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At least 1,171 records · Page 65Linked to original sources
PubMed1997

Effects of volatile anaesthetics on the membrane potential and ion channels of cultured neocortical astrocytes.

Volatile anaesthetics cause changes in the membrane resting potential of central neurons. This effect probably arises from actions on neuronal ion channels, but may also involve alterations in the ion composition of the extracellular space. Since glial cells play a key role in regulating the extracellular ion composition in the brains of mammals, we analyzed the effects of halothane, isoflurane and enflurane on the membrane conductances and ion channels of cultured cortical astrocytes. Astrocytes were dissociated from the neocortex of 0-2-day old rats and grown in culture for 3-4 weeks. Anaesthetic-induced changes in the membrane potential were recorded in the whole cell current-clamp configuration of the patch-clamp technique. We further studied the effects of halothane and enflurane on single ion channels in excised membrane patches. At concentrations corresponding to 1-2 MAC (1 MAC induces general anaesthesia in 50% of the patients and rats), membrane potentials recorded in the presence of enflurane, isoflurane and halothane did not differ significantly from the control values. At higher concentrations, effects of enflurane and halothane, but not of isoflurane, were statistically significant. Single-channel recordings revealed that halothane and enflurane activated a high conductance anion channel, which possibly mediated the effects observed during whole cell recordings. In less than 10% of the membrane patches, volatile anaesthetics either increased or decreased the mean open time of K+-selective ion channels without altering single-channel conductances. In summary, it seems unlikely that the actions of volatile anaesthetics described here are involved in the state of general anaesthesia. Statistically significant effects occurred at concentrations ten times higher than those required to cause half-maximal depression of action potential firing of neocortical neurons in cultured brain slices. However, it cannot be excluded that the changes observed in the membrane conductance of cortical astrocytes disturb the physiological function of these cells, thereby influencing the membrane resting potential of neurons.

Anesthetics, Inhalation↗
PubMed1999

Volatile anesthetics modulate the binding of guanine nucleotides to the alpha subunits of heterotrimeric GTP binding proteins.

The effects of volatile anesthetics on guanine nucleotide binding to the purified alpha subunits of heterotrimeric GTP binding (G) proteins were studied. At sub-anesthetic doses, halothane, isoflurane, enflurane and sevoflurane inhibit exchange of GTPgammaS for GDP bound to Galpha subunits and markedly enhance the dissociation of GTPgammaS, but fail to suppress GDPbetaS release. Nucleotide exchange from non-myristoylated Galpha(i1) is similarly inhibited in the absence of any membrane lipid or detergent. The degrees of inhibition of GDP/GTPgammaS exchange and enhancement of GTPgammaS dissociation are in the same order: alpha(i2)alpha(i1)alpha(i3)alpha(s). By contrast, Galpha(o), which is closely related to Galpha(i), is completely insensitive to anesthetics. We conclude that volatile agents, at clinically relevant doses, have a direct effect on the conformation and stability of the GTP/Mg(2+) bound state of some, but not all Galpha subunits. By destabilizing this state, volatile agents may uncouple metabotropic and other heptahelical receptors from pathways modulating neuronal excitation.

Anesthetics, Inhalation↗
PubMed1987

Screening of volatile compounds present in human blood using retention indices in gas chromatography.

The retention index in gas chromatography was introduced to screen volatile compounds in blood. Sixty-one organic compounds with high volatility were determined using a gas chromatograph with a flame ionization detector and a packed column system with 10% OV-17. Porapak P was used as a supplementary column for determining alcohol. Detection limits were determined for several substances. This method was used to analyse blood samples obtained at autopsy from patients suspected of solvent abuse. This approach proved to be superior to conventional gas chromatography in that mixed unknown volatiles in the blood could be identified simply and rapidly.

Adult↗
PubMed1975

Trace analysis of organic volatiles in water by gas chromatography-mass spectrometry with glass capillary columns.

