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  • 1
    Electronic Resource
    Electronic Resource
    β-Lumicolchicine Interacts with the Benzodiazepine Binding Site to Potentiate GABAA Receptor-Mediated Currents (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 62 (1994), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: An analogue of colchicine,β-lumicolchicine, does not bind tubulin or disrupt microtubules. However, this compound is not pharmacologically completely inactive. β-Lumicolchicine was found to competitively inhibit [3H]flunitrazepam binding and to enhance muscimol-stimulated 36Cr-uptake in mouse cerebral cortical microsacs. It also markedly potentiated GABA responses in Xenopusoocytes expressing human α1β2γ2S, but not α1β2, GABAA receptor subunits; this potentiation was reversed by the benzodiazepine receptor antagonist flumazenil. These results strongly suggest a direct effect of β-Lumicolchicine on the GABAA receptor/chloride channel complex and caution that it possesses pharmacological effects, despite its inability to disrupt microtubules. Furthermore, β-Lumicolchicine is structurally unrelated to benzodiazepines or quinolines and may provide a novel approach to the synthesis of ligands for this receptor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1994.62051790.x
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  • 2
    Electronic Resource
    Electronic Resource
    Modulation of γ-Aminobutyric AcidA Receptor-Operated Chloride Channels by Benzodiazepine Inverse Agonists Is Related to Genetic Differences in Ethanol Withdrawal Seizure Severity (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: To determine whether genetic differences in development of ethanol dependence are related to changes in γ-aminobutyric acidA (GABAA) receptor function, we measured 36Cl uptake by brain cortical membrane vesicles from withdrawal seizure prone and withdrawal seizure resistant (WSP/WSR) mice treated chronically with ethanol. Musci-mol-stimulated chloride flux was not different between WSP and WSR mice before or after ethanol treatment. Also, augmentation of muscimol action by flunitrazepam or inhibition of muscimol action by the inverse agonists Ro 15–4513 (ethyl- 8-azido-5,6-dihydro-5-methyl-6-oxo-4H-imidazo[1,5a]- [1,4]benzodiazepine-3-carboxylate) and methyl-6,7-dime- thoxy-4-ethyl-β-carboIine-3-carboxylate (DMCM) was not different for ethanol-naive WSP and WSR mice. However, chronic ethanol administration enhanced the inhibitory actions of DMCM and Ro 15–4513 on membranes from WSP but not WSR mice. Conversely, chronic ethanol treatment attenuated the action of flunitrazepam on membranes from WSR but not WSP mice, suggesting that the actions of benzodiazepine agonists and inverse agonists are under separate genetic control. These genetic differences in actions of DMCM and Ro 15–4513 indicate that sensitization to benzodiazepine inverse agonists produced by chronic ethanol treatment may be related to development of withdrawal seizures and suggest that differences in the GABA/benzodiazepine receptor complex represent alleles that have segregated during the selection of the WSP/WSR mice.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb06428.x
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  • 3
    Electronic Resource
    Electronic Resource
    Molecular Determinants of General Anesthetic Action: Role of GABAA Receptor Structure (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: Using receptors expressed from mouse brain mRNA in Xenopus oocytes, we found that enhancement of type A γ-aminobutyric acid (GABAA) receptor-gated Cl− channel response is a common action of structurally diverse anesthetics, suggesting that the GABAA receptor plays an important role in anesthesia. To determine if GABAA receptor subunit composition influences actions of anesthetics, we expressed subunit cRNAs in Xenopus oocytes and measured effects of enflurane on GABA-activated Cl− currents. Potentiation of GABA-activated currents by enflurane was dependent on the composition of GABAA receptor protein subunits; the order of sensitivity was α1β1 〉 α1β1γ2s=α1β1γ2L 〉 total mRNA. The results suggest that anesthetics with simple structures may act on the GABAA receptor protein complex to modulate the Cl− channel activity and provide a molecular explanation for the synergistic clinical interactions between benzodiazepines and general anesthetics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb03320.x
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  • 4
    Electronic Resource
    Electronic Resource
    Chronic Ethanol Treatment Alters Brain Levels of γ-Aminobutyric AcidA Receptor Subunit mRNAs: Relationship to Genetic Differences in Ethanol Withdrawal Seizure Severity (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Chronic ethanol treatment is known to alter the function of the γ-aminobutyric acidA (GABAA) benzodiazepine receptor complex. To determine if genetic differences in development of ethanol dependence are related to expression of GABAA receptor subunits, we measured whole brain levels of mRNA for the α1α3, α6, γ2s, γ2t, and γ3 receptor subunits in withdrawal seizure-prone and -resistant (WSP and WSR, respectively) mice fed an ethanol-containing liquid diet or a control diet Brain poly(A)+ RNA was converted to cDNA and amplified by the polymerase chain reaction using primers conserved among GABAA receptor subunits. Quantification was carried out by densitometric analysis of Southern blots generated using subunit-specific probes. Chronic ethanol treatment decreased the content of α1, mRNA in WSP but not WSR mice and decreased the content of α6 mRNA in WSR but not WSP mice. The content of γ3 mRNA was increased by chronic ethanol in both lines. In untreated mice, the WSP line had lower levels of α3 and α6 mRNA than the WSR line. Thus, a decrease in the content of α1 mRNA is most clearly linked with development of withdrawal signs, although the amounts of α6 and α3 may also be important in the genetic differences between WSP and WSR mice. In contrast, levels of mRNA for γ2S and γ2L subunits do not appear to be altered in ethanol dependence.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb08313.x
