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Combined Action (combined + action)
Selected AbstractsINACTIVATION OF BACTERIAL SPORES BY COMBINED ACTION OF HYDROSTATIC PRESSURE AND BACTERIOCINS IN ROAST BEEFJOURNAL OF FOOD SAFETY, Issue 4 2003N. KALCHAYANAND ABSTRACT Foodborne bacterial spores are normally resistant to high hydrostatic pressure; however, at moderate pressure, they can be induced to germinate and outgrow. At this stage, they can be killed by bacteriocin-based biopreservatives (BP-containing pediocin and nisin at 3:7 ratio; BPX, BP + 100 ,g/mL lysozyme; BPY, BPX+ 500 ,g/mL Na-EDTA). Based on this principle, spores of the meat spoilage organism, Clostridium laramie (1,2 × 102 spores/bag) alone or a mixture of four clostridial spores (5 × 103 spores/bag), Clostridium sporogenes, Clostridium perfringens, Clostridium tertium, and Clostridium laramie, were inoculated in roast beef in the presence of 5000 AU/g of bacteriocin-based biopreservatives. The roast beef samples were subjected to hydrostatic pressure (HP) at 345 MPa for 5 min at 60C and stored at 4 or 12C for 84 days or at 25C for 7 days. The HP treatment of roast beef samples inoculated with a mixture of clostridial spores could be stored for 42 days at 4C. The HP in combination with either BPX or BPY extended the shelf-life of roast beef up to 7 days at 25C. The combined treatment of HP and BP controlled the growth of C. laramie spores and extended the shelf-life of roast beef for 84 days when stored at 4C. [source] An educational computer tool for simulating long-term soil erosion on agricultural landscapesCOMPUTER APPLICATIONS IN ENGINEERING EDUCATION, Issue 3 2009F. J. Jiménez-Hornero Abstract Due to its economic and environmental impacts, soil erosion has been a major concern to farmers, engineers and policy makers in recent years. Water and tilling are two of the main agents responsible for this phenomenon and considerable efforts have been made to model them in previous work but not with educational purposes. A computer tool for facilitating any user's simulation of long-term landscape evolution in a plot due to the combined action of water and tillage erosion is presented here. It integrates a graphic user interface with two well-verified erosion models, each one independently devoted to reproduce the effects of water and tilling. This computer tool permits to the student the consideration of the erosivity index and the presence of a crop in the plot, when simulating water erosion, as well as the planning of a different type of tilling each year. Each kind of tilling corresponds to a different combination of tillage tools with their own date, tillage depth and tillage direction. A handy ASCII (XYZ) file is generated containing the long-term soil erosion spatial pattern as result. From this information, the student can derive other results that will help to understand soil erosion. An example is presented here with the aim of showing how to use this computer tool to simulate this phenomenon on an agricultural landscape with a complex topography. © 2009 Wiley Periodicals, Inc. Comput Appl Eng Educ 17: 253,262, 2009; Published online in Wiley InterScience (www.interscience.wiley.com); DOI 10.1002/cae.20193 [source] Neural protein Olig2 acts upstream of the transcriptional regulator sim1 to specify diencephalic dopaminergic neuronsDEVELOPMENTAL DYNAMICS, Issue 4 2009Nataliya Borodovsky Abstract Neural factors are expressed in neural progenitors and regulate neurogenesis and gliogenesis. Recent studies suggested that these factors are also involved in determining specific neuronal fates by regulating the expression of their target genes, thereby creating transcriptional codes for neuronal subtype specification. In the present study, we show that in the zebrafish the neural gene Olig2 and the transcriptional regulator Sim1 are co-expressed in a subset of diencephalic progenitors destined towards the dopaminergic (DA) neuronal fate. While sim1 mRNA is also detected in mature DA neurons, the expression of olig2 is extinguished prior to terminal DA differentiation. Loss of function of either Olig2 or Sim1 leads to impaired DA development. Finally, Olig2 regulates the expression of Sim1 and gain of function of Sim1 rescues the deficits in DA differentiation caused by targeted knockdown of Olig2. Our findings demonstrate for the first time that commitment of basal diencephalic