Traces of volatile organic materials in water have been concentrated by gas phase stripping and adsorption onto a porous polymer. A simple all-glass sampling device is proposed which allows efficient concentration at elevated temperatures. Sample transfer from absorbent into a gas chromatographic column is effected by a simple one-step procedure involving heat desorption. The capacity of the absorbent has been determined for a number of model substances which are found in water. Under the sampling conditions used, compounds being less volatile than benzene are usually quantitatively retained, with some exceptions. Separations were effected with highly efficient glass capillary columns. Water samples, collected from a small number of locations, included both tap water and untreated waters. A number of volatiles have been determined by gas chromatography-mass spectrometry in drinking water and in a river which flows through an industrialized area. The drinking water examined contains a large number of chlorinated and brominated compounds whereas the river water is largely free from this class of substances. Derivatives of camphor and terpenes have been identified in this particular river.

Absorption↗
PubMed1976

Column elution and concentration of volatile compounds in biological fluids.

A new solvent elution method is described for the isolation and concentration of volatile metabolites in biological fluids. The procedure involves elution of the sample with a solvent through a micro-column of an adsorbent into glass-wool and evaporation of the excess solvent in a stream of helium at room temperature. The volatiles are revocered by subsequent heat desorption into a chromatogrpaphic system. Both elution and evaporation are made in a single step using a novel sampling device. Since the technique is based on liquid-solid adsorption chromatography, the adsorbent-solvent system which gives the maximum yield of volatile constituents was studied. The method is simple, highly efficient and reproducible, requiring only small volumes of biological fluids (less than 100 mul).

Adsorption↗
PubMed1984

Determination of highly volatile organic contaminants in water by the closed-loop gaseous stripping technique followed by thermal desorption of the activated carbon filters.

Very volatile organic contaminants in water were determined by using closed-loop gaseous stripping combined with thermal desorption from the activated carbon filter into a high-resolution gas chromatograph. The operating parameters for quantitative applications were evaluated. The solvent-free thermal desorption procedure permits the determination of compounds that normally elute under the gas chromatographic solvent peak (e.g., dichloromethane and Freons). Sixteen volatile compounds with boiling points in the range -30 to 120 degrees C were determined with an overall recovery of 12-52%. Qualitative determinations of volatiles from a secondary sewage effluent were in good agreement with the results found by two more established methods.

Chromatography, Gas↗
PubMed2003

Enflurane as an internal standard in monitoring halogenated volatile anaesthetics by headspace gas chromatography-mass spectrometry.

Recently. we proposed the use of a run-only headspace-GC-MS method for the biological monitoring of ppb concentrations of unmodified volatile anaesthetics (isoflurane, sevoflurane and halothane, plus nitrous oxide) in post-shift urine of operating theatre personnel. The adoption of enflurane (a volatile anaesthetic no longer used in clinical practice) as a poper and viable internal standard improves intra-day and inter-day accuracy in halide quantitation, providing a GC-MS reference method useful in the practice of biomonitoring of exposure of operating theatre personnel to modern volatile anaesthetics (isoflurane. sevoflurane, halothane).

Anesthetics, Inhalation↗
PubMed2001

Enzymatic decomposition of elicitors of plant volatiles in Heliothis virescens and Helicoverpa zea.

Feeding by larvae of Heliothis virescens induces cotton, corn and tobacco plants to release blends of volatile organic compounds that differ in constituent proportions from blends released when Helicoverpa zea larvae feed on the same plant species. The same elicitors (and analogs) of plant biosynthesis and release of volatiles, originally identified in oral secretions of Spodoptera exigua larvae, were also found in oral secretions of H. virescens and H. zea. However, relative amounts of these compounds, particularly N-(17-hydroxylinolenoyl)-L-glutamine (volicitin), 17-hydroxylinolenic acid, and N-linolenoyl-L-glutamine, varied among batches of oral secretions, more so in H. virescens than in H. zea. This variation was due to cleavage of the amide bond of the fatty acid-amino acid conjugates by an enzyme, or enzymes, originating in the midgut. The enzymatic activity in guts of H. virescens was significantly greater than that found in guts of H. zea. Furthermore, H. zea frass contains N-linolenoyl-L-glutamine in more than 0.1% wet weight, while this conjugate comprises only 0.003% wet weight in H. virescens frass. These results indicated that physiological differences between these two species affect the proportions of volicitin and its analogs in the caterpillars. Whether this causes different proportions of volatiles to be released by plants damaged by each caterpillar species is yet to be determined.