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  • 5
    Electronic Resource
    Electronic Resource
    Ionizing Radiation Alters the Properties of Sodium Channels in Rat Brain Synaptosomes (1986)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 47 (1986), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effect of ionizing radiation on neuronal membrane function was assessed by measurement of neurotoxin-stimulated 22Na+ uptake by rat brain synaptosomes. High-energy electrons and γ photons were equally effective in reducing the maximal uptake of 22Na+ with no significant change in the affinity of veratridine for its binding site in the channel. Ionizing radiation reduced the veratridine-stimulated uptake at the earliest times measured (3 and 5 s), when the rate of uptake was greatest. Batrachotoxin-stimulated 22Na+ uptake was less sensitive to inhibition by radiation. The binding of [3H]saxitoxin to its receptor in the sodium channel was unaffected by exposure to ionizing radiation. The effect of ionizing radiation on the lipid order of rat brain synaptic plasma membranes was measured by the fluorescence polarization of the molecular probes 1,6-diphenyl-1,3,5-hexatriene and l-[4-(trimethylammonium)phenyl]-6-phenyl-l,3,5-hexatriene. A dose of radiation that reduced the veratridine-stimulated uptake of 22Na+ had no effect on the fluorescence polarization of either probe. These results demonstrate an inhibitory effect of ionizing radiation on the voltage-sensitive sodium channels in rat brain synaptosomes. This effect of radiation is not dependent on changes in the order of membrane lipids.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1986.tb04528.x
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  • 6
    Electronic Resource
    Electronic Resource
    Microtubule Depolymerization Inhibits Ethanol-Induced Enhancement of GABAA Responses in Stably Transfected Cells (1996)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 66 (1996), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: We studied whether microtubule organization is important for actions of ethanol on GABAA ergic responses by testing the effects of microtubule depolymerization on ethanol enhancement of GABA action in mouse L(tk−) cells stably transfected with GABAA receptor α1β1γ2L subunits. The microtubule-disrupting agents colchicine, taxol, and vinblastine completely blocked ethanol-induced enhancement of muscimol-stimulated chloride uptake. β-Lumicolchicine, a colchicine analogue that does not disrupt microtubules, had no effect on ethanol action. Colchicine did not alter the potentiating actions of flunitrazepam or pentobarbital on muscimol-stimulated chloride uptake. Thus, colchicine specifically inhibited the potentiating action of ethanol. From these findings, we conclude that intact microtubules are required for ethanol-induced enhancement of GABAA responses and suggest that a mechanism involving microtubules produces posttranslational modifications that are necessary for ethanol sensitivity in this cell system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1996.66031318.x
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  • 7
    Electronic Resource
    Electronic Resource
    Benzodiazepine Treatment Causes Uncoupling of Recombinant GABAA Receptors Expressed in Stably Transfected Cells (1994)
    Oxford, UK : Blackwell Science Ltd
    Journal of neurochemistry 63 (1994), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: GABAA and benzodiazepine receptors are allosterically coupled, and occupation of either receptor site increases the affinity of the other. Chronic exposure of primary neuronal cultures to benzodiazepine agonists reduces these allosteric interactions. Neurons express multiple GABAA receptor subunits, and it has been suggested that uncoupling is due to changes in the subunit composition of the receptor. To determine if uncoupling could be observed with expression of defined subunits, mouse Ltk− cells stably transfected with GABAA receptors (bovine α1, β1, and γ2L subunits) were treated with flunitrazepam (Flu) or clonazepam. The increase in [3H]Flu binding affinity caused by GABA (GABA shift or coupling) was significantly reduced in cells treated chronically with the benzodiazepines, whereas the KD and Bmax of [3H]Flu binding were unaffected. The uncoupling caused by clonazepam treatment occurred rapidly with a t1/2 of ∼30 min. The EC50 for clonazepam treatment was ∼0.3 µM, and cotreatment with the benzodiazepine antagonist Ro 15-1788 (5.6 µM) prevented the effect of clonazepam. The uncoupling observed in this system was not accompanied by receptor internalization, is unlikely to be due to changes in receptor subunit composition, and probably represents posttranslational changes. The rapid regulation of allosteric coupling by benzodiazepine treatment of the stably transfected cells should provide insights to the mechanisms of coupling between GABAA and benzodiazepine receptors as well as benzodiazepine tolerance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1471-4159.1994.63062349.x
