SEARCH · PubMed Health

Results for “phase variation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,117 records · Page 62Linked to original sources

PubMed1992

Early superoxide dismutase alterations during SV40-transformation of human fibroblasts.

The expression of superoxide dismutases (SOD) 1 and 2 was studied in 4 clones of human fibroblasts after their infection by simian virus 40 (SV40), in parallel with the alterations of chromosomes 21 and chromosome 6q arms, carrying the genes that encode for SOD1 and SOD2 respectively. For all clones, a similar scheme with 2 main phases was observed for both chromosome and SOD variations. The first phase, defined as the pre-crisis phase, was characterized by chromosomal instability, but maintenance of normal numbers of chromosome 6q arms and chromosomes 21. The level of SOD2 mRNA was high, while SOD2 activity and immunoreactive protein were low. SOD1 protein and activity were decreased. In the second phase, defined as the post-crisis phase, the accumulation of clonal chromosomal rearrangements led to the loss of 6q arms, while the number of chromosomes 21 remained normal. SOD2 mRNA level was decreased and SOD2 immunoreactive protein and activity remained low. SOD1 protein and activity increased with passages, reaching values similar to those of control cells at late passages. As in established SV40-transformed human fibroblast cell lines, good correlation was found between SOD2 activity and the relative number of 6q arms. These results allow us to reconstruct the sequence of events leading to the decrease of SOD2, a possible tumor-suppressor gene, during the process of SV40-transformation of human fibroblasts.

Cell Transformation, Viral↗

PubMed2005

Chiral separation of beta-adrenergic antagonists, profen non-steroidal anti-inflammatory drugs and chlorophenoxypropionic acid herbicides using teicoplanin as the chiral selector in capillary liquid chromatography.

Three groups of structurally diverse chiral compounds were used to study the interaction mechanism responsible for stereoselective recognition with teicoplanin as chiral selector in capillary liquid chromatography. Teicoplanin-based chiral stationary phase (CSP) was used. The effect of the variation of mobile phase composition on retention and enantioselective separation was studied. The mobile phase composition suitable for enantioresolution of the various chiral compounds differed according to the interaction forces needed for chiral recognition. Mobile phases with high buffer portion (70-90 vol.%) were preferred for separation of enantiomers of profen non-steroidal anti-inflammatory drugs and chlorophenoxypropionic acid herbicides that require hydrophobic interactions, inclusion and pi-pi interactions for stereoselective recognition with teicoplanin. Higher concentration triethylamine in the buffer (0.5-1.0%) increased resolution of these acids. On the other hand, H-bonding and electrostatic interactions are important in stereoselective interaction mechanism of beta-adrenergic antagonists with teicoplanin. These interaction types predominate in the reversed phase separation mode with high organic modifier content (95% methanol) and in polar organic mobile phases. For this reason beta-adrenergic antagonists were best enantioresolved in the polar organic mode. The mobile phase composed of methanol/acetic acid/triethylamine, 100/0.01/0.01 (v/v/v), provided enantioresolution values of all the studied beta-adrenergic antagonists in the range 1.1-1.9. Addition of teicoplanin to the mobile phase, which was suitable for enantioseparation of certain compounds on the CSP, was also investigated. This system was used to dispose of nonstereoselective interactions of analytes with silica gel support that often participate in the interaction with CSPs. Very low concentration of teicoplanin in the mobile phase (0.1 mM) resulted in enantioselective separation of 2,2- and 2,4-chlorophenoxypropionic acids.

Adrenergic beta-Antagonists↗

PubMed2006

Improved optical profiling using the spectral phase in spectrally resolved white-light interferometry.

In spectrally resolved white-light interferometry (SRWLI), the white-light interferogram is decomposed into its monochromatic constituent. The phase of the monochromatic constituents can be determined using a phase-shifting technique over a range of wavelengths. These phase values have fringe order ambiguity. However, the variation of the phase with respect to the wavenumber is linear and its slope gives the absolute value of the optical-path difference. Since the path difference is related to the height of the test object at a point, a line profile can be determined without ambiguity. The slope value, though less precise helps us determine the fringe order. The fringe order combined with the monochromatic phase value gives the absolute profile, which has the precision of phase-shifting interferometry. The presence of noise in the phase may lead to the misidentification of fringe order, which in turn gives unnecessary jumps in the precise profile. The experimental details of measurement on standard samples with SRWLI are discussed in this paper.

