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MT
Terms modified by MT Selected AbstractsPulsed saturation of the standard two-pool model for magnetization transfer.CONCEPTS IN MAGNETIC RESONANCE, Issue 1 2004Part I: The steady state Abstract A general framework for magnetization transfer (MT) of a two-pool system with linear exchange for arbitrary saturation by periodic radio-frequency pulses was derived. It is based on a novel parameterization adapted to the time evolution of saturation recovery. The conditions in tissue permit a description in analogy to partial saturation of a homogeneous liquid. In this approximation, the direct saturation of bulk water is amplified by MT. Rapid transfer equilibrates the saturation of the pools in the early phase of free evolution. This kinetic "pre-equilibrium" relaxes slowly with a common relaxation rate. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson Part A 21A: 37,49, 2004 [source] Directional change produced by perpendicularly-oriented microgrooves is microtubule-dependent for fibroblasts and epitheliumCYTOSKELETON, Issue 5 2009Douglas W. Hamilton Abstract Anisotropic substrata such as micromachined grooves can control cell shape, orientation, and the direction of cell movement, a phenomena termed topographic guidance. Although many types of cells exhibit topographic guidance, little is known regarding cell responses to conflicting topographic cues. We employed a substratum with intersecting grooves in order to present fibroblasts and epithelial cells with conflicting topographic cues. Using time-lapse and confocal microscopy, we examined cell behavior at groove intersections. Migrating fibroblasts and epithelial cells typically extended a cell process into the intersection ahead of the cell body. After travelling along the "X" groove to enter the intersection, the leading lamellipodia of the cell body encountered the perpendicular "Y" groove, and spread latterly along the "Y" groove. The formation of lateral lamellipodia resulted in cells forming "T" or "L" morphologies, which were characterized by the formation of phosphotyrosine-rich focal adhesions at the leading edges. The "Y" groove did not prove an absolute barrier to cell migration, particularly for epithelial cells. Analysis of cytoskeletal distribution revealed that F-actin bundles did not adapt closely to the groove patterns, but typically did align to either the "X" or "Y" grooves. In contrast microtubules (MT) adapted closely to the walls. Inhibition of microtubule nucleation attenuated fibroblast and epithelial cell orientation within the intersection of the perpendicular grooves. We conclude that MT may be the prime determinant of fibroblast and epithelial cell conformation to conflicting topographies. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] In vivo analysis of MT-based vesicle transport by confocal reflection microscopyCYTOSKELETON, Issue 2 2009Imre Gáspár Abstract The use of confocal reflection microscopy (CRM) for the in vivo analysis of microtubule (MT) mediated transport of lipid droplets in the developing Drosophila egg primordia is described here. The developing Drosophila oocytes are ideal objects to study MT-mediated transport in vivo: transport of e.g. the lipid droplets can be conveniently, selectively and sensitively monitored through CRM and the egg primordia are readily available for physical, chemical and/or genetic manipulations. CRM is a non-destructive way to follow vesicle movement and allows high frame rate image recording. When combined with fluorescence imaging, CRM offers simultaneous visualization of the cargo and the protein(s) of interest, i.e. a motor or a cargo adapter, thus allowing a better understanding of MT-mediated transport and spatiotemporal coordination of the transport machinery. Cell Motil. Cytoskeleton 2009. © 2009 Wiley-Liss, Inc. [source] CLIP-170 interacts with dynactin complex and the APC-binding protein EB1 by different mechanismsCYTOSKELETON, Issue 3 2003Holly V. Goodson Abstract CLIP-170 is a "cytoplasmic linker protein" implicated in endosome-microtubule interactions and in control of microtubule dynamics. CLIP-170 localizes dynamically to growing microtubule plus ends, colocalizing with the dynein activator dynactin and the APC-binding protein EB1. This shared "plus-end tracking" behavior suggests that CLIP-170 might interact with dynactin and/or EB1. We have used site-specific mutagenesis of CLIP-170 and a transfection/colocalization assay to address this question in mammalian tissue culture cells. Our results indicate that CLIP-170 interacts, directly or indirectly, with both dynactin and EB1. We find that the CLIP-170/dynactin interaction is mediated by the second metal binding motif of the CLIP-170 tail. In contrast, the CLIP-170/EB1 interaction requires neither metal binding motif. In addition, our experiments suggest that the CLIP-170 /dynactin interaction occurs via the shoulder/sidearm subcomplex of dynactin and can occur in the cytosol (i.e., it does not require microtubule binding). These results have implications for the targeting of both dynactin and EB1 to microtubule plus ends. Our data suggest that the CLIP-170/dynactin interaction can target dynactin complex to microtubule plus ends, although dynactin likely also targets MT plus ends directly via the microtubule binding motif of the p150Glued subunit. We find that CLIP-170 mutants alter p150Glued localization without affecting EB1, indicating that EB1 can target microtubule plus ends independently of dynactin. Cell Motil. Cytoskeleton 55:156,173, 2003. © 2003 Wiley-Liss, Inc. [source] Impact of substance use on the physical health of patients with bipolar disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 6 2010M. P. Garcia-Portilla Garcia-Portilla MP, Saiz PA, Benabarre A, Florez G, Bascaran MT, Díaz EM, Bousoño M, Bobes J. Impact of substance use on the physical health of patients with bipolar disorder. Objective:, To describe the impact of tobacco, alcohol and cannabis on metabolic profile and cardiovascular risk in bipolar patients. Method:, Naturalistic, cross-sectional, multicenter