Journal Article↗
PubMed1997

Defining Interaction between Electroantennogram Responses of Epiphyas postvittana (lepidoptera: Tortricidae) to Pheromone and Other Volatiles.

The potential for electroantennograms (EAGs) to assist in the measurement of atmospheric pheromone concentrations was examined in laboratory and field experiments by using multiple stimuli, the main component of the pheromone of Epiphyas postvittana, (E)-11-tetradecenyl acetate, its Z-isomer (a behavioral antagonist), and alpha-terpineol (a representative host-plant odor) were presented to the antenna simultaneously to simulate field conditions. The EAG results were compared with predictions from two models describing responses to combined stimuli. Responses are defined as log-additive if they can be described with the equation [EAG((total)) =a (log ([P(x)]+[B(y)])+c] and as linear-additive if the EAG follows the equation [EAG((total)) =a (log [P(x)])+c+a'(log [B(y)])+c'] where [B(y)] is the concentration of the stimulant background odor and [P(x)] is the concentration of an additional odor stimulus. The EAGs elicited by the added stimuli were inversely related to the concentration of the volatile in the background. EAGs elicited by all combined stimuli followed the log-additive model. Our laboratory results were validated in field tests; alpha-terpineol represents the volatiles present in orchard air. In spite of this interaction between the perception of pheromone and plant volatiles, the field EAG can be used for the measurement of atmospheric pheromone concentrations, where background odor concentrations are relatively constant.

Journal Article↗
PubMed2001

Fragrance volatiles of developing and senescing carnation flowers.

Thirteen major volatiles of the carnation flower fragrance signature have been identified by GC/MS. Of these, ten, hexanal, (2E)-hexenal, 1-hexanol, 2-hexanol, 3-hexen-1-ol, nonanal, benzaldehyde, benzyl alcohol, benzyl benzoate and caryophyllene, were quantified. The steady-state levels of these ten volatiles change independently as the flowers develop and senesce, suggesting that their synthesis is developmentally regulated. In addition, the chemical composition of the fragrance signature in naturally senesced flowers proved to be very different from that for flowers that had been induced to senesce prematurely by treatment with ethylene. Thus, senescence-related changes in carnation floral scent appear not to be directly regulated by ethylene. From cellular fractionation studies, it is evident that all of the volatiles, except 2-hexanol, are present in both membranous and cytosolic compartments, suggesting that their synthesis is membrane-associated and that they subsequently partition into the cytosol in accordance with partition coefficients.

Alcohols↗
PubMedDate not supplied

On the volatile inventory of Titan from isotopic abundances in nitrogen and methane.

We analyze recently published nitrogen and hydrogen isotopic data to constrain the initial volatile abundances on Saturn's giant moon Titan. The nitrogen data are interpreted in terms of a model of non-thermal escape processes that lead to enhancement in the heavier isotope. We show that these data do not, in fact, strongly constrain the abundance of nitrogen present in Titan's early atmosphere, and that a wide range of initial atmospheric masses (all larger than the present value) can yield the measured enhancement. The enrichment in deuterated methane is now much better determined than it was when Pinto et al. (1986. Nature 319, 388-390) first proposed a photochemical mechanism to preferentially retain the deuterium. We develop a simple linear theory to provide a more reliable estimate of the relative dissociation rates of normal and deuterated methane. We utilize the improved data and models to compute initial methane reservoirs consistent with the observed enhancement. The result of this analysis agrees with an independent estimate for the initial methane abundance based solely on the present-day rate of photolysis and an assumption of steady state. This consistency in reservoir size is necessary but not sufficient to infer that methane photolysis has proceeded steadily over the age of the solar system to produce large quantities of less volatile organics. Our analysis indicates an epoch of early atmospheric escape of nitrogen, followed by a later addition of methane by outgassing from the interior. The results also suggest that Titan's volatile inventory came in part or largely from a circum-Saturnian disk of material more reducing than the surrounding solar nebula. Many of the ambiguities inherent in the present analysis can be resolved through Cassini-Huygens data and a program of laboratory studies on isotopic and molecular exchange processes. The value of, and interest in, the Cassini-Huygens data can be greatly enhanced if such a program were undertaken prior to the prime phase of the mission.