Journal Article↗

PubMed1995

[Is the length of gestation a multiple of a fundamental cycle?].

Pregnancy duration was accurately determined using early ultrasonography in 21 patients prior to spontaneous abortion and in two successive pregnancies in each of 57 women prior to spontaneous delivery. Pregnancy durations before abortion or delivery approximated multiples of 14 days (14.4 and 13.3 days, respectively). In addition, in a given woman, the duration of two successive pregnancies carried to term was often identical; in a smaller number of cases, a difference of about 12 days (calculated value, 11.8 days) or, rarely, 24 days, was found. These values may correspond to the same functional period. These observations suggest that the duration of pregnancy (mean, 266 days) may be a multiple of the duration of the luteal phase of the menstrual cycle (12 to 14 days). Interindividual variations in luteal phase duration (standard deviation, 0.5 to 1 day) may explain inter-individual variations in pregnancy duration (standard deviation of about 15 days). The mean multiple may be 20. Thus, pregnancy duration may be determined both by fetal maturation and by a maternal time-counting mechanism. This hypothesis is discussed in the light of current data.

Abortion, Spontaneous↗

PubMed1982

Circadian variations in influx and efflux of the S phase in a partially synchronized cell system. Double-labelling with [3H]thymidine in the epithelium of the hamster cheek pouch.

By means of a double-labelling experiment, circadian variations in the kinetic parameters of the S phase of the hamster cheek pouch epithelium were studied. The evaluation of the experiment included a recently developed correction for deviations from the strict pulse interpretation of the labelling technique. Pronounced circadian variations were found in S phase influx and efflux; the diurnal mean of both was estimated as 0.5%/hr, when based on measurements of all nucleated epithelial cells. Variations in S phase influx seem mainly responsible for the diurnal variation in cell proliferation, although diurnal variation in DNA synthesis rate, and thus in mean transit time, was also found. The increases in LI and influx were closely correlated and related to the beginning of the dark period. A circadian variation in cell number was also observed.

Animals↗

PubMed2026

The Rise of Plant Pan-Genomes: From Genome Variation to Predictive Breeding.

Plant pan-genomics is entering a new phase beyond genome variation discovery, requiring a shift from cataloguing genomic diversity toward understanding how variation generates biological function and breeding value. Here, we propose that the future of plant pan-genomics will be shaped by three conceptual transitions. First, structural variation (SV), presence-absence variation (PAV), and haplotype diversity should be interpreted not merely as genomic differences, but as regulatory components that influence gene networks, chromatin organization, and complex traits. Second, the expansion from species-level pan-genomes to genus-level super pan-genomes provides an evolutionary framework for uncovering adaptive genetic modules preserved in wild relatives and overlooked during domestication. Third, integrating pan-genomes with pan-omics, three-dimensional genome analyses, and artificial intelligence will enable the transformation of genomic variation into predictive models for crop improvement. We further propose that the ultimate value of pan-genomes lies not in generating increasingly complete genome collections, but in establishing a mechanistic bridge between genome diversity, biological function, and breeding decisions. This transition will move crop improvement from empirical selection toward rational genome design, where evolutionary diversity can be systematically interpreted, predicted, and engineered.

Journal Article↗

PubMed2000

A novel mechanism for control of antigenic variation in the haemagglutinin gene family of mycoplasma synoviae.

