Distribution by Scientific Domains
Distribution within Life Sciences

Kinds of Uptake

  • acid uptake
  • active uptake
  • adenosine uptake
  • amino acid uptake
  • ammonium uptake
  • antigen uptake
  • bacterial uptake
  • brain uptake
  • brdu uptake
  • c uptake
  • ca2+ uptake
  • cadmium uptake
  • calcium uptake
  • carbon uptake
  • carnitine uptake
  • cd uptake
  • cell uptake
  • cellular uptake
  • ch4 uptake
  • cholesterol uptake
  • choline uptake
  • co2 uptake
  • decreased uptake
  • dna uptake
  • drug uptake
  • endocytic uptake
  • enhanced uptake
  • evidence uptake
  • fat uptake
  • fatty acid uptake
  • fdg uptake
  • fluoride uptake
  • foliar uptake
  • food uptake
  • gaba uptake
  • glucose uptake
  • glutamate uptake
  • h2 uptake
  • hepatic uptake
  • high uptake
  • hydrogen uptake
  • increase glucose uptake
  • increased glucose uptake
  • increased uptake
  • insulin-stimulated glucose uptake
  • intestinal uptake
  • intracellular uptake
  • ion uptake
  • iron uptake
  • k+ uptake
  • ligand uptake
  • lipid uptake
  • maximal oxygen uptake
  • maximum oxygen uptake
  • metal uptake
  • mibg uptake
  • microbial uptake
  • mitochondrial ca2+ uptake
  • moisture uptake
  • muscle glucose uptake
  • myocardial glucose uptake
  • n uptake
  • na uptake
  • net co2 uptake
  • net uptake
  • nh4+ uptake
  • nitrate uptake
  • nitrogen uptake
  • nutrient uptake
  • o2 uptake
  • oil uptake
  • oxygen uptake
  • p uptake
  • particle uptake
  • peak oxygen uptake
  • phosphate uptake
  • phosphorus uptake
  • photosynthetic co2 uptake
  • plant uptake
  • protein uptake
  • radioiodine uptake
  • rapid uptake
  • reduced uptake
  • resource uptake
  • root uptake
  • salt uptake
  • selective uptake
  • serotonin uptake
  • significant uptake
  • silicon uptake
  • sodium uptake
  • specific uptake
  • substrate uptake
  • taurine uptake
  • thymidine uptake
  • tissue uptake
  • tracer uptake
  • treatment uptake
  • tumor uptake
  • tumour uptake
  • water uptake
  • zinc uptake
  • zn uptake

  • Terms modified by Uptake

  • uptake ability
  • uptake activity
  • uptake behavior
  • uptake capacity
  • uptake data
  • uptake decreased
  • uptake efficiency
  • uptake experiment
  • uptake flux
  • uptake inhibition
  • uptake inhibitor
  • uptake kinetics
  • uptake mechanism
  • uptake pathway
  • uptake pattern
  • uptake process
  • uptake property
  • uptake rate
  • uptake ratio
  • uptake site
  • uptake studies
  • uptake system
  • uptake value
  • uptake velocity

  • Selected Abstracts


    ADDICTION, Issue 5 2009
    No abstract is available for this article. [source]


    ABSTRACT Effective water diffusion coefficient (Deff) was determined from the kinetics of moisture gain in a yerba mate bed. A value of 1.5 10,9 0.4 10,9 m2/s was obtained at 40C and 90% relative humidity, by fitting experimental data to the series solution of Fick's second law. A model was developed to predict moisture profile and water uptake in packaged yerba mate. In order to simulate moisture gain in the packaged food, the model considers that the global process of humidity gain is controlled by combined mechanisms of package permeability, product sorption balances and water diffusion within the food bed. The explicit finite difference method was used to numerically solve the resulting equations. The validity of the model was tested by comparing predicted and experimental moisture profiles for high (WVTR , 20 g/m2/day) and low (WVTR , 400 g/m2/day) barrier packages. The model was found to adequately predict the profile of moisture content. [source]


    JOURNAL OF PHYCOLOGY, Issue 5 2010
    Ccile Jauzein
    Alexandrium catenella (Whedon et Kof.) Balech has exhibited seasonal recurrent blooms in the Thau lagoon (South of France) since first reported in 1995. Its appearance followed a strong decrease (90%) in phosphate (PO43,) concentrations in this environment over the 1970,1995 period. To determine if this dinoflagellate species has a competitive advantage in PO43, -limited conditions in terms of nutrient acquisition, semicontinuous cultures were carried out to characterize phosphorus (P) uptake by A. catenella cells along a P-limitation gradient using different dilution rates (DRs). Use of both inorganic and organic P was investigated from measurements of 33PO43, uptake and alkaline phosphatase activity (APA), respectively. P status was estimated from cellular P and carbon contents (QP and QC). Shifts in trends of QP/QC and QP per cell (QPcell,1) along the DR gradient allowed the definition of successive P-stress thresholds for A. catenella cells. The maximal uptake rate of 33PO43, increased strongly with the decrease in DR and the decrease in QP/QC, displaying physiological acclimations to PO43, limitation. Concerning maximal APA per cell, the observation of an all-or-nothing pattern along the dilution gradient suggests that synthesis of AP was induced and maximized at the cellular scale as soon as PO43, limitation set in. APA variations revealed that the synthesis of AP was repressed over a PO43, threshold between 0.4 and 1 ,M. As lower PO43, concentrations are regularly observed during A. catenella blooms in Thau lagoon, a significant portion of P uptake by A. catenella cells in the field may come from organic compounds. [source]


