SEARCH · PubMed Health

Results for “Transition Elements”

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 595 records · Page 33Linked to original sources

PubMed2003

Study of the fragmentation mechanism of protonated 6-hydroxychlorzoxazone: application in simultaneous analysis of CYP2E1 activity with major human cytochrome P450s.

The application of liquid chromatography tandem mass spectrometry for simultaneous analysis of major human cytochrome P450 activities via a single atmospheric pressure ionization (API) LC/MS/MS method has been hampered by the preferred detection of 6-hydroxychlorzoxazone (HCZ), the metabolite of the CYP2E1 probe, chlorzoxazone, under negative API. An initial simulation of the dissociation constants suggested the potential ionization of the enol form of HCZ at low pH, and the accurate mass measurements confirmed the presence of the protonated HCZ signal under (+) ESI at pH 3. However, the CID spectrum of the protonated HCZ resulted in a few intense, but uncommon, fragment ions that could be utilized for specific selected reaction monitoring (SRM) transitions. The deduced elemental compositions of these fragment ions indicated possible aromatic ring opening for the first two intense product ions at m/z 130 and 115, as well as chlorine radical loss for the third ion at m/z 151. Further precursor and product ion scan studies, along with the deuterium ion exchange in solution, revealed the involvement of three distinct pathways of fragmentation. The m/z 186-->130 transition, which was shown to be specific in human plasma and rat hepatic microsomes, was further combined with the SRM transition of reserpine (internal standard) and eight probe substrates for human cytochrome P450 isoforms. This led to the development of a full LC/MS/MS method capable of analyzing a total of nine human P450 activities within 3 min, including CYP2E1, using a single assay in the (+) ESI mode. The HCZ assay showed excellent linearity with a coefficient of determination (R2) greater than 0.98 at dynamic range of 0.05 (LOQ) to 40 microM. Preliminary data from the three-day validation of the HCZ assay indicated that the accuracy and precision for quality control samples was within +/- 15% of the spiked concentration at all levels.

Chlorzoxazone↗

PubMed2005

Copper increases the damage to DNA and proteins caused by reactive oxygen species.

Copper [Cu(II)] is an ubiquitous transition and trace element in living organisms. It increases reactive oxygen species (ROS) and free-radical generation that might damage biomolecules like DNA, proteins, and lipids. Furthermore, ability of Cu(II) greatly increases in the presence of oxidants. ROS, like hydroxyl (.OH) and superoxide (.O(2)) radicals, alter both the structure of the DNA double helix and the nitrogen bases, resulting in mutations like the AT-->GC and GC-->AT transitions. Proteins, on the other hand, suffer irreversible oxidations and loss in their biological role. Thus, the aim of this investigation is to characterize, in vitro, the structural effects caused by ROS and Cu(II) on bacteriophage lambda DNA or proteins using either hydrogen peroxide (H(2)O(2)) or ascorbic acid with or without Cu(II). Exposure of DNA to ROS-generating mixtures results in electrophoretic (DNA breaks), spectrophotometric (band broadening, hypochromic, hyperchromic, and bathochromic effects), and calorimetric (denaturation temperature [T(d)], denaturation enthalpy [DeltaH], and heat capacity [C(p)] values) changes. As for proteins, ROS increased their thermal stability. However, the extent of the observed changes in DNA and proteins were distinct, depending on the efficiency of the systems assayed to generate ROS. The resulting effects were most evident when Cu(II) was present. In summary, these results show that the ROS, .O2 and .OH radicals, generated by the Cu(II) systems assayed deeply altered the chemical structure of both DNA and proteins. The physiological relevance of these structural effects should be further investigated.

Bacteriophage lambda↗

PubMed1992

Cortical dynamics of visual motion perception: short-range and long-range apparent motion.