High-frequency phase and antigenic variation of homologous lipoprotein haemagglutinins has been seen in both the major avian mycoplasma pathogens, Mycoplasma synoviae and Mycoplasma gallisepticum. The expression and, hence, antigenic variation of the pMGA gene family (encoding these lipoproteins in M. gallisepticum) is controlled by variation in the length of a trinucleotide repeat motif 5' to the promoter of each gene. However, such a mechanism was not detected in preliminary observations on M. synoviae. Thus, the basis for control of variation in the vlhA gene family (which encodes the homologous haemagglutinin in M. synoviae) was investigated to enable comparison with its homologue in M. gallisepticum and with other lipoprotein gene families in mycoplasmas. The start point of transcription was identified 119 bp upstream of the initiation codon, but features associated with control of transcription in other mycoplasma lipoprotein genes were not seen. Comparison of three copies of vlhA revealed considerable sequence divergence at the 3' end of the gene, but conservation of the 5' end. Southern blot analysis of M. synoviae genomic DNA revealed that the promoter region and part of the conserved 5' coding sequence occurred as a single copy, whereas the remainder of the coding sequence occurred as multiple copies. A 9.7 kb fragment of the genome was found to contain eight tandemly repeated regions partially homologous to vlhA, all lacking the putative promoter region and the single-copy 5' end of vlhA, but extending over one of four distinct overlapping regions of the 3' coding sequence. Examination of sequential clones of M. synoviae established that unidirectional recombination occurs between the pseudogenes and the expressed vlhA, with duplication of pseudogene sequence and loss of the corresponding region previously seen in the expressed gene. Expression of the 5' end of two variants of the vlhA gene showed that they differed in their reaction with monoclonal antibodies specific for this region. These data suggest that the control of vlhA antigenic variation in M. synoviae is achieved by multiple gene conversion events using a repertoire of coding sequences to generate a chimeric expressed gene, with the greatest potential for variation generated in the region encoding the haemagglutinin. Thus, completely distinct mechanisms have been adopted to control antigenic variation in homologous gene families.

Amino Acid Sequence↗

PubMedDate not supplied

Assessment of phase and amplitude effects due to susceptibility variations in MR imaging of the brain.

Susceptibility effects due to the presence of hemorrhage have been observed in a substantial number of patients and are a potential source of artifact in in vivo spectroscopy. The studies so far have concentrated on observations of phase differences, but amplitude variations also exist. This article reviews the degree to which the two are independent and suggests that at least three different pulse sequences are necessary to characterize effects due to local field inhomogeneities arising in clinical studies.

Brain Diseases↗

PubMed1989

Infrared study of phospholipid hydration. New thermodynamic data about the main phase transition of saturated phosphatidylcholine water multidispersions.

Infrared spectra measurements are performed with fully hydrated phospholipid multilamellar dispersions. The temperature profiles of the delta (OH) bending vibration at 1645 cm-1, corresponding to the water molecules, show three marked transitions in such temperature ranges that they can be respectively associated with the fusion of free water molecules, with pretransition phenomena and with the main phase transition. From absorbance variations and calorimetric data, main phase transition enthalpies and entropies were calculated for both the acyl chains and the polar head-water regions. Negative contributions of the polar head-water region are consistent with previous results, indicating a more ordered water layer in the fluid phase. On the other hand, a decrease of the amount of bound water molecules with increasing chain length is pointed out.

Liposomes↗

PubMedDate not supplied

A mathematical analysis of the mortality kinetics of Drosophila melanogaster exposed to gamma radiation.

A mathematical model with nonlinear time-varying characteristics has been developed which describes the relationship between the kinetics of natural aging and radiation-induced delayed mortality. Based on this model, it appears that there is an immediate effect of radiation which is continuously, but nonlinearly, increasing in severity. Two phases appear in this variation, corresponding to the two phases (plateau and dying phase) of the mortality curves for control populations. Accordingly, S/E (survival time post-irradiation/further expectation of life) can best be interpreted as an increasing function during the plateau phase of normal mortality curves, which levels off during the ensuing dying phase.

Aging↗

PubMed1985

The role of cerebral blood volume changes in brain specific-gravity measurements.

Cerebral blood volume (CBV) was calculated in gerbils from specific-gravity (SG) changes between normal and saline-perfused brains. Furthermore, changes in CBV were investigated during ischemia using carbon-14-labeled dextran (MW 70,000) as an intravascular marker. Both data were used to evaluate the possible error due to a change in CBV on the measurement of ischemic brain edema by the SG method. The methodological error found was 0.0004 for a 100% CBV change. This error is insignificant, being less than the standard deviation in the SG measured for the gerbil cortex (SG 1.0494 +/- 0.0006). Thus, CBV changes are not responsible for the SG variations observed during the first phase of ischemia. These variations are better explained as an increase of brain water content during ischemia.

Animals↗

PubMed2003

Shear stiffness estimation using intravoxel phase dispersion in magnetic resonance elastography.

Dynamic MR elastography (MRE) is a phase-contrast technique in which the periodic shear motion of an object is encoded as variations in the phase of the reconstructed images. An alternative MRE method is presented whereby waves are depicted as intensity variations in the magnitude images due to intravoxel phase dispersion (IVPD). A theoretical framework is developed to model how the IVPD magnitude data are related to the underlying shear wave motion, and how they can be used to estimate shear stiffness. The results are shown in a series of phantom experiments to demonstrate that IVPD MRE complements phase-contrast MRE.