DA neurons is regulated by the combined action of the neural protein Olig2 and its downstream neuronal specific effector Sim1. Developmental Dynamics 238:826,834, 2009. © 2009 Wiley-Liss, Inc. [source] Quantifying the evidence for ecological synergiesECOLOGY LETTERS, Issue 12 2008Emily S. Darling Abstract There is increasing concern that multiple drivers of ecological change will interact synergistically to accelerate biodiversity loss. However, the prevalence and magnitude of these interactions remain one of the largest uncertainties in projections of future ecological change. We address this uncertainty by performing a meta-analysis of 112 published factorial experiments that evaluated the impacts of multiple stressors on animal mortality in freshwater, marine and terrestrial communities. We found that, on average, mortalities from the combined action of two stressors were not synergistic and this result was consistent across studies investigating different stressors, study organisms and life-history stages. Furthermore, only one-third of relevant experiments displayed truly synergistic effects, which does not support the prevailing ecological paradigm that synergies are rampant. However, in more than three-quarters of relevant experiments, the outcome of multiple stressor interactions was non-additive (i.e. synergies or antagonisms), suggesting that ecological surprises may be more common than simple additive effects. [source] Microbiological evaluation of toxicity of three polycyclic aromatic hydrocarbons and their decomposition products formed by advanced oxidation processesENVIRONMENTAL TOXICOLOGY, Issue 3 2003Teresa Jamroz Abstract The toxicity of benzo[a]pyrene, chrysene, and fluorene and their decomposition products formed by advanced oxidation processes (AOPs) was investigated using biotests with Escherichia coli and Vibrio fischeri. The polycyclic aromatic hydrocarbons (PAHs) were not highly toxic to either bacterial strain; the toxicity of their degradation products depended on the method of chemical processing. Inhibition of more than 27% was observed with products formed by oxidation of the PAHs, by AOP methods without hydrogen peroxide. Toxicity as high as 100% was observed after the combined action of hydrogen peroxide and other oxidizing agents. © 2003 Wiley Periodicals, Inc. Environ Toxicol 18: 187,191, 2003 [source] Development of human plasmacytoid dendritic cells depends on the combined action of the basic helix-loop-helix factor E2-2 and the Ets factor Spi-B,EUROPEAN JOURNAL OF IMMUNOLOGY, Issue 9 2008Maho Nagasawa Abstract Plasmacytoid dendritic cells (pDC) are central players in the innate and adaptive immune response against viral infections. The molecular mechanism that underlies pDC development from progenitor cells is only beginning to be elucidated. Previously, we reported that the Ets factor Spi-B and the inhibitors of DNA binding protein 2 (Id2) or Id3, which antagonize E-protein activity, are crucially involved in promoting or impairing pDC development, respectively. Here we show that the basic helix-loop-helix protein E2-2 is predominantly expressed in pDC, but not in their progenitor cells or conventional DC. Forced expression of E2-2 in progenitor cells stimulated pDC development. Conversely, inhibition of E2-2 expression by RNA interference impaired the generation of pDC suggesting a key role of E2-2 in development of these cells. Notably, Spi-B was unable to overcome the Id2 enforced block in pDC development and moreover Spi-B transduced pDC expressed reduced Id2 levels. This might indicate that Spi-B contributes to pDC development by promoting E2-2 activity. Consistent with notion, simultaneous overexpression of E2-2 and Spi-B in progenitor cells further stimulated pDC development. Together our results provide additional insight into the transcriptional network controlling pDC development as evidenced by the joint venture of E2-2 and Spi-B. [source] The baroreflex is counteracted by autoregulation, thereby preventing circulatory instabilityEXPERIMENTAL PHYSIOLOGY, Issue 4 2004Roberto Burattini The aims of this study were (a) to apply in the animal with intact baroreflex a two-point method for estimation of overall, effective open-loop gain, G0e, which results from the combined action of baroregulation and total systemic autoregulation on peripheral resistance; (b) to predict specific baroreflex gain