    JOURNAL OF PHYCOLOGY, Issue 1 2009
    Jess M. Mercado
    The role of carbonic anhydrase (CA) in inorganic carbon acquisition (dissolved inorganic carbon, DIC) was examined in Alboran Sea phytoplankton assemblages. The study area was characterized by a relatively high variability in nutrient concentration and in abundance and taxonomic composition of phytoplankton. Therefore, the relationship between environmental variability and capacity for using HCO3, via external CA (eCA) was examined. Acetazolamide (AZ, an inhibitor of eCA) inhibited the primary productivity (PP) in 50% of the samples, with inhibition percentages ranging from 13% to 60%. The AZ effect was more prominent in the samples that exhibited PP >1 mg C m,3 h,1, indicating that the contribution of eCA to the DIC photosynthetic flux was irrelevant at low PP. The inhibition of primary productivity by AZ was significantly correlated to the abundance of diatoms. However, there was no a relationship between AZ effect and CO2 partial pressure (pCO2) or nutrient concentration, indicating that the variability in the PP percentage supported by eCA was mainly due to differences in taxonomic composition of the phytoplankton assemblages. Ethoxyzolamide (EZ, an inhibitor of both external and internal CA) affected 13 of 14 analyzed samples, with PP inhibition percentages varying from 50% to 95%. The effects of AZ and EZ were partially reversed by doubling DIC concentration. These results imply that CA activity (external and/or internal) was involved in inorganic carbon acquisition in most the samples. However, EZ effect was not correlated with pCO2 or taxonomic composition of the phytoplankton. [source]


    JOURNAL OF PHYCOLOGY, Issue 2 2007
    T. Alwyn
    Marine phytoplankton and macroalgae acquire important resources, such as inorganic nitrogen, from the surrounding seawater by uptake across their entire surface area. Rates of ammonium and nitrate uptake per unit surface area were remarkably similar for both marine phytoplankton and macroalgae at low external concentrations. At an external concentration of 1 ,M, the mean rate of nitrogen uptake was 102 nmolcm,2h,1 (n=36). There was a strong negative relationship between log surface area:volume (SA:V) quotient and log nitrogen content per cm2 of surface (slope=,0.77), but a positive relationship between log SA:V and log maximum specific growth rate (,max; slope=0.46). There was a strong negative relationship between log SA:V and log measured rate of ammonium assimilation per cm2 of surface, but the slope (,0.49) was steeper than that required to sustain ,max (,0.31). Calculated rates of ammonium assimilation required to sustain growth rates measured in natural populations were similar for both marine phytoplankton and macroalgae with an overall mean of 6.21.4 nmolcm,2h,1 (n=15). These values were similar to maximum rates of ammonium assimilation in phytoplankton with high SA:V, but the values for algae with low SA:V were substantially less than the maximum rate of ammonium assimilation. This suggests that the growth rates of both marine phytoplankton and macroalgae in nature are often constrained by rates of uptake and assimilation of nutrients per cm2 surface area. [source]


    JOURNAL OF PHYCOLOGY, Issue 3 2006
    Anna Christina Tyler
    Macroalgae, often the dominant primary producers in shallow estuaries, can be important regulators of nitrogen (N) cycling. Like phytoplankton, actively growing macroalgae release N to the water column; yet little is known about the quantity or nature of this release. Using 15N labeling in laboratory and field experiments, we estimated the quantity of N released relative to assimilation and gross uptake by Gracilaria vermiculophylla (Ohmi) Papenfuss (Rhodophyta, Gracilariales), a non-native macroalgae. Field experiments were carried out in Hog Island Bay, a shallow back-barrier lagoon on the Virginia coast where G. vermiculophylla makes up 85%,90% of the biomass. There was good agreement between laboratory and field measurements of N uptake and release. Daily N assimilation in field experiments (32.37.2 ,mol Ng dw,1d,1) was correlated with seasonal and local N availability. The average rate of N release across all sites and dates (65.811.6 ,mol Ng dw,1d,1) was 67% of gross daily uptake, and also varied among sites and seasons (range=33%,99%). Release was highest when growth rates and nutrient availability were low, possibly due to senescence during these periods. During summer biomass peaks, estimated N release from macroalgal mats was as high as 17 mmol Nm,2d,1. Our results suggest that most estimates of macroalgal N uptake severely underestimate gross N uptake and that N is taken up, transformed, and released to the water column on short time scales (minutes,hours). [source]


    JOURNAL OF PHYCOLOGY, Issue 1 2005
    Robert J. M. Hudson
    First page of article [source]


