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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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Effects of ethanol and n-butanol on the fluidity of supported lipid bilayers. Chem Phys Lipids 2021; 238:105091. [PMID: 33992653 DOI: 10.1016/j.chemphyslip.2021.105091] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2021] [Revised: 05/05/2021] [Accepted: 05/11/2021] [Indexed: 11/21/2022]
Abstract
The interactions of molecules such as short-chain alcohols with the mammalian plasma membrane are thought to play a role in anesthetic effects. We have examined the concentration-dependent effects of ethanol and n-butanol on the fluidity of planar model lipid bilayer structures supported on mica. The supported model bilayer was composed of 1,2-dioleoyl-sn-phosphatidylcholine (DOPC), cholesterol, and sphingomyelin, and the bilayers were formed by vesicle fusion from extruded unilamellar vesicles (133 nm diameter, polydispersity index of 0.17). Controlled amounts of ethanol and n-butanol were added during vesicle deposition. Translational diffusion constants were obtained utilizing fluorescence recovery after photobleaching (FRAP) measurements on the micrometer scale with perylene as the fluorophore. The translational diffusion constants increased and then decreased with increasing ethanol concentration, with the bilayer structure degrading at ca. 0.8 M ethanol. A similar trend was observed for n-butanol at lower alcohol concentrations owing to greater interactions with phospholipid bilayer constituents. For n-butanol, the integrity of the planar bilayer structure deteriorated at ca. 0.4 M n-butanol. The results are consistent with bilayer interdigitation.
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Sarin H. Pressure regulated basis for gene transcription by delta-cell micro-compliance modeled in silico: Biphenyl, bisphenol and small molecule ligand models of cell contraction-expansion. PLoS One 2020; 15:e0236446. [PMID: 33021979 PMCID: PMC7537880 DOI: 10.1371/journal.pone.0236446] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2020] [Accepted: 07/06/2020] [Indexed: 12/19/2022] Open
Abstract
Molecular diameter, lipophilicity and hydrophilicity exclusion affinity limits exist for small molecule carrier-mediated diffusion or transport through channel pores or interaction with the cell surface glycocalyx. The molecular structure lipophilicity limit for non-specific carrier-mediated transmembrane diffusion through polarity-selective transport channels of the cell membrane is Lexternal structure ∙ Hpolar group-1 of ≥ 1.07. The cell membrane channel pore size is > 0.752 and < 0.758 nm based on a 3-D ellipsoid model (biphenyl), and within the molecular diameter size range 0.744 and 0.762 nm based on a 2-D elliptical model (alkanol). The adjusted van der Waals diameter (vdWD, adj; nm) for the subset of halogenated vapors is predictive of the required MAC for anesthetic potency at an initial (-) Δ Cmicro effect. The molecular structure L ∙ Hpolar group-1 for Neu5Ac is 0.080, and the L ∙ Hpolar group-1 interval range for the cell surface glycocalyx hydrophilicity barrier interaction is 0.101 (Saxitoxin, Stx; Linternal structure ∙ Hpolar group-1) - 0.092 (m-xylenediamine, Lexternal structure · Hpolar group). Differential predictive effective pressure mapping of gene activation or repression reveals that p-dioxin exposure results in activation of AhR-Erβ (Arnt)/Nrf-2, Pparδ, Errγ (LxRα), Dio3 (Dio2) and Trα limbs, and due to high affinity Dio2 and Dio3 (OH-TriCDD, Lext · H-1: 1.91–4.31) exothermy-antagonism (Δ contraction) with high affinity T4/rT3-TRα-mediated agonism (Δ expansion). co-planar PCB metabolite exposure (Lext · H-1: 1.95–3.91) results in activation of AhR (Erα/β)/Nrf2, Rev-Erbβ, Errα, Dio3 (Dio2) and Trα limbs with a Δ Cmicro contraction of 0.89 and Δ Cmicro expansion of 1.05 as compared to p-dioxin. co-, ortho-planar PCB metabolite exposure results in activation of Car/PxR, Pparα (Srebf1,—Lxrβ), Arnt (AhR-Erβ), AR, Dio1 (Dio2) and Trβ limbs with a Δ Cmicro contraction of 0.73 and Δ Cmicro expansion of 1.18 (as compared to p-dioxin). Bisphenol A exposure (Lext struct ∙ H-1: 1.08–1.12, BPA–BPE, Errγ; BPAF, Lext struct ∙ H-1: 1.23, CM Erα, β) results in increased duration at Peff for Timm8b (Peff 0.247) transcription and in indirect activation of the AhR/Nrf-2 hybrid pathway with decreased duration at Peff 0.200 (Nrf1) and increased duration at Peff 0.257 (Dffa). The Bpa/Bpaf convergent pathway Cmicro contraction-expansion response increase in the lower Peff interval is 0.040; in comparison, small molecule hormone Δ Cmicro contraction-expansion response increases in the lower Peff intervals for gene expression ≤ 0.168 (Dex· GR) ≥ 0.156 (Dht · AR), with grade of duration at Peff (min·count) of 1.33x105 (Dex/Cort) and 1.8–2.53x105 (Dht/R1881) as compared to the (-) coupled (+) Δ CmicroPeff to 0.136 (Wnt5a, Esr2) with applied DES (1.86x106). The subtype of trans-differentiated cell as a result of an applied toxin or toxicant is predictable by delta-Cmicro determined by Peff mapping. Study findings offer additional perspective on the basis for pressure regulated gene transcription by alterations in cell micro-compliance (Δ contraction-expansion, Cmicro), and are applicable for the further predictive modeling of gene to gene transcription interactions, and small molecule modulation of cell effective pressure (Peff) and its potential.
