The Croonian Lecture, 1983 - Voltage-gated ion channels in the nerve membrane

1983 ◽  
Vol 220 (1218) ◽  
pp. 1-30 ◽  
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Molecular Mechanisms ◽  
Essential Feature ◽  
Ionic Currents ◽  
Fluctuation Analysis ◽  
Gating Current ◽  
Nervous Impulse ◽  
Voltage Gated Ion Channels ◽  
Kinetics Of

In the Croonian Lecture for 1957, Sir Alan Hodgkin described the role of the channels selective for sodium and potassium ions in the conduction of the nervous impulse. An essential feature of these channels is the manner in which the complex kinetics of their opening and closing is controlled by the electric field across the membrane, and the purpose of the present lecture is to consider the advances that have been made in the past 25 years towards an understanding of the underlying molecular mechanisms. One such advance has been the successful recording, independently of the ionic currents, of the small asymmetry current known as the gating current, that accompanies the conformational changes that take place in the sodium channels. A quantitative analysis of the characteristics of the gating current suggests that activation is brought about by two more or less independent processes operating in parallel, to one of which the slower mechanism of inactivation is coupled sequentially. However, it is clear that a complete picture of the gating system will only be arrived at by combining evidence of this kind with that provided by other new lines of approach such as studies of single ion channels in various tissues by means of fluctuation analysis and the patch-clamping technique, and a reinvestigation of the kinetics of activation of the potassium channels.

scholarly journals Intermediate state trapping of a voltage sensor

2012 ◽  
Vol 140 (6) ◽  
pp. 635-652 ◽  
Author(s):  
Jérôme J. Lacroix ◽  
Stephan A. Pless ◽  
Luca Maragliano ◽  
Fabiana V. Campos ◽  
Jason D. Galpin ◽  
...  
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Intermediate State ◽  
Molecular Mechanisms ◽  
Voltage Sensor ◽  
Functional Coupling ◽  
Kv Channel ◽  
New Information ◽  
Helical Turn ◽  
Voltage Gated Ion Channels

Voltage sensor domains (VSDs) regulate ion channels and enzymes by undergoing conformational changes depending on membrane electrical signals. The molecular mechanisms underlying the VSD transitions are not fully understood. Here, we show that some mutations of I241 in the S1 segment of the Shaker Kv channel positively shift the voltage dependence of the VSD movement and alter the functional coupling between VSD and pore domains. Among the I241 mutants, I241W immobilized the VSD movement during activation and deactivation, approximately halfway between the resting and active states, and drastically shifted the voltage activation of the ionic conductance. This phenotype, which is consistent with a stabilization of an intermediate VSD conformation by the I241W mutation, was diminished by the charge-conserving R2K mutation but not by the charge-neutralizing R2Q mutation. Interestingly, most of these effects were reproduced by the F244W mutation located one helical turn above I241. Electrophysiology recordings using nonnatural indole derivatives ruled out the involvement of cation-Π interactions for the effects of the Trp inserted at positions I241 and F244 on the channel’s conductance, but showed that the indole nitrogen was important for the I241W phenotype. Insight into the molecular mechanisms responsible for the stabilization of the intermediate state were investigated by creating in silico the mutations I241W, I241W/R2K, and F244W in intermediate conformations obtained from a computational VSD transition pathway determined using the string method. The experimental results and computational analysis suggest that the phenotype of I241W may originate in the formation of a hydrogen bond between the indole nitrogen atom and the backbone carbonyl of R2. This work provides new information on intermediate states in voltage-gated ion channels with an approach that produces minimum chemical perturbation.