    JOURNAL OF PHYCOLOGY, Issue 4 2004
    Neill G. Barr
    Ammonium is assimilated in algae by the glutamine synthetase (GS),glutamine:2-oxoglutarate aminotransferase pathway. In addition to the assimilation of external ammonium taken up across the cell membrane, an alga may have to reassimilate ammonium derived from endogenous sources (i.e. nitrate reduction, photorespiration, and amino acid degradation). Methionine sulfoximine (MSX), an irreversible inhibitor of GS, completely inhibited GS activity in Ulva intestinalis L. after 12 h. However, assimilation of externally derived ammonium was completely inhibited after only 1,2 h in the presence of MSX and was followed by production of endogenous ammonium. However, endogenous ammonium production in U. intestinalis represented only a mean of 4% of total assimilation attributable to GS. The internally controlled rate of ammonium uptake (Vi) was almost completely inhibited in the presence of MSX, suggesting that Vi is a measure of the maximum rate of ammonium assimilation. After complete inhibition of ammonium assimilation in the presence of MSX, the initial or surge (Vs) rate of ammonium uptake in the presence of 400 ,M ammonium chloride decreased by only 17%. However, the amount that the rate of ammonium uptake decreased by was very similar to the uninhibited rate of ammonium assimilation. In addition, the decrease in the rate of ammonium uptake in darkness (in the absence of MSX) in the presence of 400 ,M ammonium chloride matched the decrease in the rate of ammonium assimilation. However, in the presence of 10 ,M ammonium chloride, MSX completely inhibited ammonium assimilation but had no effect on the rate of uptake. [source]


    JOURNAL OF PHYCOLOGY, Issue 3 2004
    Julia C. Phillips
    The competitive ability for N uptake by four intertidal seaweeds, Stictosiphonia arbuscula (Harvey) King et Puttock, Apophlaea lyallii Hook. f. et Harvey, Scytothamnus australis Hook. f. et Harvey, and Xiphophora gladiata (Labillardire) Montagne ex Harvey, from New Zealand is described by the uptake kinetics for NO3,, NH4+, and urea. This is the first study to report uptake kinetics for N uptake by a range of southern hemisphere intertidal seaweeds in relation to season and zonation. Species growing at the highest shore positions had higher NO3, and urea uptake at both high and low concentrations and had unsaturable NH4+ uptake in both summer and winter. Although there was evidence of some feedback inhibition of Vmax for NO3, uptake by Stictosiphonia arbuscula growing at the lower vertical limits of its range, rates were high compared with species growing lower on the shore. Our results highlight the superior competitive ability for N uptake of certain high intertidal seaweeds, and consistent with our previous findings we can conclude that intertidal seaweeds in southeast New Zealand are adapted to maximizing N acquisition in a potentially N-limiting environment. [source]


    JOURNAL OF PHYCOLOGY, Issue 2 2002
    Ana T. Lombardi
    The purpose of the present investigation was to evaluate possible ecological and physiological functions of mucilaginous capsules produced by the freshwater algae Kirchneriella aperta Teiling (Chlorococcales) as related to copper ions. All experiments were performed using synthetic media under laboratory-controlled conditions. Copper interactions were investigated by distinguishing between adsorption onto the mucilaginous material present at the surface of the cells, intracellular uptake, and differentiation between total dissolved copper and free copper ions in the culture medium. Kirchneriella aperta is sensitive to copper, as revealed by a 96-h EC50 value of 10,9.22 M Cu2+. We demonstrated that the mucilaginous capsules were able to sequester copper ions from the medium through a passive mechanism, thus providing the cell with a mechanism able to postpone the toxic effects of copper. The organic material that diffuses into the test medium as well as the mucilaginous capsules produced by K. aperta both effectively complex copper; thus, toxicity must be related to free copper ions and not the total dissolved copper concentration in the medium. [source]

    Erythropoiesis-stimulating agents: development, detection and dangers,

    Stefan E. Franz
    Abstract Epoetin alfa, the first member of the family of erythropoiesis stimulating agents (ESAs), was introduced to the market in 1989. Since then development has progressed to epoetins of the third generation. Currently drugs that use alternative approaches to stimulate erythropoiesis are under development. Uptake of all available ESAs into doping has occurred rapidly after their introduction. A multitude of dangers to health are associated with the illicit use of these substances. Different approaches to detect ESAs in doping control have been developed to comply with the very diverse nature of the compounds used. Future developments in the field of ESA require the development of new techniques in doping analysis. This review gives an overview of the development of ESA and its detection methods as well as future developments. [Correction made here after initial online publication] Copyright 2009 John Wiley & Sons, Ltd. [source]

    Uptake and transport of roxarsone and its metabolites in water spinach as affected by phosphate supply

    Lixian Yao
    Abstract Roxarsone (ROX) is widely used as a feed additive in intensive animal production. While an animal is fed with ROX, the As compounds in the manure primarily occur as ROX and its metabolites, including arsenate (As[V]), arsenite (As[III]), monomethylarsonic acid (MMA), and dimethylarsinic acid (DMA). Animal manure is commonly land applied with phosphorous fertilizers in China. A pot experiment was conducted to investigate the phytoavailability of ROX, As(V), As(III), MMA, and DMA in water spinach (Ipomoea aquatica), with the soil amended with 0, 0.25, 0.50, 1.0, and 2.0,g PO4/kg, respectively, plus 2% (w/w manure/soil) chicken manure (CM) bearing ROX and its metabolites. The results indicate that this species of water spinach cannot accumulate ROX and MMA at detectable levels, but As(V), As(III), and DMA were present in all plant samples. Increased phosphorous decreased the shoot As(V) and As(III) in water spinach but did not affect the root As(V). The shoot DMA and root As(III) and DMA were decreased/increased and then increased/decreased by elevated phosphorous. The total phosphorous content (P) in plant tissue did not correlate with the total As or the three As species in tissues. Arsenate, As(III), and DMA were more easily accumulated in the roots, and phosphate considerably inhibited their upward transport. Dimethylarsinic acid had higher transport efficiency than As(V) and As(III), but As(III) was dominant in tissues. Conclusively, phosphate had multiple effects on the accumulation and transport of ROX metabolites, which depended on their levels. However, proper utilization of phosphate fertilizer can decrease the accumulation of ROX metabolites in water spinach when treated with CM containing ROX and its metabolites. Environ. Toxicol. Chem. 2010;29:947,951. 2009 SETAC [source]