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Affiliation(s)
- Hemant Sarin
- Freelance Investigator in Translational Science and Medicine, Charleston, West Virginia, United States of America
- * E-mail:
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Baluška F, Yokawa K, Mancuso S, Baverstock K. Understanding of anesthesia - Why consciousness is essential for life and not based on genes. Commun Integr Biol 2016; 9:e1238118. [PMID: 28042377 PMCID: PMC5193047 DOI: 10.1080/19420889.2016.1238118] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2015] [Revised: 08/05/2016] [Accepted: 09/14/2016] [Indexed: 01/14/2023] Open
Abstract
Anesthesia and consciousness represent 2 mysteries not only for biology but also for physics and philosophy. Although anesthesia was introduced to medicine more than 160 y ago, our understanding of how it works still remains a mystery. The most prevalent view is that the human brain and its neurons are necessary to impose the effects of anesthetics. However, the fact is that all life can be anesthesized. Numerous theories have been generated trying to explain the major impact of anesthetics on our human-specific consciousness; switching it off so rapidly, but no single theory resolves this enduring mystery. The speed of anesthetic actions precludes any direct involvement of genes. Lipid bilayers, cellular membranes, and critical proteins emerge as the most probable primary targets of anesthetics. Recent findings suggest, rather surprisingly, that physical forces underlie both the anesthetic actions on living organisms as well as on consciousness in general.
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Affiliation(s)
| | - Ken Yokawa
- IZMB, University of Bonn, Kirschalle, Bonn, Germany
| | - Stefano Mancuso
- Department of Plant, Soil and Environmental Science & LINV, University of Florence, Sesto Fiorentino, Italy
| | - Keith Baverstock
- Department of Environmental Science, University of Eastern Finland, Kuopio, Finland
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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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Graesbøll K, Sasse-Middelhoff H, Heimburg T. The thermodynamics of general and local anesthesia. Biophys J 2014; 106:2143-56. [PMID: 24853743 DOI: 10.1016/j.bpj.2014.04.014] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2014] [Revised: 03/28/2014] [Accepted: 04/07/2014] [Indexed: 10/25/2022] Open
Abstract
General anesthetics are known to cause depression of the freezing point of transitions in biomembranes. This is a consequence of ideal mixing of the anesthetic drugs in the membrane fluid phase and exclusion from the solid phase. Such a generic law provides physical justification of the famous Meyer-Overton rule. We show here that general anesthetics, barbiturates, and local anesthetics all display the same effect on melting transitions. Their effect is reversed by hydrostatic pressure. Thus, the thermodynamic behavior of local anesthetics is very similar to that of general anesthetics. We present a detailed thermodynamic analysis of heat capacity profiles of membranes in the presence of anesthetics. Using this analysis, we are able to describe experimentally observed calorimetric profiles and predict the anesthetic features of arbitrary molecules. In addition, we discuss the thermodynamic origin of the cutoff effect of long-chain alcohols and the additivity of the effect of general and local anesthetics.
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Affiliation(s)
- Kaare Graesbøll
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark
| | | | - Thomas Heimburg
- Niels Bohr Institute, University of Copenhagen, Copenhagen, Denmark.