Spanish study. Current use of tobacco, alcohol and cannabis was determined based on patient self-reports. Metabolic syndrome was defined using the National Health and Nutrition Examination Survey 1999,2000 and the American Heart Association/National Heart, Lung and Blood Institute criteria, and cardiovascular risk using the Framingham and the Systematic Coronary Risk Evaluation functions. Results:, Mean age was 46.6 years, 49% were male. Substance use: 51% tobacco, 13% alcohol and 12.5% cannabis. Patients who reported consuming any substance were significantly younger and a higher proportion was male. After controlling for confounding factors, tobacco was a risk factor for coronary heart disease (CHD) (unstandardized linear regression coefficient 3.47, 95% confidence interval 1.85,5.10). Conclusion:, Substance use, mainly tobacco, was common in bipolar patients. Tobacco use negatively impacted CHD risk. [source] Magnetic motor threshold and response to TMS in major depressive disorderACTA PSYCHIATRICA SCANDINAVICA, Issue 3 2002O. T. Dolberg Dolberg OT, Dannon PN, Schreiber S, Grunhaus L. Magnetic motor threshold and response to TMS in major depressive disorder. Acta Psychiatr Scand 2002: 106: 220,223. © Blackwell Munksgaard 2002. Objective:,The aim of this study was to examine motor threshold (MT) during treatment with transcranial magnetic stimulation (TMS). Method:,The TMS was administered to 46 patients with depression and 13 controls. TMS was performed at 90% power of measured MT. The stimulation frequency was 10 Hz for 6 s, for 20 trains, with 30 s inter-train intervals. The trial included 20 sessions. Patients and controls were assessed on various outcome measures. Results:,The MT values were comparable between patients and controls. Neither demographic nor clinical variables were factors in determining MT. MT was not shown to have any predictive value regarding outcome of treatment. Conclusion:,In this study, MT at baseline or changes in MT during the treatment period were not able to discriminate between patients and controls and were not found to have any predictive value with regard to treatment outcome. [source] The characteristics of heroin users entering treatment: findings from the Australian Treatment Outcome Study (ATOS)DRUG AND ALCOHOL REVIEW, Issue 5 2005JOANNE ROSS Abstract The current study aimed to describe the characteristics (demographics, drug use, mental and physical health) of entrants to treatment for heroin dependence in three treatment modalities; and to compare these characteristics with heroin users not in or seeking treatment. Participants were 825 current heroin users recruited from Sydney, Adelaide and Melbourne: 277 entering methadone/buprenorphine maintenance treatment (MT), 288 entering detoxification (DTX), 180 entering drug-free residential rehabilitation (RR) and 80 not in treatment (NT). Treatment entrants were generally long-term heroin users with previous treatment experience. The majority of the sample (55%) were criminally active in the month preceding interview. Injection-related health problems (74%) and a history of heroin overdose (58%) were commonly reported. There were high degrees of psychiatric co-morbidity, with 49% reporting severe psychological distress, 28% having current major depression, 37% having attempted suicide and 42% having a lifetime history of post-traumatic stress disorder. Personality disorders were also prevalent, with 72% meeting criteria for antisocial personality disorder and 47% screening positive for borderline personality disorder. Striking similarities were noted between the non-treatment and treatment groups in length of heroin use career, drug use and treatment histories. [source] Voltammetric Studies of the Interactions Between Ferrocene-Labeled Glutathione and Proteins in Solution or Immobilized onto SurfaceELECTROANALYSIS, Issue 16 2009Yong Peng Abstract Glutathione (GSH) tagged with a ferrocene (Fc) label at its C-terminal was synthesized via coupling ferrocenyl amine to glutathione using o -(benzotriazol-1-yl)- N,N,N,,N, -tetramethyluronium (HBTU)/1-hydroxybenzotrizole (HOBt). The presence of Fc yielded well defined voltammetric signals, rendering the Fc-tagged GSH (GSH-Fc) suitable for electrochemical studies of GSH binding to other biological species. The interaction of GSH-Fc with bovine serum albumin (BSA) was investigated, and a binding ratio of 1.41±0.06 (GSH-Fc/BSA) and an affinity constant Ka of 6.53±2.01×106,M,1 were determined. These results compare well with those measured by fluorescence using untagged GSH, suggesting that the attachment of Fc to GSH does not significantly perturb the GSH structure and binding behavior. By contrasting the binding behavior to several compounds that are known to conjugate to different domains of BSA, the voltammetric study confirmed that GSH-Fc binds at subdomain IIA of BSA with high affinity. The versatility of GSH-Fc for studying GSH binding to surface-confined proteins was also demonstrated with the GSH binding to electroinactive Zn-metallothionein (Zn7 -MT) through hydrogen binding at the region between the Zn7 -MT , and , domains. [source] Electrochemical Investigation of Strontium,Metallothionein Interactions , Analysis of Serum and Urine of Patients with OsteoporosisELECTROANALYSIS, Issue 3-5 2009Ivo Fabrik Abstract The main aim of this paper is to study interaction between strontium and metallothionein (MT), and to determine changes in strontium and thiols (MT, reduced glutathione, cysteine, and homocysteine) level in plasma, serum, and urine samples of patients treated with strontium ranelate (SrR). To investigate the interactions between MT and strontium(II) ions, adsorptive transfer stripping technique coupled with differential pulse voltammetry (DPV) the Brdicka reaction was employed. Besides standard Brdicka signals (Co, RS2Co, Cat1, Cat2, Cat3), we observed new signal related to Sr-MT interaction. Further we investigated the effect of various time of interaction, concentration of strontium(II) ions and temperature of supporting electrolyte on Brdicka signals. Optimal time of interaction was 