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Biomedical subjects

D C White

Publications and source records attributed to D C White.

At least 109 records · Page 6Linked to original sources
PubMed1989

Effect of propofol on the auditory evoked response and oesophageal contractility.

Six patients were anaesthetized with 70% nitrous oxide in oxygen supplemented by infusion of propofol 40, 80, 120, 160 and 200 micrograms kg-1 min-1 sequentially in successive 10-min periods. Auditory evoked response (AER) and lower oesophageal contractility (LOC) were monitored. The AER findings were consistent with those noted in previous studies of i.v. agents. Early cortical waves showed attenuation of Pa and Nb amplitude (P less than 0.01) and increase in Pa and Nb latency (P less than 0.01; P less than 0.05) with increasing blood concentrations of propofol. Brainstem waves were not affected significantly. LOC, provoked and spontaneous, showed no consistent relationship with blood concentration of propofol. The two variables AER and LOC were not related.

Adolescent↗
PubMed1989

Characterization of bacteria that suppress rhizoctonia damping-off in bark compost media by analysis of Fatty Acid biomarkers.

Examination of cucumber roots (Cucumis sativus L.) grown in bark compost media and of the surrounding edaphic substrate showed profiles of polar lipid fatty acids commonly found in bacteria. The composition of fatty acids in these profiles differed significantly between roots grown in a medium naturally suppressive to Rhizoctonia damping-off and roots from a conducive medium. Cucumber roots from the suppressive medium had higher proportions of cis-vaccenic acid (18:1 omega 7c) and the iso-branched monoenoic fatty acid i17:1 omega 8 but lower proportions of several iso- and anteiso-branched fatty acids compared with roots from the conducive medium. The concentrations of the bacterial fatty acids were significantly lower in the surrounding media. However, the suppressive and conducive growth substrates had differences in the composition of the bacterial fatty acids similar to those found between the cucumber roots proper. These results suggest major differences in bacterial community composition between suppressive and conducive systems. Fatty acid analyses were also utilized to examine the effects on bacterial community composition of root colonization by Flavobacterium balustinum 299, a biocontrol agent. The concentration of the most prominent fatty acid in this bacterium, i17:1 omega 8, was increased on roots produced from inoculated seeds in a medium rendered suppressive by the treatment. This change was concomitant with a significant increase in the concentration of 18:1 omega 7c, not present in the lipids of the antagonist, indicating a shift in the microflora from a conducive to a suppressive bacterial community.

Journal Article↗
PubMed1988

Changes in the ATPase activity of insect fibrillar flight muscle during sinusoidal length oscillation probed by phosphate-water oxygen exchange.

Extensive phosphate-water oxygen exchange occurs when ATP is hydrolyzed in an [18O]water medium by length oscillated and Ca2+-activated, chemically skinned fibers from the flight muscle of the giant waterbug Lethocerus indicus. For fibers which are length oscillated under conditions not optimal for ATPase activity or oscillatory work, the pattern of exchange shows two pathways for hydrolysis. One pathway has low exchange, because steps controlling Pi release are rapid; the other pathway has high exchange and slow Pi release. Steps controlling Pi release appear rate-limiting for changes in the high-exchange ATPase activity that occur on varying the frequency and amplitude of oscillation. On length oscillation under conditions of optimal ATPase activity or work, only the high-exchange pathway is present. Cross-bridges following the high-exchange pathway are therefore responsible for oscillatory work, the physiological function of the muscle, and behave uniformly with respect to oxygen exchange. The single pathway and the magnitude of the ATPase activity are both similar to results with isometric strained fibers (Lund, J., Webb, M. R., and White, D. C. S. (1987) J. Biol. Chem. 262, 8584-8590). A qualitative model is suggested for oscillatory work by cross-bridges, arising from the common periodicity of the thick and thin filaments in insect flight muscle.

Adenosine Triphosphatases↗
PubMed1988

Propofol and emesis.

Ninety patients scheduled to undergo minor gynaecological surgery were divided into three groups. Group 1 received propofol only, for both induction and maintenance of anaesthesia. Group 2 were given propofol for induction and maintenance but inhaled 66% nitrous oxide in addition. Group 3 had propofol for induction only and were given nitrous oxide and enflurane thereafter. The incidence of nausea in group 1 was 0%, in group 2, 3.4% and in group 3, 9.4%. No patient vomited.

Adult↗
PubMed1988

Microbial biomass, activity, and community structure of water and particulates retrieved by backflow from a waterflood injection well.