The kinetics of voltage-gated ion channels

1994 ◽  
Vol 27 (4) ◽  
pp. 339-434 ◽  
Author(s):  
R. D. Keynes
Keyword(s):  
Ion Channels ◽  
Ionic Currents ◽  
Giant Axon ◽  
General Information ◽  
Squid Giant Axon ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Kinetics Of ◽  
Electrical Data ◽  
Gated Ion Channels

When Hodgkin & Huxley (1952) first embarked on the analysis of their voltageclamp data on the ionic currents in the squid giant axon, they hoped to be able to deduce a mechanism from it, but it soon became clear that the electrical data would by themselves yield only very general information about the class of system likely to be involved.

scholarly journals Emergence of ion channel modal gating from independent subunit kinetics

2016 ◽  
Vol 113 (36) ◽  
pp. E5288-E5297 ◽  
Author(s):  
Brendan A. Bicknell ◽  
Geoffrey J. Goodhill
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Ionic Currents ◽  
Analytical Framework ◽  
Stochastic Simulations ◽  
Coarse Grained ◽  
Wide Range ◽  
Intracellular Ca ◽  
Modal Gating ◽  
Kinetics Of

Many ion channels exhibit a slow stochastic switching between distinct modes of gating activity. This feature of channel behavior has pronounced implications for the dynamics of ionic currents and the signaling pathways that they regulate. A canonical example is the inositol 1,4,5-trisphosphate receptor (IP3R) channel, whose regulation of intracellular Ca2+ concentration is essential for numerous cellular processes. However, the underlying biophysical mechanisms that give rise to modal gating in this and most other channels remain unknown. Although ion channels are composed of protein subunits, previous mathematical models of modal gating are coarse grained at the level of whole-channel states, limiting further dialogue between theory and experiment. Here we propose an origin for modal gating, by modeling the kinetics of ligand binding and conformational change in the IP3R at the subunit level. We find good agreement with experimental data over a wide range of ligand concentrations, accounting for equilibrium channel properties, transient responses to changing ligand conditions, and modal gating statistics. We show how this can be understood within a simple analytical framework and confirm our results with stochastic simulations. The model assumes that channel subunits are independent, demonstrating that cooperative binding or concerted conformational changes are not required for modal gating. Moreover, the model embodies a generally applicable principle: If a timescale separation exists in the kinetics of individual subunits, then modal gating can arise as an emergent property of channel behavior.

scholarly journals Gating currents

2018 ◽  
Vol 150 (7) ◽  
pp. 911-932 ◽  
Author(s):  
Francisco Bezanilla
Keyword(s):  
Membrane Proteins ◽  
Conformational Changes ◽  
Structural Changes ◽  
Ionic Currents ◽  
Gating Current ◽  
Gating Currents ◽  
Basic Principles ◽  
Voltage Dependent ◽  
Voltage Gated Ion Channels ◽  
Gating Charges

Many membrane proteins sense the voltage across the membrane where they are inserted, and their function is affected by voltage changes. The voltage sensor consists of charges or dipoles that move in response to changes in the electric field, and their movement produces an electric current that has been called gating current. In the case of voltage-gated ion channels, the kinetic and steady-state properties of the gating charges provide information of conformational changes between closed states that are not visible when observing ionic currents only. In this Journal of General Physiology Milestone, the basic principles of voltage sensing and gating currents are presented, followed by a historical description of the recording of gating currents. The results of gating current recordings are then discussed in the context of structural changes in voltage-dependent membrane proteins and how these studies have provided new insights on gating mechanisms.

scholarly journals Mechanistic insights from resolving ligand-dependent kinetics of conformational changes at ATP-gated P2X1R ion channels

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
Alistair G. Fryatt ◽  
Sudad Dayl ◽  
Paul M. Cullis ◽  
Ralf Schmid ◽  
Richard J. Evans
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Kinetics Of

scholarly journals The intrinsic instability of the hydrolase domain of lipoprotein lipase facilitates its inactivation by ANGPTL4-catalyzed unfolding

