Home About us Contact
|
Home About us Contact | ||
|
|
||
Osmotic Gradient (osmotic + gradient)
Selected AbstractsHypertonicity-induced decrease in aquaporin-4 expression in retinal pigmented epithelial cellsACTA OPHTHALMOLOGICA, Issue 2009F WILLERMAIN Purpose Osmotic gradients regulate subretinal water content and might be acutely changed during macular oedema. Moreover, since RPE cells express tight junctions, water molecules must use specific channels to cross their hydrophobic membrane. Aquaporins (AQP) are good candidates to assume this function. In this work, we investigated the effects of osmotic stress on the expression of AQP in RPE cells. Methods ARPE-19 cells were grown in different hypertonic conditions. AQP1 and AQP4 expressions were assessed by Western blot and RT-PCR. Chemical inhibitors were used to specifically block lysosomes and proteasome function. Cell proliferation was investigated by BRDU incorporation, and cell viability by flow cytometry. Cell cycle was studied by Western blot and flow cytometry. Results Hypertonic stress rapidly decreased AQP4 expression on ARPE cells. The effect was reversed by proteasome inhibition, but was likely ubiquitinylation-independent. At 24h post-hypertonic stress, cell viability was not affected but cell proliferation was decreased. Cell cycle was also modified as the percentage of cells in G0/G1 phase decreased and the percentage of cells in S and G2/M phase increased. Conclusion Hypertonic stress strongly reduced AQP4 expression and RPE cell proliferation. Those results might contribute to our understanding of macular oedema formation. [source] Evidence for intestinal chloride secretionEXPERIMENTAL PHYSIOLOGY, Issue 4 2010Michael Murek Intestinal fluid secretion is pivotal in the creation of an ideal environment for effective enzymatic digestion, nutrient absorption and stool movement. Since fluid cannot be actively secreted into the gut, this process is dependent on an osmotic gradient, which is mainly created by chloride transport by the enterocyte. A pathological dysbalance between fluid secretion and absorption leads to obstruction or potentially fatal diarrhoea. This article reviews the widely accepted model of intestinal chloride secretion with an emphasis on the molecular players involved in this tightly regulated process. [source] Curvature properties of novel forms of phosphatidylcholine with branched acyl chainsFEBS JOURNAL, Issue 10 2000Richard M. Epand We studied the properties of a series of phosphatidylcholine molecules with branched acyl chains. These lipids have previously been shown to have marked stimulatory effects on the side-chain cleavage activity of cytochrome P450SCC (CYP11A1), an enzyme of the inner mitochondrial membrane. The synthetic lipids used were diacyl phosphatidylcholines with the decanoyl, dodecanoyl or tetradecanoyl chain having a hexyl, octyl or decyl straight chain aliphatic branch at the 2-position. All three lipids lowered the bilayer to hexagonal phase transition temperature of dielaidoyl phosphatidylethanolamine, the lipids with longer acyl chains being more effective in this regard. As pure lipids all of the forms were found by X-ray diffraction to be predominantly in the hexagonal phase (HII) over the entire temperature range of 7,75 °C. The properties of the HII phase were unusual with regard to the small size of the lattice spacings and the small temperature dependence of the spacings. We used tetradecane to relieve hydrocarbon packing constraints to determine the intrinsic radius of curvature of the lipid monolayer. The elastic bending modulus was measured in the presence of tetradecane by introducing an osmotic gradient across the hexagonal phase cylinders with aqueous solutions of poly(ethylene glycol). The elastic bending modulus was found to be higher than that observed with other lipids and to increase with temperature. Both the small intrinsic radius of curvature and the high elastic bending modulus indicate that the presence of these lipids in bilayer membranes will impose a high degree of negative curvature strain. [source] The model of fungal population dynamics affected by nystatinINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 1 2010Sergei I. Voychuk Abstract Fungal diseases are acute problems of the up-to-day medicine. Significant increase of resistance of microorganisms to the medically used antibiotics and a lack of new effective drugs follows in a growth of dosage of existing chemicals to solve the problem. Quite often such approach results in side effects on humans. Detailed study of fungi-antibiotic dynamics can identify new mechanisms and bring new ideas to overcome the microbial resistance with a lower dosage of antibiotics. In this study, the dynamics of the microbial population under antibiotic treatment was investigated. The effects of nystatin on the population of Saccharomyces cerevisiae yeasts were used as a model system. Nystatin effects were investigated both in liquid and solid media by viability tests. Dependence of nystatin action on osmotic gradient was evaluated in NaCl solutions. Influences of glucose and yeast extract were additionally analyzed. A "stepwise" pattern of the cell death caused by nystatin was the most intriguing. This pattern manifested in periodical changes of the stages of cell death against stages of resistance to the antibiotic. The mathematical