this, mutation of beta1 N-glycosylation sites abolished all effects of beta1 on Channel gating. Data also suggest an interaction between the cis effect of alpha sialic acids and the trans effect of beta1 sialic acids on Channel gating. Thus, beta1 sialic acids had no effect gating on the of the heavily glycosylated skeletal muscle alpha subunit. However, when glycosylation of the skeletal muscle alpha subunit was reduced through chimeragenesis such that alpha sialic acids did not impact gating, beta1 sialic acids caused a significant hyperpolarizing shift in Channel gating. Together, the data indicate that beta1 N-linked sialic acids can modulate Nav gating through an apparent saturating electrostatic mechanism. A model is proposed in which a spectrum of differentially sialylated Nav can directly modulate Channel gating, thereby impacting cardiac, skeletal muscle, and neuronal excitability.
Olaf S. Andersen - One of the best experts on this subject based on the ideXlab platform.
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Divergent effects of anesthetics on lipid bilayer properties and Sodium Channel Function
European Biophysics Journal, 2017Co-Authors: Karl F. Herold, Olaf S. Andersen, Hugh C. HemmingsAbstract:General anesthetics revolutionized medicine by allowing surgeons to perform more complex and much longer procedures. This widely used class of drugs is essential to patient care, yet their exact molecular mechanism(s) are incompletely understood. One early hypothesis over a century ago proposed that nonspecific interactions of anesthetics with the lipid bilayer lead to changes in neuronal Function via effects on membrane properties. This model was supported by the Meyer–Overton correlation between anesthetic potency and lipid solubility and despite more recent evidence for specific protein targets, in particular ion-Channels, lipid bilayer-mediated effects of anesthetics is still under debate. We therefore tested a wide range of chemically diverse general anesthetics on lipid bilayer properties using a sensitive and Functional gramicidin-based assay. None of the tested anesthetics altered lipid bilayer properties at clinically relevant concentrations. Some anesthetics did affect the bilayer, though only at high supratherapeutic concentrations, which are unlikely relevant for clinical anesthesia. These results suggest that anesthetics directly interact with membrane proteins without altering lipid bilayer properties at clinically relevant concentrations. Voltage-gated Na^+ Channels are potential anesthetic targets and various isoforms are inhibited by a wide range of volatile anesthetics. They inhibit Channel Function by reducing peak Na^+ current and shifting steady-state inactivation toward more hyperpolarized potentials. Recent advances in crystallography of prokaryotic Na^+ Channels, which are sensitive to volatile anesthetics, together with molecular dynamics simulations and electrophysiological studies will help identify potential anesthetic interaction sites within the Channel protein itself.
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Combined Stopped-Flow and Electrophysiological Experiments Suggest Direct Sodium Channel Inhibition by Model Fluorobenzene Anesthetics
Biophysical Journal, 2013Co-Authors: Karl F. Herold, Olaf S. Andersen, William A. Lee, R. Lea Sanford, Edmond I. Eger, Hugh C. HemmingsAbstract:General anesthetics are often proposed to affect membrane properties through interactions with the lipid bilayer. Though recent studies have shown that inhaled anesthetics can interact more specifically with certain membrane proteins such as ion Channels. For example, volatile anesthetics inhibit voltage-gated Sodium Channels to reduce neurotransmitter release. Fluorobenzenes (FBs), once considered for clinical use, were abandoned due to their flammability and toxicity but are still valuable model anesthetics for investigating the molecular mechanisms of anesthetics. We examined the properties of four FB compounds, 1,2-DiFB, 1,4-DiFB, 1,3,5-TriFB and HexaFB on lipid bilayer and Sodium Channel Function at equipotent clinically relevant concentrations. Effects on lipid bilayer properties were tested using a gramicidin Channel based stopped-flow fluorescence assay for lipid bilayer perturbation; effects on Sodium Channel Function were tested using whole-cell voltage-clamp electrophysiology on neuronal cells (ND7/23). The stopped-flow results showed that all four FBs minimally affected lipid bilayer properties, whereas the Sodium Channels were strongly inhibited by all four anesthetics. Inhibition of peak Sodium current was voltage-dependent as a pre-pulse to a voltage at which half the Channels were in the fast inactivated state (V1/2) revealed strong inhibition compared to a pre-pulse to a voltage at which the majority of the Channels were in the resting state (V0). The FBs produce a left-shift in the voltage of half-maximal inactivation (V1/2, also known as h∞ or availability), with 1,2-DiFB showing the greatest and HexaFB the least shift; these changes are comparable to those observed with modern inhaled anesthetics such as isoflurane. Together these results suggest that these compounds alter Sodium Channel Function through direct interactions with the Channels, though we cannot exclude that membrane effects may become involved at high, supra-pharmacological concentrations.
