Application of microcolumn ion chromatography using anion exchangers modified with dextran sulfate for the determination of alkali and alkaline-earth metal ions

Microcolumn ion chromatography using anion exchangers modified with dextran sulfate has been applied to the determination of alkali and alkaline-earth metal ions contained in guinea pig serum and bovine serum. These serums contained Na⁺, NH₄⁺, K⁺, Mg²⁺ and Ca²⁺ and they were indirectly detected at 200 nm. The determination was done without any pretreatment procedure other than dilution.     

Concentration dependent effects of dextran on the physical properties of acid milk gels

The effect of dextran from Leuconostoc mesenteroides (DEX₅₀₀), added to milk prior to acidification with glucono-δ-lactone (GDL) or Streptococcus thermophilus DSM20259, was studied with respect to polysaccharide concentration. The incorporation of 5–30 g/kg DEX₅₀₀ significantly affected gelation behavior. Increasing DEX₅₀₀ concentrations resulted in a linear increase of gel stiffness (GDL gels: R² = 0.96; microbial acidification: R² = 0.94; P < 0.05) and 30 g/kg DEX₅₀₀ resulted in a 2-fold higher stiffness compared to gels without polysaccharide. The respective stirred gels depicted a significant reduction in syneresis, which decreased from 30.4% (0 g/kg DEX₅₀₀) to 22.0% (30 g/kg DEX₅₀₀) for chemically acidified gels after 1 d of storage. Physical characteristics of DEX₅₀₀ in aqueous solution were helpful to explain its behavior in the complex system milk.     

Application of 2-aminopyridine fluorescence labeling in the analysis of in vivo and in vitro metabolism of dextran sulfate sodium by size-exclusion high-performance liquid chromatography

The present study describes a size-exclusion high-performance liquid chromatographic method for the separation and quantification of sulfated polysaccharides, such as dextran sulfate sodium (DSS). Pyridylamination of DSS was achieved without difficulty using 2-aminopyridine as a fluorometric label. In addition, 0.1–0.2 M phosphate buffer (pH 3.0) was found to be the mobile phase which produced the best separation. In vitro enzymatic degradation of the pyridylamino-DSS (PA-DSS₅₀₀₀, M_r 5000) using α-amylase and the in vivo metabolism in the rat feces after oral administration of PA-DSS₅₀₀₀ were then evaluated. Two small peaks of approximately M_r 380 and 600 appeared after co-incubation with α-amylase, indicating PA-DSS₅₀₀₀ may be considerably depolymerized. In vivo, however, PA-DSS₅₀₀₀ excreted in the feces was mainly of PA-DSS₅₀₀₀ polymer. No peaks of less than M_r 5000 were not clearly detectable in the feces because of background fluorescence attributable to gut lumen contents. This method of fluorometric analysis allows fairly selective detection of sulfated polysaccharides in biological materials.     

Priming effect of dextran sulphates on lipopolysaccharide-induced tumour necrosis factor production in mice

Abstract Dextran sulphate (DS) 500 (M.W. 500 000) is commonly used as a reticuloendothelial (RE) blocker. We found that lipopolysaccharide (LPS)-induced tumour necrosis factor (TNF) production in sera was enhanced when mice were pretreated with DS500. When mice were pretreated with DS1000 (M.W. 1 000 000), TNF activity in sera was also significantly enhanced by the LPS injection in comparison with the saline-treated group, but not by the pretreatment with the low molecular weight of DS5 (M.W. 5 000), neutral dextran (Dex) 500, or positively-charged diethylaminoethyl dextran (DEAE-Dex) 500. The enhancement of LPS-induced TNF production occurred from 2 h after DS500 pretreatment. Pretreatment with DS500 or DS1000 significantly suppressed the carbon clearance from the blood in mice from 2 h after DS injection, but this suppression was not detected by the pretreatment with DS5, Dex500, or DEAE-Dex500. We suggest that negative-charge and high molecular weight are essential for dextran derivatives to enhance LPS-induced TNF production, and that the enhancing effect of DS is closely related to the suppression of the RE function.     