Atmosphere↗
PubMedDate not supplied

The effect of Yucca schidigera extract on canine and feline faecal volatiles occurring concurrently with faecal aroma amelioration.

Addition of Yucca schidigera extract (YSE) products to canine or feline diets improved faecal aroma as monitored by a human panel. Odour port-gas chromatography (GC) indicated different odour component types in dog faecal volatiles and, in particular, 'faecal'-type odours due to methyl sulfides. GC-mass spectrometry demonstrated several chemical compound classes present in faecal volatiles and quantitation in the cat indicated apparently significant changes in the concentrations of several compounds on YSE treatment, although these were not necessarily aroma components. The potential for direct YSE alteration of aroma perception in a mixture of volatiles, possibly by binding, was demonstrated.

Animals↗
PubMed1998

Responses of laryngeal capsaicin-sensitive receptors to volatile anesthetics in anesthetized dogs.

The responses of laryngeal capsaicin (CAPS)-sensitive receptors to halothane, enflurane, isoflurane and sevoflurane were evaluated in anesthetized spontaneously breathing dogs from the afferent activity of the internal branch of the superior laryngeal nerve. The CAPS-sensitive receptors were clearly distinguished from irritant receptors by their responsiveness to CAPS and their lack of responsiveness to water. All the CAPS-sensitive receptors were significantly stimulated by all volatile anesthetics in a concentration-related manner, and the activation by halothane, enflurane, and isoflurane was significantly greater than by sevoflurane. In contrast, responses of irritant receptors to the volatile anesthetics were divided into three types (stimulation, inhibition or non-response), and did not differ among anesthetics. In conclusion, the present study demonstrated that the CAPS-sensitive receptors were consistently stimulated by halogenated volatile anesthetics and especially by halothane, enflurane, and isoflurane, and that these responses were dissimilar to the variable responses of irritant receptors.

Afferent Pathways↗
PubMed1977

Effect of volatile and gaseous exudates of germinating seeds of some plants on the germinative potentialities of some fungal spores in relation to their ability of absorption of some sugars and nitrogen sources.

Volatile and gaseous exudates of germinating seeds of Z. mays, P. armeniaca, C. sativus, and C. olitorius stimulated the spore germination of B. piluliferum. This stimulation was accompanied with an increase in sugar and nitrogen source absorption during the spore germination. On the other hand, the volatile and gaseous exudates of the germinating seeds of P. sativum inhibited the absorption of both sugar and nitrogen source, as well as the percentage of spore germination. In case of B. cinerea, the effect of the volatile and gaseous exudates of the germinating seeds of all plants used on the fungal spore germination differed according to both the sugar and nitrogen source absorbed.

Absorption↗
PubMed1998

Concentration measures of volatile anesthetics in the aqueous phase using calcium sensitive electrodes.

Volatile anesthetic concentrations have been difficult to measure, but are an important experimental parameter for in vitro studies of anesthetic actions. Calcium sensitive electrodes were investigated as a means of continuously monitoring anesthetic concentrations in artificial cerebrospinal fluids (ACSF). Anesthetic-induced Ca2+ electrode signals were compared at room (22 degrees C) and physiological (35 degrees C) temperatures. Electrophysiological measures of anesthetic effects on synaptic potentials provided a bioassay. Halothane and isoflurane produced negative changes in calcium electrode potentials which were linearly related to concentrations over a clinically useful range (0.5-1.5 MAC). Anesthetic-induced voltages persisted in nominally zero Ca2+ ACSF and even in deionized water. A good correlation (r>0.9) was found for calcium electrode measures of anesthetic concentration and synaptic response depression produced by halothane, at both 22 and 35 degrees C. These results support three conclusions: (1) calcium sensitive electrodes provide a useful measure of volatile anesthetic concentrations in aqueous solution. (2) Care must be taken when using these electrodes for Ca2+ concentration measurements, if a volatile anesthetic is also to be used, since the anesthetic could introduce an appreciable error (>50%). (3) A temperature change of 13 degrees C had surprisingly little effect on Ca2+ electrode responses or on synaptic depression produced by anesthetics.