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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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8
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Abstract
BACKGROUND Anesthetic blood solubility predicts pharmacokinetics for inhaled agents and is essential for determination of blood anesthetic concentrations from end-tidal gas concentrations using Henry's Law. Though used to model anesthetic effects in humans, there are limited interspecies solubility comparisons that include modern haloethers. This study aimed to measure hematocrit-adjusted blood:gas anesthetic partition coefficients (λ B:G) for desflurane, sevoflurane, isoflurane, and methoxyflurane in humans and animals. METHODS Whole blood was collected from 20 rats, 8 horses, and 4 each of cats, cattle, humans, dogs, goats, pigs, rabbits, and sheep. Plasma or cell volume was removed to adjust all samples to a packed cell volume of 40%. A single-agent calibration gas headspace was added to blood in a glass syringe and was mixed and equilibrated at 37°C for 2 h. Agent concentrations in the calibration gas and syringe headspace were measured using gas chromatography. Anesthetic solubility in saline, citrate-phosphate-dextrose-adenine, and olive oil were similarly measured. RESULTS Except for goats, all animal species had at least one λ B:G measurement that differed significantly from humans. For each agent, λ B:G positively correlated with serum triglyceride concentrations, but this only explained 25% of interspecies variability. Desflurane was significantly less soluble in blood than sevoflurane in some species (e.g., humans) but not in others (e.g., rabbits). CONCLUSIONS Anesthetic partition coefficients differ significantly between humans and most animals for haloether anesthetics. Because of their similar λ B:G values, goats may be a better animal model for inhaled anesthetic pharmacokinetics in people.
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Weng Y, Yang L, Corringer PJ, Sonner JM. Anesthetic sensitivity of the Gloeobacter violaceus proton-gated ion channel. Anesth Analg 2009; 110:59-63. [PMID: 19933531 DOI: 10.1213/ane.0b013e3181c4bc69] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
A prokaryotic member of the gamma-aminobutyric acid type A receptor superfamily (GLIC) was recently cloned from the cyanobacterium Gloeobacter violaceus, its function characterized, and its 3-dimensional x-ray diffraction crystal structure determined. We report its modulation by 9 anesthetics using 2-electrode voltage clamping in Xenopus laevis oocytes. Desflurane, halothane, isoflurane, sevoflurane, and propofol inhibited currents through GLIC at and below concentrations used clinically. Hill numbers averaged 0.3, indicating negative cooperativity or multiple sites or mechanisms of action. A 2-site model fit the data for desflurane and halothane better than a 1-site model. Xenon and etomidate modulated GLIC at or above clinical concentrations, with no cooperativity. Ethanol and nitrous oxide did not modulate GLIC at surgical anesthetic concentrations. These investigations lay the groundwork for further structural and functional studies of anesthetic actions on GLIC.
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Affiliation(s)
- Yun Weng
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, CA 94143-0464, USA
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Abstract
INTRODUCTION Tolerance is observed for a variety of central nervous system depressants including ethanol, which is an anesthetic, but has not been convincingly demonstrated for a potent halogenated volatile anesthetic. Failure to demonstrate tolerance to these agents may be the result of inadequate exposure to anesthetic. In this study, we exposed Xenopus laevis tadpoles to surgical anesthetic concentrations of isoflurane for 1 wk. METHODS Xenopus laevis tadpoles were produced by in vitro fertilization, and exposed to isoflurane (0.59%, 0.98%, 1.52%) or oxygen for 1 wk starting from the time of fertilization. RESULTS Changes in anesthetic EC(50) were small and not in a consistent direction. Control animals had an anesthetic EC(50) of 0.594% +/- 0.003% isoflurane. Tadpoles exposed to 1.52% isoflurane had a lower EC(50) than controls (by 16%), whereas tadpoles raised under 0.59% and 0.98% isoflurane had higher EC(50)s than control (by 4.7% and 7.4%, respectively). CONCLUSION We provide the first description of week-long exposures of vertebrates to surgical anesthetic concentrations of isoflurane, and the first report of such exposures in developing vertebrates. Tolerance to isoflurane does not occur in developing Xenopus laevis tadpoles. Taken together with studies in other organisms, the development of tolerance to ethanol but not isoflurane suggests that mechanisms shared by these drugs probably do not account for the development of tolerance.
