RESUMEN
BACKGROUND: Volatile anesthetics decrease Ca²âº entry through voltage-dependent Ca²âº channels. Ca influences neurotransmitter release and neuronal excitability. Because volatile anesthetics act specifically on the spinal cord to produce immobility, we examined the effect of isoflurane and the nonimmobilizers F6 (1, 2-dichlorohexafluorocyclobutane) and F8 (2, 3-dichlorooctafluorobutane) on CaV1 and CaV2 Ca²âº channels in spinal cord motor neurons and dorsal root ganglion neurons. METHODS: Using patch clamping, we compared the effects of isoflurane with those of F6 and F8 on CaV1 and CaV2 channels in isolated, cultured adult rat spinal cord motor neurons and on CaV1 and CaV2 channels in adult rat dorsal root ganglion sensory neurons. RESULTS: In spinal cord motor neurons, isoflurane, but not F6 or F8, inhibited currents through CaV1 channels. Isoflurane and at least one of the nonimmobilizers inhibited currents through CaV1 and CaV2 channels in dorsal root ganglion neurons and CaV2 in spinal cord motor neurons. CONCLUSIONS: The findings that isoflurane, but not nonimmobilizers, inhibited CaV1 Ca²âº channels in spinal cord motor neurons are consistent with the notion that spinal cord motor neurons might mediate isoflurane-induced immobility. Additional studies are required to examine whether inhibition of CaV1 calcium currents in spinal cord motor neurons is sufficient or whether actions on other channels/proteins contribute to isoflurane-induced immobility.
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Anestésicos por Inhalación/farmacología , Bloqueadores de los Canales de Calcio/farmacología , Canales de Calcio Tipo L/efectos de los fármacos , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Isoflurano/farmacología , Neuronas Motoras/efectos de los fármacos , Médula Espinal/efectos de los fármacos , Animales , Ganglios Espinales/citología , Ganglios Espinales/efectos de los fármacos , Técnicas de Placa-Clamp , Cultivo Primario de Células , Ratas , Ratas Sprague-Dawley , Células Receptoras Sensoriales/efectos de los fármacos , Médula Espinal/citologíaRESUMEN
BACKGROUND: Modulation of γ-aminobutyric acid type A receptors (GABAARs) by general anesthetics may contribute to their ability to produce amnesia. Receptors containing α5 subunits, which mediate tonic and slow synaptic inhibition, are co-localized with ß3 and γ2 subunits in dendritic layers of the hippocampus and are sensitive to low (amnestic) concentrations of anesthetics. Because α5 and ß3 subunits influence performance in hippocampus-dependent learning tasks in the presence and absence of general anesthetics, and the experimental inhaled drug 1,2-dichlorohexafluorocyclobutane (F6) impairs hippocampus-dependent learning, we hypothesized that F6 would modulate receptors that incorporate α5 and ß3 subunits. We hypothesized further that the ß3(N265M) mutation, which controls receptor modulation by general anesthetics, would similarly influence modulation by F6. METHODS: Using whole-cell electrophysiologic recording techniques, we tested the effects of F6 at concentrations ranging from 4 to 16 µM on receptors expressed in human embryonic kidney 293 cells. We measured drug modulation of wild-type α5ß3 and α5ß3γ2L GABAARs and receptors harboring the ß3(N265M) mutation. We also tested the effects of F6 on α1ß2γ2L receptors, which were reported previously to be insensitive to this drug when expressed in Xenopus oocytes. RESULTS: F6 enhanced the responses of wild-type α5ß3γ2L but not α1ß2γ2L receptors to low concentrations of GABA in a concentration-dependent manner. Receptors that incorporated the mutant ß3(N265M) subunit were insensitive to F6. When applied together with a high concentration of GABA, F6 blocked currents through α5ß3 but not α5ß3γ2L receptors. F6 did not alter deactivation of α5ß3γ2L receptors after brief high- concentration pulses of GABA. CONCLUSIONS: The nonimmobilizer F6 modulates GABAARs in a manner that depends on subunit composition and mode of receptor activation by GABA, supporting a possible role for α5-containing receptors in suppression of learning and memory by F6. Furthermore, common structural requirements indicate that similar molecular mechanisms may be responsible for the enhancing effects of F6 and conventional general anesthetics.