This article describes further evidence for a new neural network theory of biological motion perception. The theory clarifies why parallel streams V1----V2, V1----MT, and V1----V2----MT exist for static form and motion form processing among the areas V1, V2, and MT of visual cortex. The theory suggests that the static form system (Static BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast and to direction-of-motion, whereas the motion form system (Motion BCS) generates emergent boundary segmentations whose outputs are insensitive to direction-of-contrast but sensitive to direction-of-motion. The theory is used to explain classical and recent data about short-range and long-range apparent motion percepts that have not yet been explained by alternative models. These data include beta motion, split motion, gamma motion and reverse-contrast gamma motion, delta motion, and visual inertia. Also included are the transition from group motion to element motion in response to a Ternus display as the interstimulus interval (ISI) decreases; group motion in response to a reverse-contrast Ternus display even at short ISIs; speed-up of motion velocity as interflash distance increases or flash duration decreases; dependence of the transition from element motion to group motion on stimulus duration and size, various classical dependencies between flash duration, spatial separation, ISI, and motion threshold known as Korte's laws; dependence of motion strength on stimulus orientation and spatial frequency; short-range and long-range form-color interactions; and binocular interactions of flashes to different eyes.

Attention↗

PubMed1986

Adenosquamous carcinoma of the stomach. A clinicopathologic analysis of 28 cases.

Twenty-eight cases of primary adenosquamous carcinoma (ASC) of the stomach were studied clinicopathologically. These cases were classified into two types, 16 with differentiated type adenocarcinomatous component (DAC) and 12 with undifferentiated type adenocarcinomatous component (UAC), according to the degree of glandular formation of the adenocarcinomatous elements. A large number with adenocarcinomas, including 131 with differentiated type and 133 with undifferentiated type, were studied as controls. As a consequence, with respect to biologic behavior, ASC with DAC was similar to the differentiated type adenocarcinoma, and ASC with UAC to the undifferentiated type adenocarcinoma. Accordingly, the behavioristic feature of ASC seemed to be governed by the adenocarcinomatous component. Histologically, a close relationship between neoplastic adenomatous and squamous components was evident in the intermingling areas, thereby suggesting a transition of both elements. In addition, a mucoepidermoid pattern was occasionally detected in the squamous component. Judging from the biologic behavior and histologic findings, the majority of ASC probably derives from the squamous metaplasia in an adenocarcinoma. The prognosis of ASC was less favorable than that of adenocarcinoma because of the more extensive tumor depth and higher frequencies of lymphatic and vascular permeations of the carcinoma cells.

Adenocarcinoma↗

PubMed2005

Composite distal nephron-derived renal cell carcinoma with chromophobe and collecting duct carcinomatous elements.

Chromophobe renal cell carcinoma (RCC) and collecting duct carcinoma (CDC) are derived from the collecting duct epithelia, although their morphology, molecular biologic characteristics and clinical behaviors are quite different. Herein is presented a case of RCC possessing the chromophobe RCC and CDC elements occurring in a 64 year-old Japanese woman. The patient was referred to Yokohama City University Hospital with complaints of persistent back pain and fever. Radiologic examinations revealed a left renal tumor, and radical nephrectomy was performed. The patient died with multiple metastases, 8 months after the operation. The resected tumor showed an invasive growth, and its cut surface was heterogenous with hemorrhage and necrosis. Histologically, the tumor was composed of chromophobe elements with dedifferentiation, and CDC elements. The chromophobe and CDC elements had obvious histological transition. Lectin histochemistry and immunohistochemistry confirmed that this tumor was derived from the distal nephron. c-KIT, p53 and Ki67 antigen showed differential localization between the chromophobe and CDC elements, even in the transitional areas. Along with the previous reports, the present case seemed to be composite RCC derived from the collecting duct, which might present clues to elucidate carcinogenesis in the distal nephron.

Carcinoma, Renal Cell↗

PubMed2004

Spatial structures and dynamics of kinetically constrained models of glasses.

