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Jeong DJ, Kim KW, Suh BC. Dual regulation of Kv7.2/7.3 channels by long-chain n-alcohols. J Gen Physiol 2022; 155:213769. [PMID: 36534082 PMCID: PMC9767652 DOI: 10.1085/jgp.202213191] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2022] [Revised: 10/31/2022] [Accepted: 12/02/2022] [Indexed: 12/23/2022] Open
Abstract
Normal alcohols (n-alcohols) can induce anesthetic effects by acting on neuronal ion channels. Recent studies have revealed the effects of n-alcohols on various ion channels; however, the underlying molecular mechanisms remain unclear. Here, we provide evidence that long-chain n-alcohols have dual effects on Kv7.2/7.3 channels, resulting in channel activation as the net effect. Using heterologous expression systems, we found that n-alcohols could differentially regulate the Kv7.2/7.3 channel depending on their chain length. Treatment with short-chain ethanol and propanol diminished Kv7.2/7.3 currents, whereas treatment with long-chain hexanol and octanol enhanced the currents. However, the long-chain alcohols failed to potentiate Kv7.2 currents pre-activated by retigabine. Instead, they inhibited the currents, similar to short-chain ethanol. The stimulatory effect of the long-chain n-alcohols was also converted into an inhibitory one in the mutant Kv7.2(W236L) channels, while the inhibitory effect of ethanol did not differ between wild-type Kv7.2 and mutant Kv7.2(W236L). The inhibition of currents by n-alcohols was also seen in Kv7.1 channel which does not have the tryptophan (W) residue in S5. These findings suggest that long-chain n-alcohols exhibit dual effects through independent working sites on the Kv7.2 channel. Finally, we confirmed that the hydroxyl group with a negative electrostatic potential surface is essential for the dual actions of n-alcohol. Together, our data suggest that long-chain n-alcohols regulate Kv7.2/7.3 channels by interacting with both stimulatory and inhibitory sites and that their stimulatory action depends on the conserved tryptophan 236 residue in S5 and could be important for triggering their anesthetic effects.
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Affiliation(s)
- Da-Jeong Jeong
- Department of Brain Sciences, Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea
| | - Kwon-Woo Kim
- Department of Brain Sciences, Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea
| | - Byung-Chang Suh
- Department of Brain Sciences, Daegu Gyeongbuk Institute of Science and Technology, Daegu, Republic of Korea,Correspondence to Byung-Chang Suh:
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Speigel IA, Hemmings Jr. HC. Relevance of Cortical and Hippocampal Interneuron Functional Diversity to General Anesthetic Mechanisms: A Narrative Review. Front Synaptic Neurosci 2022; 13:812905. [PMID: 35153712 PMCID: PMC8825374 DOI: 10.3389/fnsyn.2021.812905] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2021] [Accepted: 12/30/2021] [Indexed: 01/04/2023] Open
Abstract
General anesthetics disrupt brain processes involved in consciousness by altering synaptic patterns of excitation and inhibition. In the cerebral cortex and hippocampus, GABAergic inhibition is largely mediated by inhibitory interneurons, a heterogeneous group of specialized neuronal subtypes that form characteristic microcircuits with excitatory neurons. Distinct interneuron subtypes regulate specific excitatory neuron networks during normal behavior, but how these interneuron subtypes are affected by general anesthetics is unclear. This narrative review summarizes current principles of the synaptic architecture of cortical and interneuron subtypes, their contributions to different forms of inhibition, and their roles in distinct neuronal microcircuits. The molecular and cellular targets in these circuits that are sensitive to anesthetics are reviewed in the context of how anesthetics impact interneuron function in a subtype-specific manner. The implications of this functional interneuron diversity for mechanisms of anesthesia are discussed, as are their implications for anesthetic-induced changes in neural plasticity and overall brain function.
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Affiliation(s)
- Iris A. Speigel
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, United States
- *Correspondence: Iris A. Speigel
| | - Hugh C. Hemmings Jr.