Agar↗

PubMed1986

Phase-locking in the cochlear nerve of the guinea-pig and its relation to the receptor potential of inner hair-cells.

The high-frequency limit of phase-locking has been measured in fibres of the auditory nerve in the guinea-pig. It is shown that phase-locking begins to decline at about 600 Hz and is no longer detectable above 3.5 kHz which is about 1 octave lower than in the cat, squirrel monkey and some birds. Direct measurements of the cochlear afferent fibre synaptic delay are consistent with indirect estimates from phase-locking, both giving values of 0.7-0.8 ms. Measurements of the receptor potentials of inner hair-cells in the guinea pig cochlea indicate that as the stimulus frequency is increased there is a progressive decrease in the a.c. component compared to the steady depolarization. The cause of this decline is the low-pass filtering of the a.c. component by the hair-cell membrane. The cut-off and slope of the decline in the a.c. component is consistent with the suggestion that this process is the limiting factor in cochlear nerve fibre phase-locking. The implications of these findings for interspecies variation in phase-locking cut-off, for cochlear mechanisms and for the encoding of complex sounds are discussed.

Acoustic Stimulation↗

PubMed2000

Preovulatory follicular status and diet affect the insulin and glucose content of follicles in high-yielding dairy cows.

Insulin and glucose may be limiting factors for ovarian function in dairy cows genetically selected for high milk yield. The effects of nutrition on the intrafollicular content of insulin and glucose were investigated in Israeli Holstein dairy cattle fed a basic total mixed ration and producing 34-39kg of milk daily. In experiment 1, carried out in 11 oestrus-synchronised cows, little variation in insulin concentration was found in plasma sampled during the luteal phase, but high variation was found in plasma sampled during the follicular phase. Therefore, in order to prevent confounding the effects of diet and of phase in cycle in the following experiments, experimental diets were fed during the luteal phase of synchronised oestrus cycles. In experiment 2, designed as Latin-Square, six cows received sequentially diets containing 17.1 (control) or 19.7% of crude protein, using two sources of supplementary protein, i.e. soyabean meal (SBM) and corn gluten meal (CGM), differing in ruminal degradability and leucine content. When dry matter intake was used as covariant, plasma insulin on day 16 was 29.5 and 26.4% higher in cows fed diets containing SBM and CGM than in the control (P<0.05). In experiment 3, 17 cows were individually fed the basic diet and then switched to isoenergetic diets containing SBM (n=5), CGM (n=6) or corn grain (CG, n=6) given from day 10 to 16 of the synchronised oestrus cycle. On the eve of day 16, and in the morning of day 17, they were administered PGF(2alpha) and the content of 26 largest follicles was aspirated by using the transvaginal ovum pick-up technique. Follicles were sorted into two classes (preovulatory and subordinate) according to oestradiol concentration and the progesterone:oestradiol ratio in follicular fluid (FF). Higher concentrations of insulin (0.282 versus 0.127ng/ml, P<0.0001) and of glucose (0.614 versus 0.386g/l, P<0.002), were found in FF from preovulatory follicles. The insulin concentration in the FF of cows fed the CG diet was 26% higher than in their counterparts fed CGM (P<0.04), SBM being intermediate. Dietary effects did not reach significance in subordinate follicles. The finding that preovulatory follicular status is associated with increased intrafollicular insulin and glucose suggests that insulin is involved in follicular maturation. The nutritional effect on intrafollicular glucose and insulin may have practical implications to optimise feeding in dairy cows during phases of the oestrus cycle.

Animal Feed↗

PubMed1982

Flow cytometry of lung carcinoma: a comparison of DNA stemline and cell cycle distribution with histology.

Flow cytometry studies of the DNA distribution of 33 lung tumors were carried out. All of the carcinomas (32 cases) had aneuploid DNA modal values, ranging from 2.15c to 5.05c; in the single case of carcinoid studied, the tumor cells were diploid. DNA ploidy levels tended to be higher for epidermoid than adenocarcinoma; they were the same in lymph node metastases as in the primary tumor. Cell cycle distributions calculated from the tumor cell DNA values showed considerable variation, ranging from 9% to 58% for the S phase and from less than 1% to 29% for the G2M phase. Whether these variations have clinical significance is not known at this time.