Kob and Andersen's simple lattice models for the dynamics of structural glasses are analyzed. Although the particles have only hard core interactions, the imposed constraint that they cannot move if surrounded by too many others causes slow dynamics. On Bethe lattices, a dynamical transition to a partially frozen phase occurs. In finite dimensions there exist rare mobile elements that destroy the transition. At low vacancy density v, the spacing Xi between mobile elements diverges exponentially or faster in 1/v. Within the mobile elements, the dynamics is intrinsically cooperative, and the characteristic time scale diverges faster than any power of 1/v (although slower than Xi). The tagged-particle diffusion coefficient vanishes roughly as Xi(-d).

Journal Article↗

PubMed1997

Thrombogenicity of hydrophilic and nonhydrophilic microcatheters and guiding catheters.

PURPOSE: To assess in a swine model the in vivo thrombogenicity of various microcatheters and guiding catheters as a function of catheter material, catheter coating, and duration of implantation. METHODS: Microcatheters (Tracker 18 and Fastracker 18, Target Therapeutics, Fremont, Calif; Magic 1.8, Balt, Montmorency, France; and Transit, Cordis Endovascular Systems, Miami Lakes, Fla) were placed through 6F guiding catheters (Fasguide, Target Therapeutics, and Envoy, Cordis Endovascular Systems) into the common carotid arteries of swine for 30 minutes (short term), 90 minutes (medium term), and 35 days (long term). Guiding catheters were implanted for 5 hours. At the end of the implantation periods the catheters were retracted and fixed for scanning electron microscopy. RESULTS: The surface of the Fastracker microcatheter was devoid of debris after both short- and medium-term implantation. The Tracker microcatheter had minimal accumulation of cellular elements whereas the Transit microcatheter showed moderate accumulation of nondeformed red blood cells. Neither the Tracker nor the Transit microcatheter showed evidence of increasing debris accumulation after medium-term implantation as compared with short-term implantation. The Magic microcatheter was coated with gross thrombus after both short- and medium-term implantation. The Fasguide guiding catheter was nearly devoid of debris, while the Envoy guiding catheter had moderate thrombus formation. Long-term implantation of the Fastracker microcatheter was well tolerated whereas that of the Transit catheter resulted in vessel occlusion. CONCLUSIONS: Hydrophilic microcatheters and guiding catheters are less thrombogenic than their nonhydrophilic counterparts, but not all hydrophilic coatings are equally hypothrombogenic. Degree of thrombogenicity depends on catheter material rather than surface morphology. Medium-term implantation did not yield increasing thrombus formation relative to short-term implantation.

Animals↗

PubMed2006

The importance of atmospheric deposition, charge and atomic mass to the dynamics of minor and rare elements in developing, ageing, and wilted leaves of beech (Fagus sylvatica L.).

The amounts of sixty elements in developing, maturing, senescent and wilting leaves, and in the wintering dead leaves attached to the branches, are reported for a beech (Fagus sylvatica) forest on mor Podzol in south Sweden, a site with no local sources of pollution or geological anomalies. The amounts (contents per leaf) of K (potassium), Rb (rubidium), Cs (caesium), Cu (copper) and P (phosphorus) were highest in young leaves, decreasing throughout the growing season and usually in the subsequent winter. The entirely opposite pattern with a continuous, mostly even increase of the amounts was measured with Be (beryllium), Ba (barium), Hg (mercury), Al (aluminium), Tl (thallium), Pb (lead), Bi (bismuth), V (vanadium), W (tungsten), As (arsenic), Sb (antimony), and Se (selenium). Amounts of rare-earth elements and some transition metals, such as Co (cobalt), Ti (titanium), and the actinides Th (thorium) and U (uranium) were more stable during the growing season, after an initial increase in early summer, but increased greatly in the winter. This winter increase in dead attached leaves has to be accounted for by uptake from long-distance transported constituents in dry and wet deposition. It was similar to deposition rate estimates using moss carpets from the same locality. A passive uptake was positively related to ionic charge and atomic mass. However, the amounts of several, mainly non-essential elements, such as Ni (nickel), Sc (scandium), Zr (zirconium), Cr (chromium), Ag (silver), and Cd (cadmium) were not much lower in the young or maturing leaves than in the wintered dead leaves of this deciduous (hardwood) forest and a proportion apparently originated from internal translocation in the trees. Seasonal fluxes or cycling of many of the scarce or rare elements reported here have never been studied before in forest ecosystems.