Enhanced stability of β-galactosidase in parenchymal and nonparenchymal liver cells by conjugation with dextran

In order to enhance the stability of β-galactosidase, we conjugated the enzyme with dextran T-10 (M_r approx. 10 000). The conjugate contained 9–10 mol dextran/mol protein (β-galactosidase, M_r 68 000), and the specific activity retained after conjugation was 90 ± 4% (n = 3) of the initial activity. Uptake and degradation of native and conjugated β-galactosidase in isolated hepatocytes and nonparenchymal liver cells was studied. There was a marked increase in stability against degradation in both cell types when β-galactosidase was conjugated with Dextran. The degradation of dextran-conjugated enzyme was reduced by 35% in hepatocytes and by 43% in nonparenchymal cells, after 80 and 40 min, respectively, as compared with the free enzyme. However, there was insignificant difference between the uptake of native and conjugated enzyme into the liver cells. Upon intravenous infusion into rats, native and conjugated enzyme were cleared from plasma with only a slight difference in the clearance rate. The observed stability of dextran-conjugated β-galactosidase towards cellular degradation was in accordance with the in vitro experiments. The conjugate showed marked thermal stability at 50°C and enhanced resistance towards proteolysis by the broad specific protease subtilopeptidase A. This demonstrates that dextran conjugation may be used as a means of stabilizing lysosomal enzymes for therapeutic purposes.     

Application of percolation theory principles to the analysis of interaction of adenylate cyclase complex proteins in cell membranes

Summary Lateral protein movement in cell membranes takes place in a medium with obstacles. These obstacles are: (a) aggregates of major integral proteins immobilized by submembraneous structures and cytoskeleton, and (b) membrane lipids in the gel phase. Hormonal activation of the adenylate cyclase complex is associated with lateral mobility of the constituent proteins. Modification of the interaction of these proteins due to variation of the fluid lipid fraction in reticulocyte membranes has been studied. A decrease in the percentage of fluid lipids in membranes resulted in the inhibition (up to the full cessation) of the interaction of -adrenoreceptors with regulatory N_s-proteins. The interaction of N_s-proteins with catalytic proteins stopped as well. On the other hand, an increase in the fluid lipid fraction led to a more intensive interaction. These facts do not arise from the functional damage of interacting proteins. Conseqently, hormonal activation of the adenylate cyclase complex depends on the fraction of fluid lipids in the membrane. The data obtained are in conformity with the percolation theory which makes it possible to characterize long-distance protein movement in a medium (fluid lipids) containing obstacles. Thus, interacting proteins prove to diffuse within distances greatly exceeding protein sizes. As a consequence, the intrinsic activity of a -agonist, isoproterenol, varies from 1 to 0 depending on the fluid lipid fraction. Our findings also suggest that in vitro there are no -receptors precoupled with N_s-proteins in rat reticulocyte membranes in the absence of guanine nucleotides.     

基于大型底栖无脊椎动物确定河流营养盐浓度阈值——以西苕溪上游流域为例

水体富营养化是一个全球性的问题,中国也面临严重威胁.目前,中国的水体富营养化研究主要集中在湖泊和水库,对河流的研究极少.根据大型底栖无脊椎动物的群落结构对营养盐胁迫的响应,运用非参数转变点分析方法计算西苕溪上游营养盐浓度突变点.结果表明:总氮和总磷的突变点分别为1.409mg·mL-1和0.033～0.035mg·mL-1.参照点的总氮和总磷浓度基本都低于阈值,城市干扰点则全部高于阈值,而当总氮和总磷超过各自阈值时会导致大型底栖无脊椎动物群落结构的严重退化.通过建立与水生生物群落结构有关的水体营养盐标准,可充分发挥生物监测在水环境管理中的作用,为计算水体中总氮和总磷的最大日负荷总量提供科学数据.     

Addition of oligosaccharide decreases the freezing lesions on human red blood cell membrane in the presence of dextran and glucose