240,s. Under temperature of supporting electrolyte 20,°C, we measured linear dependence of Cat3 signal height on strontium(II) ions concentration. After that we have investigated the possibility of strontium-MT interactions, we were interested in strontium, MT and low molecular mass thiols levels in serum and urine of patients treated with strontium(II) ions to cure osteoporosis. Strontium concentration determined by atomic absorption spectrometry was 55±5,,g/L before and 10,500±1,400,,g/L at the 30th day of SrR administration. Levels of metallothionein in serum ranged from 0.1 to 6.4,,M. Correlation between serum strontium concentration and MT level was determined and correlation coefficient was R=0.93. [source] Voltammetric Investigation of Zinc Release from Metallothioneins Modulated by the Glutathione Redox Couple and Separated with a Porous MembraneELECTROANALYSIS, Issue 20 2008Lin Liu Abstract Glutathione (GSH), in addition to serving as a redox buffer in cellular environment, has been suggested as a modulator in metal regulation and homeostasis by metallothioneins (MTs). The interactions of MTs with both GSH and its oxidized form GSSG have been shown to govern the direction of metal transfer. Common methods for the determination of zinc release from MTs modulated by GSH/GSSG either involve radioactive species or enzymes or are labor-intensive. In this study, upon separation of Zn2+ from the reaction mixture of MTs and GSH with a centrifugal filter membrane, differential pulse voltammetry (DPV) was used for the Zn2+ quantification. The same approach is extended to the studies of metal transfer between Zn7MT with a GSH/GSSG mixture and that between Zn7MT with GSSG. The concomitant conversion between the free thiol and disulfide bonds was confirmed with UV-vis spectrophotometry. The results demonstrate that GSSG, GSH, and the GSH/GSSG mixture all modulate zinc release from Zn7MT. The percentage of zinc release increases in the order of GSH, GSSG, and the GSH/GSSG mixture. The new approach is demonstrated to be well suited for investigation of redox regulation of MT and its reaction with zinc-containing enzymes. [source] Voltammetry as a Virtual Potentiometric Sensor in Modeling of a Metal-Ligand System and Refinement of Stability Constants.ELECTROANALYSIS, Issue 8 2004Part 1. Abstract A mathematical conversion of data coming from nonequilibrium and dynamic voltammetric techniques (a direct current sampled (DC) and differential pulse (DP) polarography) into potentiometric sensor type of data is described and tested on a dynamic metal-ligand system. A combined experiment involving DCP, DPP and glass electrode potentiometry (GEP) was performed on a single solution sample containing a fixed [LT],:,[MT] ratio (acid-base titration). Dedicated potentiometric software ESTA was successfully employed in the refinement operations performed on virtual potentiometric (VP) data obtained from DC and DP polarography. It was possible to refine stability constants either separately, from VP-DC or VP-DP, or simultaneously from any combination of VP-DC, VP-DP and GEP. The concept of VP-DC or VP-DP is reported for the first time and numerous documented and possible advantages are discussed. The proposed procedure can be easily utilized also by nonelectrochemists who are interested in, e.g., the ligand design strategies. [source] Partial oxidation and oxidative polymerization of metallothioneinELECTROPHORESIS, Issue 20 2008Hajo Haase Abstract One mechanism for regulation of metal binding to metallothionein (MT) involves the non-enzymatic or enzymatic oxidation of its thiols to disulfides. Formation and speciation of oxidized MT have not been investigated in detail despite the biological significance of this redox biochemistry. While metal ion-bound thiols in MT are rather resistant towards oxidation, free thiols are readily oxidized. MT can be partially oxidized to a state in which some of its thiols remain reduced and bound to metal ions. Analysis of the oxidation products with SDS-PAGE and a thiol-specific labeling technique, employing eosin-5-iodoacetamide, demonstrates higher-order aggregates of MT with intermolecular disulfide linkages. The polymerization follows either non-enzymatic or enzymatic oxidation, indicating that it is a general property of oxidized MT. Supramolecular assemblies of MT add new perspectives to the complex redox and metal equilibria of this protein. [source] Biomarker study of a municipal effluent dispersion plume in two species of freshwater musselsENVIRONMENTAL TOXICOLOGY, Issue 3 2002F. Gagné Abstract The toxicological effects of a primary-treated municipal effluent plume were investigated in two species of freshwater mussels, Elliptio complanata and Dreissena polymorpha, exposed for 62 days at sites upstream and downstream of an effluent outfall in the St. Lawrence River (Quebec, Canada). Levels of metallothioneins (MT), cytochrome P4501A1 activity, DNA damage, total lipids, relative levels of vitellins, and phagocytic activity (in E. complanata hemocytes) were determined after the exposure period. A parallel analysis measured heavy metals and coprostanol in mussel tissues. The results show that significant levels of coprostanol and some metals (specifically, Cu, Hg, Sb, Se, and Zn) had accumulated in mussels caged 5 km downstream of the effluent plume. Mixed-function oxidase activity, MT in gills, total lipids, DNA damage (in D. polymorpha only), and total hemolymph bacteria (in E. complanata only) had increased in these mussels, while levels of total cadmium (Cd), MT in digestive glands or whole soft tissues, phagocytic activity, and DNA damage in the digestive gland (in E. complanata only) were diminished. The exposure of mussels to surface waters contaminated by a municipal effluent led to many stress responses, depending on both the tissues and the species being examined. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 149,159, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10046 [source] Molluscan shellfish biomarker study of the Quebec, Canada, Saguenay Fjord with the soft-shell clam, Mya arenariaENVIRONMENTAL TOXICOLOGY, Issue 3 2002C. Blaise Abstract A spatial and temporal survey of six sites in the Saguenay Fjord and of one adjacent site in the St. Lawrence River estuary (Quebec, Canada) was undertaken to study the possible effects of anthropogenic contaminant input on soft-shell clam (Mya arenaria) populations. Bivalve sampling sites were selected because they reflected a range of areas representative of either no known (or apparent) pollution sources or of areas potentially influenced by different gradients and types of contamination sources. The most upstream site selected in the Saguenay Fjord, nearest to a highly populated and industrialized sector, and the most downstream site, near its mouth with the St. Lawrence River estuary, spanned a distance of some 70 km and encompassed the entire intertidal area suitable for Mya arenaria habitat. To measure effects in collected animals, we used a comprehensive battery of biomarkers composed of metallothionein-like proteins (MT), 7-ethoxyresorufin O-deethylase activity (EROD), DNA damage (DD), lipid peroxidation (LPO), vitellinlike proteins (Vn), phagocytosis (PHAG), nonspecific esterase (NspE) activity, and condition factor (weight-to-length ratio of clams). Vn, PHAG, DD, and NspE biomarkers were assayed in hemolymph (or hemocytes), whereas others (MT, EROD, LPO) were determined in the digestive gland. Whole-tissue metal content was also quantified in clams collected in the spatial survey. The spatial survey conducted in June 1997 showed significant effects at all sites, and principal component analysis indicated in addition that the more important responses were linked to the MT, LPO, and NspE biomarkers. Clams collected from sites closest to the upstream reaches of the fjord generally displayed higher levels of tissue metals (cadmium, manganese), as well as greater responses of NspE activity, MT, LPO, and PHAG. Animals collected from sites influenced by municipal wastewaters had higher levels of Vn, suggesting the presence of environmental estrogens. The results of the temporal survey (six monthly samplings of clams at three sites from May through October, 1997) showed that the bivalve reproductive cycle (vitellogenesis and spawning) can modulate the expression of several biomarkers. Vn levels, for example, were positively correlated with DD and EROD and negatively correlated with MT, suggesting that reproduction can influence the susceptibility of clams to some contaminants. Discrimination analysis over the 6 months of sampling revealed that the mean value of the discriminant function changed significantly over time, suggesting important changes in the relative contribution of each biomarker. In short, this study has provided evidence that clam populations in the Saguenay Fjord are impacted by multiple sources of contamination whose effects can be modulated by reproduction. © 2002 Wiley Periodicals, Inc. Environ Toxicol 17: 170,186, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/tox.10048 [source] Uptake kinetics and subcellular compartmentalization of cadmium in acclimated and unacclimated earthworms (Eisenia andrei)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2010Shuo Yu Abstract Acclimation to cadmium (Cd) levels exceeding background concentrations may influence the ability of earthworms to accumulate Cd with minimum adverse effects. In the present study, earthworms (Eisenia andrei) were acclimated by exposure to 20,mg/kg Cd (dry wt) in Webster soil for 28 d. A 224-d bioaccumulation test was subsequently conducted with both acclimated and unacclimated worms exposed in Webster soils spiked with 20,mg/kg and 100,mg/kg Cd (dry wt). Uptake kinetics and subcellular compartmentalization of Cd were examined. Results suggest that acclimated earthworms accumulated more Cd and required a longer time to reach steady state than unacclimated worms. Most of the Cd was present in the metallothionein (MT) fraction. Cadmium in the MT fraction increased approximately linearly with time and required a relatively longer time to reach steady state than Cd in cell debris and granule fractions, which quickly reached steady state. Cadmium in the cell debris fraction is considered potentially toxic, but low steady state concentrations observed in the present study would not suggest the potential for adverse effects. Future use of earthworms in ecological risk assessment should take into consideration pre-exposure histories of the test organisms. A prolonged test period may be required for a comprehensive understanding of Cd uptake kinetics and compartmentalization. Environ. Toxicol. Chem. 2010;29:1568,1574. © 2010 SETAC [source] Protein-based electrochemical biosensor for detection of silver(I) ions,ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2010Sona Krizkova Abstract Silver(I) ions are extremely toxic to aquatic animals. Hence, monitoring of these ions in the environment is needed. The aim of the present study was to suggest a simple biosensor for silver(I) ions detection. The suggested biosensor is based on the modification of a hanging mercury drop electrode (HMDE) by the heavy metal binding protein metallothionein (MT) for silver(I) ions detection. Metallothionein accumulated for 120 s onto the HMDE surface. After rinsing the electrode, the biosensor (MT modified HMDE) was prepared prior to detection of silver(I) ions. The biosensor was immersed in a solution containing silver(I) ions. These ions were bound to the MT structure. Furthermore, the electrode was rinsed and transferred to a pure supporting electrolyte solution, in which no interference was present. Under these experimental conditions, other signals relating to heavy metals naturally occurring in MT were not detected. This phenomenon confirms the strong affinity of silver(I) ions for MT. The suggested biosensor responded well to higher silver(I) ion concentrations. The relative standard deviation for measurements of concentrations higher than 50,µM was approximately 2% (n,=,8). In the case of concentrations lower than 10,µM, the relative standard deviation increased to 10% (n,=,8). The detection limit (3,signal/noise) for silver(I) ions was estimated as 500,nM. Environ. Toxicol. Chem. 2010;29:492,496. © 2009 SETAC [source] Trout density and health in a stream with variable water temperatures and trace element concentrations: Does a cold-water source attract trout to increased metal exposure?ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2009David D. Harper Abstract A history of hard-rock mining has resulted in elevated concentrations of heavy metals in Prickly Pear Creek (MT, USA). Remediation has improved water quality; however, dissolved zinc and cadmium concentrations still exceed U.S. Environmental Protection Agency water-quality criteria. Physical habitat, salmonid density, fish health, and water quality were assessed, and metal concentrations in fish tissues, biofilm, and macroinvertebrates were determined to evaluate the existing condition in the watershed. Cadmium, zinc, and lead concentrations in fish tissues, biofilm, and invertebrates were significantly greater than those at the upstream reference site and an experimental site farther downstream of the confluence. Fish densities were greatest, and habitat quality for trout was better, downstream of the confluence, where water temperatures were relatively cool (16°C). Measures of fish health (tissue metal residues, histology, metallothionein concentrations, and necropsies), however, indicate that the health of trout at this site was negatively affected. Trout were in colder but more contaminated water and were subjected to increased trace element exposures and associated health effects. Maximum water temperatures in Prickly Pear Creek were significantly lower directly below Spring Creek (16°C) compared to those at an experimental site 10 km downstream (26°C). Trout will avoid dissolved metals at concentrations below those measured in Prickly Pear Creek; however, our results suggest that the preference of trout to use cool water temperatures may supersede behaviors to avoid heavy metals. [source] Biokinetics of cadmium and zinc in a marine bacterium: Influences of metal interaction and pre-exposureENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2008Dongshi Chen Abstract The uptake kinetics of Cd and Zn, as influenced by metal interaction and metal pre-exposure, was examined in the gram-positive marine bacterium Bacillus firmus over a wide range of ambient free-Cd and -Zn concentrations. Bacteria were exposed to experimental media with different concentrations of Cd and Zn over a short, 15-min period. Zinc was found to be an effective competitive inhibitor of Cd uptake when the Zn2+ concentration ([Zn2+]) was increased to 10,8 M, whereas the Cd concentration (ranging from 10,9 to 10,6 M) did not affect Zn uptake. Inhibition of Cd uptake was dependent on [Zn2+] instead of the [Zn2+] to Cd2+ concentration ratio. Cadmium uptake at different [Zn2+] was significantly inhibited by a sulfur ligand (SH) blocker (N -ethylmaleimide) and a Ca-channel blocker (lanthanum), suggesting that competition between Cd and Zn most likely occurred via binding to the same transport sites. Cadmium efflux also was determined in the presence of different [Zn2+]. A biphasic depuration of Cd was found when [Zn2+] was greater than 10,8 M, whereas the calculated Cd efflux rate was independent of [Zn2+]. We further exposed B. firmus at different Cd or Zn concentrations for 24 h, then determined the metal uptake and efflux kinetics as well as the metallothionein (MT) induction. Both the Cd and Zn cellular concentrations increased with greater exposed metal concentration, but the MT levels and efflux were little affected by the elevated metal concentration. To some extent, however, the Cd uptake was reduced with an elevated intracellular Zn concentration, suggesting that at high Cd concentrations, intracellular Zn can suppress the Cd uptake in B. firmus. These results help to understand the interactions of metals in the marine environments. [source] Influence of in-stream diel concentration cycles of dissolved trace metals on acute toxicity to one-year-old cutthroat trout (Oncorhynchus clarki lewisi)ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2007David A. Nimick Abstract Extrapolating results of laboratory bioassays to streams is difficult, because conditions such as temperature and dissolved metal concentrations can change substantially on diel time scales. Field bioassays conducted for 96 h in two mining-affected streams compared the survival of hatchery-raised, metal-näive westslope cutthroat trout (Oncorhynchus clarki lewisi) exposed to dissolved (0.1-,m filtration) metal concentrations that either exhibited the diel variation observed in streams or were controlled at a constant value. Cadmium and Zn concentrations in these streams increased each night by as much as 61 and 125%, respectively, and decreased a corresponding amount the next day, whereas Cu did not display a diel concentration cycle. In High Ore Creek (40 km south of Helena, MT, USA), survival (33%) after exposure to natural diel-fluctuating Zn concentrations (range, 214,634 ,g/L; mean, 428 ,g/L) was significantly (p = 0.008) higher than survival (14%) after exposure to a controlled, constant Zn concentration (422 ,g/L). Similarly, in Dry Fork Belt Creek (70 km southeast of Great Falls, MT, USA), survival (75%) after exposure to diel-fluctuating Zn concentrations (range, 266,522 ,g/L; mean, 399 ,g/L) was significantly (p = 0.022) higher than survival (50%) in the constant-concentration treatment (392 ,g/L). Survival likely was greater in these diel treatments, both because the periods of lower metal concentrations provided some relief for the fish and because toxicity during periods of higher metal concentrations was lessened by the simultaneous occurrence each night of lower water temperatures, which reduce the rate of metal uptake. Based on the present study, current water-quality criteria appear to be protective for streams with diel concentration cycles of Zn (and, perhaps, Cd) for the hydrologic conditions tested. [source] Metallothionein gene expression and protein levels in triploid and diploid oysters Crassostrea gigas after exposure to