Asunto(s)
Anestésicos/farmacología , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Moduladores del GABA/farmacología , Mutación , Receptores de GABA-A/efectos de los fármacos , Receptores de GABA-A/genética , Ácido gamma-Aminobutírico/farmacología , Relación Dosis-Respuesta a Droga , Células HEK293 , Humanos , Cinética , Potenciales de la Membrana , Receptores de GABA-A/metabolismoRESUMEN
BACKGROUND: Numerous studies demonstrate that anesthetic-induced unconsciousness is accompanied by activation of hypothalamic sleep-promoting neurons, which occurs through both pre- and postsynaptic mechanisms. However, the correlation between drug exposure, neuronal activation, and onset of hypnosis remains incompletely understood. Moreover, the degree to which anesthetics activate both endogenous populations of γ-aminobutyric acid (GABA)ergic sleep-promoting neurons within the ventrolateral preoptic (VLPO) and median preoptic nuclei remains unknown. METHODS: Mice were exposed to oxygen, hypnotic doses of isoflurane or halothane, or 1,2-dichlorohexafluorocyclobutane (F6), a nonimmobilizer. Hypothalamic brain slices prepared from anesthetic-naive mice were also exposed to oxygen, volatile anesthetics, or F6 ex vivo, both in the presence and absence of tetrodotoxin. Double-label immunohistochemistry was performed to quantify the number of c-Fos-immunoreactive nuclei in the GABAergic subpopulation of neurons in the VLPO and the median preoptic areas to test the hypothesis that volatile anesthetics, but not nonimmobilizers, activate sleep-promoting neurons in both nuclei. RESULTS: In vivo exposure to isoflurane and halothane doubled the fraction of active, c-Fos-expressing GABAergic neurons in the VLPO, whereas F6 failed to affect VLPO c-Fos expression. Both in the presence and absence of tetrodotoxin, isoflurane dose-dependently increased c-Fos expression in GABAergic neurons ex vivo, whereas F6 failed to alter expression. In GABAergic neurons of the median preoptic area, c-Fos expression increased with isoflurane and F6, but not with halothane exposure. CONCLUSIONS: Anesthetic unconsciousness is not accompanied by global activation of all putative sleep-promoting neurons. However, within the VLPO hypnotic doses of volatile anesthetics, but not nonimmobilizers, activate putative sleep-promoting neurons, correlating with the appearance of the hypnotic state.
Asunto(s)
Anestésicos/farmacología , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Neuronas/efectos de los fármacos , Reclutamiento Neurofisiológico/efectos de los fármacos , Sueño/efectos de los fármacos , Animales , Glutamato Descarboxilasa/metabolismo , Ratones , Ratones Endogámicos C57BL , Área Preóptica/citología , Área Preóptica/efectos de los fármacos , Proteínas Proto-Oncogénicas c-fos/metabolismo , Ácido gamma-Aminobutírico/fisiologíaRESUMEN
A prior exposure to the volatile anesthetic isoflurane has been shown to induce neuroprotection in rats. This phenomenon is called preconditioning. We designed this study to determine whether the potency of volatile anesthetics in inducing neuropreconditioning is related to their potency to induce anesthesia. Cerebellar slices of adult male Sprague-Dawley rats were exposed to various concentrations of isoflurane, halothane, sevoflurane, desflurane or the nonimmobilizer 1,2-dichlorohexafluorocyclobutane for 15 min, followed by a 15-min drug-free period, and then were subjected to oxygen-glucose deprivation for 10 min at 37 degrees C. After a 5-h recovery at 37 degrees C, brain slices were used for quantification of cell injury by spectrophotometric measurement of formazan produced from 2,3,5-triphenyltetrazolium chloride. All four volatile anesthetics induced a concentration-dependent preconditioning effect. The EC50 for this effect induced by isoflurane, halothane, sevoflurane or desflurane was 221, 173, 184 and 929 microM, respectively. This EC50 was linearly correlated with the aqueous concentration of one minimum alveolar concentration. The volatile anesthetic preconditioning-induced neuroprotection was abolished by DL-threo-beta-hydroxyaspartic acid, DL-threo-beta-benzyloxyaspartate or dihydrokainate, glutamate transporter inhibitors. The volatile nonimmobilizer 1,2-dichlorohexafluorocyclobutane at any concentrations tested in the study did not induce a significant preconditioning effect. Isoflurane preconditioning did not change the oxygen-glucose deprivation-induced glutamate accumulation. These results suggest that the preconditioning-induced neuroprotection by volatile anesthetics is not agent-specific. Mechanisms that are involved in inducing anesthesia may contribute to the induction of preconditioning effect by volatile anesthetics. Modification of glutamate transporter activity may be one of such mechanisms to induce these protective effects.
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Anestésicos por Inhalación/farmacología , Isquemia Encefálica/prevención & control , Cerebelo/efectos de los fármacos , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Animales , Isquemia Encefálica/patología , Hipoxia de la Célula , Cerebelo/patología , Glucosa/deficiencia , Técnicas In Vitro , Masculino , RatasRESUMEN
The interactions between water and n-perfluoroalkanes or substituted alpha-(omega-)fluoroalkanes used in blood substitute formulations were investigated experimentally and using ab initio calculations. The solubility of water in C(6)-C(9) perfluoroalkanes and five C(8) analogues of substituted fluoroalkanes was measured in the temperature range between 288 and 318 K at atmospheric pressure, using a Karl Fischer coulometer. From these data, the thermodynamic functions and partial molar solvation quantities such as Gibbs energy, enthalpy, and entropy were determined and compared with the interaction energies in 1:1 water-fluoroalkane complexes in vacuum, obtained using B3LYP/6-311++G(d,p). The experimental solubility data indicates a significant specific interaction between the water and the alpha-(omega-)substitute atom (H, I, Br, or Cl) in the fluoroalkanes.