Although incubation with glucose before freezing can increase the recovery of human red blood cells frozen with polymer, this method can also result in membrane lesions. This study will evaluate whether addition of oligosaccharide (trehalose, sucrose, maltose, or raffinose) can improve the quality of red blood cell membrane after freezing in the presence of glucose and dextran. Following incubation with glucose or the combinations of glucose and oligosaccharides for 3 h in a 37 °C water bath, red blood cells were frozen in liquid nitrogen for 24 h using 40% dextran (W/V) as the extracellular protective solution. The postthaw quality was assessed by percent hemolysis, osmotic fragility, mean corpuscle volume (MCV), distribution of phosphatidylserine, the postthaw 4 °C stability, and the integrity of membrane. The results indicated the loading efficiency of glucose or oligosaccharide was dependent on their concentrations. Moreover, addition of trehalose or sucrose could efficiently decrease osmotic fragility of red blood cells caused by incubation with glucose before freezing. The percentage of damaged cell following incubation with glucose was 38.04 ± 21.68% and significantly more than that of the unfrozen cells (0.95 ± 0.28%, P < 0.01). However, with the increase of the concentrations of trehalose, the percentages of damaged cells were decreased steadily. When the concentration of trehalose was 400 mM, the percentage of damaged cells was 1.97 ± 0.73% and similar to that of the unfrozen cells (P > 0.05). Moreover, similar to trehalose, raffinose can also efficiently prevent the osmotic injury caused by incubation with glucose. The microscopy results also indicated addition of trehalose could efficiently decrease the formation of ghosts caused by incubation with glucose. In addition, the gradient hemolysis study showed addition of oligosaccharide could significantly decrease the osmotic fragility of red blood cells caused by incubation with glucose. After freezing and thawing, when both glucose and trehalose, sucrose, or maltose were on the both sides of membrane, with increase of the concentrations of sugar, the percent hemolysis of frozen red blood cells was firstly decreased and then increased. When the total concentration of sugars was 400 mM, the percent hemolysis was significantly less than that of cells frozen in the presence of dextran and in the absence of glucose and various oligosaccharides (P < 0.01). However, when both glucose and trehalose were only on the outer side of membrane, with increase of the concentrations of sugars, the percent hemolysis was increased steadily. Furthermore, addition of oligosaccharides can efficiently decrease the osmotic fragility and exposure of phosphatidylserine of red blood cells frozen with glucose and dextran. In addition, trehalose or raffinose can also efficiently mitigate the malignant effect of glucose on the postthaw 4 °C stability of red blood cells frozen in the presence of dextran. Finally, addition of trehalose can efficiently protect the integrity of red blood cell membrane following freezing with dextran and glucose. In conclusion, addition of oligosaccharide can efficiently reduce lesions of freezing on red blood cell membrane in the presence of glucose and dextran.     

Amelioration of dextran sulfate sodium-induced colitis in mice by oral administration of beta-caryophyllene, a sesquiterpene

beta-Caryophyllene (BCP), a naturally occurring plant sesquiterpene, was examined for anti-inflammatory activity in a mouse model of experimental colitis induced by dextran sulfate sodium (DSS). Colitis was induced by exposing male BALB/c mice to 5% DSS in drinking water for 7 days. BCP in doses of 30 and 300 mg/kg was administered orally once a day, beginning concurrently with exposure to DSS. The body weight and colon length were measured, and histological damage and myeloperoxidase (MPO) activity as well as inflammatory cytokines were assessed in both serum and colonic tissue after 7 days of treatment with DSS. The DSS treatment damaged the colonic tissue, increased MPO activity and inflammatory cytokines, lowered the body weight, and shortened the length of the colon. Oral administration of BCP at 300 mg/kg significantly suppressed the shortening of colon length and slightly offset the loss of body weight. BCP treatment (300 mg/kg) also significantly reduced the inflammation of colon and reversed the increase in MPO activity that had been induced by exposure to DSS. Further, BCP significantly suppressed the serum level of IL-6 protein (a 55% reduction) as well as the level of IL-6 mRNA in the tissue. These results demonstrate that BCP ameliorates DSS-induced experimental colitis, and may be useful in the prevention and treatment of colitis.     

Beneficial and preventive effect of chitin nanofibrils in a dextran sulfate sodium-induced acute ulcerative colitis model

Chitin nanofibrils, which are prepared from dried crab shells by a grinding method, are newly developed natural materials with uniform widths of approximately 10-20 nm. The bioactivities of chitin nanofibrils have not been investigated. In this study, we examined the preventive effects of chitin nanofibrils in a mouse model of dextran sulfate sodium (DSS)-induced acute ulcerative colitis. The results indicated that chitin nanofibrils improved clinical symptoms and suppressed ulcerative colitis. Furthermore, chitin nanofibrils suppressed myeloperoxidase activation in the colon and decreased serum interleukin-6 concentrations. Conversely, chitin powder did not suppress DSS-induced acute ulcerative colitis. Our results suggested that chitin nanofibrils have potential as a functional substance for inflammatory bowel disease patients.     

Some statistical considerations in the determination of thresholds in ELISA

The presentation of quantitative results from ELISAs is very variable, and, in particular, the positive-negative threshold or critical value is poorly defined. A simple statistical model is presented which demonstrates how this value may be determined. Depending on what assumptions are made it is possible to estimate the necessary parameters in several different ways. These methods generally form a hierarchy, and greater precision can be achieved by combining variances from several plates. More problematical is the determination of the negative control, and indeed its definition. The results of a series of ELISAs taken from a study of polyphagous predators of the cereal aphid S. avenae are used to illustrate the methods. The ELISAs were done over a period of three months using 86 plates. Recommendations are made for the numbers and levels of controls to be used in future studies.     