cadmium and zincENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2006Véronique Marie Abstract Quantitative real-time polymerase chain reaction (PCR) was used to compare for the first time the differential expression of metallothionein (MT) isoform genes, together with biosynthesis of the total MT proteins, in the gills of triploid and diploid juvenile Pacific oyster Crassostrea gigas in response to cadmium (Cd) and zinc (Zn) exposure. Oysters were exposed to Cd (0.133 ,M), Zn (15.3 ,M), and Cd+Zn for 14 d. Results showed similar response capacities to metal exposures in the two populations. No significant difference was revealed in terms of MT gene expression, MT protein synthesis, and Cd accumulation. However, triploid oysters bioaccumulated Zn 30% less efficiently than diploid oysters. Among the three MT isoform genes, CgMT2 appeared to be more expressed than CgMT1, whereas CgMT3 appeared to be anecdotal (106 times lower than CgMT2). CgMT2 and CgMT1 gene expression levels were increased sevenfold in the presence of Cd, whereas Zn appeared to have no effect. A twofold increase in MT protein levels occurred in response to Cd exposure. Discrepancies between mRNA and protein levels suggest that in C. gigas MT are regulated at the transcriptional level, as well as at the translational level. [source] Subcellular cadmium distribution, accumulation, and toxicity in a predatory gastropod, Thais clavigera, fed different preyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2006Ma-Shan Cheung Abstract Bioaccumulation and toxicity of Cd were investigated in a marine predatory whelk, Thais clavigera, after being fed with the rock oyster, Saccostrea cucullata, or the herbivorous snail, Monodonta labio, for up to four weeks. The oysters and snails had different subcellular Cd distributions and concentrations in their bodies given their different metal-handling strategies and were exposed to dissolved Cd for two weeks before being fed to the whelks. After four weeks of dietary exposure, the Cd body concentrations in T. clavigera increased from 3.1 ,g/g to between 22.9 and 41.8 ,g/g and to between 22.7 and 24.1 ,g/g when they were fed with oyster and snail prey, respectively. An increasing proportion of Cd was found to be distributed in the metallothionein (MT)-like proteins and organelle fractions, whereas the relative distribution in the metal-rich granules fraction decreased when the whelks were fed Cd-exposed prey. At the highest Cd dosage, more Cd was distributed in the pool of metal-rich granules when the whelks were fed the oysters than when they were fed the snails. Among all the biomarkers measured (MT induction, condition index, lipid peroxidation, and total energy reserve including carbohydrate, lipid, and protein), only MT showed a significant difference from the control treatments, and MT was the most sensitive biomarker for dietary Cd exposure. No toxicity was found in the whelks fed different Cd-exposed prey as revealed by various biomarkers at the different biological levels. Our results imply that metal fractionation in prey can alter the subsequent subcellular metal distribution in predators and that dietary Cd toxicity to the whelks was low, even when the accumulated Cd body concentrations were high. [source] Reduced growth of rainbow trout (Oncorhynchus mykiss) fed a live invertebrate diet pre-exposed to metal-contaminated sedimentsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004James A. Hansen Abstract Juvenile rainbow trout (Oncorhynchus mykiss) were fed live diets of Lumbriculus variegatus cultured in metal-contaminated sediments from the Clark Fork River Basin (MT, USA), an uncontaminated reference sediment, or an uncontaminated culture medium. Fish were tested in individual chambers; individual growth as well as the nutritional quality and caloric value of each trout's consumed diet were determined. Growth was measured following 14, 28, 42, 56, and 67 d of exposure. A subset of fish was sampled at 35 d for whole-body metals. Metals (whole body, digestive tract, and liver) and histology were measured at the end of the test. We observed significant growth inhibition in trout fed the contaminated diets; growth inhibition was associated with reductions in conversion of food energy to biomass rather than with reduced food intake. Growth inhibition was negatively correlated with As in trout tissue residues. Histological changes in contaminated treatments included hepatic necrosis and degenerative alterations in gallbladder. The present study provides evidence that metal-contaminated sediments can pose a hazard to trout health through a dietary exposure pathway. [source] Association of heavy metals with metallothionein and other proteins in hepatic cytosol of marine mammals and seabirdsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2004Tokutaka Ikemoto Abstract Distribution of Cu, Zn, Cd, Ag, Hg, and Se were determined in hepatocytosol of northern fur seals (Callorhinus ursinus), black-footed albatrosses (Diomedea nigripes), and Dall's porpoises (Phocoenoides dalli). Copper, Zn, and Cd were accumulated preferentially in metallothionein (MT) fraction and their contents in MT fraction increased with the amounts in the hepatocytosol. Silver was bound to both high-molecular-weight substances (HMWS) and MT in the hepatocytosol for all three species, whereas the distribution of Ag in the cytosol was different among the three species. In northern fur seals, Ag mainly was bound to MT, whereas it mainly was associated with HMWS in Dall's porpoises. In contrast, Ag was distributed almost equally in both HMWS and MT for black-footed albatrosses. Mercury content in HMWS and Se content in HMWS and low-molecular-weight substances (LMWS) increased with their contents in hepatocytosol for all the three species. A significant positive correlation was found between Se and Hg contents in high-molecular weight (HMW) fraction in cytosol. The molar ratio of Hg and Se was close to unity in HMW fraction of the specimens with high Hg concentration in cytosol, implying that the Hg,Se complex was bound to the HMWS. Analysis of metals in