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  • 8
    Electronic Resource
    Electronic Resource
    Activation of Calcium-Phospholipid-Dependent Protein Kinase Enhances Benzodiazepine and Barbiturate Potentiation of the GABAA Receptor (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 60 (1993), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: Abstract: The effect of calcium-phospholipid-dependent protein kinase (PKC) on GABAA receptor function was examined in Xenopus oocytes expressing recombinant human GABAA receptor using two-electrode voltage-clamp measurements. Phorbol 12-myristate 13-acetate (PMA), a potent activator of PKC, inhibited GABA-gated chloride currents by ∼72% in oocytes expressing αlβ1γ2L subunit cDNAs. Phorbol 12-monomyristate (PMM), a negative control analogue of PMA, did not alter GABAA receptor responses. To investigate whether activation of PKC could alter the modulatory responses of the receptor complex, the effect of PMA on benzodiazepine and barbiturate potentiation of GABA responses was assessed. In oocytes expressing αlβ1γ2s subunit cDNAs, diazepam (300 nM) potentiated GABA responses by ∼160%. Following PMA (5-25 nM/) treatment, diazepam potentiation was significantly increased to 333%. No effect of the inactive phorbol ester PMM (25 nM) was observed on diazepam potentiation of GABA responses. PMA enhancement of diazepam potentiation of GABA responses was also observed in oocytes expressing αlβ1γ2Ssubunit cDNAs, indicating that the unique PKC site present in the Tγ2LL subunit is not required for observing the PMA effect. PMA (5-25 nM) also enhanced pentobarbital potentiation of GABA responses. In oocytes expressing αlβ1γ2L subunit cDNAs, pentobarbital (25 μM) potentiated GABA receptor responses by ∼97%. Following treatment with PMA (5-25 nM), pentobarbital potentiation of GABA responses increased to ∼ 156%. The present results suggest that protein phosphorylation may alter the coupling between the allosteric modulatory sites within the GABAA receptor complex.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1993.tb13432.x
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  • 9
    Electronic Resource
    Electronic Resource
    Cyclic AMP-Dependent Protein Kinase Decreases γ-Aminobutyric AcidA Receptor-Mediated 36Q1− Uptake by Brain Microsacs (1991)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of neurochemistry 57 (1991), S. 0 
    Details
    ISSN: 1471-4159
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Medicine
    Notes: The effect of cyclic AMP (cAMP)-dependent protein phosphorylation on γ-aminobutyric acidA (GABAA) receptor function was examined using isolated brain membrane vesicles (microsacs). Muscimol-stimulated 36C1− uptake was studied in mouse brain microsacs permeabilized to introduce the catalytic subunit of cAMP- dependent protein kinase (PKA). At both submaximal and maximally effective concentrations of muscimol, PKA inhibited muscimol-stimulated 36C1− uptake by ∼25%. Jn parallel experiments, PKA and [γ-32P]ATP were introduced into the microsacs, and we attempted to immunoprecipitatc the entire GABAA receptor complex, under nondenaturing conditions, using an anti-α1-subunit antibody. Data from such experiments show that PKA increases the phosphorylation of several microsac proteins, including a 66-kDa polypeptide specifically immunoprecipitated with the GABAA receptor anti-α1 subunit antibody. Phosphopeptide mapping of the 66-kDa polypeptide demonstrated a 14-kDa fragment similar to that obtained with the purified, PKA-phosphorylated GABAA receptor. These results provide evidence that the catalytic subunit of PKA inhibits the function of brain G ABAAreceptors and demonstrate that this functional change is concomitant with an increase in protein phosphorylation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1471-4159.1991.tb03806.x
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  • 10
    Electronic Resource
    Electronic Resource
    ANESTHETICS AND ION CHANNELS: Molecular Models and Sites of Action1 (2001)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Pharmacology 41 (2001), S. 23-51 
    Details
    ISSN: 0362-1642
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Chemistry and Pharmacology
    Notes: Abstract The mechanisms of general anesthesia in the central nervous system are finally yielding to molecular examination. As a result of research during the past several decades, a group of ligand-gated ion channels have emerged as plausible targets for general anesthetics. Molecular biology techniques have greatly accelerated attempts to classify ligand-gated ion channel sensitivity to general anesthetics, and have identified the sites of receptor subunits critical for anesthetic modulation using chimeric and mutated receptors. The experimental data have facilitated the construction of tenable molecular models for anesthetic binding sites, which in turn allows structural predictions to be tested. In vivo significance of a putative anesthetic target can now be examined by targeted gene manipulations in mice. In this review, we summarize from a molecular perspective recent advances in our understanding of mechanisms of action of general anesthetics on ligand-gated ion channels.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.pharmtox.41.1.23
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