毛乌素沙地流动沙丘不同深度土壤渗漏特征

沙地的土壤深漏是沙地水分循环及水量平衡中的重要环节,对这一分量的准确测算,能够增进对沙地降雨的分配、转移及运输过程规律的认识。利用土壤深层水量渗漏测试记录仪(YWB-01),对毛乌素沙地典型的流动沙丘50、100 cm和200 cm的3个层次的土壤渗漏水量进行定点实时监测,定量分析降雨条件下沙地土壤渗漏特征,得出以下结论:(1)在降雨条件下,2016年4—6月3个沙层的渗漏过程都不明显,从7月开始,渗漏过程与降雨过程的一致性随沙层的增加而逐渐减弱;(2)随沙层深度的增加,累计渗漏天数以及连续渗漏天数在增加,累计渗漏水量、最大日渗漏水量逐渐减小,渗漏水量的波动也逐渐减小;渗漏水量10 mm的天数和渗漏水量所占的比例明显减少;(3)对降雨量和各沙层渗漏水量日、周、半月、月累积量之间进行相关分析和线性拟合后发现,越往深处渗漏水量对降雨的响应越弱,月渗漏水量与月降雨量的关系更密切。     

An examination of the thresholds of enrichment: a resource-based growth model

A model of single-species growth in the chemostat on two non-reproducing, growth-limiting, noninhibitory, perfectly substitutable resources is considered. The medium in the growth vessel is enriched by increasing the input concentration of one of the resources. Analytical methods are used to determine the effects of enrichment on the asymptotic behaviour of the model for different dilution rates. It is shown that there exists a threshold value for the dilution rate which depends on the maximal growth rate of the species on each of the resources. Provided the dilution rate is below the threshold, enrichment is beneficial in the sense that the carrying capacity of the environment is increased, regardless of which resource is used to enrich the environment. When the dilution rate is increased beyond the threshold, it becomes important to consider which resource is used for enrichment. For one of the resources it is shown that, while moderate enrichment can be beneficial, sufficient enrichment leads to the extinction of the microbial population. For the other resource, enrichment leads from washout or initial condition dependent outcomes to survival, and is thus beneficial. There are important implications of these results to the management of natural aquatic ecosystems. For example, while enrichment may be beneficial to the microbial species during the summer months, it can lead to their decimation during spring run-off, when the natural dilution rate is higher.Research partially supported by an Ontario Graduate Scholarship. This author's contribution was motivated by results in her Ph.D. thesis at McMaster UniversityResearch supported by the National Sciences and Engineering Research Council of Canada.     

棉铃虫经济阈值研究中的几个问题

就华北棉区棉田棉铃虫经济阈值研究中的若干问题展开讨论。作者分析指出：１）用幼虫部分龄期的为害量取代全部龄期的为害量,导致经济阈值的过高估计;２）用一个世代为害期前半段中半段的单虫为害量取代整个世纪的单虫为害量,导致经济阈值的过高或过低估计;３）将以蕾为主的蕾铃被害量等同于成铃减少量,导致算出的经济阈值成倍下降;４）在确定产量损失与为害量关系的试验时,当某一处理的产量差异不显著,不能断言这一为害量对     

生态阈值确定方法综述

生态系统在环境条件变化时表现出的剧变或阈值现象是当前生态学研究的热点,但是生态阈值定量检测的困难阻碍了这一主题的研究与应用.本文从典型案例入手,通过分析潜在生态阈值的S型曲线式、补给-压力式和跃迁式驱动-响应机理,归纳了局部加权回归散点平滑法、分段回归、高斯模型、拐点分析软件、稳态转换检测软件、指示种阈值分析和系统动力...     

Disruption of GABAA in the insect antennal lobe generally increases odor detection and discrimination thresholds

Studies of olfactory function show that disruption of GABA A receptors within the insect antennal lobe (AL) disrupts discrimination of closely related odors, suggesting that local processing within the AL specifically enhances fine odor discrimination. It remains unclear, however, how extensively AL function has been disrupted in these circumstances. Here we psychophysically characterize the effect of GABA A blockade in the AL of the moth Manduca sexta. We used 2 GABA A antagonists and 3 Pavlovian-based behavioral assays of olfactory function. In all cases, we used matched saline-injected controls in a blind study. Using a stimulus generalization assay, we found that GABA A disruption abolished the differential response to related odors, suggesting that local processing mediates fine odor discrimination. We then assessed the effect of GABA A antagonist on discrimination thresholds. Moths were differentially conditioned to respond to one odor (reinforced conditioned stimulus [CS+]) but not a second (unreinforced conditioning stimulus [CS-]) then tested for a significant differential conditioned response between them across a series of increasing concentrations. Here, GABA A blockade disrupted discrimination of both similar and dissimilar odor pairs as indicated by generally increased discrimination thresholds. Finally, using a detection threshold assay, we established that GABA A blockade also increases detection thresholds. Because detection is a prerequisite of discrimination, this later finding suggests that disrupted discrimination may be due to impairment of the ability to detect. We conclude that the loss of ability to detect and subsequently discriminate is attributable to a loss of ability of the AL to provide a clear neural signal from background.     

