351
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Kennard LE, Chumbley JR, Ranatunga KM, Armstrong SJ, Veale EL, Mathie A. Inhibition of the human two-pore domain potassium channel, TREK-1, by fluoxetine and its metabolite norfluoxetine. Br J Pharmacol 2005; 144:821-9. [PMID: 15685212 PMCID: PMC1576064 DOI: 10.1038/sj.bjp.0706068] [Citation(s) in RCA: 151] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2004] [Revised: 10/14/2004] [Accepted: 10/21/2004] [Indexed: 10/25/2022] Open
Abstract
1. Block of the human two-pore domain potassium (2-PK) channel TREK-1 by fluoxetine (Prozac) and its active metabolite, norfluoxetine, was investigated using whole-cell patch-clamp recording of currents through recombinant channels in tsA 201 cells. 2. Fluoxetine produced a concentration-dependent inhibition of TREK-1 current that was reversible on wash. The IC50 for block was 19 microM. Block by fluoxetine was voltage-independent. Fluoxetine (100 microM) produced an 84% inhibition of TREK-1 currents, but only a 31% block of currents through a related 2-PK channel, TASK-3. 3. Norfluoxetine was a more potent inhibitor of TREK-1 currents with an IC50 of 9 microM. Block by norfluoxetine was also voltage-independent. 4. Truncation of the C-terminus of TREK-1 (delta89) resulted in a loss of channel function, which could be restored by intracellular acidification or the mutation E306A. The mutation E306A alone increased basal TREK-1 current and resulted in a loss of the slow phase of TREK-1 activation. 5. Progressive deletion of the C-terminus of TREK-1 had no effect on the inhibition of the channel by fluoxetine. The E306A mutation, on the other hand, reduced the magnitude of fluoxetine inhibition, with 100 microM producing only a 40% inhibition. 6. It is concluded that fluoxetine and norfluoxetine are potent inhibitors of TREK-1. Block of TREK-1 by fluoxetine may have important consequences when the drug is used clinically in the treatment of depression.
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Affiliation(s)
- Louise E Kennard
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
| | - Justin R Chumbley
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
| | - Kishani M Ranatunga
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
| | - Stephanie J Armstrong
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
| | - Emma L Veale
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
| | - Alistair Mathie
- Blackett Laboratory, Biophysics Section, Department of Biological Sciences, Imperial College London, Exhibition Road, London SW7 2AZ
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352
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Hemmings HC, Yan W, Westphalen RI, Ryan TA. The General Anesthetic Isoflurane Depresses Synaptic Vesicle Exocytosis. Mol Pharmacol 2005; 67:1591-9. [PMID: 15728262 DOI: 10.1124/mol.104.003210] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
General anesthetics have marked effects on synaptic transmission, but the mechanisms of their presynaptic actions are unclear. We used quantitative laser-scanning fluorescence microscopy to analyze the effects of the volatile anesthetic isoflurane on synaptic vesicle cycling in cultured neonatal rat hippocampal neurons monitored using either transfection of a pH-sensitive form of green fluorescent protein fused to the luminal domain of VAMP (vesicle-associated membrane protein), (synapto-pHluorin) or vesicle loading with the fluorescent dye FM 1-43. Isoflurane reversibly inhibited action potential-evoked exocytosis over a range of concentrations, with little effect on vesicle pool size. In contrast, exocytosis evoked by depolarization in response to an elevated extracellular concentration of KCl, which is insensitive to the selective Na+ channel blocker tetrodotoxin, was relatively insensitive to isoflurane. Inhibition of exocytosis by isoflurane was resistant to bicuculline, indicating that this presynaptic effect is not caused by the well known GABA(A) receptor modulation by volatile anesthetics. Depression of exocytosis was mimicked by a reduction in stimulus frequency, suggesting a reduction in action potential initiation, conduction, or coupling to Ca2+ channel activation. There was no evidence for a direct effect on endocytosis. The effects of isoflurane on synaptic transmission are thus caused primarily by inhibition of action potential-evoked synaptic vesicle exocytosis at a site upstream of Ca2+ entry and exocytosis, possibly as a result of Na+ channel blockade and/or K+ channel activation, with the possibility of lesser contributions from Ca2+ channel blockade and/or soluble N-ethylmaleimide-sensitive factor attachment protein receptor-mediated vesicle fusion.
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Affiliation(s)
- Hugh C Hemmings
- Department of Anesthesiology, Weill Medical College of Cornell University, New York, New York 10021, USA.
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353
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Berg AP, Talley EM, Manger JP, Bayliss DA. Motoneurons express heteromeric TWIK-related acid-sensitive K+ (TASK) channels containing TASK-1 (KCNK3) and TASK-3 (KCNK9) subunits. J Neurosci 2005; 24:6693-702. [PMID: 15282272 PMCID: PMC6729708 DOI: 10.1523/jneurosci.1408-04.2004] [Citation(s) in RCA: 166] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Background potassium currents carried by the KCNK family of two-pore-domain K+ channels are important determinants of resting membrane potential and cellular excitability. TWIK-related acid-sensitive K+ 1 (TASK-1, KCNK3) and TASK-3 (KCNK9) are pH-sensitive subunits of the KCNK family that are closely related and coexpressed in many brain regions. There is accumulating evidence that these two subunits can form heterodimeric channels, but this evidence remains controversial. In addition, a substantial contribution of heterodimeric TASK channels to native currents has not been unequivocally established. In a heterologous expression system, we verified formation of heterodimeric TASK channels and characterized their properties; TASK-1 and TASK-3 were coimmunoprecipitated from membranes of mammalian cells transfected with the channel subunits, and a dominant negative TASK-1(Y191F) construct strongly diminished TASK-3 currents. Tandem-linked heterodimeric TASK channel constructs displayed a pH sensitivity (pK approximately 7.3) in the physiological range closer to that of TASK-1 (pK approximately 7.5) than TASK-3 (pK approximately 6.8). On the other hand, heteromeric TASK channels were like TASK-3 insofar as they were activated by high concentrations of isoflurane (0.8 mm), whereas TASK-1 channels were inhibited. The pH and isoflurane sensitivities of native TASK-like currents in hypoglossal motoneurons, which strongly express TASK-1 and TASK-3 mRNA, were best represented by TASK heterodimeric channels. Moreover, after blocking homomeric TASK-3 channels with ruthenium red, we found a major component of motoneuronal isoflurane-sensitive TASK-like current that could be attributed to heteromeric TASK channels. Together, these data indicate that TASK-1 and TASK-3 subunits coassociate in functional channels, and heteromeric TASK channels provide a substantial component of background K(+) current in motoneurons with distinct modulatory properties.
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Affiliation(s)
- Allison P Berg
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA
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354
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Zhou XL, Loukin SH, Coria R, Kung C, Saimi Y. Heterologously expressed fungal transient receptor potential channels retain mechanosensitivity in vitro and osmotic response in vivo. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 34:413-22. [PMID: 15711808 DOI: 10.1007/s00249-005-0465-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/15/2004] [Revised: 12/22/2004] [Accepted: 12/23/2004] [Indexed: 10/25/2022]
Abstract
The budding yeast Saccharomyces cerevisiae has a mechanosensitive channel, TrpY1, a member of the Trp superfamily of channels associated with various sensations. Upon a hyperosmotic shift, a yeast cell releases Ca(2+) from the vacuole to the cytoplasm through this channel. The TRPY1 gene has orthologs in other fungal genomes, including TRPY2 of Kluyveromyces lactis and TRPY3 of Candida albicans. We subcloned TRPY2 and TRPY3 and expressed them in the vacuole of S. cerevisiae deleted of TRPY1. The osmotically induced Ca(2+) transient was restored in vivo as reported by transgenic aequorin. Patch-clamp examination showed that the TrpY2 or the TrpY3 channel was similar to TrpY1 in unitary conductance, rectification properties, Ca(2+) sensitivity, and mechanosensitivity. The retention of mechanosensitivity of transient receptor potential channels in a foreign setting, shown here both in vitro and in vivo, implies that these mechanosensitive channels, like voltage-gated or ligand-gated channels, do not discriminate their settings. We discuss various mechanisms, including the possibility that stress from the lipid bilayer by osmotic force transmits forces to the transmembrane domains of these channels.
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Affiliation(s)
- Xin-Liang Zhou
- Laboratory of Molecular Biology, University of Wisconsin-Madison, Madison, WI 53706, USA
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355
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Chemin J, Patel A, Duprat F, Zanzouri M, Lazdunski M, Honoré E. Lysophosphatidic Acid-operated K+ Channels. J Biol Chem 2005; 280:4415-21. [PMID: 15572365 DOI: 10.1074/jbc.m408246200] [Citation(s) in RCA: 78] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Lysophosphatidic acid (LPA) is an abundant cellular lipid with a myriad of biological effects. It plays an important role in both inter- and intracellular signaling. Activation of the LPA1-3 G-protein-coupled receptors explains many of the extracellular effects of LPA, including cell growth, differentiation, survival, and motility. However, LPA also acts intracellularly, activating the nuclear hormone receptor peroxisome proliferator-activated receptor-gamma that regulates gene transcription. This study shows that the novel subfamily of mechano-gated K2P channels comprising TREK-1, TREK-2, and TRAAK is strongly activated by intracellular LPA. The LPA-activated 2P domain K+ channels are intracellular ligand-gated K+ channels such as the Ca2+- or the ATP-sensitive K+ channels. LPA reversibly converts these mechano-gated, pH- and voltage-sensitive channels into leak conductances. Gating conversion of the 2P domain K+ channels by intracellular LPA represents a novel form of ion channel regulation. Thus, the TREK and TRAAK channels should be included in the LPA-associated physiological and disease states.