by correcting the effective gain for the autoregulation gain; and (c) to discuss why the effective gain is usually as low as 1,2 units. G0e was estimated from two measurements of both cardiac output, Q, and mean systemic arterial pressure, P: one in the reference state (set-point) and the other in a steady-state reached 1,3 min after a small cardiac output perturbation. In anaesthetized cats and dogs a cardiac output perturbation was accomplished by partial occlusion of the inferior vena cava and by cardiac pacing, respectively. Average (±s.e.m.) estimates of G0e were 1.4 ± 0.2 (n= 8) in the cat and 1.5 ± 0.4 (n= 5) in the dog. The specific baroreflex open-loop gain, G0b, found after correction for total systemic autoregulation, was 3.3 ± 0.4 in the cat and 2.8 ± 0.8 in the dog. A model-based analysis showed that, with G0e as low as 1.4, the closed-loop response of P to a stepwise perturbation in Q results in damped oscillations that disappear in about 1 min. The amplitude and duration of these oscillations, which have a frequency of about 0.1 Hz, increase with increasing G0e and cause instability when G0e is about 3. We conclude that autoregulation reduces the effectiveness of baroreflex gain by about 55%, thereby preventing instability of blood pressure response. [source] Interleukin-4 supports interleukin-12-induced proliferation and interferon-, secretion in human activated lymphoblasts and T helper type 1 cellsIMMUNOLOGY, Issue 1 2006Martin A. Kriegel Summary Interleukin-12 (IL-12) and IL-4 are known to differentially promote T helper (Th) cell differentiation. While IL-12 induces interferon-, (IFN-,) production and maturation of Th1 cells, IL-4 is thought to antagonize IL-12 and to favour Th2 development. Here we studied the combined action of various concentrations of common ,-chain (,c -chain) cytokines, including IL-4 and the Th1 cytokine IL-12, in human activated lymphoblasts and Th1 cells. IL-4 and IL-7 potentiated IL-12-induced proliferation at every concentration tested (1,10 ng/ml) without increasing rescue from apoptosis, indicating that proliferation was directly affected by these cytokine combinations. With regards to cytokine secretion, IL-2 together with IL-12 initiated tumour necrosis factor-, synthesis, enhanced IFN-, production, and shedding of soluble IL-2 receptor , as expected. Importantly, combining IL-4 with IL-12 also enhanced IFN-, secretion in lymphoblasts and a Th1 cell line. Investigating signal transduction in lymphoblasts induced by these cytokines, we found that not only IL-2 but also IL-4 enhances signal transducer and activator of transcription 3 (STAT3) tyrosine phosphorylation by IL-12. Tyrosine phosphorylations of janus kinase 2 (JAK-2), tyrosine kinase 2 (TYK2), extracellular signal-regulated kinase (ERK) and STAT4, STAT5 and STAT6 were not potentiated by combinations of these cytokines, suggesting specificity for increased STAT3 phosphorylation. In conclusion, two otherwise antagonizing cytokines co-operate in activated human lymphoblasts and Th1 cells, possibly via STAT3 as a converging signal. These data demonstrate that IL-4 can directly enhance human Th1 cell function independently of its known actions on antigen-presenting cells. These findings should be of importance for the design of cytokine-targeted therapies of human Th-cell-driven diseases. [source] Elastoplastic multiphase model for simulating the response of piled raft foundations subject to combined loadingsINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 9 2006G. Hassen Abstract A multiphase model and corresponding computational time-saving finite element code is proposed in this paper for predicting the settlements experienced by a piled raft foundation when subject to the combined action of vertical and lateral loadings. This model, which is formulated in the framework of an elastoplastic behaviour for the soil and the reinforcing piles as well, explicitly accounts for the shear and flexural behaviour of the latter. Starting from a simple analytical example where all the concepts attached to this model are clearly illustrated, the main stages leading to its finite element implementation are then presented. The numerical tool thus elaborated, is applied to the simulation of a pile-reinforced strip foundation submitted to a horizontally applied seismic load in addition to a permanent vertical load. One of the key results of such a