Site and Mechanism of Action of Resin Acids on Voltage-Gated Ion Channels
Site and Mechanism of Action of Resin Acids on Voltage-Gated Ion Channels

Author: Malin Silverå Ejneby

Publisher: Linköping University Electronic Press

Published: 2018-05-15

Total Pages: 58

ISBN-13: 9176853187

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Voltage-gated ion channels are pore-forming membrane proteins that open or close their gates when the voltage across the membrane is changed. They underlie the electrical activity that enables the heart to pump blood and the brain to receive and send signals. Changes in expression, distribution, and functional properties of voltage-gated ion channels can lead to diseases, such as epilepsy, cardiac arrhythmia, and pain-related disorders. Drugs that modulate the function of voltage-gated ion channels control these diseases in some patients, but the existing drugs do not adequately help all patients, and some also have severe side effects. Resin acids are common components of pine resins, with a hydrophobic three-ringed motif and a negatively charged carboxyl group. They open big-conductance Ca2+-activated K+ (BK) channels and voltage-gated potassium (KV) channels. We aimed to characterize the binding site and mechanism of action of resin acids on a KV channel and explore the effect of a resin acid by modifying the position and valence of charge of the carboxyl group. We tested the effect on several voltage-gated ion channels, including two KV channels expressed in Xenopus laevis oocytes and several voltage-gated ion channels expressed in cardiomyocytes. For this endeavour different electrophysiological techniques, ion channels, and cell types were used together with chemical synthesis of about 140 resin-acid derivatives, mathematical models, and computer simulations. We found that resin acids bind between the lipid bilayer and the Shaker KV channel, in the cleft between transmembrane segment S3 and S4, on the extracellular side of the voltage-sensor domain. This is a fundamentally new interaction site for small-molecule compounds that otherwise usually bind to ion channels in pockets surrounded by water. We also showed that the resin acids open the Shaker KV channel via an electrostatic mechanism, exerted on the positively charged voltage sensor S4. The effect of a resin acid increased when the negatively charged carboxyl group (the effector) and the hydrophobic three-ringed motif (anchor in lipid bilayer) were separated by three atoms: longer stalks decreased the effect. The length rule, in combination with modifications of the anchor, was used to design new resin-acid derivatives that open the human M-type (Kv7.2/7.3) channel. A naturally occurring resin acid also reduced the excitability of cardiomyocytes by affecting the voltage-dependence of several voltage-gated ion channels. The major finding was that the resin acid inactivated sodium and calcium channels, while it activated KV channels at more negative membrane voltages. Computer simulations confirmed that the combined effect on different ion channels reduced the excitability of a cardiomyocyte. Finally, the resin acid reversed induced arrhythmic firing of the cardiomyocytes. In conclusion, resin acids are potential drug candidates for diseases such as epilepsy and cardiac arrhythmia: knowing the binding site and mechanism of action can help to fine tune the resin acid to increase the effect, as well as the selectivity.

Molecular Mechanisms of Resin Acids and Their Derivatives on the Opening of a Potassium Channel
Molecular Mechanisms of Resin Acids and Their Derivatives on the Opening of a Potassium Channel