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Affiliation(s)
- Jean Chemin
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UMR 6097, Institut Paul Hamel, 660 route des Lucioles, Sophia-Antipolis, 06560 Valbonne, France
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356
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Abstract
TREK-1, TREK-2 and TRAAK are members of the two-pore domain K+ (K2P) channel family and are activated by membrane stretch and free fatty acids. TREK-1 has been shown to be sensitive to temperature in expression systems. We studied the temperature-sensitivity of TREK-2 and TRAAK in COS-7 cells and in neuronal cells. In transfected COS-7 cells, TREK-2 and TRAAK whole-cell currents increased approximately 20-fold as the bath temperature was raised from 24 degrees C to 42 degrees C. Similarly, in cell-attached patches of COS-7 cells, channel activity was very low, but increased progressively as the bath temperature was raised from 24 degrees C to 42 degrees C. The thresholds for activation of TREK-2 and TRAAK were approximately 25 degrees C and approximately 31 degrees C, respectively. Other K2P channels such as TASK-3 and TRESK-2 were not significantly affected by an increase in temperature from 24 degrees C to 37 degrees C. When the C-terminus of TREK-2 was replaced with that of TASK-3, its sensitivity to free fatty acids and protons was abolished, but the mutant could still be activated by heat. At 37 degrees C, TREK-1, TREK-2 and TRAAK were sensitive to arachidonic acid, pH and membrane stretch in both cell-attached and inside-out patches. In cerebellar granule and dorsal root ganglion neurones, TREK-1, TREK-2 and TRAAK were generally inactive in the cell-attached state at 24 degrees C, but became very active at 37 degrees C. In cell-attached patches of ventricular myocytes, TREK-1 was also normally closed at 24 degrees C, but was active at 37 degrees C. These results show that TREK-2 and TRAAK are also temperature-sensitive channels, are active at physiological body temperature, and therefore would contribute to the background K+ conductance and regulate cell excitability in response to various physical and chemical stimuli.
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Affiliation(s)
- Dawon Kang
- Department of Physiology, Gyeongsang National University School of Medicine, Jinju, Korea
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357
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Lopes CMB, Rohács T, Czirják G, Balla T, Enyedi P, Logothetis DE. PIP2 hydrolysis underlies agonist-induced inhibition and regulates voltage gating of two-pore domain K+ channels. J Physiol 2005; 564:117-29. [PMID: 15677683 PMCID: PMC1456043 DOI: 10.1113/jphysiol.2004.081935] [Citation(s) in RCA: 154] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
Two-pore (2-P) domain potassium channels are implicated in the control of the resting membrane potential, hormonal secretion, and the amplitude, frequency and duration of the action potential. These channels are strongly regulated by hormones and neurotransmitters. Little is known, however, about the mechanism underlying their regulation. Here we show that phosphatidylinositol 4,5-bisphosphate (PIP2) gating underlies several aspects of 2-P channel regulation. Our results demonstrate that all four 2-P channels tested, TASK1, TASK3, TREK1 and TRAAK are activated by PIP2. We show that mechanical stimulation may promote PIP2 activation of TRAAK channels. For TREK1, TASK1 and TASK3 channels, PIP2 hydrolysis underlies inhibition by several agonists. The kinetics of inhibition by the PIP2 scavenger polylysine, and the inhibition by the phosphatidylinositol 4-kinase inhibitor wortmannin correlated with the level of agonist-induced inhibition. This finding suggests that the strength of channel PIP2 interactions determines the extent of PLC-induced inhibition. Finally, we show that PIP2 hydrolysis modulates voltage dependence of TREK1 channels and the unrelated voltage-dependent KCNQ1 channels. Our results suggest that PIP2 is a common gating molecule for K+ channel families despite their distinct structures and physiological properties.
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Affiliation(s)
- Coeli M B Lopes
- Department of Physiology and Biophysics, Mount Sinai School of MedicineNew York, NY 10029, USA
| | - Tibor Rohács
- Department of Physiology and Biophysics, Mount Sinai School of MedicineNew York, NY 10029, USA
| | - Gábor Czirják
- Department of Physiology, Semmelweis UniversityBudapest, H-1444, Hungary
| | - Tamás Balla
- Endocrinology and Reproduction Research BranchNICHD, NIH, Bethesda, MD 20892, USA
| | - Péter Enyedi
- Department of Physiology, Semmelweis UniversityBudapest, H-1444, Hungary
- Endocrinology and Reproduction Research BranchNICHD, NIH, Bethesda, MD 20892, USA
- P. Enyedi: Department of Physiology, Semmelweis University, Budapest, Hungary, H-1444.
| | - Diomedes E Logothetis
- Department of Physiology and Biophysics, Mount Sinai School of MedicineNew York, NY 10029, USA
- Corresponding authors D. E. Logothetis: Department of Physiology and Biophysics, Mount Sinai School of Medicine, New York, NY 10029, USA.
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358
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Besana A, Robinson RB, Feinmark SJ. Lipids and two-pore domain K+ channels in excitable cells. Prostaglandins Other Lipid Mediat 2005; 77:103-10. [PMID: 16099395 DOI: 10.1016/j.prostaglandins.2004.10.005] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2004] [Accepted: 10/27/2004] [Indexed: 11/30/2022]
Abstract
Two-pore domain potassium channels (2PK) make up the newest branch of the potassium channel super-family. The channels are time- and voltage-independent and carry leak or "background" currents that are regulated by many different signaling molecules. These currents play an important role in setting the resting membrane potential and excitability of excitable cells, and, as a consequence, modulation of 2PK channel activity is thought to underlie the function of physiological processes as diverse as the sedation of anesthesia, regulation of normal cardiac rhythm and synaptic plasticity associated with simple forms of learning. Lipids, including arachidonate and its lipoxygenase metabolites, platelet-activating factor and anandamide have been identified as important mediators of some 2PK channels. Regulation can be effected by several different mechanisms. Some channels are regulated by G-protein-coupled receptors using well described signaling pathways that terminate in the activation of protein kinase C, whereas others are modulated by the direct interaction of the lipid with the channel.
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Affiliation(s)
- Alessandra Besana
- Center for Molecular Therapeutics, Department of Pharmacology, Columbia University, 630 W168th Street, New York, NY 10032, USA
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359
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Hughes S, Magnay J, Foreman M, Publicover SJ, Dobson JP, El Haj AJ. Expression of the mechanosensitive 2PK+ channel TREK-1 in human osteoblasts. J Cell Physiol 2005; 206:738-48. [PMID: 16250016 DOI: 10.1002/jcp.20536] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
TREK-1 is a mechanosensitive member of the two-pore domain potassium channel family (2PK+) that is also sensitive to lipids, free fatty acids (including arachidonic acid), temperature, intracellular pH, and a range of clinically relevant compounds including volatile anaesthetics. TREK-1 is known to be expressed at high levels in excitable tissues, such as the nervous system, the heart and smooth muscle, where it is believed to play a prominent role in controlling resting cell membrane potential and electrical excitability. In this report, we use RT-PCR, Western blotting and immunohistochemistry to confirm that human derived osteoblasts and MG63 cells express TREK-1 mRNA and protein. In addition, we show gene expression of TREK2c and TRAAK channels. Furthermore, whole cell patch clamp electrophysiology demonstrates that these cells express a spontaneously active, outwardly rectifying potassium "background leak" current that shares many similarities to TREK-1. The outward current is largely insensitive to TEA and Ba2+, and is sensitive to application of lysophosphatidylcholine (LPC). In addition, blocking TREK-1 channel activity is shown to upregulate bone cell proliferation. It is concluded that human osteoblasts functionally express TREK-1 and that these channels contribute, at least in part, to the resting membrane potential of human osteoblast cells. We hypothesise a possible role for TREK-1 in mechanotransduction, leading to bone remodelling.
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Affiliation(s)
- Steven Hughes
- Institute of Science and Technology in Medicine, Keele University Medical School, Hartshill Campus, Thornburrow Drive, Hartshill, Stoke-on-Trent, United Kingdom
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360
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Liu C, Au JD, Zou HL, Cotten JF, Yost CS. Potent activation of the human tandem pore domain K channel TRESK with clinical concentrations of volatile anesthetics. Anesth Analg 2004; 99:1715-1722. [PMID: 15562060 DOI: 10.1213/01.ane.0000136849.07384.44] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The tandem pore domain K channel family mediates background K currents present in excitable cells. Currents passed by certain members of the family are enhanced by volatile anesthetics, thus suggesting a novel mechanism of anesthesia. The newest member of the family, termed TRESK (TWIK [tandem pore domain weak inward rectifying channel]-related spinal cord K channel), has not been studied for anesthetic sensitivity. We isolated the coding sequence for TRESK from human spinal cord RNA and functionally expressed it in Xenopus oocytes and transfected COS-7 cells. With both whole-cell voltage-clamp and patch-clamp recording, TRESK currents increased up to three-fold by clinical concentrations of isoflurane, halothane, sevoflurane, and desflurane. Nonanesthetics (nonimmobilizers) had no effect on TRESK. Various IV anesthetics, including etomidate, thiopental, and propofol, have a minimal effect on TRESK currents. Amide and ester local anesthetics inhibit TRESK in a concentration-dependent manner but at concentrations generally larger than those that inhibit other tandem pore domain K channels. We also determined that TRESK is found not only in spinal cord, but also in human brain RNA. These results identify TRESK as a target of volatile anesthetics and suggest a role for this background K channel in mediating the effects of inhaled anesthetics in the central nervous system.
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Affiliation(s)
- Canhui Liu
- Department of Anesthesia and Perioperative Care, University of California San Francisco, San Francisco, California
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361
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Martinac B. Mechanosensitive ion channels: molecules of mechanotransduction. J Cell Sci 2004; 117:2449-60. [PMID: 15159450 DOI: 10.1242/jcs.01232] [Citation(s) in RCA: 353] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Cells respond to a wide variety of mechanical stimuli, ranging from thermal molecular agitation to potentially destructive cell swelling caused by osmotic pressure gradients. The cell membrane presents a major target of the external mechanical forces that act upon a cell, and mechanosensitive (MS) ion channels play a crucial role in the physiology of mechanotransduction. These detect and transduce external mechanical forces into electrical and/or chemical intracellular signals. Recent work has increased our understanding of their gating mechanism, physiological functions and evolutionary origins. In particular, there has been major progress in research on microbial MS channels. Moreover, cloning and sequencing of MS channels from several species has provided insights into their evolution, their physiological functions in prokaryotes and eukaryotes, and their potential roles in the pathology of disease.
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Affiliation(s)
- Boris Martinac
- School of Medicine and Pharmacology, QEII Medical Centre, University of Western Australia, Crawley, WA 6009, Australia.