- Department of Anesthesiology, Weill Cornell Medicine, New York, NY, United States
- Department of Pharmacology, Weill Cornell Medicine, New York, NY, United States
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3
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Oakes V, Domene C. Capturing the Molecular Mechanism of Anesthetic Action by Simulation Methods. Chem Rev 2018; 119:5998-6014. [DOI: 10.1021/acs.chemrev.8b00366] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Affiliation(s)
- Victoria Oakes
- Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
| | - Carmen Domene
- Department of Chemistry, University of Bath, Claverton Down, Bath BA2 7AY, United Kingdom
- Department of Chemistry, University of Oxford, Oxford OX1 3TA, United Kingdom
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4
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Regulatory Effect of General Anesthetics on Activity of Potassium Channels. Neurosci Bull 2018; 34:887-900. [PMID: 29948841 PMCID: PMC6129254 DOI: 10.1007/s12264-018-0239-1] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2017] [Accepted: 04/12/2018] [Indexed: 12/19/2022] Open
Abstract
General anesthesia is an unconscious state induced by anesthetics for surgery. The molecular targets and cellular mechanisms of general anesthetics in the mammalian nervous system have been investigated during past decades. In recent years, K+ channels have been identified as important targets of both volatile and intravenous anesthetics. This review covers achievements that have been made both on the regulatory effect of general anesthetics on the activity of K+ channels and their underlying mechanisms. Advances in research on the modulation of K+ channels by general anesthetics are summarized and categorized according to four large K+ channel families based on their amino-acid sequence homology. In addition, research achievements on the roles of K+ channels in general anesthesia in vivo, especially with regard to studies using mice with K+ channel knockout, are particularly emphasized.
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5
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Covarrubias M, Barber AF, Carnevale V, Treptow W, Eckenhoff RG. Mechanistic Insights into the Modulation of Voltage-Gated Ion Channels by Inhalational Anesthetics. Biophys J 2016; 109:2003-11. [PMID: 26588560 DOI: 10.1016/j.bpj.2015.09.032] [Citation(s) in RCA: 38] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2015] [Revised: 08/31/2015] [Accepted: 09/30/2015] [Indexed: 12/20/2022] Open
Abstract
General anesthesia is a relatively safe medical procedure, which for nearly 170 years has allowed life saving surgical interventions in animals and people. However, the molecular mechanism of general anesthesia continues to be a matter of importance and debate. A favored hypothesis proposes that general anesthesia results from direct multisite interactions with multiple and diverse ion channels in the brain. Neurotransmitter-gated ion channels and two-pore K+ channels are key players in the mechanism of anesthesia; however, new studies have also implicated voltage-gated ion channels. Recent biophysical and structural studies of Na+ and K+ channels strongly suggest that halogenated inhalational general anesthetics interact with gates and pore regions of these ion channels to modulate function. Here, we review these studies and provide a perspective to stimulate further advances.
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Affiliation(s)
- Manuel Covarrubias
- Department of Neuroscience and Farber Institute for Neuroscience, Sidney Kimmel Medical College at Thomas Jefferson University, Philadelphia, Pennsylvania.
| | - Annika F Barber
- Department of Neuroscience, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
| | - Vincenzo Carnevale
- Institute for Computational Molecular Science, College of Science and Technology, Temple University, Philadelphia, Pennsylvania
| | - Werner Treptow
- Laboratorio de Biologia Teorica e Computacional, Universidade de Brasilia, Brazil
| | - Roderic G Eckenhoff
- Department of Anesthesiology and Critical Care, University of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania
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6
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Alkanols inhibit voltage-gated K(+) channels via a distinct gating modifying mechanism that prevents gate opening. Sci Rep 2015; 5:17402. [PMID: 26616025 PMCID: PMC4663795 DOI: 10.1038/srep17402] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 10/28/2015] [Indexed: 12/27/2022] Open
Abstract
Alkanols are small aliphatic compounds that inhibit voltage-gated K+ (Kv) channels through a yet unresolved gating mechanism. Kv channels detect changes in the membrane potential with their voltage-sensing domains (VSDs) that reorient and generate a transient gating current. Both 1-Butanol (1-BuOH) and 1-Hexanol (1-HeOH) inhibited the ionic currents of the Shaker Kv channel in a concentration dependent manner with an IC50 value of approximately 50 mM and 3 mM, respectively. Using the non-conducting Shaker-W434F mutant, we found that both alkanols immobilized approximately 10% of the gating charge and accelerated the deactivating gating currents simultaneously with ionic current inhibition. Thus, alkanols prevent the final VSD movement(s) that is associated with channel gate opening. Applying 1-BuOH and 1-HeOH to the Shaker-P475A mutant, in which the final gating transition is isolated from earlier VSD movements, strengthened that neither alkanol affected the early VSD movements. Drug competition experiments showed that alkanols do not share the binding site of 4-aminopyridine, a drug that exerts a similar effect at the gating current level. Thus, alkanols inhibit Shaker-type Kv channels via a unique gating modifying mechanism that stabilizes the channel in its non-conducting activated state.