Oil field injection water was allowed to back flow from two wells at the Packard drill site in Los Angeles, Calif., and was sampled at various times to obtain information about the biomass, potential activity, and community structure of the microbiota in the reservoir formation and in the injection water. Biomass was greatest in water samples that came from the zone near the injection site and dropped off sharply in subsequent samples, which were assumed to come from zones farther away from the well. Samples obtained from near the well also had visible exopolysaccharide blankets, as seen in scanning electron microscopic preparations. In one of the wells that was sampled, rates of glucose or acetate incorporation into microbial lipids correlated with biomass; but in the other well, activities correlated with the sampling time (volume of water that back flowed). Transmission electron micrographs showed a diverse, gram-negative bacterial population in a variety of physiological states. The analysis of the phospholipid ester-linked fatty acid profiles of the samples revealed consistently large proportions of 18:1omega7c fatty acids, indicating the presence of many anaerobes, facultative organisms, or both. Proportions of cyclopropyl fatty acids and ratios of trans/cis monoenoic compounds increased with the volume of water that back flowed (analogous with the distance into the formation), while the ratio of unsaturated/saturated compounds decreased, possibly indicating higher levels of stress or starvation in the microbial communities farthest from the injection well. Greater than 90% of the total biomass was trapped on glass fiber filters, indicating that the microbiota were largely attached to particles or were clumped. These sampling techniques and analytical methods may prove useful in monitoring for problems with microbes (e.g., plugging) in waterflood operations and in the preparation of water injection wells for enhanced oil recovery by the use of microbes.

Journal Article↗
PubMed1988

Phospholipid Fatty Acid Composition of the Syntrophic Anaerobic Bacterium Syntrophomonas wolfei.

The membrane phospholipid fatty acids (PLFAs) from several cocultures and a pure culture of Syntrophomonas wolfei were determined by capillary column gas chromatography. Cocultures of S. wolfei with a Desulfovibrio sp. contained PLFAs from both organisms, whereas PLFAs from a coculture with Methanospirillum hungatei contained very little biomass to analyze. The pure culture of S. wolfei grown on crotonate provided the best material for analysis of the PLFAs. The predominant PLFAs of S. wolfei were the monounsaturated 16:1omega7c and 16:1omega9c and the saturated 16:0 and 14:0. A low concentration of the diunsaturated 18:2omega6 was detected. The PLFA analysis provides additional information for consideration in the determination of the profile of PLFAs obtained from anaerobic environments. In addition, this information may aid in the understanding of the physiology and phylogeny of S. wolfei and other syntrophic bacteria.

Journal Article↗
PubMed1988

Mineralization of trichloroethylene by heterotrophic enrichment cultures.

Microbial consortia capable of aerobically degrading more than 99% of exogenous trichloroethylene (TCE) (50 mg/liter) were collected from TCE-contaminated subsurface sediments and grown in enrichment cultures. TCE at concentrations greater than 300 mg/liter was not degraded, nor was TCE used by the consortia as a sole energy source. Energy sources which permitted growth included tryptone-yeast extract, methanol, methane, and propane. The optimum temperature range for growth and subsequent TCE consumption was 22 to 37 degrees C, and the pH optimum was 7.0 to 8.1. Utilization of TCE occurred only after apparent microbial growth had ceased. The major end products recovered were hydrochloric acid and carbon dioxide. Minor products included dichloroethylene, vinylidine chloride, and, possibly, chloroform.

Journal Article↗
PubMed1988

Cross-bridge kinetics in asynchronous insect flight muscle.

Calcium-activated insect flight muscle is further activated by small applied strain. We have investigated the mechanism of strain activation by measuring the extent of oxygen exchange between phosphate and water during ATP hydrolysis by Ca2+ -activated, chemically skinned fibers from the flight muscle of the giant waterbug Lethocerus indicus at different degrees of strain. The maximally activated insect fibres show a pattern of oxygen exchange which is well fitted by a single pathway of ATP hydrolysis. This differs from results with rabbit muscle, which show a more complicated form of oxygen exchange. We ascribe this difference to the different pattern of distribution of myosin heads on the thick filament. Calcium-activated, but unstrained, insect fibres also require more than a simple pathway of ATP hydrolysis to account for the pattern of oxygen exchange. The transition between the more complex pathway and the simple pathway occurs over a very narrow range of strain, centred at zero strain (rest length in the relaxed fibres). We describe how the experimental results of strain activation might occur, based upon Wray's description of filament geometries, but taking into account likely sarcomere mechanics. The pattern of oxygen exchange found in fully activated insect fibres suggests that the process of phosphate release from the actomyosin is rate limiting, implying that the main tension-generating state is an AM.ADP.Pi complex.

Actomyosin↗
PubMed1987

Changes in the ATPase activity of insect fibrillar flight muscle during calcium and strain activation probed by phosphate-water oxygen exchange.