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362
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Multiple synaptic and membrane sites of anesthetic action in the CA1 region of rat hippocampal slices. BMC Neurosci 2004; 5:52. [PMID: 15579203 PMCID: PMC543467 DOI: 10.1186/1471-2202-5-52] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2004] [Accepted: 12/03/2004] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Anesthesia is produced by a depression of central nervous system function, however, the sites and mechanisms of action underlying this depression remain poorly defined. The present study compared and contrasted effects produced by five general anesthetics on synaptic circuitry in the CA1 region of hippocampal slices. RESULTS At clinically relevant and equi-effective concentrations, presynaptic and postsynaptic anesthetic actions were evident at glutamate-mediated excitatory synapses and at GABA-mediated inhibitory synapses. In addition, depressant effects on membrane excitability were observed for CA1 neuron discharge in response to direct current depolarization. Combined actions at several of these sites contributed to CA1 circuit depression, but the relative degree of effect at each site was different for each anesthetic studied. For example, most of propofol's depressant effect (> 70 %) was reversed with a GABA antagonist, but only a minor portion of isoflurane's depression was reversed (< 20 %). Differences were also apparent on glutamate synapses-pentobarbital depressed transmission by > 50 %, but thiopental by only < 25 %. CONCLUSIONS These results, in as much as they may be relevant to anesthesia, indicate that general anesthetics act at several discrete sites, supporting a multi-site, agent specific theory for anesthetic actions. No single effect site (e.g. GABA synapses) or mechanism of action (e.g. depressed membrane excitability) could account for all of the effects produced for any anesthetic studied.
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363
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Chemin J, Patel AJ, Duprat F, Lauritzen I, Lazdunski M, Honoré E. A phospholipid sensor controls mechanogating of the K+ channel TREK-1. EMBO J 2004; 24:44-53. [PMID: 15577940 PMCID: PMC544907 DOI: 10.1038/sj.emboj.7600494] [Citation(s) in RCA: 191] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2004] [Accepted: 11/04/2004] [Indexed: 02/06/2023] Open
Abstract
TREK-1 (KCNK2 or K(2P)2.1) is a mechanosensitive K(2P) channel that is opened by membrane stretch as well as cell swelling. Here, we demonstrate that membrane phospholipids, including PIP(2), control channel gating and transform TREK-1 into a leak K(+) conductance. A carboxy-terminal positively charged cluster is the phospholipid-sensing domain that interacts with the plasma membrane. This region also encompasses the proton sensor E306 that is required for activation of TREK-1 by cytosolic acidosis. Protonation of E306 drastically tightens channel-phospholipid interaction and leads to TREK-1 opening at atmospheric pressure. The TREK-1-phospholipid interaction is critical for channel mechano-, pH(i)- and voltage-dependent gating.
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Affiliation(s)
- Jean Chemin
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Amanda Jane Patel
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Fabrice Duprat
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Inger Lauritzen
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Michel Lazdunski
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
| | - Eric Honoré
- Institut de Pharmacologie, Moléculaire et Cellulaire, Institut Paul Hamel, Sophia Antipolis, Valbonne, France
- Institut de Pharmacologie, Moléculaire et Cellulaire, CNRS-UMR 6097, Institut Paul Hamel, 660, Route des Lucioles, Sophia Antipolis, 06560 Valbonne, France. Tel.: +33 493 957702/03; Fax: +33 493 957704; E-mail:
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364
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Caley AJ, Gruss M, Franks NP. The effects of hypoxia on the modulation of human TREK-1 potassium channels. J Physiol 2004; 562:205-12. [PMID: 15486012 PMCID: PMC1665483 DOI: 10.1113/jphysiol.2004.076240] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Two-pore-domain potassium channels are a family of ion channels that are widely believed to play an important role in maintaining and regulating neuronal excitability. It has been shown that they can be modulated by an extraordinarily diverse range of endogenous and exogenous factors. One particular member of the family, TREK-1 (also known as KCNK2), is activated by increasing temperature, membrane stretch and internal acidosis, but is also sensitive to the presence of certain polyunsaturated fatty acids (such as arachidonic acid), neuroprotectants (such as riluzole) and volatile and gaseous general anaesthetics (such as halothane and nitrous oxide). It has recently been reported that TREK-1 channels are also affected by oxygen concentrations, and that at the levels of hypoxia that occur in the normal human brain, the channels greatly change their properties and, for example, lose their ability to be modulated by arachidonic acid and internal acidosis. These reports seriously challenge the idea that TREK-1 is a target for general anaesthetics and neuroprotectants. However, in this report we show that TREK-1 is not oxygen sensitive, and its ability to be activated by anaesthetics, arachidonic acid and internal acidosis remains unaltered under conditions of hypoxia. We further show that the protocol used by previous workers to prepare hypoxic solutions of arachidonic acid results in the removal of the compound from solution.
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Affiliation(s)
- Alex J Caley
- Biophysics Section, The Blackett Laboratory, Imperial College, London SW7 2AZ, UK
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365
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Yu FH, Catterall WA. The VGL-Chanome: A Protein Superfamily Specialized for Electrical Signaling and Ionic Homeostasis. Sci Signal 2004; 2004:re15. [PMID: 15467096 DOI: 10.1126/stke.2532004re15] [Citation(s) in RCA: 255] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
Complex multicellular organisms require rapid and accurate transmission of information among cells and tissues and tight coordination of distant functions. Electrical signals and resulting intracellular calcium transients, in vertebrates, control contraction of muscle, secretion of hormones, sensation of the environment, processing of information in the brain, and output from the brain to peripheral tissues. In nonexcitable cells, calcium transients signal many key cellular events, including secretion, gene expression, and cell division. In epithelial cells, huge ion fluxes are conducted across tissue boundaries. All of these physiological processes are mediated in part by members of the voltage-gated ion channel protein superfamily. This protein superfamily of 143 members is one of the largest groups of signal transduction proteins, ranking third after the G protein-coupled receptors and the protein kinases in number. Each member of this superfamily contains a similar pore structure, usually covalently attached to regulatory domains that respond to changes in membrane voltage, intracellular signaling molecules, or both. Eight families are included in this protein superfamily-voltage-gated sodium, calcium, and potassium channels; calcium-activated potassium channels; cyclic nucleotide-modulated ion channels; transient receptor potential (TRP) channels; inwardly rectifying potassium channels; and two-pore potassium channels. This article identifies all of the members of this protein superfamily in the human genome, reviews the molecular and evolutionary relations among these ion channels, and describes their functional roles in cell physiology.
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Affiliation(s)
- Frank H Yu
- Department of Pharmacology, Mailstop 357280, University of Washington, Seattle, WA 98195-7280, USA
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366
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Ouyang W, Hemmings HC. Depression by isoflurane of the action potential and underlying voltage-gated ion currents in isolated rat neurohypophysial nerve terminals. J Pharmacol Exp Ther 2004; 312:801-8. [PMID: 15375177 DOI: 10.1124/jpet.104.074609] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We characterized the effects of the volatile anesthetic isoflurane on the ion currents that contribute to the action potential (AP) in isolated rat neurohypophysial (NHP) nerve terminals using patch-clamp electrophysiology. Mean resting membrane potential and AP amplitude were -62.3 +/- 4.1 and 69.2 +/- 2.9 mV, respectively, in NHP terminals. Two components of outward K(+) current (I(K)) were identified in voltage-clamp recordings: a transient I(K) and a sustained I(K) with minimal inactivation. Some terminals displayed a slowly activating I(K), probably the big Ca(2+)-activated K(+) current (BK). Isoflurane reversibly inhibited AP amplitude and increased AP half-width in normal extracellular Ca(2+) (2.2 mM). In high extracellular Ca(2+) (10 mM), isoflurane also reduced the afterhypolarization peak amplitude. A transient tetrodotoxin-sensitive Na(+) current (I(Na)) was the principal current mediating the depolarizing phase of the AP. A slowly inactivating Cd(2+)-sensitive current (probably a voltagegated Ca(2+) current; I(Ca)) followed the initial I(Na). Isoflurane reversibly inhibited both I(Na) and I(Ca) elicited by a voltage-stimulus based on an averaged AP waveform. The isoflurane IC(50) for AP waveform-evoked I(Na) was 0.36 mM. Isoflurane (0.84 +/- 0.04 mM) inhibited AP waveform-evoked I(Ca) by 37.5 +/- 0.16% (p < 0.05). The isoflurane IC(50) for peak I(K) was 0.83 mM and for sustained I(K) was 0.73 mM, with no effect on the voltage dependence of activation. The results indicate that multiple voltage-gated ion channels (Na(+) > K(+) > Ca(2+)) in NHP terminals, although not typical central nervous system terminals, are inhibited by the volatile general anesthetic isoflurane. The net inhibitory effects of volatile anesthetics on nerve terminal action potentials and excitability result from integrated actions on multiple voltage-gated currents.
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Affiliation(s)
- Wei Ouyang
- Department of Anesthesiology, Weill Medical College of Cornell University, Box 50, LC-203, 525 E. 68th St., New York, NY 10021, USA
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367
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Cotten JF, Zou HL, Liu C, Au JD, Yost CS. Identification of native rat cerebellar granule cell currents due to background K channel KCNK5 (TASK-2). ACTA ACUST UNITED AC 2004; 128:112-20. [PMID: 15363886 DOI: 10.1016/j.molbrainres.2004.06.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/12/2004] [Indexed: 11/18/2022]
Abstract
The TWIK-related, Acid Sensing K (TASK-2; KCNK5) potassium channel is a member of the tandem pore (2P) family of potassium channels and mediates an alkaline pH-activated, acid pH-inhibited, outward-rectified potassium conductance. In previous work, we demonstrated TASK-2 protein expression in newborn rat cerebellar granule neurons (CGNs). In this study, we demonstrate TASK-2 functional expression in CGNs as a component of the pH-sensitive, volatile anesthetic-potentiated, standing-outward potassium conductance (I(K,SO)). Using excised, inside-out patch-clamp technique, we studied CGNs grown in primary culture. We identified four distinct, noninactivating single channel potassium conductances, Types 1-4. Types 1-3 have previously been attributed to TASK-1 (KCNK3), TASK-3 (KCNK9) and TASK-1/TASK-3 heteromers, and TREK-2 (KCNK10) 2P potassium channel function, respectively; however, the Type 4 conductance is currently unassigned. Previous studies demonstrated that Type 4 single channel activity is potentiated by extracellular, alkaline pH and cytoplasmic arachidonic acid (10-20 microM) and inhibited by cytoplasmic tetraethylammonium (TEA; 1 mM). We determined that heterologously expressed TASK-2 channels have single channel gating, conductance properties and pH sensitivity identical to the Type 4 conductance. Additionally, we found that TASK-2 single channel activity, like the Type 4 conductance is potentiated by cytoplasmic arachidonic acid (20 microM) and inhibited by cytoplasmic TEA (1 mM). We conclude that TASK-2 mediates the Type 4 single channel conductance in CGNs as a component of I(K,SO).