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Sustitutos Sanguíneos/química , Fluorocarburos/química , Preparaciones Farmacéuticas/química , Soluciones Farmacéuticas/química , Agua/química , Sustitutos Sanguíneos/farmacología , Clorofluorocarburos/química , Clorofluorocarburos/farmacología , Fluorocarburos/farmacología , Hidrocarburos Bromados/química , Hidrocarburos Bromados/farmacología , Hidrocarburos Yodados/química , Hidrocarburos Yodados/farmacología , Modelos Químicos , Solubilidad , TermodinámicaRESUMEN
STUDY OBJECTIVES: Mometasone furoate dry powder inhaler (MF-DPI) [400 mug] is an inhaled corticosteroid (ICS) that is effective in the treatment of asthma. MF-DPI has a low potential for suppression of the hypothalamic-pituitary-adrenal (HPA) axis at its clinical dose. The effect of MF-DPI, 400 microg qd, on the HPA axis was compared to that of beclomethasone dipropionate (BDP) using hydrofluoroalkane (HFA) and chlorofluorocarbon (CFC) propellants via metered-dose inhalers (MDIs) twice daily. DESIGN AND INTERVENTIONS: This randomized, third-party blind, parallel-group study compared the effects of MF-DPI 400 mug one puff qd in the morning (n = 18), HFA-BDP 200 microg two puffs MDI bid (n = 18), and CFC-BDP 400 microg two puffs MDI bid (n = 17) for 14 days on the area under the 24-h serum cortisol concentrations curve (AUC(0-24)) and on total 24-h urinary free cortisol excretion in mild asthmatic subjects. Effects on morning/evening peak expiratory flow (PEF) and on inhaled albuterol use were also assessed. Adverse events that occurred during or > or = 30 days after the study were recorded. RESULTS: The mean decrease from baseline in the serum cortisol concentrations AUC(0-24) in the MF-DPI group was significantly less than in either the HFA-BDP (p = 0.024) or the CFC-BDP (p = 0.011) groups. Decreases in serum cortisol concentrations AUC(0-24) in the two BDP groups did not differ from one another. The MF-DPI group trended toward higher morning and evening PEF than either BDP group. Treatment-associated adverse events were reported by seven subjects in the MF-DPI group, vs one subject in the HFA-BDP and three subjects in the CFC-BDP groups; these were mild, and no subject discontinued treatment due to an adverse event. CONCLUSIONS: Fourteen days of treatment with MF-DPI 400 microg qd was associated with a significantly lesser decrease in the serum cortisol concentrations AUC(0-24) compared with HFA-BDP 200 microg MDI or CFC-BDP 400 microg MDI bid.
Asunto(s)
Propelentes de Aerosoles/farmacología , Antiasmáticos/farmacología , Antiinflamatorios/farmacología , Asma/tratamiento farmacológico , Beclometasona/farmacología , Clorofluorocarburos/farmacología , Sistema Hipotálamo-Hipofisario/efectos de los fármacos , Sistema Hipófiso-Suprarrenal/efectos de los fármacos , Pregnadienodioles/farmacología , Administración por Inhalación , Adolescente , Adulto , Propelentes de Aerosoles/administración & dosificación , Anciano , Análisis de Varianza , Antiasmáticos/administración & dosificación , Antiinflamatorios/administración & dosificación , Área Bajo la Curva , Beclometasona/administración & dosificación , Clorofluorocarburos/administración & dosificación , Creatinina/orina , Femenino , Humanos , Hidrocarburos Fluorados/administración & dosificación , Hidrocarburos Fluorados/farmacología , Hidrocortisona/sangre , Recién Nacido , Masculino , Persona de Mediana Edad , Furoato de Mometasona , Pregnadienodioles/administración & dosificaciónRESUMEN
UNLABELLED: To identify anesthetic effects that produce the different components of the complex anesthetic state, the so-called nonanesthetics/nonimmobilizer classes of compounds have been introduced. Because ionotropic gamma-aminobutyric acid type A (GABA(A)) receptors play an important role in the mediation of the central nervous system (CNS) effects of general anesthetics, and their susceptibility to modulation by various drugs depends on subunit composition, we have compared the effect of the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (F6) on GABA(A) receptors expressed in human embryonic kidney 293 cells transfected with alpha1beta2 versus alpha1beta2gamma2s subunits. Using rapid perfusion and whole-cell recording techniques, we found that, like isoflurane, F6 blocked GABA-induced currents through alpha1beta2 receptors but, unlike isoflurane, the presence of the gamma2s subunit conferred complete resistance to block by F6. Also, in contrast to isoflurane, F6 had no effect on deactivation kinetics of GABA-induced currents in either type of receptor. We conclude that modulation of alphabetagamma receptors plays little or no role in the actions of F6, but the block of alphabeta receptors may contribute to its effects on the CNS. IMPLICATIONS: Gamma-aminobutyric acidA receptors are the target of numerous drugs affecting the central nervous system. The subunit composition of the GABAA receptors governs their interaction with many drugs. We investigated whether the gamma-subunit influences the interaction with the nonimmobilizer F6.