Air Pollutants↗

PubMed2002

Effect of the aqueous extract of African mistletoe, Tapinanthus sessilifolius (P. Beauv) van Tiegh leaf on gastrointestinal muscle activity.

Effects of the aqueous extract of T. sessilifolius on the gastrointestinal muscle were investigated on smooth muscle preparations isolated from rabbit jejunum, guinea pig ileum and on gastrointestinal transit in mice. Elemental analysis of the extract was also carried out. The aqueous extract of T. sessilifolius evoked a concentration dependent contraction of the rabbit jejunum and guinea pig ileum. The contractions evoked by the extract were not attenuated either by atropine or mepyramine, but they were completely blocked by verapamil. The elemental analysis revealed the presence of Mg, Zn, Fe, Cu, and very high concentration of Ca. The intraperitoneal LD50 in mice was found to be 1500 mg/kg. The aqueous extract of T. sessilifoliius possesses active components that may be mediating the observed biological activity through calcium mobilization.

Animals↗

PubMed2004

Knock-in of nuclear localised beta-galactosidase reveals that the tyrosine phosphatase Ptprv is specifically expressed in cells of the bone collar.

Ptprv is a member of the transmembrane tyrosine phosphatase gene family reported to be expressed in osteoblasts and gonads. To better define the developmental and tissue specificity of Ptprv expression, we generated knock-in mice expressing a nuclear localised beta-galactosidase reporter under the control of resident Ptprv regulatory elements. Histochemical staining of Ptprv-nLacZ mice revealed that Ptprv expression is readily detectable in the foetal gonadal ridge of both sexes and in adult gonads where it is localised to Sertoli cells of the testis and celomic epithelial cells of the ovaries. During early limb development, Ptprv expression is prominent in the apical ectodermal ridge of the limb bud. At latter stages of development, Ptprv is predominantly expressed in the perichondrial and periosteal region of long bones, known as the bone collar. In contrast to previous indications from in vitro studies, there is little if any expression in mature osteoblasts in vivo. Analysis of Ptprv mRNA localisation by in situ hybridization in parallel with molecular markers of chondrocytes and osteoblasts confirmed the specific expression of Ptprv in immature bone collar cells. The specificity of Ptprv expression in these cells may be a useful tool to elucidate their role in the transition of skeletal elements from cartilage template to bone.

Animals↗

PubMed1984

Transition from spindles to generalized spike and wave discharges in the cat: simultaneous single-cell recordings in cortex and thalamus.

The relationships between the activity of the cortex and that of a "specific" (n. lateralis posterior, LP) and an intralaminar thalamic nucleus (n. centralis medialis, NCM) were studied in the cat during the transition from spontaneous spindles to generalized spike and wave (SW) discharge following i.m. penicillin injection. The EEG and extracellular single-unit activity were recorded in cortex and thalamus during the spindle stage and at different intervals after penicillin until well developed SW discharges were present. Computer-generated EEG averages and histograms of single-unit activity were triggered by either peaks of cortical or thalamic EEG transients or by cortical or thalamic action potentials. In agreement with previous observations, cortical neurons increasingly fired during the spindle wave as it was transformed into the "spike" of the SW complex, while a period of neuronal silence gradually developed as the "wave" of the SW complex emerged. Similar changes developed in the thalamus, particularly in LP, either concurrently with or more often after the onset of the changes in the cortex. Most neurons in NCM, continued to fire randomly even after well developed SWs and rhythmic neuronal discharges had developed in cortex and LP. Only 4/11 NCM neurons did ultimately exhibit a rhythmic firing pattern similar to that seen in the cortex and LP. The correlation between cortical and thalamic unit activity was low during spindles, but gradually increased during the development of SW discharges. These data confirm that the cortex is the leading element in the transition from spindles to SWs. Increasingly, in the course of this transition, cortical and thalamic neuronal firing becomes more intimately phase-locked. This mutual interrelationship appears to be more pronounced between cortex and "specific" than intralaminar thalamic nuclei.

