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At least 811 records · Page 45Linked to original sources
PubMed2004

A new quality control method based on a moving average of "latent reference values" selected from patients' daily test results.

The average of normals(AON) method is a quality control(QC) method that uses measured values of patients' samples instead of QC samples. Because this method is easily affected by fluctuations in the patient population and is insensitive to short-term changes in test values, we developed an alternative method based on the moving average(MA) of latent reference values(LRVs) which are the test results of patients whose other related test results are all within reference intervals. We evaluate the new methodology(MALRV) using seven commonly measured biochemical tests. The LRV of each test were selected with reference to four other items that had the highest coincidences of abnormality. The optimum amount of data needed to compute the MA is determined as that making the coefficient of variation(CV) of the consecutive MA over a study period less than 5.0%. The MALRV is computed each time a new LRV is encountered to monitor quality status continuously. The MALRV CV was within 5.0% when sample sizes were between 20 and 110. When shift and trend simulations were performed with the patient data, the corresponding alterations were detected. MALRV is a useful measure for detecting short-term alterations in patient test results, supplementing the conventional QC chart method.

Clinical Laboratory Techniques↗
PubMed1986

The selectivity filter of voltage-dependent channels formed by phosphoporin (PhoE protein) from E. coli.

Phosphoporin, an Escherichia coli outer membrane-spanning protein re-incorporated in phospholipid planar bilayers generates aqueous channels similar to those of matrix porin. One phosphoporin trimer contains three pores which are induced simultaneously but fluctuate separately between open and closed states. Membrane potential shifts this two-state equilibrium in favour of closed channels. This negative resistance occurs at lower potentials than with matrix porin channels. The phosphoporin channel is poorly anion selective for small solutes. Polyphosphates and other phosphorylated molecules specifically inhibit phosphoporin pore conductance to small ions, a property which is specific to phosphoporin. There is an excellent correlation between the effect of such solutes measured in planar bilayers and their inhibitory effect on beta-lactam antibiotic uptake in vivo by phosphoporin. It is concluded that the phosphoporin channel contains a selectivity filter which is only efficient for larger molecules, most probably through basic residues.

Adenosine Triphosphate↗
PubMed1974

Selection for high mutation rates in chemostats.

Competition experiments in chemostats show that mutator populations of Escherichia coli are more fit than wild type. The increased fitness can be explained by the appearance of new mutants better adapted to the chemostat environment. Fitness values vary between chemostats and are strongly correlated (P < 0.001) with fluctuations in population density.

Bacteriological Techniques↗
PubMed1999

Fluctuating life-history parameters indicating temporal variability in metal adaptation in riverine chironomids

Adaptation to toxicants in animal populations is influenced primarily by two counteracting forces. First, the intensity and duration of peak concentrations of toxicants is responsible for the actual level of selection pressure on the population. Second, the process of adaptation can be disrupted by gene flow as a result of crossings with nontolerant individuals. These counteracting forces were analyzed in riverine insects in which we expected that the level of metal adaptation is subject of considerable fluctuations, due to variable dilution of metals and a variable transport of nontolerant individuals in river water. To this purpose, the stability of metal adaptation in different Chironomus riparius populations was analyzed during a 5-month period in a heavily polluted lowland river. This was examined by measuring mortality, larval dry weight, and accumulation of zinc under laboratory conditions. The results showed that in midge populations originating from metal-contaminated field sites several life-history parameters (like control mortality and growth response under cadmium exposure) of the laboratory reared F1 generations showed considerable temporal variation. In addition, the presence of metal-adapted midge populations was indicated on several occasions on the metal-exposed field sites. Reference populations on the other hand, showed stable life history patterns throughout the sampling period, and no signs of metal adaptation were found. These observations showed that the actual level of metal adaptation varies considerably, both in time and space. Adaptation to metals in riverine chironomids, therefore, should be looked on as a highly dynamic process.http://link. springer-ny.com/link/service/journals/00244/bibs/37n2p175.html

Journal Article↗
PubMed1990

Spontaneous frequency of 6-thioguanine resistant mutants in CHO-AS52 cells after prolonged culturing in the absence of selective agents.