Anesthetics, Inhalation↗
PubMed1998

Volatile N-nitrosamines in gastric juice of patients with various conditions of the gastrointestinal tract determined by gas chromatography-mass spectrometry and related to intragastric pH and nitrate and nitrite levels.

Gastric juice samples of 71 patients undergoing upper gastrointestinal endoscopy were collected as well as saliva samples from 40 of these patients. Age, sex, endoscopic diagnosis and medication were recorded. The gastric juice samples were analyzed for the presence and quantity of individual volatile N-nitrosamines, which were detected by gas chromatography-mass spectrometry, without prior derivatization. The samples were screened for eight nitrosamines, i.e. N-nitrosodimethylamine, N-nitrosoethylmethylamine, N-nitrosodiethylamine, N-nitrosodi-n-propylamine, N-nitrosodi-n-butylamine, N-nitrosopyrrolidine, N-nitrosopiperidine and N-nitrosomorpholine. The pH of the fresh gastric juice as well as nitrate and nitrite levels of gastric juice and saliva were determined. The mean total level of volatile N-nitrosamines in gastric juice was found to be 4.84 nmol/l (range 0-17.7 nmol/l). The main N-nitrosamines found were N-nitrosodiethylamine (mean concentration 3.1 nmol/l), N-nitrosodimethylamine (mean concentration 0.90 nmol/l) and N-nitrosopyrrolidine (mean concentration 0.38 nmol/l). Significant correlations between mean intragastric pH values and mean N-nitrosodi-n-butylamine level (P = 0.005) and total volatile N-nitrosamine contents (P = 0.009) were observed.

Adolescent↗
PubMed1999

Non-volatile general anaesthetics reduce spinal activity by suppressing plateau potentials.

Non-volatile general anaesthetics are thought to reduce brain activity by potentiating inhibitory GABA(A) receptor channels but also cause adverse effects by suppress ing L-type calcium channels in the heart. In sections of the spinal cord, the non-volatile anaesthetics pentobarbital, thiopental and propofol reduced excitability of sensorimotor neurons by suppressing plateau potentials mediated by L-type calcium channels. This effect was independent of GABA(A) receptor potentiation but occurred in an overlapping concentration range. Therefore, the suppressive effect of non-volatile anaesthetics on L-type calcium channels can contribute to the reduction of spinal sensorimotor activity during anaesthesia. The results support the idea that general anaesthesia is achieved through several mechanisms and suggest that procedures for anaesthesia may be improved by combining selective agents for each mechanism in optimal concentrations.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2001

Effects of volatile and intravenous anesthetics on the uptake of GABA, glutamate and dopamine by their transporters heterologously expressed in COS cells and in rat brain synaptosomes.

Although the neurotransmitter uptake system is considered a possible target for the presynaptic action of anesthetic agents, observations are inconsistent concerning effects on the transporter and their clinical relevance. The present study examined the effects of volatile and intravenous anesthetics on the uptake of GABA, glutamate and dopamine in COS cells heterologously expressing the transporters for these neurotransmitters and in the rat brain synaptosomes. Halothane and isoflurane, but not thiamylal or thiopental, significantly inhibited uptake by COS cell systems of GABA, dopamine and glutamic acid in a concentration-dependent manner within clinically relevant ranges for anesthesia induced by these agents. Similarly, in synaptosomes halothane and isoflurane but not thiopental significantly suppressed the uptake of GABA and glutamic acid, respectively. These results do not support the hypothesis that volatile and intravenous anesthetics exert their action via specific inhibition of GABA uptake to enhance inhibitory GABAergic neuronal activity. Rather, they suggest that presynaptic uptake systems for various neurotransmitters including GABA may be the molecular targets for volatile anesthetic agents.

ATP-Binding Cassette Transporters↗