Action Potentials↗

PubMed2004

Contribution of the E2 transitions to the opacity of hot and dense plasmas of heavy elements by an average-atom approach.

The contribution of electric quadrupole (E2) transitions to the opacity of hot and dense plasmas is taken into account by using an average-atom model. As an example, the increase of the opacity of Au due to the E2 transition is shown to range from less than 1% to more than 10% depending on density and temperature. It reaches 15% when the density and temperature are, respectively, 100 g/cm(3) and 5000 eV. The most significant influence comes from the E2 photoionization processes.

Journal Article↗

PubMed2002

Bacterial resistance evolution by recruitment of super-integron gene cassettes.

The capture and spread of antibiotic resistance determinants by integrons underlies the rapid evolution of multiple antibiotic resistance among diverse Gram-negative clinical isolates. The association of multiple resistance integrons (MRIs) with mobile DNA elements facilitates their transit across phylogenetic boundaries and augments the potential impact of integrons on bacterial evolution. Recently, ancestral chromosomal versions, the super-integrons (SIs), were found to be genuine components of the genomes of diverse bacterial species. SIs possess evolutionary characteristics and stockpiles of adaptive functions, including cassettes related to antibiotic resistance determinants previously characterized in clinical isolates, which suggest that MRIs and their resistance genes were originally recruited from SIs and their pool of amassed genes. However, the recombination activity of integrons has never been demonstrated in a bacterium other than Escherichia coli. We introduced a naturally occurring MRI (TpR, SulR) on a conjugative plasmid into Vibrio cholerae, a species known to harbour a SI. We show that MRIs can randomly recruit genes directly from the cache of SI cassettes. By applying a selective constraint for the development of antibiotic resistance, we demonstrate bacterial resistance evolution through the recruitment a novel, but phenotypically silent, chloramphenicol acetyltransferase gene from the V. cholerae SI and its precise insertion into the MRI. The resulting resistance profile (CmR, TpR, SulR) could then be disseminated by conjugation to other clinically relevant pathogens at high frequency. These results demonstrate that otherwise phenotypically sensitive strains may still be a genetic source for the evolution of resistance to clinically relevant antibiotics through integron-mediated recombination events.

Amino Acid Sequence↗

PubMed1982

Extension of the method of partial retention of diatomic differential overlap to second row atoms and transition metals.

The method of partial retention of diatomic differential overlap (PRDDO) has been extended to the elements through the first transition series. A minimum basis set of Slatertype orbitals is employed, with optional 3d functions on atoms in the second major row. The 3d shell for transition metal atoms is a fixed-contracted double-zeta combination of Slater orbitals. The method retains the basic n(3) dependency inherent in PRDDO. Limited one-center parameterization and empirical two-center exchange integrals are included. The overall accuracy of the approach is comparable to that of the PRDDO method as previously applied to molecules containing first-row atoms only.

Journal Article↗

PubMed1999

Rotation-Vibration Constants for the nu1, nu22, nu24, nu22 + nu24, and Ground States in Pyrrole (12C4H5N).

We have recorded the infrared absorption spectrum of pyrrole at 0.005 cm-1 spectral resolution using a Fourier transform interferometer. The rotational analysis of the symmetric out-of-plane C-H bend 22(1)0 fundamental band at 722.132993(5) cm-1 was performed, allowing 6760 lines to be assigned. These lines were fitted simultaneously to literature data on nu1 [A. Mellouki, R. Georges, M. Herman, D. L. Snavely, and S. Leytner, Chem. Phys. 220, 311-322 (1997)] and microwave lines [G. Wlodarczak, L. Martinache, J. Demaison, and B. P. Van Eijck, J. Mol. Spectrosc. 127, 200-208 (1988)]. A set of rotation parameters was determined for the ground state in Ir and IIIr representations, together with vibration-rotation constants for the v1 = 1 and v22 = 1 vibrational states. The fine structure in the strongest of the hot bands in that range was highlighted by division, from the experimental data, of the spectrum of the 22(1)0 band, computed using the vibration-rotation parameters. The rotational assignment of 930 lines in the strongest hot band was performed. The 22(1)024(1)1 vibrational assignment is proposed, leading to x22,24 = 1.90 cm-1. The transition dipole matrix element for the 22(1)0 band is estimated to || || = 2 x 10(-4) D. Copyright 1999 Academic Press.