Author: Nina Ottosson

Publisher: Linköping University Electronic Press

Published: 2017-04-20

Total Pages: 66

ISBN-13: 917685521X

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Voltage-gated ion channels play fundamental roles in excitable cells, such as neurons, where they enable electric signaling. Normally, this signaling is well controlled, but brain damage, alterations in the ionic composition of the extracellular solution, or dysfunctional ion channels can increase the electrical excitability thereby causing epilepsy. Voltage-gated ion channels are obvious targets for antiepileptic drugs, and, as a rule of thumb, excitability is dampened either by closing voltagegated sodium channels (Nav channels) or by opening voltage-gated potassium channels (Kv channels). For example, several classical antiepileptic drugs block the ion-conducting pore of Nav channels. Despite the large number of existing antiepileptic drugs, one third of the patients with epilepsy suffer from intractable or pharmacoresistant seizures. Our research group has earlier described how different polyunsaturated fatty acids (PUFAs) open a Kv channel by binding close to the voltage sensor and, from this position, electrostatically facilitate the movement of the voltage-sensor, thereby opening the channel. However, PUFAs affect a wide range of ion channels, making it difficult to use them as pharmaceutical drugs; it would be desirable to find smallmolecule compounds with an electrostatic, PUFA-like mechanism of action. The aim of the research leading to this thesis was to find, characterize, and refine drug candidates capable of electrostatically opening a Kv channel. The majority of the experiments were performed on the cloned Shaker Kv channel, expressed in oocytes from the frog Xenopus laevis, and the channel activity was explored with the two-electrode voltage-clamp technique. By systematically mutating the extracellular end of the channel’s voltage sensor, we constructed a highly PUFAsensitive channel, called the 3R channel. Such a channel is a useful tool in the search for electrostatic Kv-channel openers. We found that resin acids, naturally occurring in tree resins, act as electrostatic Shaker Kv channel openers. To explore the structure-activity relationship in detail, we synthesized 120 derivatives, whereof several were potent Shaker Kv channel openers. We mapped a common resin acidbinding site to a pocket formed by the voltage sensor, the channel’s third transmembrane segment, and the lipid membrane, a principally new binding site for small-molecule compounds. Further experiments showed that there are specific interactions between the compounds and the channel, suggesting promises for further drug development. Several of the most potent Shaker Kv channel openers also dampened the excitability in dorsal-root-ganglion neurons from mice, elucidating the pharmacological potency of these compounds. In conclusion, we have found that resin-acid derivatives are robust Kv-channel openers and potential drug candidates against diseases caused by hyperexcitability, such as epilepsy.

Endogenous and Exogenous Molecules Modulating Voltage-Gated Potassium Channels
Endogenous and Exogenous Molecules Modulating Voltage-Gated Potassium Channels

Author: Damon Frampton

Publisher: Linköping University Electronic Press

Published: 2024-10-02

Total Pages: 148

ISBN-13: 9180757529

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The superfamily of voltage-gated potassium (KV) channels is crucial for the normal function of several tissues and represents an attractive pharmacological target for treating disorders such as epilepsy and cardiac arrhythmias. However, any drug designed to target a KV channel must be capable of discriminating between different members within the superfamily, lest they plague the user with deleterious side effects. Such rational design requires structural and functional insight into how the selectivity of a molecule can be tailored to suit the intended target. This thesis combines the use of electrophysiological and computational techniques to investigate the molecular basis for how the function of hKV7 and hERG channels can be modulated by different lipophilic compounds with known or suspected effects on ion channels. These include polyunsaturated fatty acids (PUFAs), cannabidiol (CBD), and synthetic cannabinoid receptor agonists (SCRAs). Using the two-electrode voltage clamp technique on Xenopus oocytes, we find that both PUFAs and CBD modulate the function of hKV7 channels in subtype-specific manners. PUFAs facilitated the activation of hKV7 channels, except for hKV7.4 channels which were instead inhibited. Molecular dynamics simulations revealed that structural differences in the voltage-sensing domain of hKV7.4 conferred a unique, inhibitory PUFA interaction site absent in the other hKV7 subtypes. Once this site was neutralised by mutagenesis, PUFAs facilitated hKV7.4 activation. In the case of CBD, we observed three different responses: inhibition of channels with hKV7.1 subunits, potentiated voltage-sensitivity of channels with hKV7.2 or hKV7.3 subunits and enhanced maximum conductance of channels with hKV7.4 or hKV7.5 subunits. However, these responses were evoked from the same interaction site in the pore domain, indicating a more complex subtype-specific mechanism of action. Finally, using an automated patch-clamp system we screened 36 different SCRAs on the cardiac channels responsible for repolarisation: hERG and hKV7.1/KCNE1. We find 28 of the SCRAs to be inhibitors of hERG and 22 to be inhibitors of hKV7.1/KCNE1. Molecular dynamics simulations suggest the increased susceptibility of hERG to SCRA-mediated inhibition may be due to a unique central cavity site that is absent from the pore domain of hKV7.1/KCNE1. In conclusion, structurally diverse lipophilic molecules of endogenous and exogenous origins can interact with KV channels and influence their function by enhancing or interfering with functional domains. In some instances, structural differences in the channel protein can explain the discrepancies in pharmacology. These findings have implications for both pharmacology (informing rational drug design) and toxicology (identifying targets through which adverse effects may occur).