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Affiliation(s)
- Joseph F Cotten
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, 513 Parnassus Ave., Room S-261, Box 0542, San Francisco, CA 94143, USA
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368
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Patel AJ, Honore E. 2P domain K+ channels: novel pharmacological targets for volatile general anesthetics. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2004; 536:9-23. [PMID: 14635644 DOI: 10.1007/978-1-4419-9280-2_2] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/21/2023]
Affiliation(s)
- Amanda J Patel
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UMR6097, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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369
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Suchyna TM, Tape SE, Koeppe RE, Andersen OS, Sachs F, Gottlieb PA. Bilayer-dependent inhibition of mechanosensitive channels by neuroactive peptide enantiomers. Nature 2004; 430:235-40. [PMID: 15241420 DOI: 10.1038/nature02743] [Citation(s) in RCA: 233] [Impact Index Per Article: 11.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2004] [Accepted: 06/03/2004] [Indexed: 01/17/2023]
Abstract
The peptide GsMTx4, isolated from the venom of the tarantula Grammostola spatulata, is a selective inhibitor of stretch-activated cation channels (SACs). The mechanism of inhibition remains unknown; but both GsMTx4 and its enantiomer, enGsMTx4, modify the gating of SACs, thus violating a trademark of the traditional lock-and-key model of ligand-protein interactions. Suspecting a bilayer-dependent mechanism, we examined the effect of GsMTx4 and enGsMTx4 on gramicidin A (gA) channel gating. Both peptides are active, and the effect increases with the degree of hydrophobic mismatch between bilayer thickness and channel length, meaning that GsMTx4 decreases the energy required to deform the boundary lipids adjacent to the channel. GsMTx4 decreases inward SAC single-channel currents but has no effect on outward currents, suggesting it is located within a Debye length of the outer vestibule of the SACs, but significantly farther from the inner vestibule. Likewise, GsMTx4 decreases gA single-channel currents. Our results suggest that modulation of membrane proteins by amphipathic peptides--mechanopharmacology--involves not only the protein itself but also the surrounding lipids. The surprising efficacy of the d form of GsMTx4 peptide has important therapeutic implications, because d peptides are not hydrolysed by endogenous proteases and may be administered orally.
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Affiliation(s)
- Thomas M Suchyna
- Department of Physiology and Biophysics, SUNY at Buffalo, Buffalo, New York 14214, USA
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370
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Callahan R, Labunskiy DA, Logvinova A, Abdallah M, Liu C, Cotten JF, Yost CS. Immunolocalization of TASK-3 (KCNK9) to a subset of cortical neurons in the rat CNS. Biochem Biophys Res Commun 2004; 319:525-30. [PMID: 15178438 DOI: 10.1016/j.bbrc.2004.05.023] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2004] [Indexed: 11/27/2022]
Abstract
Tandem pore domain (2P) K channels constitute the most diverse family of K channels and are responsible for background (leak or baseline) K currents. Of the 15 human 2P K channels, TASK-1, TASK-2, and TASK-3 are uniquely sensitive to physiologic pH changes as well as being inhibited by local anesthetics and activated by volatile anesthetics. In this study polyclonal antibodies selective for TASK-3 have been used to localize its expression in the rat central nervous system (CNS). TASK-3 immunostaining was found in rat cortex, hypothalamus, and hippocampus. Double immunofluorescent studies identified a discrete population of TASK-3 expressing neurons scattered throughout cortex. Using immunogold electron microscopy TASK-3 was identified at the cell surface associated with synapses and within the intracellular synthetic compartments. These results provide a more finely detailed picture of TASK-3 expression and indicate a role for TASK-3 in modulating cerebral synaptic transmission and responses to CNS active drugs.
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Affiliation(s)
- Robert Callahan
- Department of Anesthesia and Perioperative Care, University of California, 513 Parnassus Ave., Room S-261, San Francisco, CA 94143-0542, USA
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371
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Ishiwa D, Kamiya Y, Itoh H, Saito Y, Ohtsuka T, Yamada Y, Andoh T. Effects of isoflurane and ketamine on ATP-sensitive K channels in rat substantia nigra. Neuropharmacology 2004; 46:1201-1212. [PMID: 15111027 DOI: 10.1016/j.neuropharm.2004.01.012] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2003] [Revised: 12/19/2003] [Accepted: 01/19/2004] [Indexed: 11/16/2022]
Abstract
Whole cell recordings were made using midbrain slices to examine the effects of two different anaesthetics on ATP-sensitive K (K(ATP)) channels in principle neurons of rat substantia nigra pars compacta. When neurons were dialyzed with an ATP-free pipette solution during perfusion with a glucose-free external solution, a hyperpolarization and an outward current developed slowly in a tolbutamide-inhibitable manner. The volatile anaesthetic 3% isoflurane slightly depolarised the neurons in the presence of ATP in the pipette solution and glucose in the external solution, but it did not affect the hyperpolarization or outward current in response to omission of ATP and glucose. Ketamine, an intravenous anaesthetic, did not change the membrane potential when ATP and glucose were included; however, it reversibly inhibited the hyperpolarization and outward current induced by intracellular ATP depletion in a dose-dependent manner. These effects of ketamine were not mimicked by AP-5, an NMDA receptor antagonist, or indatraline, an inhibitor of catecholamine uptake. These findings suggest that these anaesthetics have no stimulatory action on K(ATP) channels in these neurons when intracellular ATP is preserved and that ketamine but not isoflurane inhibits K(ATP) channels when the channels were activated by low intracellular ATP.
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Affiliation(s)
- Dai Ishiwa
- Department of Anaesthesiology and Critical Care Medicine, Yokohama City University Graduate School of Medicine, 3-9 Fukuura, Kanazawa-ku, Yokohama 236-0004, Japan
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372
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Lin W, Burks CA, Hansen DR, Kinnamon SC, Gilbertson TA. Taste receptor cells express pH-sensitive leak K+ channels. J Neurophysiol 2004; 92:2909-19. [PMID: 15240769 DOI: 10.1152/jn.01198.2003] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Two-pore domain K+ channels encoded by genes KCNK1-17 (K2p1-17) play important roles in regulating cell excitability. We report here that rat taste receptor cells (TRCs) highly express TASK-2 (KCNK5; K2p5.1), and to a much lesser extent TALK-1 (KCNK16; K2p16.1) and TASK-1 (KCNK3; K2p3.1), and suggest potentially important roles for these channels in setting resting membrane potentials and in sour taste transduction. Whole cell recordings of isolated TRCs show that a leak K+ (Kleak) current in a subset of TRCs exhibited high sensitivity to acidic extracellular pH similar to reported properties of TASK-2 and TALK-1 channels. A drop in bath pH from 7.4 to 6 suppressed 90% of the current, resulting in membrane depolarization. K+ channel blockers, BaCl2, but not tetraethylammonium (TEA), inhibited the current. Interestingly, resting potentials of these TRCs averaged -70 mV, which closely correlated with the amplitude of the pH-sensitive Kleak, suggesting a dominant role of this conductance in setting resting potentials. RT-PCR assays followed by sequencing of PCR products showed that TASK-1, TASK-2, and a functionally similar channel, TALK-1, were expressed in all three types of lingual taste buds. To verify expression of TASK channels, we labeled taste tissue with antibodies against TASK-1, TASK-2, and TASK-3. Strong labeling was seen in some TRCs with antibody against TASK-2 but not TASK-1 and TASK-3. Consistent with the immunocytochemical staining, quantitative real-time PCR assays showed that the message for TASK-2 was expressed at significantly higher levels (10-100 times greater) than was TASK-1, TALK-1, or TASK-3. Thus several K2P channels, and in particular TASK-2, are expressed in rat TRCs, where they may contribute to the establishment of resting potentials and sour reception.
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Affiliation(s)
- W Lin
- Cell and Developmental Biology, University of Colorado Health Sciences Center at Fitzsimons, Aurora, Colorado 80045, USA
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373
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Abstract
Mechanosensitivity of ion channels is conventionally interpreted as being driven by a change of their in-plane cross-sectional area A(msc). This, however, does not include any factors relating to membrane stiffness, thickness, spontaneous curvature or changes in channel shape, length or stiffness. Because the open probability of a channel is sensitive to all these factors, we constructed a general thermodynamic formalism. These equations provide the basis for the analysis of the behaviour of mechanosensitive channels in lipids of different geometric and chemical properties such as the hydrophobic mismatch at the boundary between the protein and lipid or the effects of changes in the bilayer intrinsic curvature caused by the adsorption of amphipaths. This model predicts that the midpoint gamma(1/2) and the slope(1/2) of the gating curve are generally not independent. Using this relationship, we have predicted the line tension at the channel/lipid border of MscL as approximately 10 pN, and found it to be much less than the line tension of aqueous pores in pure lipid membranes. The MscL channel appears quite well matched to its lipid environment. Using gramicidin as a model system, we have explained its observed conversion from stretch-activated to stretch-inactivated gating as a function of bilayer thickness and composition.
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Affiliation(s)
- V S Markin
- Department of Anesthesiology and Pain Management, UT Southwestern, Dallas, TX 75235-9068, USA
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374
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Heurteaux C, Guy N, Laigle C, Blondeau N, Duprat F, Mazzuca M, Lang-Lazdunski L, Widmann C, Zanzouri M, Romey G, Lazdunski M. TREK-1, a K+ channel involved in neuroprotection and general anesthesia. EMBO J 2004; 23:2684-95. [PMID: 15175651 PMCID: PMC449762 DOI: 10.1038/sj.emboj.7600234] [Citation(s) in RCA: 390] [Impact Index Per Article: 19.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2004] [Accepted: 04/19/2004] [Indexed: 12/13/2022] Open
Abstract
TREK-1 is a two-pore-domain background potassium channel expressed throughout the central nervous system. It is opened by polyunsaturated fatty acids and lysophospholipids. It is inhibited by neurotransmitters that produce an increase in intracellular cAMP and by those that activate the Gq protein pathway. TREK-1 is also activated by volatile anesthetics and has been suggested to be an important target in the action of these drugs. Using mice with a disrupted TREK-1 gene, we now show that TREK-1 has an important role in neuroprotection against epilepsy and brain and spinal chord ischemia. Trek1-/- mice display an increased sensitivity to ischemia and epilepsy. Neuroprotection by polyunsaturated fatty acids, which is impressive in Trek1+/+ mice, disappears in Trek1-/- mice indicating a central role of TREK-1 in this process. Trek1-/- mice are also resistant to anesthesia by volatile anesthetics. TREK-1 emerges as a potential innovative target for developing new therapeutic agents for neurology and anesthesiology.