During ATP hydrolysis by Ca2+-activated chemically skinned fibers from the flight muscle of the giant waterbug Lethocerus indicus, there is extensive phosphate-water oxygen exchange. For unstrained fibers the pattern of exchange shows that there is more than one pathway for hydrolysis, due to the ATPase activity of cross-bridges. Multiple pathways are an established property of both vertebrate actomyosin and fibers. The pattern of exchange can be fitted by two pathways: one with low exchange because the step(s) controlling Pi release are rapid, the other with high exchange and slow Pi release. The high-exchange pathway is responsible for most of the increase in ATPase activity on Ca2+ activation. On strain activation, only the high-exchange pathway is present, accounting for all the ATPase increase and responsible for force generation. In fully activated fibers, the cross-bridges which hydrolyze ATP and generate force behave uniformly with respect to oxygen exchange. The exchange pattern shows that the rate of Pi release changes dramatically over a very narrow strain increase. Step(s) controlling Pi release are at least partially rate-limiting for the overall ATPase reaction. The results are discussed in relation to models for strain activation and the identity of force-generating states.

Adenosine Triphosphatases↗
PubMed1987

Analysis of the ATPase mechanism of myosin subfragment 1 from insect fibrillar flight muscle in the presence and absence of actin, using phosphate-water oxygen exchange measurements.

Phosphate-water oxygen exchange was measured during ATPase activity of myosin subfragment 1, isolated from Lethocerus flight muscle. The result supports a mechanism including a rapid reversible ATP cleavage step followed by slow Pi release, so that extensive exchange occurs by multiple reversals of the cleavage step. Interaction with actin accelerates Pi release and reduces the extent of exchange. These properties are similar to vertebrate skeletal muscle subfragment 1. Differences in kinetic properties between insect flight and rabbit skeletal muscle exhibited in the fibres, particularly in respect of the strain activation of insect flight muscle, are not exhibited in the isolated myosin heads and are therefore probably due to organization within the fibre lattice.

Actins↗
PubMed1987

Variation in Phospholipid Ester-Linked Fatty Acids and Carotenoids of Desiccated Nostoc commune (Cyanobacteria) from Different Geographic Locations.

Profiles of phospholipid fatty acids and carotenoids in desiccated Nostoc commune (cyanobacteria) collected from China, Federal Republic of Germany, and Antarctica and in axenic cultures of the desiccation-tolerant strains N. commune UTEX 584 and Hydrocoleum strain GOEI were analyzed. The phospholipid fatty acid contents of the three samples of desiccated Nostoc species were all similar, and the dominant compounds were 16:1omega7c, 16:0, 18:2omega6, 18:3omega3, and 18:1omega7c. In comparison with the field materials, N. commune UTEX 584 had a much higher ratio of 18:2omega6 to 18:3omega3 (5.36) and a significantly lower ratio of 18:1omega7c to 18:1omega9c (1.86). Compound 18:3 was present in large amounts in the samples of desiccated Nostoc species which had been subject, in situ, to repeated cycles of drying and rewetting, but represented only a small fraction of the total fatty acids of the strains grown in liquid culture. This finding is in contrast to the data obtained from studies on the effects of drought and water stress on higher plants. Field materials of Nostoc species contained, in contrast to the axenic strains, significant amounts of apocarotenoids and a P384 pigment which, upon reduction with NaBH(4), yielded a mixture of a chlorophyll derivative and a compound with an absorption maximum of 451 nm. A clear distinction can be made between the carotenoid contents of the axenic cultures and the desiccated field materials. In the former, beta-carotene and echinenone predominate; in the latter, canthaxanthin and the beta-gamma series of carotenoids are found.

Journal Article↗
PubMed1986

The ATPase kinetics of insect fibrillar flight muscle myosin subfragment-1.

Myosin subfragment-1 (S1) has been prepared from the fibrillar flight muscles of the giant water bug Lethocerus by chymotryptic digestion of myofibrillar suspensions in the absence of magnesium ions. The S1 obtained has a single light chain and a heavy chain with molecular weights of about 18 kDa and 90 kDa respectively. The kinetics of the elementary steps of the magnesium-dependent ATPase of insect S1 and rabbit S1 are similar, both with ATP and with ATP analogues as substrates. However, the presence of variable amounts of inactive protein within our preparation means that several rate constants cannot be obtained with as much precision in the case of insect S1. The most striking differences between the rabbit and insect S1 are values for the Vmax and the Km of actin during actin-activation of the MgATPase activity, which are up to an order of magnitude lower and greater in the insect than in the rabbit, respectively. The mechanical properties of strain activation and of capacity to do extended oscillatory work are unique to insect fibrillar flight muscle and distinguish it from vertebrate striated muscle. It is likely that these properties reflect differences in the organization of actin and myosin within the respective filament lattices rather than intrinsic differences in the ATPase mechanisms of the isolated myosin molecules from the two types of muscle.

Actomyosin↗
PubMed1986

Model system for studies of microbial dynamics at exuding surfaces such as the rhizosphere.