The Escherichia coli xanthine-guanine phosphoribosyl transferase (XPT) containing Chinese hamster ovary (CHO-AS52) cells were studied in our laboratory to evaluate its general applicability in genotoxicity testing of industrial chemicals. Our initial effort was to evaluate the stability of the 6-thioguanine sensitive phenotype. The CHO-AS52 cells were cloned and cultured continuously for over 600 days in the absence of any selective agents. The spontaneous 6-thioguanine resistant mutant frequency was quantified periodically. The frequency was found to increase continuously with time from approximately 20 x 10(-6) to a plateau of approximately 250 x 10(-6) in 122 days. The mutant frequency fluctuated around the plateau value up to the last day of our study, at 648 days after cloning. A similar observation was made for cells that were recloned or treated with aminopterin (to selectively kill 6-TG resistant mutants) at approximately 450 days after the initial cloning. Our data suggest that the xpt gene was stably incorporated in the CHO cells.

Animals↗
PubMed1997

Fluctuating asymmetry and copulation success in lekking black grouse

In lekking black grouse, Tetrao tetrixmales at the centre of the leks obtain more copulations than males at the edges. We found that males with territories at the edge of the lek obtained fewer matings and also have the most asymmetric tarsi. However, when considering the tail ornament (the lyre) no correlation between asymmetry and mating success was found. Although females are unlikely to select males on the basis of tarsus symmetry, asymmetry in this trait may reflect male condition. We suggest that males in poor condition, as reflected by higher levels of fluctuating asymmetry in the tarsi, do not achieve central positions on the lek arena. This would account for the lower success of males with higher levels of fluctuating tarsus asymmetry.

Journal Article↗
PubMed2006

Sex-biased maternal effects reduce ectoparasite-induced mortality in a passerine bird.

Duration of developmental stages in animals evolves under contrasting selection pressures of age-specific mortality and growth requirements. When relative importance of these effects varies across environments, evolution of developmental periods is expected to be slow. In birds, maternal effects on egg-laying order and offspring growth, two proximate determinants of nestling period, should enable rapid adjustment of developmental periods to even widely fluctuating mortality rates. We test this hypothesis in a population of house finches (Carpodacus mexicanus) breeding under two contrasting mortality risks: (i) a nest mite-free condition when selection on offspring survival favors a longer time in the nest; and (ii) a mite infestation when selection favors a shorter nest tenure. Mites affected survival of sons more than daughters, and females breeding under mite infestation laid male eggs last and female eggs first in the clutch, thereby reducing sons' exposure to mites and associated mortality. Strong sex bias in laying order and growth patterns enabled mite-infested offspring to achieve similar fledging size, despite a shorter nest tenure, compared with mite-free conditions. In mite-infested nests, male nestlings hatched at larger sizes, completed growth earlier, and had faster initial growth compared with mite-free nests, whereas mite-infested females grew more slowly but for a longer period of time. A combination of heavily sex-biased laying order and sex differences in growth patterns lowered mite-induced mortality by >10% in both sexes. Thus, strong maternal effects can account for frequently observed, but theoretically unexpected, concordance of mortality risks and growth patterns, especially under fluctuating ecological conditions.

Animals↗
PubMed1993

The progression of retinopathy of prematurity and fluctuation in blood gas tension.

In this study, the relationship between the fluctuation in blood oxygen and carbon dioxide tension and the progression of acute retinopathy of prematurity (ROP) was evaluated. Eighteen extremely premature infants were selected on the basis of the following criteria: gestational age less than 26 weeks, oxygen supply or mechanical ventilation for more than 50 days, transcutaneous oxygen pressure (TcPO2) recorded almost once per hour, and arterial oxygen pressure (PaO2) and arterial carbon dioxide pressure (PaCO2) measured intermittently, for over 8 weeks after birth. All of these infants developed ROP, which ceased progressing in 7 infants (group I, stage 1 or 2 ROP, international classification), but advanced in 11 (group II, stage 3 or 3+). The fluctuations in TcPO2, PaO2, and PaCO2 are represented as coefficients of both variation (CV) and mean difference (D) in these two groups. The results demonstrate that both the CV and D values of TcPO2 are significantly elevated in group II infants compared with group I infants, in the first and second 3-weeks periods, and over the entire 9-week period after birth. The incidences of extreme hyperoxemia (TcPO2 > or = 100 mm Hg) and hypoxemia (TcPO2 < 30 mm Hg) in recorded TcPO2 time series show no significant differences between these two groups. We conclude that extremely premature infants with widely fluctuating arterial oxygen tension may have a greater chance of developing progressive ROP.