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Positive Allosteric Modulation of Kv Channels by Sevoflurane: Insights into the Structural Basis of Inhaled Anesthetic Action. PLoS One 2015; 10:e0143363. [PMID: 26599217 PMCID: PMC4657974 DOI: 10.1371/journal.pone.0143363] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2015] [Accepted: 11/04/2015] [Indexed: 11/19/2022] Open
Abstract
Inhalational general anesthesia results from the poorly understood interactions of haloethers with multiple protein targets, which prominently includes ion channels in the nervous system. Previously, we reported that the commonly used inhaled anesthetic sevoflurane potentiates the activity of voltage-gated K+ (Kv) channels, specifically, several mammalian Kv1 channels and the Drosophila K-Shaw2 channel. Also, previous work suggested that the S4-S5 linker of K-Shaw2 plays a role in the inhibition of this Kv channel by n-alcohols and inhaled anesthetics. Here, we hypothesized that the S4-S5 linker is also a determinant of the potentiation of Kv1.2 and K-Shaw2 by sevoflurane. Following functional expression of these Kv channels in Xenopus oocytes, we found that converse mutations in Kv1.2 (G329T) and K-Shaw2 (T330G) dramatically enhance and inhibit the potentiation of the corresponding conductances by sevoflurane, respectively. Additionally, Kv1.2-G329T impairs voltage-dependent gating, which suggests that Kv1.2 modulation by sevoflurane is tied to gating in a state-dependent manner. Toward creating a minimal Kv1.2 structural model displaying the putative sevoflurane binding sites, we also found that the positive modulations of Kv1.2 and Kv1.2-G329T by sevoflurane and other general anesthetics are T1-independent. In contrast, the positive sevoflurane modulation of K-Shaw2 is T1-dependent. In silico docking and molecular dynamics-based free-energy calculations suggest that sevoflurane occupies distinct sites near the S4-S5 linker, the pore domain and around the external selectivity filter. We conclude that the positive allosteric modulation of the Kv channels by sevoflurane involves separable processes and multiple sites within regions intimately involved in channel gating.
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Chong Y, Kleinhammes A, Tang P, Xu Y, Wu Y. Dominant Alcohol-Protein Interaction via Hydration-Enabled Enthalpy-Driven Binding Mechanism. J Phys Chem B 2015; 119:5367-75. [PMID: 25856773 DOI: 10.1021/acs.jpcb.5b00378] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Water plays an important role in weak associations of small drug molecules with proteins. Intense focus has been on binding-induced structural changes in the water network surrounding protein binding sites, especially their contributions to binding thermodynamics. However, water is also tightly coupled to protein conformations and dynamics, and so far little is known about the influence of water-protein interactions on ligand binding. Alcohols are a type of low-affinity drugs, and it remains unclear how water affects alcohol-protein interactions. Here, we present alcohol adsorption isotherms under controlled protein hydration using in situ NMR detection. As functions of hydration level, Gibbs free energy, enthalpy, and entropy of binding were determined from the temperature dependence of isotherms. Two types of alcohol binding were found. The dominant type is low-affinity nonspecific binding, which is strongly dependent on temperature and the level of hydration. At low hydration levels, this nonspecific binding only occurs above a threshold of alcohol vapor pressure. An increased hydration level reduces this threshold, with it finally disappearing at a hydration level of h ≈ 0.2 (g water/g protein), gradually shifting alcohol binding from an entropy-driven to an enthalpy-driven process. Water at charged and polar groups on the protein surface was found to be particularly important in enabling this binding. Although further increase in hydration has smaller effects on the changes of binding enthalpy and entropy, it results in a significant negative change in Gibbs free energy due to unmatched enthalpy-entropy compensation. These results show the crucial role of water-protein interplay in alcohol binding.