    Characterization of Lead Precipitate Following Uptake by Roots of Brassica juncea

    Donald E. R. Meyers
    Abstract Seedlings of Brassica juncea (L.) Czern. were grown in solution culture for 14 d prior to exposure to Pb2+ at an activity of 31 ,M for 72 h. Electron-dense deposits found within the apoplast and symplast were analyzed using scanning transmission electron microscopy/energy dispersive spectroscopy to determine the chemical identity of the deposits and potential toxicity resistance mechanisms. Irrespective of the cellular compartment in which they were found, the deposits contained Pb, O, P, and Cl. For the extracellular deposits, the average Pb:P:O atomic ratio was 1:0.54:3.0, which together with the hexagonal crystal system suggests that Pb is present as chloropyromorphite (Pb5(PO4)3Cl). A weak Ca signal also was detected in approximately half of the spectra, possibly indicating the presence of small concentrations of phosphohedyphane (Pb3Ca2(PO4)3Cl). The evidence suggests that B. juncea resists Pb toxicity by storing precipitated Pb in the vacuole. [source]

    Uptake and elimination of hydrophobic organic contaminants in estuarine copepods: An experimental study

    Kvin Cailleaud
    Abstract Polycyclic aromatic hydrocarbons (PAHs) are considered to be rapidly biotransformed by organisms, whereas poly-chlorinated biphenyls (PCBs) are strongly bioaccumulated. In the present study, the estuarine copepod Eurytemora affinis was exposed in a continuous flow-through system to dissolved PAH (500 ng/L) and PCB (300 ng/L) mixtures for 86 h, whereas control groups were placed in a continuous flow-through system with clean water. Both PCB and PAH body residues were measured and compared in exposed and in nonexposed copepods to assess the uptake and the elimination of these two contaminant classes in this copepod species. After the exposure, exposed copepods exhibited concentration factors, based on a dry-weight basis, of 25, 750, and 1,200, respectively, for total PCBs and PAHs. The lower concentrations of PAHs in the nonexposed versus exposed copepods in contrast to small differences for PCBs suggest a higher rate of metabolism of PAHs compared with PCBs and could explain the differences observed in the accumulation. Furthermore, uptake as well as elimination of both PCBs and PAHs were compound selective in E. affinis. Therefore, higher-molecular-weight PCBs and PAHs were preferentially accumulated, while lower-molecular-weight compounds were preferentially eliminated. These results suggest the importance of copepods in the biogeochemical cycles of hydrophobic organic contaminants in estuarine ecosystems. [source]

    Uptake and translocation of p,p,-dichlorodiphenyldichloroethylene supplied in hydroponics solution to Cucurbita

    Martin P. N. Gent
    Abstract Field studies show shoots of zucchini (Cucurbita pepo L.) accumulate various hydrophobic contaminants from soil, although many other plants do not, including cucumber (Cucumis sativus L.). To investigate the mechanism for this uptake, we presented p,p,-dichlorodiphenyldichloroethylene (DDE) to these two species in hydroponics solution. A mixture of DDE bound to Tenax beads stirred with a solution of water passing through a reservoir provided a flowing solution containing DDE at approximately 2 ,g/L for many weeks duration. Approximately 90% of the DDE supplied in solution was adsorbed on the roots of both cucumber and zucchini. Less than 10% of the sorbed DDE was released subsequently when clean solution flowed past these contaminated roots for 9 d. The shoots of both species accumulated DDE, but the fraction that moved from the roots to the shoot in zucchini, ranging from 6 to 27% in various trials, was 10-fold greater than that in cucumber, 0.7 to 2%. The gradient in DDE concentration in zucchini tissues was in the order root > stem > petiole > leaf blade, indicating the movement was through the xylem in the transpiration stream. Some DDE in leaf blades might have been absorbed from the air, because the concentration in this tissue varied less with time, position in trough, or species, than did DDE in stems and petioles. The remarkable ability of zucchini to translocate DDE could not be attributed to differences in tissue composition, growth rate, distribution of weight among plant parts, or in the leaf area and rate of transpiration of water from leaves. Some other factor enables efficient translocation of hydrophobic organic contaminants in the xylem of zucchini. [source]

    Uptake and accumulation of sediment-associated 4-nonylphenol in a benthic invertebrate (Lumbriculus variegatus, freshwater oligochaete)