Blood Gas Monitoring, Transcutaneous↗
PubMed1984

Fluctuation analysis of sodium channels in epithelia.

When compiling results obtained with various techniques, it appears that the apical Na translocators are channels of high Na, Li selectivity that permit large transport rates at low driving forces. The concentration dependence of the transport rate is linear at least up to 60 mM Nao. The voltage dependence is of the Goldman-Hodgkin-Katz type or closely related to it. Outward facing surface charges have little influence. The flux ratio exponent is close to unity, compatible with single-site channels or multisite channels of low occupancy. Noise analysis has proven particularly suited for following changes in the density of conducting channels in the living preparation, and has shown that cellular and hormonal regulatory mechanisms control Na transport by changing the channel density in a variety of ways.

Aldosterone↗
PubMed1991

Characterization of high-level quinolone resistance in Campylobacter jejuni.

High-level resistance to quinolones has previously been shown to occur in Campylobacter spp. both in vitro and in patients treated with quinolones. We have selected isolates that are resistant to quinolones by plating cells from a susceptible C. jejuni strain, UA535, on medium containing nalidixic acid at 32 micrograms/ml. Fluctuation analysis indicated that resistance occurred by mutation at a frequency of 5 x 10(-8) per cell plated. Unlike what is observed with other gram-negative organisms, the nalidixic acid-resistant mutants demonstrated high-level cross-resistance (MIC, greater than or equal to 4 micrograms/ml) to newer quinolones, including ciprofloxacin, norfloxacin, and temafloxacin, yet remained susceptible to coumermycin A1 and several other unrelated antibiotics. Mutants with an identical resistance phenotype could also be selected from UA535 with ciprofloxacin and norfloxacin at a similar frequency. To study the mechanism of quinolone resistance, DNA gyrases were purified from C. jejuni UA535 and two resistant mutants by heparin-agarose and novobiocin-Sepharose chromatography. After the respective enzyme concentrations were adjusted to equivalent units of activity in the DNA supercoiling reaction, the DNA gyrases from the resistant mutants were found to be 100-fold less susceptible than the wild-type enzyme to inhibition by quinolones. Subunit switching experiments with purified A and B subunits from the wild type and one of the quinolone-resistant mutants indicated that an alteration in the A subunit was responsible for resistance. These results show that a single-step mutation can occur in vitro in the gene encoding DNA gyrase in C. jejuni, producing clinically relevant levels of resistance to the newer quinolones.

Anti-Infective Agents↗
PubMed1976

Simian virus 40-permissive cell interactions: selection and characterization of spontaneously arising monkey cells that are resistant to simian virus 40 infection.

A fraction of permissive cells survive simian virus 40 (SV40) infection. The frequency of such surviving cells depends only upon the concentration of infecting virus, both parental and progeny, to which the cells are exposed during the course of selection. Surviving clones, which can be freed of virus by cloning in the presence of SV40 antiserum, are indistinguishable from parental cells in their growth of characteristics and display no SV40 antigen; thus they are not transformed. Most surviving clones are less than 10% as susceptible as parental cells to SV40 infection; 5 to 10% are less than 1% as susceptible. None of these SV40-resistant clones is absolutely resistant to SV40 infection. Analysis of 16 independently arising resistant clones indicates that they all block SV40 infection at an early stage after adsorption and eclipse but before full uncoating. Viral mutants have been isolated that partially overcome the block to infection in these cells; these host range viruses plaque on resistant lines fivefold more efficiently than wild-type SV40 and have a characteristic plaque morphology. Fluctuation analysis indicates that resistant cells arise spontaneously during the growth of normally susceptible permissive cells. Thus, SV40-resistant cells are selected for, not induced by, SV40 infection.

Adsorption↗
PubMed2006

The maintenance of sex in bacteria is ensured by its potential to reload genes.

Why sex is maintained in nature is a fundamental question in biology. Natural genetic transformation (NGT) is a sexual process by which bacteria actively take up exogenous DNA and use it to replace homologous chromosomal sequences. As it has been demonstrated, the role of NGT in repairing deleterious mutations under constant selection is insufficient for its survival, and the lack of other viable explanations have left no alternative except that DNA uptake provides nucleotides for food. Here we develop a novel simulation approach for the long-term dynamics of genome organization (involving the loss and acquisition of genes) in a bacterial species consisting of a large number of spatially distinct populations subject to independently fluctuating ecological conditions. Our results show that in the presence of weak interpopulation migration NGT is able to subsist as a mechanism to reload locally lost, intermittently selected genes from the collective gene pool of the species through DNA uptake from migrants. Reloading genes and combining them with those in locally adapted genomes allow individual cells to readapt faster to environmental changes. The machinery of transformation survives under a wide range of model parameters readily encompassing real-world biological conditions. These findings imply that the primary role of NGT is not to serve the cell with food, but to provide homologous sequences for restoring genes that have disappeared from or become degraded in the local population.