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Affiliation(s)
- Yuan Chong
- †Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, United States
| | - Alfred Kleinhammes
- †Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, United States
| | | | | | - Yue Wu
- †Department of Physics and Astronomy, University of North Carolina, Chapel Hill, North Carolina 27599-3255, United States
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McDavid S, Bauer MB, Brindley RL, Jewell ML, Currie KPM. Butanol isomers exert distinct effects on voltage-gated calcium channel currents and thus catecholamine secretion in adrenal chromaffin cells. PLoS One 2014; 9:e109203. [PMID: 25275439 PMCID: PMC4183593 DOI: 10.1371/journal.pone.0109203] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2014] [Accepted: 09/08/2014] [Indexed: 12/20/2022] Open
Abstract
Butanol (C4H10OH) has been used both to dissect the molecular targets of alcohols/general anesthetics and to implicate phospholipase D (PLD) signaling in a variety of cellular functions including neurotransmitter and hormone exocytosis. Like other primary alcohols, 1-butanol is a substrate for PLD and thereby disrupts formation of the intracellular signaling lipid phosphatidic acid. Because secondary and tertiary butanols do not undergo this transphosphatidylation, they have been used as controls for 1-butanol to implicate PLD signaling. Recently, selective pharmacological inhibitors of PLD have been developed and, in some cases, fail to block cellular functions previously ascribed to PLD using primary alcohols. For example, exocytosis of insulin and degranulation of mast cells are blocked by primary alcohols, but not by the PLD inhibitor FIPI. In this study we show that 1-butanol reduces catecholamine secretion from adrenal chromaffin cells to a much greater extent than tert-butanol, and that the PLD inhibitor VU0155056 has no effect. Using fluorescent imaging we show the effect of these drugs on depolarization-evoked calcium entry parallel those on secretion. Patch-clamp electrophysiology confirmed the peak amplitude of voltage-gated calcium channel currents (ICa) is inhibited by 1-butanol, with little or no block by secondary or tert-butanol. Detailed comparison shows for the first time that the different butanol isomers exert distinct, and sometimes opposing, effects on the voltage-dependence and gating kinetics of ICa. We discuss these data with regard to PLD signaling in cellular physiology and the molecular targets of general anesthetics.
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Affiliation(s)
- Sarah McDavid
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Mary Beth Bauer
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Rebecca L. Brindley
- Department of Anesthesiology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Mark L. Jewell
- Department of Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
| | - Kevin P. M. Currie
- Department of Anesthesiology, Department of Pharmacology, and Vanderbilt Brain Institute, Vanderbilt University School of Medicine, Nashville, Tennessee, United States of America
- * E-mail:
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10
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Lioudyno MI, Birch AM, Tanaka BS, Sokolov Y, Goldin AL, Chandy KG, Hall JE, Alkire MT. Shaker-related potassium channels in the central medial nucleus of the thalamus are important molecular targets for arousal suppression by volatile general anesthetics. J Neurosci 2013; 33:16310-22. [PMID: 24107962 PMCID: PMC3792466 DOI: 10.1523/jneurosci.0344-13.2013] [Citation(s) in RCA: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2013] [Revised: 08/30/2013] [Accepted: 09/05/2013] [Indexed: 12/23/2022] Open
Abstract
The molecular targets and neural circuits that underlie general anesthesia are not fully elucidated. Here, we directly demonstrate that Kv1-family (Shaker-related) delayed rectifier K(+) channels in the central medial thalamic nucleus (CMT) are important targets for volatile anesthetics. The modulation of Kv1 channels by volatiles is network specific as microinfusion of ShK, a potent inhibitor of Kv1.1, Kv1.3, and Kv1.6 channels, into the CMT awakened sevoflurane-anesthetized rodents. In heterologous expression systems, sevoflurane, isoflurane, and desflurane at subsurgical concentrations potentiated delayed rectifier Kv1 channels at low depolarizing potentials. In mouse thalamic brain slices, sevoflurane inhibited firing frequency and delayed the onset of action potentials in CMT neurons, and ShK-186, a Kv1.3-selective inhibitor, prevented these effects. Our findings demonstrate the exquisite sensitivity of delayed rectifier Kv1 channels to modulation by volatile anesthetics and highlight an arousal suppressing role of Kv1 channels in CMT neurons during the process of anesthesia.