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Affiliation(s)
- C Heurteaux
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - N Guy
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - C Laigle
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - N Blondeau
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - F Duprat
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - M Mazzuca
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - L Lang-Lazdunski
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - C Widmann
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - M Zanzouri
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - G Romey
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
| | - M Lazdunski
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, Sophia-Antipolis, Valbonne, France
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS-UMR 6097, Institut Paul Hamel, 660 Route des Lucioles, Sophia-Antipolis, 06560 Valbonne, France. Tel.: +33 493 957702/03; Fax: +33 493 957704; E-mail:
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375
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Nagele P, Metz LB, Crowder CM. Nitrous oxide (N(2)O) requires the N-methyl-D-aspartate receptor for its action in Caenorhabditis elegans. Proc Natl Acad Sci U S A 2004; 101:8791-6. [PMID: 15159532 PMCID: PMC423274 DOI: 10.1073/pnas.0402825101] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Nitrous oxide (N(2)O, also known as laughing gas) and volatile anesthetics (VAs), the original and still most widely used general anesthetics, produce anesthesia by ill-defined mechanisms. Electrophysiological experiments in vertebrate neurons have suggested that N(2)O and VAs may act by distinct mechanisms; N(2)O antagonizes the N-methyl-d-aspartate (NMDA) subtype of glutamate receptors, whereas VAs alter the function of a variety of other synaptic proteins. However, no genetic or pharmacological experiments have demonstrated that any of these in vitro actions are responsible for the behavioral effects of either class of anesthetics. By using genetic tools in Caenorhabditis elegans, we tested whether the action of N(2)O requires the NMDA receptor in vivo and whether its mechanism is shared by VAs. Distinct from the action of VAs, N(2)O produced behavioral defects highly specific and characteristic of that produced by loss-of-function mutations in both NMDA and non-NMDA glutamate receptors. A null mutant of nmr-1, which encodes a C. elegans NMDA receptor, was completely resistant to the behavioral effects of N(2)O, whereas a non-NMDA receptor-null mutant was normally sensitive. The N(2)O-resistant nmr-1(null) mutant was not resistant to VAs. Likewise, VA-resistant mutants had wild-type sensitivity to N(2)O. Thus, the behavioral effects of N(2)O require the NMDA receptor NMR-1, consistent with the hypothesis formed from vertebrate electrophysiological data that a major target of N(2)O is the NMDA receptor.
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Affiliation(s)
- P Nagele
- Department of Anesthesiology, Division of Biology and Biomedical Sciences, Washington University School of Medicine, St. Louis, MO 63110, USA
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376
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Abstract
Background K+ conductances are a major determinant of membrane resting potential and input resistance, two key components of neuronal excitability. Background channels have been cloned and form a K+ channel family structurally different from Kv, KCa and Kir channels. These channels with 2P domains (K2P channels) are voltage- and time-independent. They are relatively insensitive to classical potassium channels blockers such as TEA, 4-AP, Ba2+ and Cs+. TASK and TREK subunits are widely expressed in the nervous system. Open at rest, these channels mainly contribute to the resting potential of somatic motoneurons, brainstem respiratory and chemoreceptor neurones, and cerebellar granule cells. K2P channels are regulated by numerous physical and chemical stimuli including extracellular and intracellular pH, temperature, hypoxia, pressure, bioactive lipids, and neurotransmitters. The regulation of these background K+ channels profoundly alters the neuronal excitability. For example, in Aplysia, regulation of a background potassium conductance by neurotransmitters is involved in synaptic modulation, a simple and primitive form of learning. The recent discovery that clinical compounds such as volatile anaesthetics and other neuroprotective agents including riluzole and unsaturated fatty acids activate K2P channels suggest that neuronal background K+ channels are attractive targets for the development of new drugs.
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Affiliation(s)
- Christophe Girard
- Institut de Pharmacologie moléculaire et cellulaire, CNRS UMR 6097, 660, route les Lucioles, Sophia Antipolis, 06560 Valbonne, France
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377
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Richter TA, Dvoryanchikov GA, Chaudhari N, Roper SD. Acid-sensitive two-pore domain potassium (K2P) channels in mouse taste buds. J Neurophysiol 2004; 92:1928-36. [PMID: 15140906 DOI: 10.1152/jn.00273.2004] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Sour (acid) taste is postulated to result from intracellular acidification that modulates one or more acid-sensitive ion channels in taste receptor cells. The identity of such channel(s) remains uncertain. Potassium channels, by regulating the excitability of taste cells, are candidates for acid transducers. Several 2-pore domain potassium leak conductance channels (K(2)P family) are sensitive to intracellular acidification. We examined their expression in mouse vallate and foliate taste buds using RT-PCR, and detected TWIK-1 and -2, TREK-1 and -2, and TASK-1. Of these, TWIK-1 and TASK-1 were preferentially expressed in taste cells relative to surrounding nonsensory epithelium. The related TRESK channel was not detected, whereas the acid-insensitive TASK-2 was. Using confocal imaging with pH-, Ca(2+)-, and voltage-sensitive dyes, we tested pharmacological agents that are diagnostic for these channels. Riluzole (500 microM), selective for TREK-1 and -2 channels, enhanced acid taste responses. In contrast, halothane (< or = approximately 17 mM), which acts on TREK-1 and TASK-1 channels, blocked acid taste responses. Agents diagnostic for other 2-pore domain and voltage-gated potassium channels (anandamide, 10 microM; Gd(3+), 1 mM; arachidonic acid, 100 microM; quinidine, 200 microM; quinine, 100 mM; 4-AP, 10 mM; and TEA, 1 mM) did not affect acid responses. The expression of 2-pore domain channels and our pharmacological characterization suggest that a matrix of ion channels, including one or more acid-sensitive 2-pore domain K channels, could play a role in sour taste transduction. However, our results do not unambiguously identify any one channel as the acid taste transducer.
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Affiliation(s)
- Trevor A Richter
- Dept. of Physiology and Biophysics, University of Miami School of Medicine, 1600 NW 10th Avenue, Miami, FL 33136, USA
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378
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Affiliation(s)
- Keith Buckler
- Laboratory of Physiology, University of Oxford, United Kingdom
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379
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Rehberg B, Bouillon T, Gruenewald M, Schneider J, Baars J, Urban BW, Kox WJ. Comparison of the concentration-dependent effect of sevoflurane on the spinal H-reflex and the EEG in humans. Acta Anaesthesiol Scand 2004; 48:569-76. [PMID: 15101850 DOI: 10.1111/j.1399-6576.2004.00372.x] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
BACKGROUND It has been shown that spinal reflexes such as the H-reflex predict motor responses to painful stimuli better than cortical parameters derived from the EEG. The precise concentration-dependence of H-reflex suppression by anaesthetics, however, is not known. Here we investigated this concentration-response relationship and the equilibration between the alveolar and the effect compartment for sevoflurane. METHODS In 26 patients, the H-reflex was recorded at a frequency of 0.1 Hz while anaesthesia was induced and maintained with sevoflurane at increasing and decreasing concentrations. Population pharmacodynamic modelling was performed using the NONMEM software package, yielding population mean parameters as well as indicators of interindividual variability. RESULTS Suppression of H-reflex amplitude occurred at lower concentrations (mean EC(50) 1.04 +/- 0.10 vol%, SE of NONMEM estimate) than the effect on either BIS or SEF(95) of the EEG (mean EC(50) 1.55 +/- 0.08 and 1.72 +/- 0.18 vol%, respectively), and exhibited a higher interindividual variability. The concentration-response function for the H-reflex was also steeper (mean ë 2.83 +/- 0.25). In addition, the equilibration between alveolar and effect compartment was slower for the H-reflex (mean k(e0) 0.15 +/- 0.01 min(-1)) than for BIS or SEF(95) (mean k(e0) 0.22 +/- 0.02 and 0.41 +/- 0.05 min(-1)). CONCLUSION The differences in EC(50) and slope of the concentration-response relationships for H-reflex suppression and the EEG parameters point to different underlying mechanisms. In addition, the differences in time constant for equilibration between alveolar and effect compartment confirm the notion that immobility is caused at a different anatomic site than suppression of the EEG.
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Affiliation(s)
- B Rehberg
- Department of Anaesthesiology, Charité Campus Mitte, Berlin, Germany.
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380
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Kang D, Mariash E, Kim D. Functional expression of TRESK-2, a new member of the tandem-pore K+ channel family. J Biol Chem 2004; 279:28063-70. [PMID: 15123670 DOI: 10.1074/jbc.m402940200] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
A new member of the tandem-pore K+ (K(2P)) channel family has been isolated from mouse testis complementary DNA. The new K(2P) channel was named TRESK-2, as its amino acid sequence shares 65% identity with that of TRESK-1. Mouse TRESK-2 is a 394-amino acid protein and possesses four putative transmembrane segments and two pore-forming domains. TRESK-2 has a long cytoplasmic domain joining the second and third transmembrane segments and a short carboxyl terminus. In the rat, TRESK-2 mRNA transcripts were expressed abundantly in the thymus and spleen and at low levels in many other tissues, including heart, small intestine, skeletal muscle, uterus, testis, and placenta, as judged by Northern blot analysis. TRESK-2 mRNA was also expressed in mouse and human tissues. In COS-7 cells transfected with TRESK-2 DNA, a time-independent and noninactivating K+-selective current was recorded. TRESK-2 was insensitive to 1 mm tetraethylammonium, 100 nm apamin, 1 mm 4-aminopyridine, and 10 microm glybenclamide. TRESK-2 was inhibited by 10 microm quinidine, 20 microm arachidonate and acid (pH 6.3) at 49, 43, and 23%, respectively. Single channel openings of TRESK-2 showed marked open channel noise. In symmetrical 150 mm KCl, the current-voltage relationship of TRESK-2 was slightly inwardly rectifying, with the single channel conductance 13 picosiemens (pS) at +60 mV and 16 pS at -60 mV. In inside-out patches, TRESK-2 was unaffected by the intracellular application of 10 microm guanosine 5'-O-(thiotriphosphate). These results show that TRESK-2 is a functional member of the K(2P) channel family and contributes to the background K+ conductance in many types of cells.