Bacteria↗
PubMed2000

Transcriptome analysis of fibroblast cells immediate-early after human cytomegalovirus infection.

Human cytomegalovirus (HCMV) has been shown to have the potential to alter cellular gene expression early after infection. However, one-gene approaches and the use of closed system gene expression technologies have identified only few cellular genes whose activity changed immediate-early. We therefore used serial analysis of gene expression (SAGE) to investigate the transcriptional program of human fibroblasts in response to HCMV in the immediate-early phase of infection. Differential expression of various cellular genes was monitored. Transcriptional expression changes of genes coding for ribosomal proteins reflected a general cellular response to starvation and stress. But differential regulation of genes coding for transcription factors and proteins associated with cellular metabolism, homeostasis and cell structure may represent transcriptional alterations in response to HCMV infection. Expression kinetics by 5' nuclease fluorigenic real-time PCR of selected genes revealed partial protection of infected cells against initial stress-associated alterations of gene expression and indicated fluctuations of transcriptional levels over time. Additionally, agreement with the quantitative results obtained by SAGE was observed only for genes up-regulated in HCMV-infected cells. This finding pointed to various technical and statistical parameters that all may be critical for quantitative transcriptome studies using global approaches, especially when exploring biological systems in a critical phase of cellular physiology.

Cell Cycle↗
PubMed2005

Stretch reflex instability compared in three different human muscles.

The possibility of causing instability in the stretch reflex has been examined in three different human muscles: biceps, first dorsal interosseous (FDI) of the hand and digastric. Tremor recorded as fluctuation of isometric force was compared with that occurring during contraction against a spring load. The spring compliance was selected to make the natural frequency of the part in each case appropriate for oscillations in the short latency stretch reflex. A computer model of the whole system was used to predict the frequency at which oscillations should be expected and to estimate the reflex gain required in each case to cause sustained oscillations. Estimates were computed of the autospectra of the force records and of the rectified surface EMG signals and of the coherence functions. Normal subjects showed no evidence of a distinct spectral peak during isometric recording from any of the three muscles. However, in anisometric conditions regular oscillations in force occurred in biceps, but not in FDI or digastric. The oscillations in biceps at 8-9 Hz were accompanied by similar oscillations in the EMG which were highly coherent with the force signal. The results are consistent with the presence of a strong segmental stretch reflex effect in biceps and weak or absent reflex in FDI. Digastric is known to contain no muscle spindles and therefore to lack a stretch reflex. In two subjects who volunteered that they had more tremor than normal, but had no known neurological abnormality, there was a distinct peak in the force spectrum at 8-9 Hz in biceps and FDI in isometric conditions with coherent EMG activity. The peak increased in size in anisometric conditions in biceps but not in FDI. This component appears to be of central rather than of reflex origin. No equivalent component was found in digastric records. The results are discussed in relation to the possible role of the short latency stretch reflex in the genesis of physiological tremor in different muscles.

Adult↗
PubMed2002

13CO2/12CO2 isotopic ratio measurements using a difference frequency-based sensor operating at 4.35 micrometers.

A portable modular gas sensor for measuring the 13C/12C isotopic ratio in CO2 with a precision of 0.8%(+/-1 sigma) was developed for volcanic gas emission studies. This sensor employed a difference frequency generation (DFG)-based spectroscopic source operating at 4.35 micrometers (approximately 2300 cm-1) in combination with a dual-chamber gas absorption cell. Direct absorption spectroscopy using this specially designed cell permitted rapid comparisons of isotopic ratios of a gas sample and a reference standard for appropriately selected CO2 absorption lines. Special attention was given to minimizing undesirable precision degrading effects, in particular temperature and pressure fluctuations.

Atmosphere↗
PubMed1998

Clinical neurochemistry: developments in dementia research based on brain bank material.