simulation in terms of design recommendation, lies in the conclusion that, while the shear and flexural contributions of the reinforcement play quite a negligible role in the case of a vertical load (as compared with their axial resistance), they remain absolutely essential for withstanding the seismic lateral loading. Copyright © 2006 John Wiley & Sons, Ltd. [source] Dendritic solidification of binary alloys with free and forced convectionINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2005P. Zhao Abstract Dendritic solidification with forced convection and free convection driven by contraction and thermo- solutal buoyancy is simulated in two-dimensional space using a sharp-interface model. Both pure substances and alloys are considered. The model is formulated using the finite element method and works directly with primitive variables. The coupled energy- and solutal concentration-equations, along with the Navier,Stokes equations for incompressible flow, are solved using different meshes. Temperature is solved in a fixed mesh that covers the whole domain (solid + liquid) where the solid,liquid interface is explicitly tracked using marker points. The concentration and momentum equations are solved in the liquid region using an adaptive mesh of triangular elements that conforms to the interface. The velocity boundary conditions are applied directly on the interface. The model is validated using a series of problems that have analytical, experimental and numerical results. Four simulations are presented: (1) crystal growth of succinonitrile with thermal convection under two small undercoolings; (2) dendritic growth into an undercooled pure melt with a uniform forced flow; (3) equiaxial dendritic growth of a pure substance and an alloy with contraction-induced convection; and (4) directional solidification of Pb,0.2 wt% Sb alloy with convection driven by the combined action of contraction, thermal and solutal buoyancy. Some of the simulation results are compared to those reported using other methods including the phase-field method; others are new. In each case, the effects of convection on dendritic solidification are analysed. Copyright © 2005 John Wiley & Sons, Ltd. [source] Dietary amino acids fed in free form and as protein components do not differently affect postprandial plasma insulin, glucagon, growth hormone and corticosterone responses in ratsJOURNAL OF ANIMAL PHYSIOLOGY AND NUTRITION, Issue 7-8 2006J. A. Nolles Summary This study examined, whether the postprandial fate of dietary amino acids from different amino acid sources is regulated by the responses of insulin, glucagon, corticosterone and growth hormone (GH). Male Wistar rats were cannulated in the vena jugularis and assigned to dietary groups. The diets contained 21% casein or the same amino acids in free form. In the free amino acid diets, methionine level was varied between the groups. The feed was supplied in two distinct meals. In previous experiments it was established that oxidative amino acid losses of the free amino acid diets and protein diets were different. After 3 weeks on those diets, it appeared that the differences in postprandial oxidative losses had been diminished. GH was measured every 12 min, from 144 min before the start of the experimental meal over the following 144 min. Insulin and corticosterone were measured six times from the start of the meal until 270 min after the meal. No differences have been observed between the hormonal responses to both meals at day 5 and at day 26. In conclusion, it has been found that the differences in the oxidative losses between protein and free amino acid meals are not mediated by the combined action of the insulin, glucagon, corticosterone and GH. Postprandial catabolism of amino acids is most probably regulated by substrate induction. [source] Effect of accelerated aging on the structure and properties of monolayer and multilayer packaging filmsJOURNAL OF APPLIED POLYMER SCIENCE, Issue 1 2008P. A. Tarantili Abstract The effect of accelerated aging on the structure and properties of single, metalized, and multilayer films used in food packaging was studied through the exposure of specimens of those films to repeated aging cycles in a weather meter under the combined action of ultraviolet, humidity, and heat. The aged specimens were tested for their mechanical properties and water vapor transmission characteristics, and