2021 ◽  
Vol 118 (12) ◽  
pp. e2026650118
Author(s):  
Katrine Z. Leth-Espensen ◽  
Kristian K. Kristensen ◽  
Anni Kumari ◽  
Anne-Marie L. Winther ◽  
Stephen G. Young ◽  
...  
Keyword(s):  
Lipoprotein Lipase ◽  
Conformational Changes ◽  
Molecular Mechanisms ◽  
Exchange Mass Spectrometry ◽  
Hydrogen Deuterium ◽  
Irreversible Unfolding ◽  
Deuterium Exchange Mass Spectrometry ◽  
Endothelial Receptor ◽  
Kinetics Of ◽  
Thermal Stability Of

The complex between lipoprotein lipase (LPL) and its endothelial receptor (GPIHBP1) is responsible for the lipolytic processing of triglyceride-rich lipoproteins (TRLs) along the capillary lumen, a physiologic process that releases lipid nutrients for vital organs such as heart and skeletal muscle. LPL activity is regulated in a tissue-specific manner by endogenous inhibitors (angiopoietin-like [ANGPTL] proteins 3, 4, and 8), but the molecular mechanisms are incompletely understood. ANGPTL4 catalyzes the inactivation of LPL monomers by triggering the irreversible unfolding of LPL’s α/β-hydrolase domain. Here, we show that this unfolding is initiated by the binding of ANGPTL4 to sequences near LPL’s catalytic site, including β2, β3–α3, and the lid. Using pulse-labeling hydrogen‒deuterium exchange mass spectrometry, we found that ANGPTL4 binding initiates conformational changes that are nucleated on β3–α3 and progress to β5 and β4–α4, ultimately leading to the irreversible unfolding of regions that form LPL’s catalytic pocket. LPL unfolding is context dependent and varies with the thermal stability of LPL’s α/β-hydrolase domain (Tm of 34.8 °C). GPIHBP1 binding dramatically increases LPL stability (Tm of 57.6 °C), while ANGPTL4 lowers the onset of LPL unfolding by ∼20 °C, both for LPL and LPL•GPIHBP1 complexes. These observations explain why the binding of GPIHBP1 to LPL retards the kinetics of ANGPTL4-mediated LPL inactivation at 37 °C but does not fully suppress inactivation. The allosteric mechanism by which ANGPTL4 catalyzes the irreversible unfolding and inactivation of LPL is an unprecedented pathway for regulating intravascular lipid metabolism.

scholarly journals Pulsed electric fields create pores in the voltage sensors of voltage-gated ion channels

2019 ◽  
Author(s):  
L. Rems ◽  
M. A. Kasimova ◽  
I. Testa ◽  
L. Delemotte
Keyword(s):  
Ion Channels ◽  
Membrane Proteins ◽  
Membrane Permeability ◽  
Electric Fields ◽  
Molecular Mechanisms ◽  
Pulsed Electric Fields ◽  
Pulse Treatment ◽  
Voltage Gated ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

AbstractPulsed electric fields are increasingly used in medicine to transiently increase the cell membrane permeability via electroporation, in order to deliver therapeutic molecules into the cell. One type of events that contributes to this increase in membrane permeability is the formation of pores in the membrane lipid bilayer. However, electrophysiological measurements suggest that membrane proteins are affected as well, particularly voltage-gated ion channels (VGICs). The molecular mechanisms by which the electric field could affects these molecules remain unidentified. In this study we used molecular dynamics (MD) simulations to unravel the molecular events that take place in different VGICs when exposing them to electric fields mimicking electroporation conditions. We show that electric fields induce pores in the voltage-sensor domains (VSDs) of different VGICs, and that these pores form more easily in some channels than in others. We demonstrate that poration is more likely in VSDs that are more hydrated and are electrostatically more favorable for the entry of ions. We further show that pores in VSDs can expand into so-called complex pores, which become stabilized by lipid head-groups. Our results suggest that such complex pores are considerably more stable than conventional lipid pores and their formation can lead to severe unfolding of VSDs from the channel. We anticipate that such VSDs become dysfunctional and unable to respond to changes in transmembrane voltage, which is in agreement with previous electrophyiological measurements showing a decrease in the voltage-dependent transmembrane ionic currents following pulse treatment. Finally, we discuss the possibility of activation of VGICs by submicrosecond-duration pulses. Overall our study reveals a new mechanism of electroporation through membranes containing voltage-gated ion channels.Statement of SignificancePulsed electric fields are often used for treatment of excitable cells, e.g., for gene delivery into skeletal muscles, ablation of the heart muscle or brain tumors. Voltage-gated ion channels (VGICs) underlie generation and propagation of action potentials in these cells, and consequently are essential for their proper function. Our study reveals the molecular mechanisms by which pulsed electric fields directly affect VGICs and addresses questions that have been previously opened by electrophysiologists. We analyze VGICs’ characteristics, which make them prone for electroporation, including hydration and electrostatic properties. This analysis is easily transferable to other membrane proteins thus opening directions for future investigations. Finally, we propose a mechanism for long-lived membrane permeability following pulse treatment, which to date remains poorly understood.