    Valeria Croce
    Abstract In the present work, the oligochaete Lumbriculus variegatus was exposed for 56 d to lake sediment spiked with 4-nonylphenol (4-NP), which is a breakdown product of alkylphenol polyethoxylates, an important class of nonionic surfactants. During the exposure period, the content of 4-NP was determined in the oligochaetes, sediment, overlying water, and pore water in order to monitor the distribution of the 4-NP in the compartments of the test system. Concentration of 4-NP in L. variegatus increased linearly over the course of the test, with an uptake rate coefficient of 1.9 10,2 ( 0.2 10,2; [g carbon/(g lipid-h)]). No steady state was reached at the end of the exposure period, suggesting that the elimination of 4-NP by the organism was negligible. Ingested sediments played an important role in the accumulation of 4-NP in L. variegatus, which may achieve very high 4-NP body concentrations. The 56-d biota sediment accumulation factor (BSAF) was 24 7 g carbon/g lipid. L. variegatus also was exposed to 4-NP-contaminated field sediment, and field oligochaetes and sediments were collected for 4-NP pollution assessment in aquatic ecosystem. The 4-NP uptake with natural sediment was in accordance with that measured with spiked sediments, suggesting that the bioavailability of sediment-associated 4-NP for L. variegatus was not affected by 4-NP sediment concentration and abiotic sediment characteristics. The BSAFs measured in field oligochaetes, ranging from 39 to 55 g carbon/g lipid, was relatively higher than the bioaccumulation factor measured in laboratory tests. The results suggest that 4-NP concentration can reach high levels in benthic oligochaetes; this can be an important way of exposure for their pelagic predators. [source]

    Uptake and depuration of cadmium, nickel, and lead in laboratory-exposed Tubifex tubifex and corresponding changes in the concentration of a metallothionein-like protein

    Patricia L. Gillis
    Abstract Based on weight loss in water, 2 4h is recommended for Tubifex tubifex gut clearance. Biota-to-sediment accumulation factors (BSAFs) in gut-cleared T. tubifex following six weeks of exposure to Cd-, Ni-, and Pb-spiked sediment were 12.4, 3.0, and 19.0, respectively. Tissue Ni concentrations peaked after 12 h, whereas Cd and Pb were accumulated for the duration of the exposure. Tubifex tubifex were transferred to either water (24 h) or sediment (10 weeks) to monitor changes in internal metal concentrations. After 24 h in water, only Ni concentration had declined significantly (p < 0.05), suggesting that the majority of Ni was associated with the gut content, while Cd and Pb were accumulated in the tissues. Metal depuration in sediment was described with two-compartment, first-order kinetic models (r2 = 0.7,0.8; p < 0.001), indicating that T. tubifex has both a quickly depurated and a more tightly bound pool of accumulated metal. Tubifex tubifex were also exposed to sediment spiked with just Cd (3.66 ,mol/g). Cadmium uptake and induction of metallothionein-like protein (MTLP) were rapid; both parameters were significantly elevated within 24 h of exposure. Metallothionein-like protein (8.7 1.8 nmol/g) and Cd (60.8 11.0 ,mol/g) reached maximum concentrations after 96 h and four weeks, respectively. [source]

    Prediction of uptake dynamics of persistent organic pollutants by bacteria and phytoplankton

    Sabino Del Vento
    Abstract Phytoplankton and bacteria play an important role on the biogeochemical cycles of persistent organic pollutants (POPs). However, experimental data and quantitative knowledge of the kinetics of uptake and depuration of most POPs by bacteria and phytoplankton are scarce. In the present paper, a procedure to predict the sorption kinetics to bacteria and phytoplankton is developed. The prediction method is the combination of a mechanistic model for sorption and quantitative structure,activity relationships relating bioconcentration factors and membrane permeability to the chemical physical-chemical properties. The model consists of two compartments where the first compartment is the cellular surface and the second compartment is the cell biomass or matrix. Equations for estimating uptake and depuration rate constants into the matrix and adsorption and desorption rate constants onto the surface are obtained. These expressions depend on the physical-chemical properties of the chemical, the environmental temperature, the microorganism size, and species-specific quality of organic matter. While microorganism shape has a secondary influence on uptake dynamics, microorganism size and chemical hydrophobicity arise as the key factors controlling the kinetics of POP incorporation into bacteria and plankton. Uptake, depuration, adsorption, and desorption rate constants are reported for POPs such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated dioxins and furans (PCDD/Fs), and POPs of emerging concern, such as polybrominated diphenyl ethers (PBDEs). Finally, implications of uptake and depuration dynamics on the biogeochemical cycling of POPs are discussed. [source]

    Uptake of inorganic chemicals from soil by plant leaves: Regressions of field data,

    Rebecca A. Efroymson
    Abstract The estimation of chemical concentrations in wildlife foods, such as plant foliage, is often performed for risk assessments at contaminated sites. Regression models and uptake factors for use in estimating the uptake of inorganic elements from soil by above-ground plant tissues were derived in this study. These included models for arsenic, cadmium, copper, lead, mercury, nickel, selenium, and zinc. Models were developed using published data from soil contaminated in the field and were validated using measured concentrations from two contaminated sites. Single-variable regression models of log-transformed concentrations in plants versus log-transformed concentrations in soil are generally recommended over simple uptake factors for use in estimating plant uptake of inorganic contaminants in ecological risk assessments. Multiple regression models with soil concentration and pH as the variables are also recommended for estimating the uptake of four chemicals (cadmium, mercury, selenium, and zinc) by plants. Models for use in screening risk assessments, i.e., the upper 95% prediction limits on the regressions, are recommended to provide conservative estimates of uptake of inorganic chemicals by plants. [source]

    Uptake and diverse effects of polycyclic aromatic hydrocarbons on the metabolic activity of Elliptio complanata measured by calorespirometry