the results were compared to those obtained from the original specimens. The property changes introduced into the films by aging were further explored by attenuated total reflectance spectroscopy and differential scanning calorimetry in an attempt to correlate the changes in the properties with structural characteristics. The results showed that the films made of polypropylene (PP) underwent severe chain scission upon irradiation and lost mechanical properties but still retained their impermeability to water vapor. The metallic coating could not prevent PP from degrading, as it seemed to oxidize under the aging conditions. Therefore, the metalized film showed the same mechanical response as PP, but its water impermeability dropped dramatically. Polyethylene (PE) and poly(ethylene terephthalate) (PET) films showed modest decreases in their mechanical properties, which could be attributed to crosslinking reactions taking place with PE and to the increased ultraviolet stability of PET, respectively. On the other hand, the multilayer films presented a decrease in their mechanical properties according to those of their weak component, which would be expected for a composite structure. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source] Anoxia leads to a rapid translocation of human trypsinogen 4 to the plasma membrane of cultured astrocytesJOURNAL OF NEUROCHEMISTRY, Issue 2 2010Krisztián Tárnok J. Neurochem. (2010) 115, 314,324. Abstract Trypsinogen 4 is specifically expressed in the human brain, mainly by astroglial cells. Although its exact role in the nervous tissue is yet unclear, trypsin 4-mediated pathological processes were suggested in Alzheimer's disease, multiple sclerosis and ischemic injury. In the present study, we analyzed the intracellular distribution of fluorescently tagged human trypsinogen 4 isoforms during normal and anoxic conditions in transfected mouse primary astrocytes. Our results show that initiation of anoxic milieu by the combined action of KCN treatment and glucose deprivation rapidly leads to the association of leader peptide containing trypsinogen 4 constructs to the plasma membrane. Using rhodamine 110 bis-(CBZ-L-isoleucyl-L-prolyl-L-arginine amide), a synthetic chromogen peptide substrate of trypsin, we show that anoxia can promote extracellular activation of trypsinogen 4 indicating that extracellular activation of human trypsinogen 4 can be an important component in neuropathological changes of the injured human brain. [source] The RYR1 g.1843C>T mutation is associated with the effect of the IGF2 intron3-g.3072G>A mutation on muscle hypertrophyANIMAL GENETICS, Issue 1 2007A. Stinckens Summary Muscle growth is a complex phenomenon regulated by many factors, whereby net growth results from the combined action of synthesis and turnover. In pigs, two quantitative trait nucleotides (QTN) are known to have an important influence on muscle growth and fat deposition: one QTN is located in the ryanodine receptor 1 (RYR1) gene (RYR1 g.1843C>T) and the other, a paternally expressed QTN, is in the insulin-like growth factor 2 (IGF2) gene (IGF2 intron3-g.3072G>A). The mutation in IGF2 abrogates in vitro interaction with a repressor, which leads to a threefold increase of IGF2 expression in post-natal muscle. The family of the calpains, a family of Ca2+ -sensitive muscle endopeptidases, and their specific inhibitor calpastatin play an important role in post-natal protein degradation, also influencing muscle and carcass traits. This study investigated the possible interactions between the genotypes of the RYR1 and IGF2 QTN on IGF2 expression. Samples were taken from several muscles and from pigs at several ages, and messenger RNA expression levels were measured using a real-time quantification assay. IGF2 expression in m. longissimus dorsi of animals with mutations in both IGF2 and RYR1 was significantly lower than in animals that inherited the IGF2 mutation but were homozygous wildtype for RYR1. [source] Digestive peptidases and proteinases in the midgut gland of the pink shrimp Farfantepenaeus paulensis (Crustacea, Decapoda, Penaeidae)AQUACULTURE RESEARCH, Issue 7 2009Diego Souza Buarque Abstract Proteases from the midgut gland of the Farfantepenaeus paulensis juveniles were assessed. Enzyme activity was determined using protease substrates and inhibitors. The effect of pH, temperature and calcium on proteolytic