Asunto(s)
Anestésicos/farmacología , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Antagonistas del GABA/farmacología , Antagonistas de Receptores de GABA-A , Línea Celular , Canales de Cloruro/antagonistas & inhibidores , Canales de Cloruro/efectos de los fármacos , Humanos , Potenciales de la Membrana/efectos de los fármacos , Técnicas de Placa-Clamp , Proteínas Recombinantes/antagonistas & inhibidores , Ácido gamma-Aminobutírico/farmacologíaRESUMEN
Metered inhalers using chlorofluorocarbon (CFC) propellents have been gradually replaced by new devices that use hydrofluoroalkanes (HFAs) as their propellents, which are less harmful to the environment. This reformulation led to a substantial improvement of the previous technologies applied to inhalation devices and of the physical characteristics of drugs delivered. In particular, inhaled corticosteroids, such as beclomethasone dipropionate (BDP) which is of fundamental importance in the long-term management of bronchial asthma, took advantage of this reformulation. Unlike the preparation beclomethasone dipropionate and chlorofluorocarbon (BDP-CFC) which was a suspension, that of beclomethasone dipropionate and a hydrofluoroalkane (BDP-HFA) is a solution and produces an aerosol with a mean aerodynamic particle size of 1.1 microm, which is much smaller than the particle size of 3.5-4.0 microm, obtained with the BDP-CFC. The particles of BDP-HFA can then deposit in the lungs in a larger amount, and particularly in the more peripheral airways where the inflammatory process starts in the case of bronchial asthma. A 12-week use of BDP-HFA ensured a significant better control of the bronchial response to methacholine (MCh) than the corresponding use of BDP-CFC for the same duration. The therapeutic performance of BDP-HFA proved much higher and allowed the substantial reduction of the therapeutic daily dose for the clinical asthma management, being the increased and more peripheral deposition of BDP-HFA is presumed to play a crucial role.
Asunto(s)
Propelentes de Aerosoles/farmacología , Antiasmáticos/administración & dosificación , Asma/tratamiento farmacológico , Bronquios/efectos de los fármacos , Hidrocarburos Fluorados/farmacología , Cloruro de Metacolina , Administración por Inhalación , Adulto , Propelentes de Aerosoles/administración & dosificación , Anciano , Asma/fisiopatología , Beclometasona/administración & dosificación , Broncoconstrictores , Clorofluorocarburos/administración & dosificación , Clorofluorocarburos/farmacología , Estudios Cruzados , Método Doble Ciego , Femenino , Humanos , Hidrocarburos Fluorados/administración & dosificación , Masculino , Inhaladores de Dosis Medida , Persona de Mediana Edad , Pruebas de Función RespiratoriaRESUMEN
The nonimmobilizer 1,2-dichlorohexafluorocyclobutane (F6; also known as 2N) causes amnesia and seizures at concentrations less than and more than, respectively, than that predicted to cause immobility (MACpred). The molecular and cellular basis of these effects is not known. We reported previously that F6 has no effect on synaptic gamma aminobutyric acid (GABA)A receptors located on the somata of hippocampal pyramidal cells. However, in hippocampal neurons, GABAA receptors that are located subsynaptically have different pharmacologic properties from those at extrasynaptic sites, and these classes of receptors may serve different physiologic functions. Therefore, we investigated the effects of F6 and isoflurane on currents mediated predominantly by extrasynaptic GABAA receptors harvested from hippocampal neurons by exposing nucleated excised patches to brief, high-concentration pulses of GABA. We found that extrasynaptic GABAA receptors in the majority of neurons located in the pyramidal cell layer are insensitive to F6 at concentrations up to 110 microM, although receptors harvested from one putative interneuron were potently inhibited by 43 microM of F6. By contrast, isoflurane consistently reduced the peak amplitude and slowed deactivation of currents mediated by extrasynaptic receptors, similar to its effect on synaptic receptors. These results demonstrate the selective sensitivity of extrasynaptic GABAA receptors on pyramidal neurons to isoflurane but not F6.
Asunto(s)
Anestésicos por Inhalación/farmacología , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Isoflurano/farmacología , Neuronas/efectos de los fármacos , Receptores de GABA-A/efectos de los fármacos , Algoritmos , Animales , Técnicas In Vitro , Masculino , Potenciales de la Membrana/efectos de los fármacos , Técnicas de Placa-Clamp , Células Piramidales/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Sinapsis/efectos de los fármacosAsunto(s)
Bovinos/metabolismo , Clorofluorocarburos de Metano/farmacología , Clorofluorocarburos/farmacología , Efecto Invernadero , Metano/metabolismo , Animales , Bovinos/microbiología , Clorofluorocarburos/química , Clorofluorocarburos de Metano/química , Cobalto/química , Cobalto/metabolismo , Mucosa Gástrica/metabolismo , Estómago/efectos de los fármacos , Estómago/microbiología , Vitamina B 12/química , Vitamina B 12/metabolismoRESUMEN
BACKGROUND: 1,1,1,2 Tetrafluoroethane is a hydrofluoroalkane (HFA) that is replacing chlorofluorocarbons (CFC) as a medical aerosol propellant in an attempt to reduce damage to the ozone layer. This study compared the effects of HFA- and CFC-based inhalers on four anaesthetic gas monitoring systems. METHODS: The HFA- and CFC-based inhalers were activated in close proximity to the sample line of two Datex Ohmeda, an Agilent and a Siemens infrared anaesthetic agent monitoring systems. The effects were recorded on each system for five common anaesthetic agents. RESULTS: The HFA inhaler caused either maximal false positive readings (with the exception of desflurane) or transient measurement failure on all systems. The Datex Ohmeda AS/3 system misidentified the HFA inhaler as carbon dioxide at low concentration (2 +/- 0 mm Hg). The CFC-based inhaler caused a minor false-positive reading (0.4 +/- 0%) for halothane only on the Datex Ohmeda AS/3 system only and was misidentified as carbon dioxide at 33.3 (sd 2.1) mm x Hg and 22.4 (8.9) mm x Hg by the Agilent and Siemens systems. CONCLUSIONS: The HFA inhaler adversely affected all equipment tested. The infrared spectra of HFA and the common anaesthetic gases have considerable overlap at the 8-12 microm range that is not shared by the CFCs. The differences in spectral overlap explain the different effects of the HFA and CFC propellants. Anaesthetic gas concentration data may be erroneous using the HFA-based inhalers.