Principles and Practice of Phytotherapy
Principles and Practice of Phytotherapy

Author: Kerry Bone

Publisher: Elsevier Health Sciences

Published: 2013-01-08

Total Pages: 1076

ISBN-13: 0702052973

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The authoritative and comprehensive modern textbook on western herbal medicine - now in its second edition This long-awaited second edition of Principles and Practice of Phytotherapy covers all major aspects of herbal medicine from fundamental concepts, traditional use and scientific research through to safety, effective dosage and clinical applications. Written by herbal practitioners with active experience in clinical practice, education, manufacturing and research, the textbook is both practical and evidence based. The focus, always, is on the importance of tailoring the treatment to the individual case. New insights are given into the herbal management of approxiately 100 modern ailments, including some of the most challenging medical conditions, such as asthma, inflammatory bowel disease and other complex autoimmune and inflammatory conditions, and there is vibrant discussion around the contribution of phytotherapy in general to modern health issues, including health ageing. Fully referenced throughout, with more than 10, 000 citations, the book is a core resource for students and practitioners of phytotherapy and naturopathy and will be of value to all healthcare professionals - pharmacists, doctors, nurses - with an interest in herbal therapeutics. 50 evidence-based monographs, including 7 new herbs Rational guidance to phytotherapeutic strategies in the consulting room New appendices provide useful information on topics such as herbal actions, dosage in children and reading and interpreting herbal clinical trials Comprehensive revision of vital safety data, including an extensive herb-drug interaction chart. 50 evidence-based monographs, including 7 new herbs Rational guidance to phytotherapeutic strategies in the consulting room New appendices provide useful information on topics such as herbal actions, dosage in children and reading and interpreting herbal clinical trials Comprehensive revision of vital safety data, including an extensive herb-drug interaction chart.

Index Medicus
Index Medicus

Author:

Publisher:

Published: 2004

Total Pages: 1666

ISBN-13:

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Vols. for 1963- include as pt. 2 of the Jan. issue: Medical subject headings.

Piezo Channels
Piezo Channels

Author:

Publisher: Academic Press

Published: 2017-07-17

Total Pages: 350

ISBN-13: 0128096217

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Piezo Channels, Volume 79, the latest volume in the Current Topics in Membranes series provides the necessary membrane research to assist readers in discovering the current state of a particular field and future directions. New chapters in the updated volume include A Tour de Force: The Discovery, Properties, and Function of Piezo Channels, Piezo1 Channels in Vascular Development and the Sensing of Shear Stress, the Origin of the Force: The Force-From-Lipids Principle Applied to Piezo Channels, Genetic Diseases of PIEZO1 and PIEZO2 Dysfunction, and The Structural Basis for Sensing by the Piezo1 Protein. Users of this series will find an up-to-date presentation of the current knowledge in the field of Piezo Channels. - Written by leading experts in the field - Contains original material, both textual and illustrative, that make it a very relevant reference - Presented in a very comprehensive manner - Ideal reference for both researchers in the field and general readers who will find this book to be relevant and up-to-date

Voltage Gated Sodium Channels
Voltage Gated Sodium Channels

Author: Peter C. Ruben

Publisher: Springer Science & Business Media

Published: 2014-04-15

Total Pages: 328

ISBN-13: 3642415881

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A number of techniques to study ion channels have been developed since the electrical basis of excitability was first discovered. Ion channel biophysicists have at their disposal a rich and ever-growing array of instruments and reagents to explore the biophysical and structural basis of sodium channel behavior. Armed with these tools, researchers have made increasingly dramatic discoveries about sodium channels, culminating most recently in crystal structures of voltage-gated sodium channels from bacteria. These structures, along with those from other channels, give unprecedented insight into the structural basis of sodium channel function. This volume of the Handbook of Experimental Pharmacology will explore sodium channels from the perspectives of their biophysical behavior, their structure, the drugs and toxins with which they are known to interact, acquired and inherited diseases that affect sodium channels and the techniques with which their biophysical and structural properties are studied.

Biomembrane Electrochemistry
Biomembrane Electrochemistry

Author: Martin Blank

Publisher:

Published: 1994

Total Pages: 628

ISBN-13:

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In October 1986, the Office of Naval Research initiated a five-year program for electrochemical research on biological and model membranes. The program explored the physical basis of biological sensory and energy-transducing processes by focusing on the electrochemical properties of integral membrane proteins (i.e., channel structures) associated with ion-transport processes. The major research areas covered were interfaces and lipid layers, channels (structure and function), and signal transduction. This volume contains papers from that program as well as some related studies. Annotation copyright by Book News, Inc., Portland, OR