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Affiliation(s)
- Maria I. Lioudyno
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697-4561
| | - Alexandra M. Birch
- Center for the Neurobiology of Learning and Memory and Department of Anesthesiology and Perioperative Care, University of California, Irvine, Orange, California 92868, and
| | - Brian S. Tanaka
- Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California 92697-4025
| | - Yuri Sokolov
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697-4561
| | - Alan L. Goldin
- Department of Microbiology and Molecular Genetics, University of California, Irvine, Irvine, California 92697-4025
| | - K. George Chandy
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697-4561
| | - James E. Hall
- Department of Physiology and Biophysics, University of California, Irvine, Irvine, California 92697-4561
| | - Michael T. Alkire
- Center for the Neurobiology of Learning and Memory and Department of Anesthesiology and Perioperative Care, University of California, Irvine, Orange, California 92868, and
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Heler R, Bell JK, Boland LM. Homology model and targeted mutagenesis identify critical residues for arachidonic acid inhibition of Kv4 channels. Channels (Austin) 2013; 7:74-84. [PMID: 23334377 PMCID: PMC3667888 DOI: 10.4161/chan.23453] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Polyunsaturated fatty acids such as arachidonic acid (AA) exhibit inhibitory modulation of Kv4 potassium channels. Molecular docking approaches using a Kv4.2 homology model predicted a membrane-embedded binding pocket for AA comprised of the S4-S5 linker on one subunit and several hydrophobic residues within S3, S5 and S6 from an adjacent subunit. The pocket is conserved among Kv4 channels. We tested the hypothesis that modulatory effects of AA on Kv4.2/KChIP channels require access to this site. Targeted mutation of a polar residue (K318) and a nonpolar residue (G314) within the S4-S5 linker as well as a nonpolar residue in S3 (V261) significantly impaired the effects of AA on K (+) currents in Xenopus oocytes. These residues may be important in stabilizing (K318) or regulating access to (V261, G314) the negatively charged carboxylate moiety on the fatty acid. Structural specificity was supported by the lack of disruption of AA effects observed with mutations at residues located near, but not within the predicted binding pocket. Furthermore, we found that the crystal structure of the related Kv1.2/2.1 chimera lacks the structural features present in the proposed AA docking site of Kv4.2 and the Kv1.2/2.1 K (+) currents were unaffected by AA. We simulated the mutagenic substitutions in our Kv4.2 model to demonstrate how specific mutations may disrupt the putative AA binding pocket. We conclude that AA inhibits Kv4 channel currents and facilitates current decay by binding within a hydrophobic pocket in the channel in which K318 within the S4-S5 linker is a critical residue for AA interaction.
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Affiliation(s)
- Robert Heler
- Department of Biology, University of Richmond, Richmond, VA, USA
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12
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Polley A, Vemparala S. Partitioning of ethanol in multi-component membranes: Effects on membrane structure. Chem Phys Lipids 2013; 166:1-11. [DOI: 10.1016/j.chemphyslip.2012.11.005] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Revised: 11/23/2012] [Accepted: 11/24/2012] [Indexed: 12/12/2022]
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Barber AF, Liang Q, Covarrubias M. Novel activation of voltage-gated K(+) channels by sevoflurane. J Biol Chem 2012; 287:40425-32. [PMID: 23038249 DOI: 10.1074/jbc.m112.405787] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
BACKGROUND Halogenated inhaled anesthetics modulate voltage-gated ion channels by unknown mechanisms. RESULTS Biophysical analyses revealed novel activation of K(v) channels by the inhaled anesthetic sevoflurane. CONCLUSION K(v) channel activation by sevoflurane results from the positive allosteric modulation of activation gating. SIGNIFICANCE The unique activation of K(v) channels by sevoflurane demonstrates novel anesthetic specificity and offers new insights into allosteric modulation of channel gating. Voltage-gated ion channels are modulated by halogenated inhaled general anesthetics, but the underlying molecular mechanisms are not understood. Alkanols and halogenated inhaled anesthetics such as halothane and isoflurane inhibit the archetypical voltage-gated Kv3 channel homolog K-Shaw2 by stabilizing the resting/closed states. By contrast, sevoflurane, a more heavily fluorinated ether commonly used in general anesthesia, specifically activates K-Shaw2 currents at relevant concentrations (0.05-1 mM) in a rapid and reversible manner. The concentration dependence of this modulation is consistent with the presence of high and low affinity interactions (K(D) = 0.06 and 4 mM, respectively). Sevoflurane (<1 mM) induces a negative shift in the conductance-voltage relation and increases the maximum conductance. Furthermore, suggesting possible roles in general anesthesia, mammalian Kv1.2 and Kv1.5 channels display similar changes. Quantitative description of the observations by an economical allosteric model indicates that sevoflurane binding favors activation gating and eliminates an unstable inactivated state outside the activation pathway. This study casts light on the mechanism of the novel sevoflurane-dependent activation of Kv channels, which helps explain how closely related inhaled anesthetics achieve specific actions and suggests strategies to develop novel Kv channel activators.