the hepatocytosol by high-performance liquid chromatography/inductively coupled plasma,mass spectrometry (HPLC/ICP-MS) suggests that multiple isoforms of MT are present in hepatocytosol of the three species and that the metal profiles in hepatocytosols are different among the species. To our knowledge, this is the first report on the association of Ag with HMWS and MT in hepatocytosol of marine mammals and seabirds. Also, distribution and interaction of Hg and Se were investigated for the first time in hepatocytosol of the higher trophic marine animals. [source] Linking metal bioaccumulation of aquatic insects to their distribution patterns in a mining-impacted riverENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2004Daniel J. Cain Abstract Although the differential responses of stream taxa to metal exposure have been exploited for bioassessment and monitoring, the mechanisms affecting these responses are not well understood. In this study, the subcellular partitioning of metals in operationally defined metal-sensitive and detoxified fractions were analyzed in five insect taxa. Samples were collected in two separate years along an extensive metal contamination gradient in the Clark Fork River (MT, USA) to determine if interspecific differences in the metal concentrations of metal-sensitive fractions and detoxified fractions were linked to the differences in distributions of taxa relative to the gradient. Most of the Cd, Cu, and Zn body burdens were internalized and potentially biologically active in all taxa, although all taxa appeared to detoxify metals (e.g., metal bound to cytosolic metal-binding proteins). Metal concentrations associated with metal-sensitive fractions were highest in the mayflies Epeorus albertae and Serratella tibialis, which were rare or absent from the most contaminated sites but occurred at less contaminated sites. Relatively low concentrations of Cu were common to the tolerant taxa Hydropsyche spp. and Baetis spp., which were widely distributed and dominant in the most contaminated sections of the river. This suggested that distributions of taxa along the contamination gradient were more closely related to the bioaccumulation of Cu than of other metals. Metal bioaccumulation did not appear to explain the spatial distribution of the caddisfly Arctopsyche grandis, considered to be a bioindicator of metal effects in the river. Thus, in this system the presence/absence of most of these taxa from sites where metal exposure was elevated could be differentiated on the basis of differences in metal bioaccumulation. [source] Isoform-specific quantification of metallothionein in the terrestrial gastropod Helix pomatia.ENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Abstract The two function-specific metallothionein (MT) isoforms characterized from the midgut gland and mantle tissue of Helix pomatia differ substantially in their metal-binding preferences, as well as molecular and biochemical features. These differences make them potential candidates for biomarker studies based on a differential, isoform-specific approach. To prove this hypothesis, induction experiments with two metals (Cd and Cu) that are normally bound by the two isoforms were compared with a range of organic chemicals and physical stressors under laboratory conditions to test the responsiveness of the two isoforms to the stressors applied. In addition, field studies were conducted with Roman snails and substrate samples collected from different metal-contaminated sites in Austria to test the suitability of the two isoforms as biomarkers under field conditions. The results of these combined laboratory and field studies confirmed the validity of the biomarker approach with the two metal- and tissue-specific isoforms. It is demonstrated that the Cd-binding MT specifically and exclusively responds to Cd exposure by increasing concentrations, whereas the Cu-binding MT isoform decreases in its concentration upon exposure to physical stress (X-ray irradiation and cold). This suggests researchers should adopt, under certain preconditions, a dual biomarker approach by combining the simultaneous quantification of Cd-MT concentrations in the midgut gland as a biomarker for Cd pollution and of Cu-MT concentration in the mantle as a biomarker for the impairment of snails by additional physical stressors. [source] Variation of metallothionein and metal concentrations in the digestive gland of the clam Ruditapes decussatus: Sex and seasonal effectsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 3 2001Maria A. Serafim Abstract Metallothionein (MT) and metal (Cd, Cu, and Zn) concentrations were determined in the digestive gland of male and female Ruditapes decussatus. Clams were collected monthly during the period of sexual development, from June to September, at two different sites of a coastal lagoon, the Ria Formosa Lagoon, on the south coast of Portugal. The MT concentrations were determined in the heat-treated cytosolic fraction of the digestive gland of both male and female clams. Total metal (Cd, Cu, and Zn) concentrations in the heat-treated cytosol of the digestive gland were also determined in both sexes. The MT and metal concentrations in the digestive gland were not sex dependent in this species. Therefore, these results suggest that random samples can be used to determine MT and metal concentrations in the digestive gland of R. decussatus. Seasonal and site-specific dependency, however, were detected for MT, Cd, and Cu concentrations. The maximum concentration levels of MT, Cd, and Cu were detected in July and August for both sexes in the same area. Zinc concentrations, however, did not show marked seasonal variations, indicating that this species is able to regulate zinc concentrations. The highest MT concentrations were significantly related to the highest metal concentrations. [source] Subjective mental time: the functional architecture of projecting the self to past and futureEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 10 2009Shahar Arzy Abstract Human experience takes place in the line of mental time (MT) created through ,self-projection' of oneself to different time-points in the past or future. Here we manipulated self-projection in MT not only with respect to one's life events but also with respect to one's faces from different past and future time-points. Behavioural and event-related functional magnetic resonance imaging activity showed three independent effects characterized by (i) similarity between past recollection and future imagination, (ii) facilitation of judgements related to the future as compared with the past, and (iii) facilitation of judgements related to time-points distant from the present. These effects were found with respect to faces and events, and also suggest that brain mechanisms of MT are independent of whether actual life episodes have to be re-experienced or pre-experienced, recruiting a common cerebral network including the anteromedial temporal, posterior parietal, inferior frontal, temporo-parietal and insular cortices. These behavioural and neural data suggest that self-projection in time is a fundamental aspect of MT, relying on neural structures encoding memory, mental imagery and self. [source] Regulation of the norepinephrine transporter by ,-synuclein-mediated interactions with microtubulesEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 6 2007Alexis M. Jeannotte Abstract ,-Synuclein (,-Syn) regulates catecholaminergic neurotransmission. We demonstrate that ,-Syn regulates the activity and surface expression of the norepinephrine transporter (NET), depending on its expression levels. In cells co-transfected with NET and low amounts of ,-Syn, NET activity and cell surface expression were increased and protein interactions with ,-Syn decreased, compared with cells transfected with NET alone. Converse effects were observed at higher levels of ,-Syn expression. Treatment with nocodazole and other microtubule (MT) destabilizers abolished the expression-dependent bimodal regulation of NET by ,-Syn. At low ,-Syn levels, nocodazole had no effect on NET surface expression or protein interactions, while inducing increases in these measures at higher levels. Cells that were transfected with NET alone displayed no sensitivity to nocodazole, indicating that ,-Syn expression was necessary for the MT-dependent changes in NET activity. MT destabilizers also caused a significant increase in [3H]-NE uptake in brainstem primary neurons and synaptosomes from the frontal cortex, but not striatal synaptosomes. These findings suggest that the surface localization and activity of NET is modulated by ,-Syn in a manner that is both dependent on interactions with the MT cytoskeleton and varies across brain regions. [source] Heteromodal connections supporting multisensory integration at low levels of cortical processing in the monkeyEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 11 2005Céline Cappe Abstract While multisensory integration is thought to occur in higher hierarchical cortical areas, recent studies in man and monkey have revealed plurisensory modulations of activity in areas previously thought to be unimodal. To determine the cortical network involved in multisensory interactions, we performed multiple injections of different retrograde tracers in unimodal auditory (core), somatosensory (1/3b) and visual (V2 and MT) cortical areas of the marmoset. We found three types of heteromodal connections linking unimodal sensory areas. Visuo-somatosensory projections were observed originating from visual areas [probably the ventral and dorsal fundus of the superior temporal area (FSTv and FSTd), and middle temporal crescent (MTc)] toward areas 1/3b. Somatosensory projections to the auditory cortex were present from S2 and the anterior bank of the lateral sulcus. Finally, a visuo-auditory projection arises from an area anterior to the superior temporal sulcus (STS) toward the auditory core. Injections in different sensory regions allow us to define the frontal convexity and the temporal opercular caudal cortex as putative polysensory areas. A quantitative analysis of the laminar distribution of projecting neurons showed that heteromodal connections could be either feedback or feedforward. Taken together, our results provide the anatomical pathway for multisensory integration at low levels of information processing in the primate and argue against a strict hierarchical model. [source] Melatonin inhibits hippocampal long-term potentiationEUROPEAN JOURNAL OF NEUROSCIENCE, Issue 9 2005Louisa M. Wang Abstract The goal of this study is to investigate the effect of the hormone melatonin on long-term potentiation and excitability measured by stimulating the Schaffer collaterals and recording the field excitatory postsynaptic potential from the CA1 dendritic layer in hippocampal brain slices from mice. Application of melatonin produced a concentration-dependent inhibition of the induction of long-term potentiation, with a concentration of 100 nm producing an ,,50% inhibition of long-term potentiation magnitude. Long-duration melatonin treatments of 6 h were also effective at reducing the magnitude of long-term potentiation. Melatonin (100 nm) did not alter baseline evoked responses or paired-pulse facilitation recorded at this synapse. The inhibitory actions of melatonin were prevented by application of the melatonin (MT) receptor antagonist luzindole as well as the MT2 receptor subtype antagonist 4-phenyl-2-propionamidotetraline. These inhibitory actions of melatonin were lost in mice deficient in MT2 receptors but not those deficient in MT1 receptors. In addition, application of the protein kinase A inhibitor H-89 both mimicked the effects of melatonin and precluded further inhibition by melatonin. Finally, the application an activator of adenylyl cyclase, forskolin, overcame the inhibitory effects of melatonin on LTP without affecting the induction of long-term potentiation on its own. These results suggest that hippocampal synaptic plasticity may be constrained by melatonin through a mechanism involving MT2-receptor-mediated regulation of the adenylyl cyclase,protein kinase A pathway. [source] | |||||||||||||||||||||||||||||||||||||||||||