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Several Different Mechanisms (several + different_mechanism)
Selected AbstractsFormation and ageing of L-glutamic acid spherulitesCRYSTAL RESEARCH AND TECHNOLOGY, Issue 7 2010R. Beck Abstract Polycrystalline spherulites of L-glutamic acid have been crystallized by pH-shift precipitation from stirred aqueous solutions. The time dependent behaviour of the spherulites has been studied during the crystallization process and batch filtration tests have been performed. It has been shown that the FBRM mean chord length of the investigated spherulites decreases in the course of time. The fact that the size reduction progresses faster at higher temperature and the solubility of resuspended polycrystalline particles decreasing with time, implies an ageing mechanism to be responsible for the observed changes in the particle size. It has been shown that the surface area decreases with time, ruling out particle breakage as a possible explanation for the decrease in particle size. XRD and Raman studies of L-glutamic acid, however, show only marginal differences in the crystalline structure of particles obtained from different time stages. The ageing may occur due to several different mechanisms like phase transformation and Ostwald ripening. L-glutamic acid spherulites after 3 h exhibit a 3-fold higher value for the cake resistance as compared to particles after 0.5 h. However, particles obtained after 22 h exhibit an 8-fold lower cake resistance as compared to the initially obtained spherulites, The increase in the cake resistance is attributed to the appearance of small plate-like crystals and a change in the interaction between the crystal surface and the solution. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Foot temperature in diabetic polyneuropathy: innocent bystander or unrecognized accomplice?DIABETIC MEDICINE, Issue 3 2005S. B. Rutkove Abstract Aim To explore mechanisms by which temperature could influence the pathogenesis and symptoms of diabetic polyneuropathy. Methods We conducted a literature review attempting to identify mechanisms by which diabetic polyneuropathy could be affected by temperature. Results Cooling can theoretically hasten the progression of diabetic polyneuropathy through several different mechanisms. Specifically, cooling can enhance neuronal ischaemia, increase formation of reactive oxygen species, slow axonal transport, increase protein kinase C activity, and interfere with immune function. Short-term temperature fluctuations (both warming and cooling) can initiate and exacerbate neuropathic pain by causing neuronal hyperexcitability and functional deafferentation. Although normal fluctuations of distal extremity temperature may be sufficient for these effects, impaired thermoregulation may make the distal extremities more susceptible to temperature extremes. Eventually, a ,vicious cycle' may ensue, resulting in neuronal deterioration with further disruption of temperature regulation. Limited epidemiological data suggest a higher prevalence of diabetic polyneuropathy in populations living in colder locations, supporting our hypothesis. Conclusions Variations in foot temperature may play an important but as yet unrecognized role in the development and symptoms of diabetic polyneuropathy. Further basic and clinical research exploring this concept could help elucidate the natural history of diabetic polyneuropathy and lead to novel therapeutic strategies. [source] Connections between species diversity and genetic diversityECOLOGY LETTERS, Issue 7 2005Mark Vellend Abstract Species diversity and genetic diversity remain the nearly exclusive domains of community ecology and population genetics, respectively, despite repeated recognition in the literature over the past 30 years of close parallels between these two levels of diversity. Species diversity within communities and genetic diversity within populations are hypothesized to co-vary in space or time because of locality characteristics that influence the two levels of diversity via parallel processes, or because of direct effects of one level of diversity on the other via several different mechanisms. Here, we draw on a wide range of studies in ecology and evolution to examine the theoretical underpinnings of these hypotheses, review relevant empirical literature, and outline an agenda for future research. The plausibility of species diversity,genetic diversity relationships is supported by a variety of theoretical and empirical studies, and several recent studies provide direct, though preliminary support. Focusing on potential connections between species diversity and genetic diversity complements other approaches to synthesis at the ecology,evolution interface, and should contribute to conceptual unification of biodiversity research at the levels of genes and species. [source] Redox regulation of ascorbic acid transport: Role of transporter and intracellular sulfhydrylsBIOFACTORS, Issue 4 2004James M. May Abstract Ascorbic acid is one of the most sensitive cellular defenses against oxidant damage. However, it requires a sodium- and energy-dependent transporter to enter cells against a concentration gradient. To test the hypothesis that ascorbate transport is sensitive to redox stress, we studied changes in transport of the vitamin in response to sulfhydryl modification of the protein and to GSH depletion in cultured endothelial cells. Transport of ascorbic acid, measured as the uptake of radiolabeled ascorbate, was inhibited by the membrane-impermeant sulfhydryl reagents thorin, p -chloromercuribenzene sulfonic acid, and 5,5,-dithiobis-(2-nitrobenzoic acid) in a dose-dependent manner without significant depletion of intracellular GSH. Sulfhydryl reagents capable of penetrating the plasma membrane, including phenylarsine oxide, p -chloromercuribenzoic acid, and N-ethylmaleimide, inhibited transport and lowered cellular GSH. Diamide, which induces disulfide formation, increased ascorbate transport over a narrow concentration range under conditions in which GSH was not depleted. On the other hand, specific depletion of intracellular GSH by several different mechanisms did inhibit transport. Together, these results suggest that the ascorbate transporter is sensitive to redox modulation. This relates in part to sulfhydryl groups exposed on the exofacial ascorbate transporter, and to sulfhydryl groups that are sensitive to changes in the redox state of intracellular GSH. [source] | ||||||||||