Journal Article↗

PubMed1998

Theoretical analysis of "Switching" in a localized model for mountain pine beetle mass attack

The dynamic interaction between mountain pine beetles (MPB) and hosts (generally lodgepole pine) is reviewed briefly. In particular, successful "switching" from initial foci of attack to nearby hosts which may be higher-quality resources is a potentially critical element initiating the transition from endemic to epidemic population levels. A coupled partial differential equation model for MPB dispersal and host response is reviewed. The equations are decoupled making an adiabatic assumption for MPB chemotaxis, and a "local" projection is made using the leading eigenfunction for the MPB density equation. This projection yields a system of ordinary differential equations for the spatio-temporal responses at individual trees. These equations are analysed to determine what factors control successful "switching" in a two-tree model. The results suggest that stand thinning ameliorates outbreaks mainly through interference with the chemical ecology via a change in micro-climate rather than by altering host vigor.Copyright 1998 Academic Press Limited

Journal Article↗

PubMed1996

Behavioral effects of MK-801 in morphine-dependent and non-dependent mice.

The behavioral effects of MK-801 were compared in morphine-dependent and non-dependent mice. The dose of MK-801 selected for these studies was previously demonstrated to attenuate some of the morphine withdrawal signs. Subjects were repeatedly exposed to morphine (8 days, b.i.d., 10-100 mg/kg, s.c.). Twenty-four hours after last morphine injection mice received naloxone (0.1 mg/kg, s.c.) and the observation was commenced. Animals were pretreated with either MK-801 (0.1 mg/kg, i.p.) or saline 30 min prior to testing. It was found that the behavioral effects of MK-801 (decreased sociability, and increased rate of transitions between behavioral elements, locomotion, grooming) were less pronounced in morphine-dependent compared to non-dependent subjects. However, the intensified almost stereotypic eating possibly reflected increased psychotomimetic potency of MK-801 in morphine-withdrawn animals.

Analgesics, Opioid↗

PubMed2006

Mechanics and deformation of the nucleus in micropipette aspiration experiment.

Robust biomechanical models are essential for the study of nuclear mechanics and deformation and can help shed light on the underlying mechanisms of stress transition in nuclear elements. Here, we develop a computational model for an isolated nucleus undergoing micropipette aspiration. Our model includes distinct components representing the nucleoplasm and nuclear envelope. The nuclear envelope itself comprises three layers: inner and outer nuclear membranes and one thicker layer representing the nuclear lamina. The nucleoplasm is modeled as a viscoelastic Maxwell material with a single time constant, while a modified Maxwell model, equivalent to a spring and a dashpot in series and both in parallel with a spring, is adopted for the inner and outer nuclear membranes. The nuclear envelope layer is taken as a linear elastic material. The proposed computational model, validated using experimental observations of Guilak et al. [2000. Viscoelastic properties of the cell nucleus. Biochemical and Biophysical Research Communications 269, 781-786] and Deguchi et al. [2005, Flow-induced hardening of endothelial nucleus as an intracellular stress-bearing organelle. Journal of Biomechanics 38, 1751-1759], is employed to study nuclear mechanics and deformation in micropipette aspiration and to shed light on the contribution of individual nuclear components on the response. The results indicate that the overall response of an isolated nucleus in micropipette aspiration is highly sensitive to the apparent stiffness of the nuclear lamina. This observation suggests that micropipette aspiration is an effective technique for examining the influence of various kinds of alteration in the nuclear lamina, such as mutations in the gene encoding lamin A, and also structural remodeling due to mechanical perturbation.

Animals↗