An autoclavable all-glass system for studying microbial dynamics at permeable surfaces is described. Standard hydrophobic or hydrophilic membranes (46-mm diameter) of various pore sizes were supported on a glass frit through which nutrient solutions were pumped by a peristaltic pump. The pump provided a precisely controlled flow at speeds of 0.5 to 500 ml of defined or natural cell exudates per h, which passed through the membrane into a receiving vessel. The construction allowed a choice of membranes, which could be modified. The system was tested with a bacterium, isolated from rape plant roots (Brassica napus L.), that was inoculated on a hydrophilic membrane filter and allowed to develop into a biofilm. A defined medium with a composition resembling that of natural rape root exudate was pumped through the membrane at 0.5 ml/h. Scanning electron microscopic examinations indicated that the inoculum formed microcolonies embedded in exopolymers evenly distributed over the membrane surface. The lipid composition and content of poly-beta-hydroxybutyrate in free-living and adhered cells were determined by gas chromatography. The bacterial consumption of amino acids in the exudate was also studied.

Amino Acids↗
PubMed1986

Effect of nutrient deprivation on lipid, carbohydrate, DNA, RNA, and protein levels in Vibrio cholerae.

The response of Vibrio cholerae to low nutrient levels was determined by measuring the concentrations of lipids, carbohydrates, DNA, RNA, and proteins over a 30-day starvation period. Ultrastructural integrity was observed by transmission electron microscopy. Total lipids and carbohydrates declined rapidly within the first 7 days, while DNA and protein exhibited a more constant decline over the 30 days of starvation. In contrast, RNA showed little decrease upon starvation. Although neutral lipids were lost, the percentage of neutral lipids did not decline as rapidly as the phospholipids. Detectable levels of poly-beta-hydroxybutyrate disappeared completely by 7 days. Carbohydrate profiles revealed the relative loss of the five-carbon sugar ribose and N-acetylglucosamine and a relative increase in the total six-carbon sugars, especially glucose. Morphologically, ribosomes appeared to exhibit no structural change, while inclusion bodies and mesosomelike structures disappeared completely, and cell wall and membrane integrity was lost. The data suggest that V. cholerae differs somewhat from other marine vibrios in its response to low nutrients but shares some characteristics in common with them. The data also suggest that certain lipids and carbohydrates may provide the endogenous energy sources needed for dormancy preparation and cell maintenance under nutrient starvation.

Bacterial Proteins↗
PubMed1986

Phospholipid ester-linked fatty acid profile changes during nutrient deprivation of Vibrio cholerae: increases in the trans/cis ratio and proportions of cyclopropyl fatty acids.

The phospholipid ester-linked fatty acids of 0-day-, 7-day-, and 30-day-starved cultures of Vibrio cholerae were compared. Statistically significant trends were noted in the fatty acid profiles as the cells starved. The amount of the cis-monoenoic fatty acids declined (e.g., 16:1 omega 7c: 0 day, 39%; 7 day, 18%; 30 day, 11%). In contrast, the saturated fatty acids, the cyclopropyl derivatives of the cis-monoenoic fatty acids, and trans-monoenoic fatty acids increased during starvation. For instance, the amounts of 16:1 omega 7t were: 0 day, 1%; 7 day, 13%; 30 day, 17%; which increased the trans/cis ratio for 16:1 omega 7 from 0.02 (0 day) to 0.70 (7 day) to 1.56 (30 day). This may be due to the reported high turnover rates of cis-monoenoic fatty acids of membrane phospholipids and the availability of enzymes for the metabolism of these isomers. During starvation-induced phospholipid loss, the cis-monoenoic fatty acids would, therefore, be preferentially utilized. The ability to either synthesize trans-monoenoic acids (which are not easily metabolized by bacteria) or modify the more volatile cis-monoenoic acids to their cyclopropyl derivatives may be a survival mechanism which helps maintain a functional (although structurally altered) membrane during starvation-induced lipid utilization. In addition, a trans/cis fatty acid ratio significantly greater than that reported for most bacterial cultures and environmental samples (less than 0.1) may be used as a starvation or stress lipid index. Such a ratio could help determine the nutritional status of ultramicrobacteria and other reported dormant cells in natural aquatic environments.(ABSTRACT TRUNCATED AT 250 WORDS)

Cyclopropanes↗
PubMed1986

A method for the separation and characterization of archaebacterial signature ether lipids.

A reproducible high performance liquid chromatography (HPLC) method for the separation of diethers and tetraethers isolated from archaebacterial phospholipids is reported. Fourier transform infrared spectroscopy was used for structural confirmation of these signature lipids. A mixture of tetraethers from a thermoacidophilic archaebacteria was resolved into three major components by the normal phase separation. These components were differentiated by Fourier self-deconvolution of infrared spectra. The application of the HPLC technique to environmental samples may provide an accurate assessment of archaebacterial biomass in various microbial communities.

Archaea↗