    Marcos A. Cheney
    Abstract Polycyclic aromatic hydrocarbons (PAHs) are important contaminants of world water resources, with effects on aquatic life. Metabolic responses to short-term acute toxicities of naphthalene, anthracene, and chrysene were investigated in the freshwater bivalve mollusk Elliptio complanata using differential scanning calorespirometry coupled with uptake and scanning electron microscopy. Comparing the uptakes of naphthalene, anthracene, and chrysene with that of inulin, which is known to occupy only extracellular space, showed that all compounds studied were taken up. The PAHs studied had diverse effects on the metabolic activity of E. complanata. Naphthalene and, to a lesser degree, chrysene caused stimulation of heat rates, possibly due to uncoupling of oxidative metabolism. Differential scanning calorespirometry coupled with studies of rates of oxygen consumption by the gill tissue exposed to the PAHs showed similar diverse patterns of respiratory rate stimulation and inhibition. Analysis of results of scanning electron microscopy suggested that irreversible damage to the gill tissue occurred in the presence of anthracene but not in the presence on naphthalene or chrysene. The batch calorespirometric method coupled with uptake and spectroscopy proved to be a useful technique to assess the toxicity of PAHs on the control of energy flux in gills of a freshwater bivalve mollusk. [source]

    Effect of bile salts, lipid, and humic acids on absorption of benzo[a]pyrene by isolated channel catfish (Ictalurus punctatus) intestine segments

    Lynn P. Weber
    Abstract Dietary absorption of lipophilic contaminants may be a significant route of exposure in aquatic organisms. Bile salts, lipids, and humic acids are important factors that may influence the intestinal absorption of a contaminant such as benzo[a]pyrene (BaP). We hypothesized that bile salts, monoglycerides, and free fatty acids would increase BaP intestinal absorption, while triglycerides, humic acids, and sediment would decrease BaP intestinal absorption. We have established and validated an in vitro model to examine modification of 3H-BaP absorption in everted intestinal segments from channel catfish (Ictalurus punctatus). Uptake of BaP into the everted intestinal segments continued to increase over the times examined in this study (60 min) and apparently occurs passively; thus, fugacity-based models of uptake are supported. Absorption of BaP into intestinal cells was significantly decreased by the addition of monoglycerides and free fatty acids to bile salts in the incubation media. Addition of triglycerides decreased BaP absorption even further. Humic acids may have decreased BaP intestinal absorption, while natural sediment may have increased BaP absorption. The results of this study suggest that all lipids may decrease intestinal uptake of lipophilic contaminants if they remain in unabsorbable excess in the intestinal lumen by retaining BaP in lipid/bile micelles. In contrast, if triglycerides are hydrolyzed into monoglycerides/free fatty acids prior to absorption, lipophilic contaminant uptake will likely be facilitated. Thus, it may be the hydrolytic state of lipids that determines its effects on BaP absorption. Humic acids alone may decrease dietary uptake of BaP, but our results suggest that other components in natural sediment may counteract this effect to cause a slight enhancement of BaP uptake. Further studies are needed to determine the dietary conditions necessary for bio-accumulation to contribute significantly to lipophilic contaminant body burdens in benthivorous fish. Finally, the everted intestinal segment technique has the potential to be used in other species and with different contaminants. [source]

    Interaction between Anticonvulsants and Human Placental Carnitine Transporter

    EPILEPSIA, Issue 3 2004
    Shu-Pei Wu
    Summary: Purpose: To examine the inhibitory effect of anticonvulsants (AEDs) on carnitine transport by the human placental carnitine transporter. Methods: Uptake of radiolabeled carnitine by human placental brush-border membrane vesicles was measured in the absence and presence of tiagabine (TGB), vigabatrin (VGB), gabapentin (GBP), lamotrigine (LTG), topiramate (TPM), valproic acid (VPA), and phenytoin (PHT). The mechanism of the inhibitory action of TGB was determined. Results: Most of the AEDs inhibited placental carnitine transport. Kinetic analyses showed that TGB had the greatest inhibitory effect [50% inhibitory concentration (IC50, 190 ,M)], and the order of inhibitory potency was TGB > PHT > GBP > VPA > VGB, TPM > LTG. Further studies showed that TGB competitively inhibited carnitine uptake by the human placental carnitine transporter, suggesting that it may be a substrate for this carrier. Conclusions: Although the involvement of carnitine deficiency in fetal anticonvulsant syndrome requires further evaluation, potential interference with placental carnitine transport by several AEDs was demonstrated. Despite the higher inhibitory potency of TGB, given the therapeutic unbound concentrations, the results for VPA and PHT are probably more clinically significant. [source]

    Tauroursodeoxycholic acid mobilizes ,-PKC after uptake in human HepG2 hepatoma cells

    Helena Glasova
    Abstract Background Tauroursodeoxycholic acid (TUDCA) may exert anticholestatic effects via Ca++ - and ,-protein kinase C (,-PKC)-dependent apical vesicular insertion of canalicular transporters in cholestatic hepatocytes (Hepatology 2001; 33: 1206,16). Tauroursodeoxycholic acid is mainly taken up into liver cells by Na+ -taurocholate cotransporting polypeptide (Ntcp). Tauroursodeoxycholic acid selectively translocates ,-PKC, a key mediator of regulated exocytosis, to hepatocellular membranes. It is unclear whether TUDCA exerts its effects on ,-PKC after carrier-mediated uptake into liver cells or by interaction with extracellular/membraneous structures. Materials and methods Human hepatoblastoma HepG2 cells lacking Ntcp were stably transfected with pcDNA31/Ntcp or sham-transfected with pcDNA31 [+]. Distribution of ,-PKC was studied using a Western blotting technique. Uptake of [3H]taurocholic acid (TCA) was determined radiochemically. Results [3H]taurocholic acid uptake was approximately 180-fold higher in Ntcp-transfected than in sham-transfected cells. Phorbol 12-myristate 13-acetate (1 mol L,1; positive control) increased membrane binding of ,-PKC by 34% in Ntcp-transfected and by 37% in sham-transfected cells. Tauroursodeoxycholic acid (10 mol L,1) increased membrane-associated ,-PKC by 19% in Ntcp-transfected, but not in sham-transfected cells (,13%). Taurocholic acid (10 mol L,1) did not affect the distribution of ,-PKC. Conclusion Carrier-mediated uptake is a prerequisite for TUDCA-induced translocation of ,-PKC to hepatocellular membranes. [source]