Adenocarcinoma↗

PubMed2000

The continuum model and G1-control of the mammalian cell cycle.

The continuum model of the mammalian division cycle proposes that there are no G1-phase specific controls or events. The G1 phase is simply the time when processes begun in the previous cell cycle are completed. In this review, the continuum model is applied the variability of the G1-phase, the existence of G1-less cells, the ubiquitous G1-phase arrest phenomenon, the effect of over-expressed cyclins on G1-phase length, the statistical variation of the cell cycle, the reports of G1-phase syntheses, the proposed variation in retinoblastoma protein phosphorylation in G1-phase, and the myriad findings put forward to support the G1-control model of the mammalian division cycle. The continuum model is a valid description of the mammalian division cycle.

Animals↗

PubMed2003

Glycemic control in diabetic CAPD patients assessed by continuous glucose monitoring system (CGMS).

INTRODUCTION: From 20% to 40% of all patients commencing dialysis are diabetic. The quality of glycemic control is an important determinant of outcome. The aims of this study were to investigate the use of the continuous glucose monitoring system (CGMS) to assess overall 24-hour glycemic control and the effects of both nonglucose containing and more biocompatible alternative peritoneal dialysis solutions in insulin-treated continuous ambulatory peritoneal dialysis (CAPD) patients. METHODS: We studied 8 insulin treated diabetic CAPD patients. A CGMS probe was inserted [allowing automatic measurement of interstitial fluid (ISF) glucose every 5 minutes, for a 72-hour period]. The patients were then allowed home with CGMS monitoring to assess the effect on glycemic control of three differing peritoneal dialysis regimes. Phase 1 consisted of three exchanges of 1.36% glucose and one of 3.86% glucose, utilizing a lactate/bicarbonate buffer. Phase 2 was identical but used lactate-buffered fluid alone. Phase 3 utilized a minimally glycemic combination of one amino acid, one icodextrin, and two 1.36% glucose lactate/bicarbonate-containing exchanges. RESULTS: ISF glucose measured by CGMS correlated well with venous glucose measurements (r2 = 0.82, P < 0.0001). There was a statistically significant difference in the mean ISF glucose between all three phases (P < 0.0001). The variation in glycemic control was tighter during phase 3 [mean coefficient of variation (CV) 0.21 +/- 0.03]. CONCLUSION: CGMS appears to be a clinically useful tool to gain additional insights into the glycemic control of diabetic CAPD patients. More biocompatible and nonglucose-containing dialysis fluids seem to be associated with improvements in glycemic control in this group of patients.

Adult↗

PubMed2001

Differential sensitivity to etoposide (VP-16)-induced S phase delay in a panel of small-cell lung carcinoma cell lines with G1/S phase checkpoint dysfunction.

PURPOSE: The highly schedule-dependent cytotoxic agent etoposide (VP-16) is initially effective in the treatment of small-cell lung cancer (SCLC), particularly in multidrug combination chemotherapy. Heterogeneity in cellular sensitivity to cell cycle arrest may underpin the inadequacy of low-dose extended-cycle single-agent regimes in tumours with partially dysfunctional apoptotic signalling pathways. We have studied the longevity and dose dependency of cell cycle and to a limited extent the apoptotic responses of a panel of seven unselected SCLC cell lines, screened for TP53 status. METHODS: Cells were analysed using flow cytometry for the cell cycle responses and field inversion gel electrophoresis for apoptotic patterns. The mitotic inhibitor nocodazole was used to assess and correct cell line response data for differences in cell cycle traverse per se. RESULTS: An overall lack of G1/S arrest and muted DNA fragmentation were consistent with the presence of TP53 gene abnormalities. Maximal G2 arrest but with clear recovery potential occurred at an exposure dose (ED, concentration of drug x time) value of approximately 24 microM h. Higher doses (ED values >48 microM h) revealed a wide variation in S phase delay that was independent of population doubling time and could not be compensated for by drug concentration changes alone. CONCLUSION: The results suggest that heterogeneity in the in vitro sensitivity of unselected SCLC cell lines to S phase arrest is demonstrable at ED values projected to be critical for clinical activity. Such variation in S phase responsiveness may reflect differences in checkpoint activation and offer a functional target for the design of more-effective combination therapy.

Antineoplastic Agents, Phytogenic↗