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Thiazolidinedione insulin sensitizers alter lipid bilayer properties and voltage-dependent Sodium Channel Function: implications for drug discovery
The Journal of general physiology, 2011Co-Authors: Radda Rusinova, Karl F. Herold, Hugh C. Hemmings, R. Lea Sanford, Denise V. Greathouse, Olaf S. AndersenAbstract:The thiazolidinediones (TZDs) are used in the treatment of diabetes mellitus type 2. Their canonical effects are mediated by activation of the peroxisome proliferator–activated receptor γ (PPARγ) transcription factor. In addition to effects mediated by gene activation, the TZDs cause acute, transcription-independent changes in various membrane transport processes, including glucose transport, and they alter the Function of a diverse group of membrane proteins, including ion Channels. The basis for these off-target effects is unknown, but the TZDs are hydrophobic/amphiphilic and adsorb to the bilayer–water interface, which will alter bilayer properties, meaning that the TZDs may alter membrane protein Function by bilayer-mediated mechanisms. We therefore explored whether the TZDs alter lipid bilayer properties sufficiently to be sensed by bilayer-spanning proteins, using gramicidin A (gA) Channels as probes. The TZDs altered bilayer elastic properties with potencies that did not correlate with their affinity for PPARγ. At concentrations where they altered gA Channel Function, they also altered the Function of voltage-dependent Sodium Channels, producing a prepulse-dependent current inhibition and hyperpolarizing shift in the steady-state inactivation curve. The shifts in the inactivation curve produced by the TZDs and other amphiphiles can be superimposed by plotting them as a Function of the changes in gA Channel lifetimes. The TZDs’ partition coefficients into lipid bilayers were measured using isothermal titration calorimetry. The most potent bilayer modifier, troglitazone, alters bilayer properties at clinically relevant free concentrations; the least potent bilayer modifiers, pioglitazone and rosiglitazone, do not. Unlike other TZDs tested, ciglitazone behaves like a hydrophobic anion and alters the gA monomer–dimer equilibrium by more than one mechanism. Our results provide a possible mechanism for some off-target effects of an important group of drugs, and underscore the importance of exploring bilayer effects of candidate drugs early in drug development.
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Thiazolidinediones Alter Lipid Bilayer Properties and Native Voltage-Gated Sodium Channel Function
Biophysical Journal, 2010Co-Authors: Radda Rusinova, Karl F. Herold, Hugh C. Hemmings, Roger E. Koeppe, Olaf S. AndersenAbstract:Thiazolidinediones (TZD) are selective peroxizome-proliferator receptor gamma (PPARγ) agonists that are used to treat hyperglycemia in type 2 diabetes. In addition to their hypoglycemic actions they have anti-inflammatory, anti-atherosclerotic and cardiovascular effects, but PPARγ activation does not account for all their actions. Three TZDs - troglitazone (Resulin), rosiglitazone (Avandia), and pioglitazone (Actos) - have been marketed; troglitazone was subsequently withdrawn due to hepatotoxicity and a precursor TZD - ciglitazone- was discontinued after phase II trials. TZDs, with troglitazone being the most potent, modulate L-type calcium and delayed-rectifier potassium Channels by a seemingly PPARγ-independent mechanism. This could result from the adsorption of the amphiphilic TZDs to the membrane/solution interface, which can alter bilayer properties such as thickness, intrinsic curvature and the elastic moduli, and thus membrane protein Function. We therefore examined whether TZDs alter lipid bilayer properties. We exploited the sensitivity of gramicidin Channels to changes in bilayer properties to test for TZD-induced bilayer effects. TZDs alter gramicidin Channel Function and shift the monomer-dimer equilibrium toward the conducting dimers. Using gramicidin Channels of different lengths we find that the TZD effects do not vary with changes in hydrophobic mismatch. Increasing bilayer stiffness with cholesterol amplifies the TZD-mediated changes in gramicidin Channel Function. Based on the concentrations at which we observe changes in gramicidin lifetime and appearance frequency, the potency is troglitazone>rosiglitazone>ciglitazone>pioglitazone, consistent with their effects on native membrane proteins. We examined the TZDs effects in native membranes using neuronal voltage-gated Sodium Channels (NaV) using whole-cell recordings. All TZDs caused a negative shift in the voltage-dependence of inactivation at concentrations similar to those that alter gramicidin Channel Function. Our results show that TZDs affect bulk membrane properties at concentrations that modulate native ion Channels.