Asunto(s)
Propelentes de Aerosoles/farmacología , Anestesia por Inhalación/instrumentación , Anestésicos por Inhalación/análisis , Hidrocarburos Fluorados/farmacología , Monitoreo Intraoperatorio/instrumentación , Albuterol/administración & dosificación , Albuterol/farmacología , Broncodilatadores/administración & dosificación , Broncodilatadores/farmacología , Clorofluorocarburos/farmacología , Reacciones Falso Positivas , Humanos , Ipratropio/administración & dosificación , Ipratropio/farmacología , Nebulizadores y Vaporizadores , Espectrofotometría Infrarroja/instrumentaciónRESUMEN
Trifluoroacetylated (TFA)-protein adducts were investigated by immunoblotting in liver and plasma of guinea pigs treated with the hepatotoxic anaesthetic halothane or the chlorofluorocarbon replacement 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123). Male outbred Hartley guinea pigs (320-400 g) were administered HCFC-123 (1, 5, 10 and 15 mmol/kg b.w.) or halothane (positive control, 10 mmol/kg b.w.) i.p. in corn oil. Blood and liver samples were collected 24 h after administration of HCFC-123 or halothane. Immunoreactive bands were demonstrated in liver microsomes at all HCFC-123 and halothane concentrations, and in plasma of animals treated with 10 and 15 mmol/kg b.w. HCFC-123 and 10 mmol/kg b.w. halothane, while no alteration of microsomal P450 content or monooxygenase activities markers of the P450 2A, 2E1 and 2B isoforms was observed. Instead, when HCFC-123 was administered at doses of 1 and 5 mmol/kg b.w., the 2E1-dependent p-nitrophenol hydroxylase activity was enhanced. The presence of TFA-proteins in plasma was always associated with hepatic damage. However, mild liver damage in some animals treated with 1 or 5 mmol/kg b.w. HCFC-123 was not associated with the presence of TFA-proteins in plasma. This indicates a lower threshold dose for the appearance of TFA-proteins or damage in the liver (1 mmol/kg b.w.) than for the presence of TFA-proteins in plasma (10 mmol/kg b.w.), thus suggesting that the presence of TFA-proteins in plasma may be the result of liver damage.
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Anestésicos por Inhalación/farmacología , Clorofluorocarburos/farmacología , Halotano/farmacología , Hígado/efectos de los fármacos , Hígado/metabolismo , Proteínas/química , Ácido Trifluoroacético/química , Alanina Transaminasa/sangre , Animales , Aspartato Aminotransferasas/sangre , Compuestos Azo , Biomarcadores , Enfermedad Hepática Inducida por Sustancias y Drogas/enzimología , Enfermedad Hepática Inducida por Sustancias y Drogas/patología , Clorofluorocarburos de Etano , Colorantes , Creatina Quinasa/sangre , Sistema Enzimático del Citocromo P-450/metabolismo , Relación Dosis-Respuesta a Droga , Electroforesis en Gel de Poliacrilamida , Cobayas , Immunoblotting , Hígado/enzimología , Masculino , Ácido Trifluoroacético/sangreRESUMEN
BACKGROUND: The rate of onset of drug actions in experiments with brain slices in vitro can vary widely. One factor that influences the rate is access to tissue sites of action. To study the effects of the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (F6, also termed 2N in the literature) on physiologic processes under defined tissue concentrations, the authors performed electrophysiologic measurements of the effects of F6 and halothane, measured the uptake of these agents into brain tissue, and performed computational modeling to determine concentration-depth profiles during drug application. METHODS: Hippocampal brain slices 500 microm thick were prepared from adult rats. Evoked population responses in the CA1 region were obtained using extracellular recordings and electrical stimulation of the Schaffer collateral pathway. F6 (24 microm) and halothane (270 microm) were applied via superfusion for 40 min. Uptake of drug into tissue slices was measured using gas chromatography. Computational modeling was used to obtain estimates of drug diffusion coefficients in brain tissue and to calculate tissue concentration as a function of time and depth during drug application. RESULTS: Halothane reduced the amplitude of the evoked population spike and reduced the population excitatory postsynaptic potential slope. F6 had no effect on either measure. Uptake experiments yielded a diffusion coefficient of 0.1 x 10-6 cm2/s for F6 and 0.8 x 10-6 cm2/s for halothane. After 40 min of drug application, the concentration reached at tissue depths from which physiologic signals were obtained, approximately the top 200 microm of the slice, was estimated to be 58% of the final equilibrium value for F6 and 93% for halothane. CONCLUSIONS: Diffusion into tissue is substantially slower for F6 than for halothane, and its impact is great enough that this must be considered when designing or interpreting in vitro experiments. However, impaired access does not account for the lack of effect of F6 on electrophysiologic responses in rat hippocampal slices.