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Sonner JM. A hypothesis on the origin and evolution of the response to inhaled anesthetics. Anesth Analg 2008; 107:849-54. [PMID: 18713893 DOI: 10.1213/ane.0b013e31817ee684] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
In this article, I present an evolutionary explanation for why organisms respond to inhaled anesthetics. It is conjectured that organisms today respond to inhaled anesthetics owing to the sensitivity of ion channels to inhaled anesthetics, which in turn has arisen by common descent from ancestral, anesthetic-sensitive ion channels in one-celled organisms (i.e., that the response to anesthetics did not arise as an adaptation of the nervous system, but rather of ion channels that preceded the origin of multicellularity). This sensitivity may have been refined by continuing selection at synapses in multicellular organisms. In particular, it is hypothesized that 1) the beneficial trait that was selected for in one-celled organisms was the coordinated response of ion channels to compounds that were present in the environment, which influenced the conformational equilibrium of ion channels; 2) this coordinated response prevented the deleterious consequences of entry of positive charges into the cell, thereby increasing the fitness of the organism; and 3) these compounds (which may have included organic anions, cations, and zwitterions as well as uncharged compounds) mimicked inhaled anesthetics in that they were interfacially active, and modulated ion channel function by altering bilayer properties coupled to channel function. The proposed hypothesis is consistent with known properties of inhaled anesthetics. In addition, it leads to testable experimental predictions of nonvolatile compounds having anesthetic-like modulatory effects on ion channels and in animals, including endogenous compounds that may modulate ion channel function in health and disease. The latter included metabolites that are increased in some types of end-stage organ failure, and genetic metabolic diseases. Several of these predictions have been tested and proved to be correct.
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Affiliation(s)
- James M Sonner
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, CA 94143-0464, USA.
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Won A, Oh I, Brosnan R, Eger EI, Sonner JM. Hypothermia decreases ethanol MAC in rats. J Anesth 2006; 20:247-50. [PMID: 16897251 DOI: 10.1007/s00540-006-0412-y] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2006] [Accepted: 04/11/2006] [Indexed: 11/29/2022]
Abstract
Despite the known capacity of hypothermia to increase anesthetic potency (decrease the partial pressure required to produce anesthesia), many in vitro studies examine the effects of ethanol and other anesthetics in oocytes or isolated neurons at room temperature. We tested whether, as predicted for potent inhaled anesthetics, a proportionate increase in solubility with hypothermia matched a decrease in ethanol minimum alveolar concentration (MAC), and thereby made the use of a single anesthetic concentration appropriate regardless of temperature. We determined ethanol MAC in normothermic (37.3 degrees C) and hypothermic (28.5 degrees C) rats, and, at the two temperatures, also determined ethanol solubilities in olive oil and saline. Ethanol MAC decreased, while olive oil/gas and saline/gas partition coefficients increased. However, the increase in the saline/gas partition coefficient did not match the decrease in MAC, and thus the aqueous-phase partial pressure producing absence of movement in 50% of rats (EC50) values for ethanol decreased by 17%. Although this decrease is not large, it may be important for comparative estimates of the in vitro effects of ethanol at different temperatures.
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Affiliation(s)
- Albert Won
- Department of Anesthesia and Perioperative Care, S-455, University of California, San Francisco, CA 94143-0464, USA
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Vemparala S, Saiz L, Eckenhoff RG, Klein ML. Partitioning of anesthetics into a lipid bilayer and their interaction with membrane-bound peptide bundles. Biophys J 2006; 91:2815-25. [PMID: 16877515 PMCID: PMC1578482 DOI: 10.1529/biophysj.106.085324] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Molecular dynamics simulations have been performed to investigate the partitioning of the volatile anesthetic halothane from an aqueous phase into a coexisting hydrated bilayer, composed of 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) lipids, with embedded alpha-helical peptide bundles based on the membrane-bound portions of the alpha- and delta-subunits, respectively, of nicotinic acetylcholine receptor. In the molecular dynamics simulations halothane molecules spontaneously partitioned into the DOPC bilayer and then preferentially occupied regions close to lipid headgroups. A single halothane molecule was observed to bind to tyrosine (Tyr-277) residue in the alpha-subunit, an experimentally identified specific binding site. The binding of halothane attenuated the local loop dynamics of alpha-subunit and significantly influenced global concerted motions suggesting anesthetic action in modulating protein function. Steered molecular dynamics calculations on a single halothane molecule partitioned into a DOPC lipid bilayer were performed to probe the free energy profile of halothane across the lipid-water interface and rationalize the observed spontaneous partitioning. Partitioned halothane molecules affect the hydrocarbon chains of the DOPC lipid, by lowering of the hydrocarbon tilt angles. The anesthetic molecules also caused a decrease in the number of peptide-lipid contacts. The observed local and global effects of anesthetic binding on protein motions demonstrated in this study may underlie the mechanism of action of anesthetics at a molecular level.