model was proposed to describe cell-antibiotic interactions and nystatin viability effects in the liquid medium. The model implies that antibiotic ability to cause a cells death is significantly affected by the intracellular compounds, which came out of cells after their osmotic barriers were damaged © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010 [source] RHEOLOGY OF DOUBLE (W/O/W) EMULSIONS PREPARED WITH SOYBEAN MILK AND FORTIFIED WITH CALCIUMJOURNAL OF TEXTURE STUDIES, Issue 5 2010ANDRÉS L. MÁRQUEZ ABSTRACT The objective of this work was to study the rheological behavior of water-in-oil-in-water (w/o/w) emulsions prepared with soybean milk and sunflower oil, with different calcium solutions as the internal aqueous phase, in order to evaluate them as a vegetable substitute of whipped dairy cream. The obtained systems exhibited a creamy texture, which was attributed to the swelling of w/o droplets because of the osmotic gradient generated by the inclusion of soluble salts in the internal aqueous phase. A secondary factor could be the flocculation of w/o droplets due to the interaction of released calcium with soybean proteins at the interface. Consequently, the increase of calcium chloride content produced emulsions with higher consistency. A pasteurization produced flocculation and coalescence of w/o droplets only at high calcium chloride content. These double emulsions could be a potential alternative to the whipped dairy cream, because of their texture, reduced fat content and calcium contribution. PRACTICAL APPLICATIONS This article deals with the formulation of novel calcium-fortified food emulsions prepared with soybean milk and sunflower oil. Because calcium needs to be isolated from soybean milk components (proteins and phospholipids), we proposed to include calcium salts in the internal aqueous phase of a water-in-oil-in-water (w/o/w) emulsion. The practical applications of this research could include the formulation of low lipid content emulsions and the isolation of a component which is incompatible with the continuous aqueous phase. Particularly, this work leads to the understanding of how the inclusion of calcium salts in the internal aqueous phase of a w/o/w emulsion prepared with soybean milk affects the rheology and microstructure of the system. The results led to the conclusion that these emulsions can work as a whipped dairy cream substitute with vegetal components, low lipid content and important calcium contribution. [source] Assimilate transport in grapevines -effect of phloem disruptionAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 3 2001J.J.(KOBUS) HUNTER Abstract Assimilate translocation in mature grapevines (cv. Gewürztraminer and cv. Harslevelü) under field conditions was investigated during the growth season by quantifying individual sugars and organic acids in mature leaves, shoot bark and berries, as affected by girdling the shoot just above the bunches. Tissue was sampled at berry set, pea size, veraison and ripeness stages of the vine. Invertase activity was determined in the shoot bark at ripeness. In the leaves, malic acid concentrations reached lowest levels at pea size, but increased thereafter. Tartaric acid decreased after peaking at pea size stage. Tartaric acid concentrations increased with girdling. Despite the increase in leaf age, sucrose concentrations remained virtually stable during the season, emphasising the importance of mature leaves for nourishing bunches. Girdling resulted in a build-up of sucrose in the leaves. In the bark, malic and tartaric acid stayed more or less the same during the growth period, but increased above the girdle. As a result of phloem disruption, sucrose also increased. The increase in glucose and tartaric acid is believed to result from catabolic cleavage of sucrose by invertase. Invertase activity was evident in the bark (of mature Harslevelü vines) at ripeness, which may indicate involvement in osmotic adjustments and gradients in the bark/phloem structure. In the berries, malic and tartaric acids reached peak concentrations at pea size. The volume increase during the ripening period, and in the case of malic acid also respiratory loss, resulted in a decrease in organic acid concentration. Malic acid continued to decrease after the initial decline, whereas tartaric acid stayed virtually stable. Girdling had no marked effect on organic acid accumulation in the berries. Sucrose concentrations were low during the first part of the season, but increased thereafter. Sucrose concentrations during ripening increased with girdling, which may represent a concentration effect and/or import from the rest of the vine. Sucrose concentrations (in mature Harslevelü vines) were indeed lower below than above the girdle. Comparison of sucrose concentrations in the leaves, bark and berries showed the existence of a decreasing concentration gradient, in line with the source:sink transport concept. An equally prominent decrease in sucrose:glucose ratio in the berries from the start of the ripening period indicates that vacuolar integrity (compartmentation) was affected in the ripening berry, most probably allowing hydrolysis of sucrose by invertase and decreasing osmotic potential within the berry. The results provide further evidence for the hypothesis of an osmotic gradient driven transport to the berry. [source] | ||||||||||