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Anestésicos por Inhalación/farmacocinética , Encéfalo/metabolismo , Algoritmos , Animales , Fenómenos Químicos , Química Física , Clorofluorocarburos/farmacocinética , Clorofluorocarburos/farmacología , Cromatografía de Gases , Simulación por Computador , Ciclobutanos/farmacocinética , Ciclobutanos/farmacología , Difusión , Electrofisiología , Halotano/farmacocinética , Halotano/farmacología , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Técnicas In Vitro , Masculino , Potenciales de la Membrana/efectos de los fármacos , Potenciales de la Membrana/fisiología , Modelos Biológicos , Ratas , Ratas Sprague-DawleyRESUMEN
UNLABELLED: In animals, the conventional inhaled anesthetic, isoflurane, impairs learning fear to context and fear to tone, doing so at concentrations that produce amnesia in humans. Nonimmobilizers are inhaled compounds that do not produce immobility in response to noxious stimulation, nor do they decrease the requirement for conventional inhaled anesthetics. Like isoflurane, the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N) impairs learning at concentrations less than those predicted from its lipophilicity to produce anesthesia. The capacity of the nonimmobilizer di-(2,2,2,-trifluoroethyl) ether (flurothyl) to affect learning and memory has not been studied. Both nonimmobilizers can cause convulsions. We hypothesized that if isoflurane, 2N, and flurothyl act by the same mechanism to impair learning and memory, their effects should be additive. We found that isoflurane, 2N, and flurothyl (each, alone) impaired learning fear to context and fear to tone in rats, with the nonimmobilizers doing so at concentrations less than those that cause convulsions. (Fear was defined by freezing [volitional immobility] in the presence of the conditioned stimulus [context or tone].) However, the combination of isoflurane and 2N or flurothyl produced an antagonistic rather than an additive effect on learning, a finding in conflict with our hypothesis. And flurothyl was no less potent than 2N (at least no less potent relative to the concentration of each that produced convulsions) in its capacity to impair learning. We conclude that conventional inhaled anesthetics and nonimmobilizers impair learning and memory by different mechanisms. The basis for this impairment remains unknown. IMPLICATIONS: Conventional inhaled anesthetics and nonimmobilizers are antagonistic in their effects on learning and memory, and this finding suggests that they impair learning and memory, at least in part, by different mechanisms.
Asunto(s)
Anestésicos por Inhalación/farmacología , Clorofluorocarburos/antagonistas & inhibidores , Clorofluorocarburos/farmacología , Condicionamiento Psicológico/efectos de los fármacos , Convulsivantes/farmacología , Ciclobutanos/antagonistas & inhibidores , Ciclobutanos/farmacología , Miedo/efectos de los fármacos , Flurotilo/antagonistas & inhibidores , Flurotilo/farmacología , Isoflurano/farmacología , Estimulación Acústica , Algoritmos , Amígdala del Cerebelo/efectos de los fármacos , Amígdala del Cerebelo/fisiología , Animales , Conducta Animal/efectos de los fármacos , Ambiente , Hipocampo/efectos de los fármacos , Hipocampo/fisiología , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
UNLABELLED: There are acetylcholine receptors throughout the central nervous system, and they may mediate some forms and aspects of convulsive activity. Most high-affinity binding sites on nicotinic acetylcholine receptors for nicotine, cytisine, and epibatidine in the brain contain the beta2 subunit of the receptor. Transitional inhaled compounds (compounds less potent than predicted from their lipophilicity and the Meyer-Overton hypothesis) and nonimmobilizers (compounds that do not produce immobility despite a lipophilicity that suggests anesthetic qualities as predicted from the Meyer-Overton hypothesis) can produce convulsions. The nonimmobilizer flurothyl [di-(2,2,2,-trifluoroethyl)ether] blocks the action of gamma-aminobutyric acid on gamma-aminobutyric acid(A) receptors, whereas the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N, also called F6) does not. 2N can block the action of acetylcholine on nicotinic acetylcholine receptors. We examined the relative capacities of these compounds to cause convulsions in mice having and lacking the beta2 subunit of the acetylcholine receptor. The partial pressure causing convulsions in half the mice (the 50% effective concentration [EC(50)]) was the same as in control mice. For the knockout mice, the EC(50) for flurothyl was 0.00170 +/- 0.00030 atm (mean +/- SD), and for 2N, it was 0.0345 +/- 0.0041 atm. For the control mice, the respective values were 0.00172 +/- 0.00057 atm and 0.0341 +/- 0.0048 atm. The ratio of the 2N to flurothyl EC(50) values was 20.8 +/- 3.5 for the knockout mice and 21.7 +/- 7.0 for the control mice. These results do not support the notion that acetylcholine receptors are important mediators of the capacity of 2N or flurothyl to cause convulsions. However, we also found that both nonimmobilizers inhibit rat alpha4beta2 neuronal nicotinic acetylcholine receptors at EC(50) partial pressures (0.00091 atm and 0.062 atm for flurothyl and 2N, respectively) that approximate those that produce convulsions (0.0015 atm and 0.04 atm). IMPLICATIONS: The results from the present study provide conflicting data concerning the notion that acetylcholine receptors mediate the capacity of nonimmobilizers to produce convulsions.