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Affiliation(s)
- Dawon Kang
- Department of Physiology and Biophysics, The Chicago Medical School, Rosalind Franklin University of Medicine and Science, 3333 Green Bay Road, North Chicago, IL 60064, USA
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381
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Kang D, Han J, Talley EM, Bayliss DA, Kim D. Functional expression of TASK-1/TASK-3 heteromers in cerebellar granule cells. J Physiol 2004; 554:64-77. [PMID: 14678492 PMCID: PMC1664745 DOI: 10.1113/jphysiol.2003.054387] [Citation(s) in RCA: 109] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
TASK-1 and TASK-3 are functional members of the tandem-pore K+ (K2P) channel family, and mRNAs for both channels are expressed together in many brain regions. Although TASK-1 and TASK-3 subunits are able to form heteromers when their complementary RNAs are injected into oocytes, whether functional heteromers are present in the native tissue is not known. Using cultured cerebellar granule (CG) neurones that express mRNAs of both TASK-1 and TASK-3, we studied the presence of heteromers by comparing the sensitivities of cloned and native K+ channels to extracellular pH (pHo) and ruthenium red. The single-channel conductance of TASK-1, TASK-3 and a tandem construct (TASK-1/TASK-3) expressed in COS-7 cells were 14.2 +/- 0.4, 37.8 +/- 0.7 and 38.1 +/- 0.7 pS (-60 mV), respectively. TASK-3 and TASK-1/TASK-3 (and TASK-3/TASK-1) displayed nearly identical single-channel kinetics. TASK-3 and TASK-1/TASK-3 expressed in COS-7 cells were inhibited by 26 +/- 4 and 36 +/- 2 %, respectively, when pHo was changed from 8.3 to 7.3. In outside-out patches from CG neurones, the K+ channel with single channel properties similar to those of TASK-3 was inhibited by 31 +/- 7 % by the same reduction in pHo. TASK-3 and TASK-1/TASK-3 expressed in COS-7 cells were inhibited by 78 +/- 7 and 3 +/- 4 %, respectively, when 5 microm ruthenium red was applied to outside-out patches. In outside-out patches from CG neurones containing a 38 pS channel, two types of responses to ruthenium red were observed. Ruthenium red inhibited the channel activity by 77 +/- 5 % in 42 % of patches (range: 72-82 %) and by 5 +/- 4 % (range: 0-9 %) in 58 % of patches. When patches contained more than three 38 pS channels, the average response to ruthenium red was 47 +/- 6 % inhibition (n= 5). These electrophysiological studies show that native 38 pS K+ channels of the TASK family in cultured CG neurones consist of both homomeric TASK-3 and heteromeric TASK-1/TASK-3.
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Affiliation(s)
- Dawon Kang
- Department of Physiology and Biophysics, Finch University of Health Sciences/The Chicago Medical School3333 Green Bay Road, North Chicago, IL 60064
| | - Jaehee Han
- Department of Physiology and Biophysics, Finch University of Health Sciences/The Chicago Medical School3333 Green Bay Road, North Chicago, IL 60064
| | - Edmund M Talley
- Department of Pharmacology, University of Virginia Health SystemPO Box 800735, 5015 Jordan Hall, 1300 Jefferson Park Avenue, Charlottesville, VA 22908–0735, USA
| | - Douglas A Bayliss
- Department of Pharmacology, University of Virginia Health SystemPO Box 800735, 5015 Jordan Hall, 1300 Jefferson Park Avenue, Charlottesville, VA 22908–0735, USA
| | - Donghee Kim
- Department of Physiology and Biophysics, Finch University of Health Sciences/The Chicago Medical School3333 Green Bay Road, North Chicago, IL 60064
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382
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Harinath S, Sikdar SK. Trichloroethanol enhances the activity of recombinant human TREK-1 and TRAAK channels. Neuropharmacology 2004; 46:750-60. [PMID: 14996553 DOI: 10.1016/j.neuropharm.2003.11.023] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2003] [Revised: 10/22/2003] [Accepted: 11/12/2003] [Indexed: 11/22/2022]
Abstract
Human TREK-1 and TRAAK (hTREK-1 and hTRAAK) are the recently cloned tandem pore-domain potassium channels that are highly expressed in the central nervous system (CNS). The roles of 2P domain K+ channels in general anesthesia and neuroprotection have been proposed recently. We have investigated the ability of 2,2,2-trichloroethanol (an active metabolite of the general anesthetic chloral hydrate (CH)) to modulate the activity of hTREK-1 and hTRAAK channels expressed heterologously in Chinese hamster ovary cells by using whole-cell patch-clamp recording. Trichloroethanol potentiated hTREK-1 and hTRAAK channel activity in a reversible, concentration-dependent manner. The parent compound CH also augmented the activity of both the channels reversibly. CH activation of hTREK-1 was transient followed by a rapid inhibition, whereas hTRAAK activation was not followed by inhibition. Deletions of the carboxy terminal domain (Delta89, Delta100 and Delta119) of hTREK-1 did not abolish sensitivity to TCE (20 mM) suggesting that C-terminal tail is not essential for the activation of hTREK-1 by TCE. The hTREK-1 currents consisted of an instantaneous and a time-dependent component. The time-dependent current was reduced by trichloroethanol (20 mM). Our findings identify TREK-1 and TRAAK channels as molecular targets for trichloroethanol and suggest that activation of these channels might contribute to the CNS depressant effects of CH.
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Affiliation(s)
- S Harinath
- Molecular Biophysics Unit, Indian Institute of Science, Bangalore 560 012, India
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383
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Gruss M, Bushell TJ, Bright DP, Lieb WR, Mathie A, Franks NP. Two-pore-domain K+ channels are a novel target for the anesthetic gases xenon, nitrous oxide, and cyclopropane. Mol Pharmacol 2004; 65:443-52. [PMID: 14742687 DOI: 10.1124/mol.65.2.443] [Citation(s) in RCA: 213] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Nitrous oxide, xenon, and cyclopropane are anesthetic gases that have a distinct pharmacological profile. Whereas the molecular basis for their anesthetic actions remains unclear, they behave very differently to most other general anesthetics in that they have little or no effect on GABAA receptors, yet strongly inhibit the N-methyl-d-aspartate subtype of glutamate receptors. Here we show that certain members of the two-pore-domain K+ channel superfamily may represent an important new target for these gaseous anesthetics. TREK-1 is markedly activated by clinically relevant concentrations of nitrous oxide, xenon, and cyclopropane. In contrast, TASK-3, a member of this family that is very sensitive to volatile anesthetics, such as halothane, is insensitive to the anesthetic gases. We demonstrate that the C-terminal cytoplasmic domain is not an absolute requirement for the actions of the gases, although it clearly plays an important modulatory role. Finally, we show that Glu306, an amino acid that has previously been found to be important in the modulation of TREK-1 by arachidonic acid, membrane stretch and internal pH, is critical for the activating effects of the anesthetic gases.
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Affiliation(s)
- Marco Gruss
- Biophysics Section, Department of Biological Sciences, The Blackett Laboratory, Imperial College London, London, United Kingdom
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384
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Danthi S, Enyeart JA, Enyeart JJ. Caffeic Acid Esters Activate TREK-1 Potassium Channels and Inhibit Depolarization-Dependent Secretion. Mol Pharmacol 2004; 65:599-610. [PMID: 14978238 DOI: 10.1124/mol.65.3.599] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
In whole-cell and single-channel patch-clamp recordings from bovine adrenal fasciculata cells, it was discovered that selected caffeic acid derivatives dramatically enhanced the activity of background TREK-1 K+ channels. Cinnamyl 1-3,4-dihydroxy-alpha-cyanocinnamate (CDC), activated TREK-1 when this agent was applied externally to cells or outside-out patches at concentrations of 5 to 10 microM. Structure/activity studies showed that native bTREK-1 channels were also activated by other caffeic acid esters, including caffeic acid phenethyl ester (CAPE), which contain a benzene or furan ring in the ester side chain. The activation of bTREK-1 by caffeic acid derivatives did not occur through inhibition of lipoxygenases because other potent lipoxygenase inhibitors failed to activate bTREK-1. In bovine adrenal zona fasciculata (AZF) cells, bTREK-1 K+ channels set the resting membrane potential. Inhibition of these channels by corticotropin leads to depolarization-dependent Ca2+ entry and cortisol secretion. CDC, which activates up to thousands of dormant bTREK-1 channels in AZF cells, was found to overwhelm the inhibition of bTREK-1 by corticotropin, reverse the membrane depolarization, and inhibit corticotropin-stimulated cortisol secretion. These results identify selected caffeic acid derivatives as novel K+ channel openers that activate TREK-1 background K+ channels. Because of their ability to stabilize the resting membrane potential and oppose electrical activity and depolarization-dependent Ca2+ entry, these compounds may have therapeutic potential as neuroprotective or cardioprotective agents.
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Affiliation(s)
- Sanjay Danthi
- Department of Neuroscience, College of Medicine and Public Health, the Ohio State University, Columbus, OH 43210-1239, USA
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385
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Rudolph U, Möhler H. ANALYSIS OFGABAARECEPTORFUNCTION ANDDISSECTION OF THEPHARMACOLOGY OFBENZODIAZEPINES ANDGENERALANESTHETICSTHROUGHMOUSEGENETICS. Annu Rev Pharmacol Toxicol 2004; 44:475-98. [PMID: 14744255 DOI: 10.1146/annurev.pharmtox.44.101802.121429] [Citation(s) in RCA: 414] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
GABAA receptors are molecular substrates for the regulation of vigilance, anxiety, muscle tension, epileptogenic activity, and memory functions, and the enhancement of GABAA receptor-mediated fast synaptic inhibition is the basis for the pharmacotherapy of various neurological and psychiatric disorders. Two kinds of GABAA receptor-targeted mutant mice have been generated: (a) knockout mice that lack individual GABAA receptor subunits (alpha1, alpha5, alpha6, beta2, beta3, gamma2, delta, and rho1) and (b) knockin mice that carry point mutations affecting the action of modulatory drugs [alpha1(H101R), alpha2(H101R), alpha3(H126R), alpha5(H105R), and beta3(N265M)]. Whereas the knockout mice have provided information primarily with respect to the regulation of subunit gene transcription, receptor assembly, and some physiological functions of individual receptor subtypes, the point-mutated knockin mice in which specific GABAA receptor subtypes are insensitive to diazepam or some general anesthetics have revealed the specific contribution of individual receptor subtypes to the pharmacological spectrum of diazepam and general anesthetics.
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Affiliation(s)
- Uwe Rudolph
- Institute of Pharmacology and Toxicology, University of Zürich, Winterthurerstrasse 190, CH-8057 Zürich.