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Affiliation(s)
- Annika F Barber
- Department of Neuroscience, Jefferson Medical College of Thomas Jefferson University, Philadelphia, PA 19107, USA
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Zhang J, Qu X, Covarrubias M, Germann MW. Insight into the modulation of Shaw2 Kv channels by general anesthetics: structural and functional studies of S4-S5 linker and S6 C-terminal peptides in micelles by NMR. BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES 2012; 1828:595-601. [PMID: 23031574 DOI: 10.1016/j.bbamem.2012.09.025] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2012] [Revised: 09/23/2012] [Accepted: 09/24/2012] [Indexed: 12/20/2022]
Abstract
The modulation of the Drosophila Shaw2 Kv channel by 1-alkanols and inhaled anesthetics is correlated with the involvement of the S4-S5 linker and C-terminus of S6, and consistent with stabilization of the channel's closed state. Structural analysis of peptides from S4-S5 (L45) and S6 (S6c), by nuclear magnetic resonance and circular dichroism spectroscopy supports that an α-helical conformation was adopted by L45, while S6c was only in an unstable/dynamic partially folded α-helix in dodecylphosphocholine micelles. Solvent accessibility and paramagnetic probing of L45 revealed that L45 lies parallel to the surface of micelles with charged and polar residues pointing towards the solution while hydrophobic residues are buried inside the micelles. Chemical shift perturbation introduced by 1-butanol on residues Gln320, Thr321, Phe322 and Arg323 of L45, as well as Thr423 and Gln424 of S6c indicates possible anesthetic binding sites on these two important components in the channel activation apparatus. Diffusion measurements confirmed the association of L45, S6c and 1-butanol with micelles which suggests the capability of 1-butanol to influence a possible interaction of L45 and S6c in the micelle environment.
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Affiliation(s)
- Jin Zhang
- Department of Chemistry, Georgia State University, Atlanta, GA 30303, USA
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15
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Molecular mapping of general anesthetic sites in a voltage-gated ion channel. Biophys J 2012; 101:1613-22. [PMID: 21961587 DOI: 10.1016/j.bpj.2011.08.026] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2011] [Revised: 08/11/2011] [Accepted: 08/15/2011] [Indexed: 12/20/2022] Open
Abstract
Several voltage-gated ion channels are modulated by clinically relevant doses of general anesthetics. However, the structural basis of this modulation is not well understood. Previous work suggested that n-alcohols and inhaled anesthetics stabilize the closed state of the Shaw2 voltage-gated (Kv) channel (K-Shaw2) by directly interacting with a discrete channel site. We hypothesize that the inhibition of K-Shaw2 channels by general anesthetics is governed by interactions between binding and effector sites involving components of the channel's activation gate. To investigate this hypothesis, we applied Ala/Val scanning mutagenesis to the S4-S5 linker and the post-PVP S6 segment, and conducted electrophysiological analysis to evaluate the energetic impact of the mutations on the inhibition of the K-Shaw2 channel by 1-butanol and halothane. These analyses identified residues that determine an apparent binding cooperativity and residue pairs that act in concert to modulate gating upon anesthetic binding. In some instances, due to their critical location, key residues also influence channel gating. Complementing these results, molecular dynamics simulations and in silico docking experiments helped us visualize possible anesthetic sites and interactions. We conclude that the inhibition of K-Shaw2 by general anesthetics results from allosteric interactions between distinct but contiguous binding and effector sites involving inter- and intrasubunit interfaces.
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