Asunto(s)
Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Flurotilo/farmacología , Receptores Nicotínicos/fisiología , Convulsiones/inducido químicamente , Animales , Antagonistas de Receptores de GABA-A , Ratones , Ratones Endogámicos C57BL , Ratones NoqueadosRESUMEN
Volatile anesthetic agent, 1-chloro-1,2,2-trifluorocyclobutane (F3), was found to alter gramicidin A channel function by enhancing Na(+) transport (. Biophys. J. 77:739-746). Whether this functional change is associated with structural alternation is evaluated by circular dichroism and nuclear magnetic resonance spectroscopy. The circular dichroism and nuclear magnetic resonance results indicate that at low millimolar concentrations, 1-chloro-1,2,2-trifluorocyclobutane causes minimal changes in gramicidin A channel structure in sodium dodecyl sulfate micelles. All hydrogen bonds between channel backbones are well maintained in the presence of 1-chloro-1,2,2-trifluorocyclobutane, and the channel structure is stable. The finding supports the notion that low affinity drugs such as volatile anesthetics and alcohols can cause significant changes in protein function without necessarily producing associated changes in protein structure. To understand the molecular mechanism of general anesthesia, it is important to recognize that in addition to structural changes, other protein properties, including dynamic characteristics of channel motions, may also be of functional significance.
Asunto(s)
Gramicidina/farmacología , Canales Iónicos , Anestésicos/farmacología , Clorofluorocarburos/farmacología , Dicroismo Circular , Ciclobutanos/farmacología , Relación Dosis-Respuesta a Droga , Gramicidina/química , Enlace de Hidrógeno , Espectroscopía de Resonancia Magnética , Micelas , Modelos Moleculares , Protones , Sodio/metabolismo , Dodecil Sulfato de Sodio/farmacología , Triptófano/químicaRESUMEN
UNLABELLED: Malignant hyperthermia (MH) is an autosomal dominant, potentially fatal pharmacogenetic disorder of skeletal muscle. Approximately half of all known MH families show a linkage to the ryanodine receptor type 1 (RY1) gene. Although our knowledge of the diagnosis, genetics, and therapy of MH has improved, the exact pathogenesis and the role of volatile anesthetics as trigger substances for an MH crisis remain unknown. Compounds that do not obey the Meyer-Overton hypothesis (i.e., nonimmobilizers) are today an important part of research on anesthetic mechanisms. We designed this study to test the hypothesis that the nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N) compared with halothane has different effects on in vitro muscle contractures of muscle bundles from MH-susceptible (MHS) individuals. In vitro muscle contracture tests were performed with either halothane (approximately 660 microM, equivalent to approximately 4 minimum alveolar anesthetic concentration [MAC]) or 2N ( approximately 100 microM, equivalent to approximately 5 times predicted MAC). MAC is defined as the anesthetic concentration that prevents nocifensive movements after a surgical stimulus in 50% of subjects. In contrast to halothane, 2N caused only minimal muscle contractures in muscle bundles from six MHS patients (0.13 g [0.04-0.31 g] vs 1.95 g [1.60-4.70 g], median values and ranges; P = 0.004). Halothane and 2N differ in their effects on muscle contractures of MHS individuals, possibly because of a differing action on MH RY1. IMPLICATIONS: Using in vitro contracture tests, we showed that halothane and the nonimmobilizer 1,2-dichlorohexafluorocyclobutane differ in their effects on contractures of muscle bundles from individuals susceptible to malignant hyperthermia (MH) as a result of their differing action on MH ryanodine receptors. These findings render this receptor a possible molecular target for volatile anesthetic action.