activity was assayed. Caseinolytic activity was analysed in substrate-sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE). Trypsin, chymotrypsin and leucine aminopeptidase activity was detected. Proteolytic activity was strongly inhibited by the specific trypsin inhibitors. Tosyl-phenylalanine chloromethyl ketone inhibited 59.3% of chymotrypsin activity. The greatest trypsin-like activity occurred at pH 8.0 and 45 °C. Chymotrypsin-like activity reached maximal values at alkaline pH (7.2,9.0) and 55 °C. CaCl2 did not increase trypsin-like activity, but rather inhibited it at concentrations of 30 (20%), 50 (30%) and 100 mM (50%). The substrate-SDS-PAGE zymogram revealed eight proteinase bands. Two possibly thermal-resistant (85 °C, 30 min) chymotrypsin isoforms were found, which were inhibited by phenyl-methyl-sulphonyl-fluoride. Aminopeptidase activity of enzyme extracts (Arg, Leu, Lys, Phe and Val) and the recommended concentrations of these essential amino acids in penaeid shrimp diets were positively correlated (P<0.05). Beause protein digestion involves the combined action of different enzymes, adequate knowledge of shrimp digestion and enzyme characteristics is required for the assessment of the digestive potential of different feed sources and development of in vitro digestibility protocols. [source] Containment of Biogenic Sulfide Production in Continuous Up-Flow Packed-Bed Bioreactors with Nitrate or NitriteBIOTECHNOLOGY PROGRESS, Issue 2 2003Casey Hubert Produced water from the Coleville oil field in Saskatchewan, Canada was used to inoculate continuous up-flow packed-bed bioreactors. When 7.8 mM sulfate and 25 mM lactate were present in the in-flowing medium, H2S production (souring) by sulfate-reducing bacteria (SRB) was prevented by addition of 17.5 mM nitrate or 20 mM nitrite. Changing the sulfate or lactate concentration of the in-flowing medium indicated that the concentrations of nitrate or nitrite required for containment of souring decreased proportionally with a lowered concentration of the electron donor lactate, while the sulfate concentration of the medium had no effect. Microbial communities were dominated by SRB. Nitrate addition did not give rise to changes in community composition, indicating that lactate oxidation and H2S removal were caused by the combined action of SRB and nitrate-reducing, sulfide-oxidizing bacteria (NR-SOB). Apparently the nitrite concentrations formed by these NR-SOB did not inhibit the SRB sufficiently to cause community shifts. In contrast, significant community shifts were observed upon direct addition of high concentrations (20 mM) of nitrite. Strains NO3A and NO2B, two newly isolated, nitrate-reducing bacteria (NRB) emerged as major community members. These were found to belong to the ,-division of the Proteobacteria, to be most closely related to Campylobacter lari, and to oxidize lactate with nitrate or nitrite as the electron acceptor. Thus the mechanism of microbial H2S removal in up-flow packed-bed bioreactors depended on whether nitrate (SRB/NR-SOB) or nitrite (SRB/NR-SOB as well as NRB) was used. However, the amount of nitrate or nitrite needed to completely remove H2S was dictated by the electron donor (lactate) concentration, irrespective of mechanism. [source] POPs , schwer abbaubare ChemikalienCHEMIE IN UNSERER ZEIT (CHIUZ), Issue 3 2007Gerhard Lammel Professor Abstract POPs, persistent organic pollutants, sind in der Umwelt schwer abbaubare, gleichzeitig bioakkumulative und toxische Stoffe. Die meisten sind mittelflüchtig und lipophil. Sie werden in der Atmosphäre zu einem erheblichen Teil an Aerosolpartikel sorbiert und nach Ablagerung am Boden oder Deposition in den Ozean in die Atmosphäre zurück verflüchtigt und können so mehrere Emissions-Transport-Depositions-Zyklen durchlaufen. Die Transport- und Verteilungsmuster und das Ferntransport-Potenzial sind damit ganz anders als bei herkömmlichen Luftschadstoffen, deren Transport nach Ablagerung aus der Atmosphäre endet. Dass weite Strecken durch mehrere, jeweils kürzere Wege überwunden werden können, wird als Grashüpfer-Effekt bezeichnet. Eine wichtige Hypothese der Umweltchemie besagt, dass die beobachtete Anreicherung von vielen persistenten und bioakkumulativen Schadstoffen in den Polargebieten, fernab der Anwendungsgebiete eine Konsequenz des Grashüpfer-Effekts sei in Verbindung mit stärkerer Kondensation in kalten