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Affiliation(s)
- Satyavani Vemparala
- Department of Chemistry and Center for Molecular Modeling, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
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Jung S, Harris RA. Sites in TM2 and 3 are critical for alcohol-induced conformational changes in GABA receptors. J Neurochem 2006; 96:885-92. [PMID: 16405501 DOI: 10.1111/j.1471-4159.2005.03617.x] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Abstract gamma-Aminobutyric acid type A (GABA(A)) receptors are molecular targets for alcohols. Previous work suggests that S270 and A291 residues in the transmembrane (TM) 2 and 3 domains of the GABA(A) receptor alpha subunit are components of an alcohol-binding pocket, and S270I and A291W mutants abolished ethanol potentiation. Our results showed that A295C and F296C residues in the TM3 of the GABA(A) receptor alpha1 subunit are accessible to hexylmethanethiosulfonate (HMTS) in the alcohol-bound state, but not in the resting state. Thus, the A295C and F296C sites become water-accessible as a result of alcohol-induced conformational changes. If S270 or A291 residues are sites of alcohol binding, then S270I or A291W mutations should prevent alcohol-induced conformational movements within the TM3 domain. To investigate this question, the accessibility of HMTS reagent to double mutants (A291W/A295C, A291W/F296C, S270I/A295C or S270I/F296C) in the presence of ethanol or hexanol was tested. The A291W or S270I mutations markedly reduced the accessibility of HMTS to all the double mutants in the ethanol-bound state, and to S270I/F296C, A291W/A295C and A291W/F296C double mutants in the hexanol-bound state, suggesting that the A291 or S270 residues are critical sites for alcohol binding and alcohol-induced conformational changes.
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Affiliation(s)
- Sangwook Jung
- Cell and Molecular Biology Program and Waggoner Center for Alcohol and Addiction Research, University of Texas at Austin, TX, USA.
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Sewell JC, Sear JW. Derivation of preliminary three-dimensional pharmacophores for nonhalogenated volatile anesthetics. Anesth Analg 2004; 99:744-751. [PMID: 15333405 DOI: 10.1213/01.ane.0000129978.92936.a2] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
We investigated the molecular basis for the immobilizing activity of nonhalogenated volatile anesthetics by using comparative molecular field analysis (CoMFA). In vivo potency data (expressed as minimum alveolar anesthetic concentrations) for 38 structurally diverse drugs were obtained from the literature. The anesthetics were randomly divided into a training-set (n = 28) used to formulate the activity models and a test-set (n = 10) used to independently assess the models' predictive power. The anesthetic structures were aligned to maximize their similarity in molecular shape and electrostatic potential to conformers of the most active drug in the group: hexanol. The individual conformers and alignments with maximum similarity (calculated with combined Carbo indices) were retained and used to derive the CoMFA activity models. The final CoMFA model explained 95.5% of the variance in the observed activities of the training-set anesthetics. The model had good predictive capability for both the training-set drugs (cross-validated r(2) = 0.824) and the randomly excluded test-set anesthetics (r(2) = 0.921). Pharmacophoric maps were derived by identifying the spatial distribution of key areas in which steric and electrostatic interactions are important in determining the immobilizing activity of the anesthetics considered.
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Affiliation(s)
- Jason C Sewell
- Nuffield Department of Anaesthetics, University of Oxford, John Radcliffe Hospital, Headington, Oxford, United Kingdom
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Harris RA, Mihic SJ. Alcohol and inhibitory receptors: unexpected specificity from a nonspecific drug. Proc Natl Acad Sci U S A 2003; 101:2-3. [PMID: 14695895 PMCID: PMC314125 DOI: 10.1073/pnas.0307281101] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Affiliation(s)
- R A Harris
- Waggoner Center for Alcohol and Addiction Research, Section of Neurobiology, Institutes for Neuroscience and Cell and Molecular Biology, University of Texas, Austin, TX 78712, USA.