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386
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Miller P, Peers C, Kemp PJ. Polymodal regulation of hTREK1 by pH, arachidonic acid, and hypoxia: physiological impact in acidosis and alkalosis. Am J Physiol Cell Physiol 2004; 286:C272-82. [PMID: 14522822 DOI: 10.1152/ajpcell.00334.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Expression of the human tandem P domain K+ channel, hTREK1, is limited almost exclusively to the central nervous system, where ambient Po2 can be as low as 20 Torr. We have previously shown that this level of hypoxia evokes a maximal inhibitory influence on recombinant hTREK1 and occludes the activation by arachidonic acid; this has cast doubt on the idea that TREK1 activation during brain ischemia could facilitate neuroprotection via hyperpolarizing neurons in which it is expressed. Using both whole cell and cell-attached patch-clamp configurations, we now show that the action of another potent TREK activator and ischemia-related event, intracellular acidification, is similarly without effect during compromised O2 availability. This occlusion is observed in either recording condition, and even the concerted actions of both arachidonic acid and intracellular acidosis are unable to activate hTREK1 during hypoxia. Conversely, intracellular alkalinization is a potent channel inhibitor, and hypoxia does not reverse this inhibition. However, increases in intracellular pH are unable to occlude either arachidonic acid activation or hypoxic inhibition. These data highlight two important points. First, during hypoxia, modulation of hTREK1 cannot be accomplished by parameters known to be perturbed in brain ischemia (increased extracellular fatty acids and intracellular acidification). Second, the mechanism of regulation by intracellular alkalinization is distinct from the overlapping structural requirements known to exist for regulation by arachidonic acid, membrane distortion, and acidosis. Thus it seems likely that hTREK1 regulation in the brain will be physiologically more relevant during alkalosis than during ischemia or acidosis.
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Affiliation(s)
- Paula Miller
- School of Biomedical Sciences, Worsley Bldg., University of Leeds, Leeds LS1 9JT, UK
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387
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Chemin J, Girard C, Duprat F, Lesage F, Romey G, Lazdunski M. Mechanisms underlying excitatory effects of group I metabotropic glutamate receptors via inhibition of 2P domain K+ channels. EMBO J 2004; 22:5403-11. [PMID: 14532113 PMCID: PMC213782 DOI: 10.1093/emboj/cdg528] [Citation(s) in RCA: 160] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Group I metabotropic glutamate receptors (mGluRs) are implicated in diverse processes such as learning, memory, epilepsy, pain and neuronal death. By inhibiting background K(+) channels, group I mGluRs mediate slow and long-lasting excitation. The main neuronal representatives of this K(+) channel family (K(2P) or KCNK) are TASK and TREK. Here, we show that in cerebellar granule cells and in heterologous expression systems, activation of group I mGluRs inhibits TASK and TREK channels. D-myo-inositol-1,4,5-triphosphate and phosphatidyl-4,5-inositol-biphosphate depletion are involved in TASK channel inhibition, whereas diacylglycerols and phosphatidic acids directly inhibit TREK channels. Mechanisms described here with group I mGluRs will also probably stand for many other receptors of hormones and neurotransmitters.
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Affiliation(s)
- Jean Chemin
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS - UMR 6097, Institut Paul Hamel, 660, Route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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388
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Shibata S, Ono K, Iijima T. Sevoflurane Inhibition of the Slowly Activating Delayed Rectifier K+ Current in Guinea Pig Ventricular Cells. J Pharmacol Sci 2004; 95:363-73. [PMID: 15272213 DOI: 10.1254/jphs.fp0040024] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/26/2022] Open
Abstract
Single ventricular cells were enzymatically isolated from guinea pig hearts and the effects of sevoflurane on the delayed rectifier K(+) current were investigated by the patch clamp method. The rapidly (I(Kr)) and slowly activating delayed rectifier K(+) current (I(Ks)) were isolated using chromanol 293B, a selective blocker for I(Ks) or E4031 (N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl]carbonyl]phenyl]methanesulfonamide dihydrochloride), a blocker for I(Kr). Sevoflurane and halothane decreased I(Ks) in a concentration-dependent manner with an IC(50) value of 0.38 mM for sevoflurane and 1.05 mM for halothane. I(Ks) inhibition was characterized by suppression of maximum conductance with little effect on activation kinetics. Inhibition occurred immediately after anesthetic application and recovered upon wash-out. In contrast to the marked inhibition of I(Ks), I(Kr) was hardly affected by sevoflurane. Under the current clamp, sevoflurane prolonged the action potential duration in a reversible manner and this effect was more marked when I(Kr) was inhibited by E4031. The results suggest that sevoflurane inhibits I(Ks), and not I(Kr), in a concentration-dependent manner at clinically relevant concentrations. The resulting prolongation of ventricular repolarization may partly account for the clinical observation of excessive QT prolongation by these anesthetics.
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Affiliation(s)
- Shigehiro Shibata
- Department of Anesthesiology, Akita City Hospital, Akita 010-0933, Japan
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389
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Abstract
The 'noble' gases have been known to have anaesthetic properties for 50 years yet only recently has their application become a clinical reality. In this review we describe the preclinical and clinical studies that have led to a resurgence of interest in the use of the element xenon as an anaesthetic. Furthermore, we highlight specific areas where xenon demonstrates advantages over other anaesthetics, including safety, beneficial pharmacokinetics, cardiovascular stability, analgesia and neuroprotection.
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Affiliation(s)
- Robert D Sanders
- Department of Anaesthetics and Intensive Care, Faculty of Medicine, Imperial College London, UK
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390
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Abstract
K(+) channels that are activated by free fatty acids (here called K(FA) channels) are found throughout the CNS and in some peripheral tissues. In addition to free fatty acids, membrane stretch (cell swelling), changes in intracellular pH and volatile anaesthetic agents also activate K(FA) channels. Neurotransmitters that bind to G(s)-protein-coupled receptors inhibit K(FA) current via cAMP-mediated phosphorylation. K(FA) channels are native members of the TREK-TRAAK family, which belongs to the tandem-pore class of K(+) (K(2P)) channels. The unique properties of K(FA) channels indicate that they are well suited to sensing various types of stress that occur in the cell.
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Affiliation(s)
- Donghee Kim
- Department of Physiology and Biophysics, Finch University of Health Sciences/The Chicago Medical School, 3333 Green Bay Road, North Chicago, IL 60064, USA.
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391
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sup-9, sup-10, and unc-93 may encode components of a two-pore K+ channel that coordinates muscle contraction in Caenorhabditis elegans. J Neurosci 2003. [PMID: 14534247 DOI: 10.1523/jneurosci.23-27-09133.2003] [Citation(s) in RCA: 60] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Genetic studies of sup-9, unc-93, and sup-10 strongly suggest that these genes encode components of a multi-subunit protein complex that coordinates muscle contraction in Caenorhabditis elegans. We cloned sup-9 and sup-10 and found that they encode a two-pore K+ channel and a novel transmembrane protein, respectively. We also found that UNC-93 and SUP-10 colocalize with SUP-9 within muscle cells, and that UNC-93 is a member of a novel multigene family that is conserved among C. elegans, Drosophila, and humans. Our results indicate that SUP-9 and perhaps other two-pore K+ channels function as multiprotein complexes, and that UNC-93 and SUP-10 likely define new classes of ion channel regulatory proteins.
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392
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Zaugg M, Lucchinetti E, Uecker M, Pasch T, Schaub MC. Anaesthetics and cardiac preconditioning. Part I. Signalling and cytoprotective mechanisms. Br J Anaesth 2003; 91:551-65. [PMID: 14504159 DOI: 10.1093/bja/aeg205] [Citation(s) in RCA: 190] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Cardiac preconditioning represents the most potent and consistently reproducible method of rescuing heart tissue from undergoing irreversible ischaemic damage. Major milestones regarding the elucidation of this phenomenon have been passed in the last two decades. The signalling and amplification cascades from the preconditioning stimulus, be it ischaemic or pharmacological, to the putative end-effectors, including the mechanisms involved in cellular protection, are discussed in this review. Volatile anaesthetics and opioids effectively elicit pharmacological preconditioning. Anaesthetic-induced preconditioning and ischaemic preconditioning share many fundamental steps, including activation of G-protein-coupled receptors, multiple protein kinases and ATP-sensitive potassium channels (K(ATP) channels). Volatile anaesthetics prime the activation of the sarcolemmal and mitochondrial K(ATP) channels, the putative end-effectors of preconditioning, by stimulation of adenosine receptors and subsequent activation of protein kinase C (PKC) and by increased formation of nitric oxide and free oxygen radicals. In the case of desflurane, stimulation of alpha- and beta-adrenergic receptors may also be of importance. Similarly, opioids activate delta- and kappa-opioid receptors, and this also leads to PKC activation. Activated PKC acts as an amplifier of the preconditioning stimulus and stabilizes, by phosphorylation, the open state of the mitochondrial K(ATP) channel (the main end-effector in anaesthetic preconditioning) and the sarcolemmal K(ATP) channel. The opening of K(ATP) channels ultimately elicits cytoprotection by decreasing cytosolic and mitochondrial Ca(2+) overload.
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Affiliation(s)
- M Zaugg
- Institute of Anaesthesiology, University Hospital Zurich, Zurich, Switzerland.
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393
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Xing Y, Zhang Y, Stabernack CR, Eger EI, Gray AT. The use of the potassium channel activator riluzole to test whether potassium channels mediate the capacity of isoflurane to produce immobility. Anesth Analg 2003; 97:1020-1024. [PMID: 14500151 DOI: 10.1213/01.ane.0000077073.92108.e7] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
UNLABELLED Inhaled anesthetics produce immobility during noxious stimulation, primarily by actions on the spinal cord. In this study, we examined whether activation of potassium channels of the KCNK subfamily alters volatile anesthetic potency. We measured the change in isoflurane minimum alveolar anesthetic concentration (MAC) during 4-h intrathecal or IV infusions of the nonspecific KCNK activator riluzole in 54 Sprague-Dawley rats. IV or intrathecal infusions of riluzole doses that did not result in permanent injury or death equally decreased isoflurane MAC. We conclude that although riluzole exhibited anesthetic effects, the similar dose response from IV or intrathecal infusion suggests systemic absorption and actions in the brain rather than the spinal cord. IMPLICATIONS Riluzole, a drug that activates potassium channels and decreases glutamatergic neurotransmission, primarily acts on supraspinal sites to produce immobility in response to noxious stimuli. This finding does not support the hypothesis that potassium channels mediate the capacity of inhaled anesthetics to produce immobility in the face of noxious stimulation.