Gebieten. Die Lipophilie ist die Voraussetzung für die Bioakkumulation und beeinflusst die Verteilung der Stoffe über mehrere Umweltmedien. Weil es sich bei den POPs im Allgemeinen um teilhalogenierte Stoffe handelt, ist der atmosphärische Abbau zumeist langsamer als für andere Luftschadstoffe, aber schneller als in den anderen Umweltkompartimenten, in denen erst bei Verweildauern von Monaten von Persistenz gesprochen wird. Ferntransport-Potenzial und Persistenz eines Stoffes sind wichtig für die Einschätzung der Gefährdung, die von ihm ausgeht. Sie sind das Ergebnis des Zusammenwirkens physikalisch-chemischer Stoffeigenschaften mit den in Raum und Zeit variablen Umweltbedingungen. Sie variieren deswegen in Raum und Zeit. POPs, persistent organic pollutants, are slowly degradable, bio-accumulative and toxic substances. Most of them are semivolatile and lipophilic. In the atmosphere they sorb to aerosol particles, and upon deposition to soil or water surfaces they may return through volatilisation, enabling them to undergo sequential cycles of emission, atmospheric transport and deposition. These patterns of transport and distribution as well as the long-range transport potential differ significantly from those of conventional air pollutants, which undergo only one such cycle. The capability to travel long distances by several hops is called the grasshopper effect. According to a key hypothesis of environmental chemistry the accumulation of persistent and bio-accumulative pollutants in polar regions, far from the areas of usage, is due to the combination of the grasshopper effect and enhanced condensation in cold areas. Lipophilicity is a prerequisite for bio-accumulation and influences the partitioning among environmental media (multicompartment compounds). As POPs are typically halogenated compounds, chemical degradation in the atmosphere is in most cases slower than of other air pollutants, but faster than in the other environmental compartments, where persistence coincides with residence times of months. The long-range transport potential and persistence are crucial for chemical hazard assessment. These characteristics result from the combined action of physico-chemical properties and environmental conditions variable in time and space. Hence, they vary in time and space. [source] Charges dispersed over the permeation pathway determine the charge selectivity and conductance of a Cx32 chimeric hemichannelTHE JOURNAL OF PHYSIOLOGY, Issue 10 2008Seunghoon Oh Previous studies have shown that charge substitutions in the amino terminus of a chimeric connexin, Cx32*43E1, which forms unapposed hemichannels in Xenopus oocytes, can result in a threefold difference in unitary conductance and alter the direction and amount of open channel current rectification. Here, we determine the charge selectivity of Cx32*43E1 unapposed hemichannels containing negative and/or positive charge substitutions at the 2nd, 5th and 8th positions in the N-terminus. Unlike Cx32 intercellular channels, which are weakly anion selective, the Cx32*43E1 unapposed hemichannel is moderately cation selective. Cation selectivity is maximal when the extracellular surface of the channel is exposed to low ionic strength solutions implicating a region of negative charge in the first extracellular loop of Cx43 (Cx43E1) in influencing charge selectivity analogous to that reported. Negative charge substitutions at the 2nd, 5th and 8th positions in the intracellular N-terminus substantially increase the unitary conductance and cation selectivity of the chimeric hemichannel. Positive charge substitutions at the 5th position decrease unitary conductance and produce a non-selective channel while the presence of a positive charge at the 5th position and negative charge at the 2nd results in a channel with conductance similar to the parental channel but with greater preference for cations. We demonstrate that a cysteine substitution of the 8th residue in the N-terminus can be modified by a methanthiosulphonate reagent (MTSEA-biotin-X) indicating that this residue lines the aqueous pore at the intracellular entrance of the channel. The results indicate that charge selectivity of the Cx32*43E1 hemichannel can be determined by the combined actions of charges dispersed over the permeation pathway rather than by a defined region that acts as a charge selectivity filter. [source] | ||||||||||||||||||||||