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18
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Cantor RS. Breaking the Meyer-Overton rule: predicted effects of varying stiffness and interfacial activity on the intrinsic potency of anesthetics. Biophys J 2001; 80:2284-97. [PMID: 11325730 PMCID: PMC1301419 DOI: 10.1016/s0006-3495(01)76200-5] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022] Open
Abstract
Exceptions to the Meyer-Overton rule are commonly cited as evidence against indirect, membrane-mediated mechanisms of general anesthesia. However, another interpretation is possible within the context of an indirect mechanism in which solubilization of an anesthetic in the membrane causes a redistribution of lateral pressures in the membrane, which in turn shifts the conformational equilibrium of membrane proteins such as ligand-gated ion channels. It is suggested that compounds of different stiffness and interfacial activity have different intrinsic potencies, i.e., they cause widely different redistributions of the pressure profile (and thus different effects on protein conformational equilibria) per unit concentration of the compound in the membrane. Calculations incorporating the greater stiffness of perfluoromethylenic chains and the large interfacial attraction of hydroxyl groups predict the higher intrinsic potency of short alkanols than alkanes, the cutoffs in potency of alkanes and alkanols and the much shorter cutoffs for their perfluorinated analogues. Both effects, increased stiffness and interfacial activity, are present in unsaturated hydrocarbon solutes, and the intrinsic potencies are predicted to depend on the magnitude of both effects and on the number and locations of multiple bonds within the molecule. Most importantly, the intrinsic potencies of polymeric alkanols with regularly spaced hydroxyl groups are predicted to rise with increasing chain length, without cutoff; such molecules should serve to distinguish unambiguously between indirect mechanisms and direct binding mechanisms of anesthesia.
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Affiliation(s)
- R S Cantor
- Department of Chemistry, Dartmouth College, Hanover, New Hampshire 03755, USA.
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Zhang Y, Trudell JR, Mascia MP, Laster MJ, Gong DH, Harris RA, Eger EI. The Anesthetic Potencies of Alkanethiols for Rats: Relevance to Theories of Narcosis. Anesth Analg 2000. [DOI: 10.1213/00000539-200011000-00045] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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Habgood MD, Begley DJ, Abbott NJ. Determinants of passive drug entry into the central nervous system. Cell Mol Neurobiol 2000; 20:231-53. [PMID: 10696512 DOI: 10.1023/a:1007001923498] [Citation(s) in RCA: 85] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
1. The blood-brain barriers restrict the passive diffusion of many drugs into the brain and constitute a significant obstacle in the pharmacological treatment of central nervous system diseases and disorders. The degree of restriction they impose is variable, with some lipid-insoluble drugs effectively excluded from the brain, while many lipid-soluble drugs do not appear to be subject to any restriction. 2. The ease with which any particular drug diffuses across the blood-brain barrier is determined largely by the number and strength of intermolecular forces "holding" it to surrounding water molecules. By quantifying the molecular features that contribute to these forces, it is possible to predict the in vivo blood-brain barrier permeability of a drug from its molecular structure. Dipolarity, polarizability, and hydrogen bonding ability are factors that appear to reduce permeability, whereas molecular volume (size) and molar refraction are associated with increased permeability. 3. Increasing the passive entry of "restricted" drugs into the central nervous system can be achieved by disrupting the blood-brain barrier (increased paracellular diffusion) or by modifying the structure of "restricted" drugs to temporarily or permanently increase their lipid solubility (increased transcellular permeability). 4. Competitive inhibition of outwardly directed active efflux mechanisms (P-glycoprotein and MRP, the multidrug resistance-related protein) can also significantly increase the accumulation of certain drugs within the central nervous system.
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Abstract
The molecular mechanisms of general anaesthetics have remained largely obscure since their introduction into clinical practice just over 150 years ago. This review describes the actions of general anaesthetics on mammalian neurotransmitter-gated ion channels. As a result of research during the last several decades, ligand-gated ion channels have emerged as promising molecular targets for the central nervous system effects of general anaesthetics. The last 10 years have witnessed an explosion of studies of anaesthetic modulation of recombinant ligand-gated ion channels, including recent studies which utilize chimeric and mutated receptors to identify regions of ligand-gated ion channels important for the actions of general anaesthetics. Exciting future directions include structural biology and gene-targeting approaches to further the understanding of general anaesthetic molecular mechanisms.
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Affiliation(s)
- M. D. Krasowski
- />Committee on Neurobiology, University of Chicago, Whitman Laboratory, 915 East 57th Street, Chicago (Illinois 60637, USA), e-mail: , , , , US
| | - N. L. Harrison
- />Committee on Neurobiology, University of Chicago, Whitman Laboratory, 915 East 57th Street, Chicago (Illinois 60637, USA), e-mail: , , , , US
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22
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Fang Z, Ionescu P, Gong D, Kendig J, Harris A, Eger EI. Maturation Decreases Ethanol Minimum Alveolar Anesthetic Concentration in Mice as Previously Demonstrated in Rats. Anesth Analg 1997. [DOI: 10.1213/00000539-199707000-00029] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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