Brain tissue obtained at autopsy continues to provide unique opportunities in current dementia research. Not only is tissue analysis still essential for diagnosis, but investigation of neurochemical pathology, at a level of resolution beyond current in vivo imaging, continues to provide new insights into the involvement of neurotransmitter signalling systems. These are relevant to therapy which, with respect to symptoms such as cognitive impairment, psychosis and depression, is currently targeted to specific transmitter (cholinergic, dopaminergic and serotonergic) systems. This paper focuses on dopaminergic, cholinergic and histaminergic parameters in Alzheimer's disease (AD), Dementia with Lewy bodies (DLB) and Parkinson's disease (PD). In the normal striatum the dopamine transporter and D2 receptor exhibit distinct rostral-caudal distributions and D2 binding is affected by genetic polymorphism at the Taq 1A locus. The transporter is reduced in both DLB and PD but not AD, correlating with severity of extrapyramidal dysfunction, and receptor abnormalities are apparent in DLB patients responding adversely to neuroleptics. Striatal nicotine receptors are lost in all 3 disorders, further reduced as a result of neuroleptic medication, and elevated as a result of tobacco use. In the thalamus there are selective reductions in presynaptic cholinergic activity in DLB in the reticular nucleus which relate to symptoms of hallucinations and fluctuating consciousness prevalent in this disorder. In the hippocampus coupling of muscarinic M1 receptors, relevant to response to cholinergic therapy, is impaired in areas most affected by beta-amyloid plaques and intact in less affected areas. Analysis of histamine H2 receptors indicates that, despite presynaptic histamine abnormalities in AD, receptor numbers are normal. Such clinically and therapeutically relevant observations on human brain neurochemistry provide a basis for improving therapeutic strategies and prospects of diagnostic in vivo chemical imaging.

Brain↗
PubMed1976

Control of synbiotic nitrogen fixation in Rhizobia. Regulation of NH4+ assimilation.

This communication is concerned with physiological, biochemical, and genetic studies of the regulation of ammonium (NH4+) assimilation by Rhizobia (root nodule bacteria) that infect leguminous plants. The major conclutions are (i) physiological studies show that Rhizobia are able to assimilate NH4+ for growth only when supplemented with certain organic nitrogen sources (e.g., L-aspartate, L-leucine, L-serine). Addition of as little as 2 mug/ml of L-aspartate supported growth on NH4+ as nitrogen source. In contrast, addition of glutamate in combination with NH4+-blocked NH4+ utilization; (ii) biochemical analysis show that glutamate synthase activity (NADP- and NAD-linked) is always present in cells capable of assimilating NH4+; also cells without glutamate synthase activity were found to be incapable of NH4+ utilization. Glutamate synthase levels were observed to fluctuate markedly depending on the available nitrogen source and on the growth stage of the culture; (iii) mutants were selected in which assimilation of NH4+ is no longer subject to inhibition (repression?) by glutamate. The levels of glutamate synthase activity (NADP-linked) (in the presence of glutamate) show approximately a two-fold increase over the level in the parent strain. The mutants no longer require supplementation with small amounts of organic nitrogen for growth in medium containing inorganic nitrogen (e.g., NH4+ or NO3-); (iv) these findings are discussed in relation to the working model of symbiotic nitrogen fixation recently proposed (O'Gara and Shanmugam (1976), Biochim. Biophys. Acta 437, 313--321).

Aspartic Acid↗
PubMed2006

Optimizing fluctuation analysis of GABAAergic IPSCs for accurate unitary currents.

Nonstationary fluctuation analysis of synaptic currents requires division of currents into bins of time, with little agreement on how to select an optimal bin width. We used simulated inhibitory postsynaptic currents (simIPSCs) in an empirical approach to establish the optimal bin width needed for estimation of the unitary current, ie. We found acceptable accuracy (< or = 5%) at bin widths shorter than the length of the stationary segment of simIPSCs that persisted when Gaussian noise was added to the simulated currents. We also studied evoked and spontaneous IPSCs mediated by receptors for gamma-aminobutyrate (GABA) in thalamic neurons. Similar to simIPSCs, analysis of the IPSCs yielded saturating relationships between bin width and accuracy of unitary current estimate. Whereas standard error decreased, the accuracy of ie estimates increased with decreasing bin width, forming a plateau at bins below 2-3 ms in duration. Using this approach, one can reliably determine the optimal bin width for nonstationary noise analysis.

Algorithms↗