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Affiliation(s)
- Yilei Xing
- Department of Anesthesia and Perioperative Care, University of California, San Francisco, California
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394
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Gurney AM, Osipenko ON, MacMillan D, McFarlane KM, Tate RJ, Kempsill FEJ. Two-pore domain K channel, TASK-1, in pulmonary artery smooth muscle cells. Circ Res 2003; 93:957-64. [PMID: 14551239 DOI: 10.1161/01.res.0000099883.68414.61] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Pulmonary vascular tone is strongly influenced by the resting membrane potential of smooth muscle cells, depolarization promoting Ca2+ influx, and contraction. The resting potential is determined largely by the activity of K+-selective ion channels, the molecular nature of which has been debated for some time. In this study, we provide strong evidence that the two-pore domain K+ channel, TASK-1, mediates a noninactivating, background K+ current (IKN), which sets the resting membrane potential in rabbit pulmonary artery smooth muscle cells (PASMCs). TASK-1 mRNA was found to be present in PASMCs, and the membranes of PASMCs contained TASK-1 protein. Both IKN and the resting potential were found to be exquisitely sensitive to extracellular pH, acidosis inhibiting the current and causing depolarization. Moreover, IKN and the resting potential were enhanced by halothane (1 mmol/L), inhibited by Zn2+ (100 to 200 micromol/L) and anandamide (10 micromol/L), but insensitive to cytoplasmic Ca2+. These properties are all diagnostic of TASK-1 channels and add to previously identified features of IKN that are shared with TASK-1, such as inhibition by hypoxia, low sensitivity to 4-aminopyridine and quinine and insensitivity to tetraethylammonium ions. It is therefore concluded that TASK-1 channels are major contributors to the resting potential in pulmonary artery smooth muscle. They are likely to play an important role in mediating pulmonary vascular responses to changes in extracellular pH, and they could be responsible for the modulatory effects of pH on hypoxic pulmonary vasoconstriction.
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Affiliation(s)
- A M Gurney
- Department of Physiology and Pharmacology, University of Strathclyde, 27 Taylor St, Glasgow, UK G4 0NR.
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395
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Contribution of TWIK-related acid-sensitive K+ channel 1 (TASK1) and TASK3 channels to the control of activity modes in thalamocortical neurons. J Neurosci 2003. [PMID: 12878686 DOI: 10.1523/jneurosci.23-16-06460.2003] [Citation(s) in RCA: 129] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The thalamocortical network is characterized by rhythmic burst activity during natural sleep and tonic single-spike activity during wakefulness. The change between these two activity modes is partially governed by transmitters acting on leak K+ currents in the thalamus, although the nature of the constituting ion channels is not yet known. In the present study, the contribution of members of the two-pore domain K+ channel family to the leak current was investigated using whole-cell patch-clamp techniques and molecular biological techniques. RT-PCR and in situ hybridization revealed the expression of TWIK-related acid-sensitive K+ channel 1 (TASK 1) and TASK3 channels in the rat dLGN. Voltage-clamp recordings of thalamocortical relay neurons in slice preparations demonstrated the existence of a current component sensitive to the TASK channel blocker bupivacaine, which reversed at the presumed K+ equilibrium potential, showed outward rectification, and contributed approximately 40% to the standing outward current at depolarized values of the membrane potential (-28 mV). The pharmacological profile was indicative of TASK channels, in that the current was sensitive to changes in extracellular pH, reduced by muscarine and increased by halothane, and these effects were occluded by a near-maximal action of bupivacaine. Pharmacological manipulation of this current under current-clamp conditions resulted in a shift between burst and tonic firing modes. It is concluded that TASK1 and TASK3 channels contribute to the muscarine- and halothane-sensitive conductance in thalamocortical relay neurons, thereby contributing to the change in the activity mode of thalamocortical networks observed during the sleep-wake cycle and on application of inhalational anesthetics.
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396
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Sonner JM, Antognini JF, Dutton RC, Flood P, Gray AT, Harris RA, Homanics GE, Kendig J, Orser B, Raines DE, Trudell J, Vissel B, Eger EI. Inhaled anesthetics and immobility: mechanisms, mysteries, and minimum alveolar anesthetic concentration. Anesth Analg 2003; 97:718-740. [PMID: 12933393 DOI: 10.1213/01.ane.0000081063.76651.33] [Citation(s) in RCA: 196] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Studies using molecular modeling, genetic engineering, neurophysiology/pharmacology, and whole animals have advanced our understanding of where and how inhaled anesthetics act to produce immobility (minimum alveolar anesthetic concentration; MAC) by actions on the spinal cord. Numerous ligand- and voltage-gated channels might plausibly mediate MAC, and specific amino acid sites in certain receptors present likely candidates for mediation. However, in vivo studies to date suggest that several channels or receptors may not be mediators (e.g., gamma-aminobutyric acid A, acetylcholine, potassium, 5-hydroxytryptamine-3, opioids, and alpha(2)-adrenergic), whereas other receptors/channels (e.g., glycine, N-methyl-D-aspartate, and sodium) remain credible candidates.
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Affiliation(s)
- James M Sonner
- *Department of Anesthesia and Perioperative Care, University of California, San Francisco, California; †Department of Anesthesiology, University of California, Davis, California; ‡Columbia University, New York, New York; §University of Texas, Austin, Texas; ∥University of Pittsburgh, Pittsburgh, Pennsylvania; ¶Stanford University, Palo Alto, California; #University of Toronto, Toronto, Canada; **Department of Anaesthesia, Harvard Medical School, Cambridge, Massachusetts; and ††Garvan Institute of Medical Research, Darlinghurst, Australia
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397
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398
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Lauritzen I, Zanzouri M, Honoré E, Duprat F, Ehrengruber MU, Lazdunski M, Patel AJ. K+-dependent cerebellar granule neuron apoptosis. Role of task leak K+ channels. J Biol Chem 2003; 278:32068-76. [PMID: 12783883 DOI: 10.1074/jbc.m302631200] [Citation(s) in RCA: 163] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Rat mature cerebellar granule, unlike hippocampal neurons, die by apoptosis when cultured in a medium containing a physiological concentration of K+ but survive under high external K+ concentrations. Cell death in physiological K+ parallels the developmental expression of the TASK-1 and TASK-3 subunits that encode the pH-sensitive standing outward K+ current IKso. Genetic transfer of the TASK subunits in hippocampal neurons, lacking IKso, induces cell death, while their genetic inactivation protects cerebellar granule neurons. Neuronal death of cultured rat granule neurons is also prevented by conditions that specifically reduce K+ efflux through the TASK-3 channels such as extracellular acidosis and ruthenium red. TASK leak K+ channels thus play an important role in K+-dependent apoptosis of cerebellar granule neurons in culture.
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Affiliation(s)
- Inger Lauritzen
- Institut de Pharmacologie Moléculaire et Cellulaire, CNRS, Institut Paul Hamel, 660 route des Lucioles, Sophia Antipolis, 06560 Valbonne, France
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399
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Arhem P, Klement G, Nilsson J. Mechanisms of anesthesia: towards integrating network, cellular, and molecular level modeling. Neuropsychopharmacology 2003; 28 Suppl 1:S40-7. [PMID: 12827143 DOI: 10.1038/sj.npp.1300142] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The mechanisms of anesthesia are surprisingly little understood. The present article summarizes current knowledge about the function of general anesthetics at different organization levels of the nervous system. It argues that a consensus view can be constructed, assuming that general anesthetics modulate the activity of ion channels, the main targets being GABA and NMDA channels and possibly voltage-gated and background channels, thereby hyperpolarizing neurons in thalamocortical loops, which lead to disruption of coherent oscillatory activity in the cortex. Two computational cases are used to illustrate the possible importance of molecular level effects on cellular level activity. Subtle differences in the mechanism of ion channel block can be shown to cause considerable differences in the modification of the oscillatory activity in a single neuron, and consequently in an associated network. Finally, the relation between the anesthesia problem and the classical consciousness problem is discussed, and some consequences of introducing the phenomenon of degeneracy into the picture are pointed out.
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Affiliation(s)
- Peter Arhem
- Department of Neuroscience and the Nobel Institute for Neurophysiology, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
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400
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Enyeart JA, Danthi S, Enyeart JJ. Corticotropin induces the expression of TREK-1 mRNA and K+ current in adrenocortical cells. Mol Pharmacol 2003; 64:132-42. [PMID: 12815169 DOI: 10.1124/mol.64.1.132] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Bovine adrenal zona fasciculata (AZF) cells express a two-pore/four-transmembrane segment bTREK-1 K+ channel that sets the resting potential and couples hormonal signals to depolarization-dependent Ca2+ entry and cortisol secretion. It was discovered that corticotropin (1-2000 pM) enhances the expression of bTREK-1 mRNA and membrane current in cultured AZF cells. Forskolin and 8-pcpt-cAMP mimicked corticotropin induction of bTREK-1 mRNA, but angiotensin II (AII) was ineffective. The induction of bTREK-1 mRNA by corticotropin was partially blocked by the A-kinase antagonist H-89. 8-(4-Chloro-phenylthio)-2-O-methyladenosine-3'-5'-cyclic monophosphate, a cAMP analog that activates cAMP-regulated guanine nucleotide exchange factors (Epac), failed to increase bTREK-1 mRNA. Corticotropin-stimulated increases in bTREK-1 mRNA were eliminated by inhibitors of protein synthesis or gene transcription. bTREK-1 current disappeared after 24 h in serum-supplemented medium, but in the presence of corticotropin, bTREK-1 expression was maintained for at least 48 h. The enhancement of bTREK-1 mRNA and ionic current contrasts with the corticotropin-induced down-regulation of the Kv1.4 voltage-gated K+ current and associated mRNA in AZF cells. These results demonstrate that corticotropin rapidly and potently induces the expression of bTREK-1 in AZF cells at the pretranslational level by a cAMP-dependent mechanism that is partially dependent on A-kinase but independent of Epac and Ca2+. They further indicate that prolonged stimulation of AZF cells by corticotropin, as occurs during long-term stress or disease, may produce pronounced changes in the expression of genes encoding ion channels, thereby reshaping the electrical properties of these cells to enhance or limit cortisol secretion.
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Affiliation(s)
- Judith A Enyeart
- Department of Neuroscience, The Ohio State University, College of Medicine, Columbus, OH, USA.
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