scholarly journals Cryo-EM structure of the KvAP channel reveals a non-domain-swapped voltage sensor topology

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Xiao Tao ◽  
Roderick MacKinnon
Keyword(s):  
Ion Channels ◽  
Conformational Changes ◽  
Voltage Sensor ◽  
Structural Domains ◽  
Structural Class ◽  
Voltage Sensors ◽  
Voltage Gated ◽  
Voltage Dependent ◽  
Voltage Gated Ion Channels ◽  
Gated Ion Channels

Conductance in voltage-gated ion channels is regulated by membrane voltage through structural domains known as voltage sensors. A single structural class of voltage sensor domain exists, but two different modes of voltage sensor attachment to the pore occur in nature: domain-swapped and non-domain-swapped. Since the more thoroughly studied Kv1-7, Nav and Cav channels have domain-swapped voltage sensors, much less is known about non-domain-swapped voltage-gated ion channels. In this paper, using cryo-EM, we show that KvAP from Aeropyrum pernix has non-domain-swapped voltage sensors as well as other unusual features. The new structure, together with previous functional data, suggests that KvAP and the Shaker channel, to which KvAP is most often compared, probably undergo rather different voltage-dependent conformational changes when they open.

scholarly journals Current Pharmacologic Strategies for Treatment of Intractable Epilepsy in Children

2021 ◽  
Vol 25 (Suppl 1) ◽  
pp. S8-18 ◽  
Author(s):  
Ja Un Moon ◽  
Kyung-Ok Cho
Keyword(s):  
Ion Channels ◽  
Molecular Mechanisms ◽  
Intractable Epilepsy ◽  
Epileptic Encephalopathy ◽  
New Drugs ◽  
Dravet Syndrome ◽  
Ohtahara Syndrome ◽  
Voltage Gated Ion Channels ◽  
Related Proteins ◽  
Gated Ion Channels

Epileptic encephalopathy (EE) is a devastating pediatric disease that features medically resistant seizures, which can contribute to global developmental delays. Despite technological advancements in genetics, the neurobiological mechanisms of EEs are not fully understood, leaving few therapeutic options for affected patients. In this review, we introduce the most common EEs in pediatrics (i.e., Ohtahara syndrome, Dravet syndrome, and Lennox-Gastaut syndrome) and their molecular mechanisms that cause excitation/inhibition imbalances. We then discuss some of the essential molecules that are frequently dysregulated in EEs. Specifically, we explore voltage-gated ion channels, synaptic transmission-related proteins, and ligand-gated ion channels in association with the pathophysiology of Ohtahara syndrome, Dravet syndrome, and Lennox-Gastaut syndrome. Finally, we review currently available antiepileptic drugs used to treat seizures in patients with EEs. Since these patients often fail to achieve seizure relief even with the combination therapy, further extensive research efforts to explore the involved molecular mechanisms will be required to develop new drugs for patients with intractable epilepsy.

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