Asunto(s)
Anestésicos/farmacología , Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Halotano/farmacología , Hipertermia Maligna/fisiopatología , Contracción Muscular/efectos de los fármacos , Adulto , Anciano , Anestésicos por Inhalación/farmacología , Femenino , Predisposición Genética a la Enfermedad , Humanos , Técnicas In Vitro , Masculino , Hipertermia Maligna/genética , Persona de Mediana Edad , Músculo Esquelético/efectos de los fármacos , Músculo Esquelético/fisiologíaRESUMEN
UNLABELLED: The nonimmobilizer 1,2-dichlorohexafluorocyclobutane (2N, also termed F6) does not suppress movement to noxious stimuli but does suppress learning of fear-potentiated startle. The mechanism whereby 2N suppresses this learning is unknown. Herein, we report the effect of 2N on suppression of two other forms of learning, fear conditioning to context and to tone. Because 2N does not cause sedation, we could study the effect of 2N on short-term memory (memory for fear conditioning measured during or immediately after training) as well as on long-term memory (measured 24 h after training). The EC(50) for suppression of long-term memory (the concentration decreasing memory by 50%) of fear conditioning to context was 2.00% plus/minus 0.01% (mean plus/minus SEM), and for fear conditioning to tone was 3.45% plus/minus 0.26%, (P < 0.05). The EC(50) for suppression of short-term memory of fear conditioning to context was 2.59% plus/minus 0.21% (P < 0.05, compared with long-term memory of context conditioning), whereas short-term memory of fear conditioning to tone was not suppressed by 3.5%, the largest concentration studied. Thus, short-term memory resists the depressant effect of 2N more than long-term memory, fear conditioning to tone is less vulnerable to the effect of 2N than fear conditioning to context, and 3.5% 2N does not preclude transmission of tone and shock signals to the site where tone-shock associations are formed. IMPLICATIONS: The nonimmobilizer 1,2-dichlorohexafluorocyclobutane has a greater depressant effect on long-term memory than short-term memory, suggesting that it impairs the processes responsible for the retention of memory more than for the formation of memory itself.
Asunto(s)
Clorofluorocarburos/farmacología , Ciclobutanos/farmacología , Memoria a Corto Plazo/efectos de los fármacos , Memoria/efectos de los fármacos , Animales , Condicionamiento Psicológico/efectos de los fármacos , Miedo , Masculino , Ratas , Ratas Sprague-DawleyRESUMEN
The effects of halothane, 1,1-dichloro-2,2,2-trifluoroethane (HCFC-123) and 1,1-dichloro-1-fluoroethane (HCFC-141b) on the P450 system in olfactory and hepatic microsomes of bovine and rat have been investigated. In the in vitro experiments, all three compounds decreased olfactory CYP-dependent activities in microsomes from both species, especially under anaerobic conditions, halothane showing the greatest effect. Hepatic activities were not affected. A selective olfactory CYP depletion was also observed in vivo after treatment with halothane, but not with HCFC-123 or HCFC-141b. A loss of olfactory ethoxycoumarin-O-deethylase activity was also found both in vitro and in vivo experiments, suggesting that a CYP2A isoform may be the main target of inactivation. The present results therefore suggest that CYP2A, the major isoform expressed in the olfactory tissue of mammals, may be particularly prone to catalyze the reductive metabolism of halothane both in anaerobic and aerobic conditions.
Asunto(s)
Anestésicos por Inhalación/efectos adversos , Clorofluorocarburos/efectos adversos , Sistema Enzimático del Citocromo P-450/metabolismo , Halotano/efectos adversos , Nariz/patología , Anestésicos por Inhalación/farmacología , Animales , Catálisis , Bovinos , Clorofluorocarburos/farmacología , Clorofluorocarburos de Etano , Halotano/farmacología , Isoenzimas , Masculino , Microsomas Hepáticos/efectos de los fármacos , Microsomas Hepáticos/enzimología , Nariz/efectos de los fármacos , Ratas , Ratas Sprague-DawleyRESUMEN
UNLABELLED: The differences in potencies of optical isomers of anesthetics support the hypothesis that anesthetics act by specific receptor interactions. Diastereoisomerism and geometrical isomerism offer further tests of this hypothesis but have not been explored. They are the subject of this report. We quantified the nonimmobilizing and convulsant properties of the cis and trans diastereomers of the nonimmobilizer 2N (1,2-dichlorohexafluorocyclobutane). Although the lipophilicity of the diastereomers predicts complete anesthesia at the partial pressures applied, neither diastereomer had anesthetic activity alone, and the cis form may have a small (10%) capacity to antagonize anesthesia, as defined by additive effects on the MAC (the minimum alveolar concentration required to suppress movement to a noxious stimulus in 50% of rats) of desflurane. Both diastereomers produced convulsions, the cis form being nearly twice as potent as the trans form: convulsant 50% effective dose (mean +/- SD) was 0.039 +/- 0.009 atmospheres (atm) for the purified cis and 0.064 +/- 0.009 atm for the purified trans isomer. The MAC value for cis-1,2-dichloroethylene equaled 0.0071 +/- 0.0006 atm, and MAC for trans-1,2-dichloroethylene equaled 0.0183 +/- 0.0031 atm. In qualitative accord with the Meyer-Overton hypothesis, the greater cis potency was associated with a greater lipophilicity. However, the product of MAC x solubility differed between the cis and trans isomers by 40%-50%. We conclude that neither the cis nor trans isomers of 2N have anesthetic properties, but isomerism does influence 2N's convulsant properties and the anesthetic properties of dichloroethylene. These isomeric effects may be as useful in defining receptor-anesthetic interactions as those found with optical isomers. IMPLICATIONS: Cis-trans isomerism can influence the convulsant properties of the nonimmobilizer 2N (1,2-dichlorohexafluorocyclobutane) and the anesthetic properties of dichloroethylene. Such isomeric effects may be as useful as those found with optical isomers in defining receptor-anesthetic interactions.