Validity of different EMG analysis methods to identify aerobic and anaerobic thresholds in speed skaters

Purpose: This study aimed to assess the validity of the first (EMGth1) and second (EMGth2) breakpoints in the EMG signal during skating. Scope: Ten well-trained long track speed skaters performed a maximal incremental skating test on a slide board. EMG signals from six lower limb muscles were recorded during the last 15 s of each stage and converted to Root Mean Square for determination EMGth1 and EMGth2 using mathematical (2 and 3 linear regressions) and visual methods. Conclusions: EMGth1 had a low detection rate (<50%) while EMGth2 could be identified visually in > 80% of cases, in 85% of cases using 2-lines and 63% using 3-lines regression. Quads (VL + VM) and Gluts (GM + GMd) had the highest EMGth2 detection rate for all methods (>70%). EMGth2 from Quads and Gluts detected by the 2-lines and 3-lines regression were not different than the second ventilatory threshold (VT2) (p > 0.05), while the visual method overestimated VT2 (p < 0.01). EMGth2 detected from Quads by the 2-lines regression method presented better correlation with VT2 stage (r = 0.91), lowest bias, and limit of agreement. We conclude that EMG is a valid non-invasive method to detect VT2 during skating when using a mathematical method to determine EMGth2.     

In vivo circulation of mouse red blood cells frozen in the presence of dextran and glucose

Loading with monosaccharide can improve the quality of human red blood cells (hRBCs) frozen with polymer. But in vivo life span of hRBCs frozen with polymer and sugar is not determined. In this study, following incubation with glucose, mouse red blood cells (mRBCs) were frozen in liquid nitrogen for 24 h using dextran as the extracellular protectant. After thawing, hemolysis, exposure of PS, and osmotic fragility of frozen mRBCs were determined in vitro. After transfusion of fluorescein isothiocyanate (FITC)-labeled mRBCs, the 24 h recovery and half life span of frozen mRBCs were determined. The data indicated the postthaw hemolysis of mRBCs frozen with dextran and glucose were significantly less than that of cells frozen with dextran (17.23% ± 5.21% vs 25.96% ± 10.07%, P = 0.034). But freezing can also result in exposure of phosphatidylserine and increase of osmotic fragility of mRBCs. After transfusion, the 24 h recovery of mRBCs frozen in the absence or presence of glucose was similar to that of the control cells (P = 0.748 and 0.971). However, the half life span of mRBCs frozen in the absence or presence of glucose was significantly less than that of the control cells (P = 0.000). In addition, incubation with glucose can not increase the life span of frozen red blood cells (7.16 ± 0.93 d vs 7.15 ± 0.34 d, P = 0.982). In conclusion, incubation with monosaccharide could significantly increase the recovery of mRBCs frozen with polymer. Although freezing can significantly shorten the half life span of frozen cells, it can not influence the 24 h recovery of frozen mRBCs. In addition, incubation with monosaccharide before freezing can not increase the life span of frozen mRBCs. So according to the above data, to increase the life span of hRBCs frozen with polymer and monosaccharide, the osmotic fragility of the frozen RBCs must be decreased in the future.     

Phase-transition and aggregation characteristics of a thermoresponsive dextran derivative in aqueous solutions

Grafting of poly(N-vinylcaprolactam) side chains onto a hydrophilic dextran backbone was found to provide the dextran with new, thermoresponsive properties in aqueous solutions. Depending on its solution concentration, the resulting dextran derivative could exhibit a temperature-induced phase-transition and critical transition temperature (T(c)). Different anions and cations of added salts, including five potassium salts and five alkali-metal chlorides, were observed to influence the T(c) value of its aqueous solution. Except for potassium iodide, all added salts were found to lower the T(c) value. The addition of the surfactant, cationic cetyltrimethylammonium bromide or anionic sodium dodecyl sulfate, resulted in an increase of the T(c) value. With the help of the Coomassie Brilliant Blue dye as a polarity probe, the formation of hydrophobic aggregates above the T(c) was revealed for this new dextran derivative in aqueous solution.