    PET visualization of microglia in multiple sclerosis patients using [11C]PK11195

    J. C. Debruyne
    Activated microglia are involved in the immune response of multiple sclerosis (MS). The peripheral benzodiazepine receptor (PBR) is expressed on microglia and up-regulated after neuronal injury. [11C]PK11195 is a positron emission tomography (PET) radioligand for the PBR. The objective of the present study was to investigate [11C]PK11195 imaging in MS patients and its additional value over magnetic resonance imaging (MRI) concerning the immuno-pathophysiological process. Seven healthy and 22 MS subjects were included. Semiquantitative [11C]PK11195 uptake values were assessed with normalization on cortical grey matter. Uptake in Gadolinium-lesions was significantly increased compared with normal white matter. Uptake in T2-lesions was generally decreased, suggesting a PBR down-regulation. However, uptake values increased whenever a clinical or MR-relapse was present, suggestive for a dynamic process with a transient PBR up-regulation. During disease progression, an increase of normal-appearing white matter (NAWM) uptake was found, propagating NAWM as the possible real burden of disease. In conclusion, [11C]PK11195 and PET are able to demonstrate inflammatory processes with microglial involvement in MS. [source]

    The role of NGF uptake in selective vulnerability to cell death in ageing sympathetic neurons

    Kliment P. Gatzinsky
    Abstract We have examined the hypothesis that differences in nerve growth factor (NGF) uptake and transport determine vulnerability to age-related neurodegeneration. Neurons projecting to cerebral blood vessels (CV) in aged rats are more vulnerable to age-related degeneration than those projecting to the iris. Uptake of NGF was therefore examined in sympathetic neurons projecting from the superior cervical ganglion (SCG) to CV and iris in young and old rats by treating the peripheral processes of these neurons with different doses of I125 -NGF. Total uptake of I125 -NGF was reduced in old CV-projecting, but not iris-projecting, neurons. Numbers of radiolabelled neurons projecting to each target were counted in sectioned ganglia. The data showed age-related reductions in numbers of labelled neurons projecting to CV, but no change in numbers of neurons projecting to the iris. Calculation of uptake of I125 -NGF per neuron unexpectedly showed no major age-related differences in either of the two neuron populations. However, uptake per neuron was considerably lower for young and old CV-projecting, compared to iris-projecting, SCG neurons. We hypothesized that variations in NGF uptake might affect neuronal survival in old age. Counts of SCG neurons using a physical disector following retrograde tracing with Fluorogold confirmed the selective vulnerability of CV-projecting neurons by showing a significant 37% loss of these neurons in the period between 15 and 24 months. In contrast, there was no significant loss of iris-projecting neurons. We conclude that vulnerability to, or protection from, age-related neurodegeneration and neuronal cell death are associated with life-long low, or high, levels of NGF uptake, respectively. [source]

    Modelling the Influence of Age, Body Size and Sex on Maximum Oxygen Uptake in Older Humans

    Patrick J. Johnson
    The purpose of this study was to describe the influence of body size and sex on the decline in maximum oxygen uptake (V,O2,max) in older men and women. A stratified random sample of 152 men and 146 women, aged 55-86 years, was drawn from the study population. Influence of age on V,O2,max, independent of differences in body mass (BM) or fat-free mass (FFM), was investigated using the following allometric model: V,O2,max= BMb (or FFMb) exp(a + (c age) + (d sex)) [epsilon]. The model was linearised and parameters identified using standard multiple regression. The BM model explained 68.8% of the variance in V,O2,max. The parameters ( s.e.e., standard error of the estimate) for lnBM (0.563 0.070), age (-0.0154 0.0012), sex (0.242 0.024) and the intercept (-1.09 0.32) were all significant (P < 0.001). The FFM model explained 69.3% of the variance in V,O2,max, and the parameters ( s.e.e) lnFFM (0.772 0.090), age (-0.0159 0.0012) and the intercept (-1.57 0.36) were significant (P < 0.001), while sex (0.077 +/, 0.038) was significant at P = 0.0497. Regardless of the model used, the age-associated decline was similar, with a relative decline of 15% per decade (0.984 exp(age)) in V,O2,max in older humans being estimated. The study has demonstrated that, for a randomly drawn sample, the age-related loss in V,O2,max is determined, in part, by the loss of fat-free body mass. When this factor is accounted for, the loss of V,O2,max across age is similar in older men and women. [source]

    Uptake and Release of Double-Walled Carbon Nanotubes by Mammalian Cells

    Vera Neves
    Abstract Efforts to develop carbon nanotubes (CNTs) as nano-vehicles for precise and controlled drug and gene delivery, as well as markers for in vivo biomedical imaging, are currently hampered by uncertainties with regard to their cellular uptake, their fate in the body, and their safety. All of these processes are likely to be affected by the purity of CNT preparation, as well as the size and concentration of CNTs used, parameters that are often poorly controlled in biological experiments. It is demonstrated herein that under the experimental conditions of standard transfection methods, DWNTs are taken up by cultured cells but are then released after 24 h with no discernable stress response. The results support the potential therapeutic use of CNTs in many biomedical settings, such as cancer therapy. [source]

    Role of the plasma membrane leaflets in drug uptake and multidrug resistance

    FEBS JOURNAL, Issue 5 2010
    Hagar Katzir
    The present study aimed to investigate the role played by the leaflets of the plasma membrane in the uptake of drugs into cells and in their extrusion by P-glycoprotein and multidrug resistance-associated protein 1. Drug accumulation was monitored by fluorescence resonance energy transfer from trimethylammonium-diphenyl-hexatriene (TMA-DPH) located at the outer leaflet to a rhodamine analog. Uptake of dye into cells whose mitochondria had been inactivated was displayed as two phases of TMA-DPH fluorescence quenching. The initial phase comprised a rapid drop in fluorescence that was neither affected by cooling the cells on ice, nor by activity of mitochondria or ABC transporters. This phase reflects the association of dye with the outer leaflet of the plasma membrane. The subsequent phase of TMA-DPH fluorescence quenching occurred in drug-sensitive cell lines with a half-life in the range 20,40 s. The second phase of fluorescence quenching was abolished by incubation of the cells on ice and was transiently inhibited in cells with active mitochondria. Thus, the second phase of fluorescence quenching reflects the accumulation of dye in the cytoplasmic leaflet of the plasma membrane, presumably as a result of flip-flop of dye across the plasma membrane and slow diffusion from the inner leaflet into the cells. Whereas activity of P-glycoprotein prevented the second phase of fluorescence quenching, the activity of multidrug resistance-associated protein 1 had no effect on this phase. Thus, P-glycoprotein appears to pump rhodamines from the cytoplasmic leaflet either to the outer leaflet or to the outer medium. [source]

    Glycation of low-density lipoprotein results in the time-dependent accumulation of cholesteryl esters and apolipoprotein B-100 protein in primary human monocyte-derived macrophages

    FEBS JOURNAL, Issue 6 2007
    Bronwyn E. Brown
    Nonenzymatic covalent binding (glycation) of reactive aldehydes (from glucose or metabolic processes) to low-density lipoproteins has been previously shown to result in lipid accumulation in a murine macrophage cell line. The formation of such lipid-laden cells is a hallmark of atherosclerosis. In this study, we characterize lipid accumulation in primary human monocyte-derived macrophages, which are cells of immediate relevance to human atherosclerosis, on exposure to low-density lipoprotein glycated using methylglyoxal or glycolaldehyde. The time course of cellular uptake of low-density lipoprotein-derived lipids and protein has been characterized, together with the subsequent turnover of the modified apolipoprotein B-100 (apoB) protein. Cholesterol and cholesteryl ester accumulation occurs within 24 h of exposure to glycated low-density lipoprotein, and increases in a time-dependent manner. Higher cellular cholesteryl ester levels were detected with glycolaldehyde-modified low-density lipoprotein than with methylglyoxal-modified low-density lipoprotein. Uptake was significantly decreased by fucoidin (an inhibitor of scavenger receptor SR-A) and a mAb to CD36. Human monocyte-derived macrophages endocytosed and degraded significantly more 125I-labeled apoB from glycolaldehyde-modified than from methylglyoxal-modified, or control, low-density lipoprotein. Differences in the endocytic and degradation rates resulted in net intracellular accumulation of modified apoB from glycolaldehyde-modified low-density lipoprotein. Accumulation of lipid therefore parallels increased endocytosis and, to a lesser extent, degradation of apoB in human macrophages exposed to glycolaldehyde-modified low-density lipoprotein. This accumulation of cholesteryl esters and modified protein from glycated low-density lipoprotein may contribute to cellular dysfunction and the increased atherosclerosis observed in people with diabetes, and other pathologies linked to exposure to reactive carbonyls. [source]

    Permeation of tetracyclines through membranes of liposomes and Escherichia coli

    FEBS JOURNAL, Issue 2 2000
    Albrecht Sigler
    Uptake of tetracycline (tc), 2-tetracyclinonitrile (CN-tc), and 9-(N,N -dimethylglycylamido)-6-demethyl-6-deoxytetracycline (DMG-DMDOT) by liposomes containing Tet repressor (TetR) and by Escherichia coli cells overexpressing TetR was examined. TetR specifically binds to tetracyclines, enhances their fluorescence and thereby allows selective detection of tetracyclines that have crossed the membranes. Analysis of the diffusion of tc and DMG-DMDOT into liposomes yielded permeation coefficients of (2.4 0.6) 10,9 cms,1 and (3.3 0.8) 10,9 cms,1, respectively. Similar coefficients were obtained for uptake of these tetracyclines by E. coli, indicating that diffusion through the cytoplasmic membrane is the rate-limiting step. The permeation coefficients translate into half-equilibration times of approximately 35 15 min and explain how efflux pumps can mediate resistance against tetracyclines. Furthermore, diffusion of CN-tc into liposomes was at least 400-fold slower than that of tc, indicating that the carboxamide group at position C2 is required for efficient permeation of tc through lipid membranes and thereby explaining the lack of antibiotic activity of CN-tc. [source]