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61.
62.
Selenium supplementation of infant formula: uptake and retention of various forms of selenium in suckling rats 总被引:1,自引:0,他引:1
Bo L nnerdal Carol E. Glazier Eric L. Lien 《The Journal of nutritional biochemistry》1992,3(12):644-652
Formula-fed infants often have lower serum selenium levels than breast-fed infants. Although no deleterious effects have been correlated to this finding, supplementation of formula with selenium is considered. In this study, we investigated the uptake and retention by suckling rat pups of 75Se from selenite, selenate, and selenomethionine added to infant formula. The molecular distribution of 75Se in liver, kidney, intestine, and plasma was followed by gel-filtration chromatography on Superose 12. 75Se-uptake was most rapid from selenomethionine (70% at 1 hr), followed by selenate (51%) and selenite (29%). This difference was explained by a higher retention of 75Se in the stomach and small intestinal wall of pups given selenite supplement. Plasma distribution of 75Se as studied by gel filtration was also different, with a higher proportion of 75Se from selenomethionine being protein-bound than from selenite or selenate. Similarly, a larger proportion of 75Se from selenomethionine became protein-bound in the liver than from selenite or selenate. In conclusion, although whole body retention after 24–48 hr was similar, the metabolic fate of selenium varies considerably with the form of selenium added to formula. Further studies are needed to study the long-term consequences of selenium accumulated in different body compartments. 相似文献
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Amanda E. Glazier Ron J. Etter 《Biological journal of the Linnean Society. Linnean Society of London》2014,113(4):897-913
The deep ocean supports a highly diverse and mostly endemic fauna, yet little is known about how or where new species form in this remote ecosystem. How speciation occurs is especially intriguing in the deep sea because few obvious barriers exist that would disrupt gene flow. Geographic and bathymetric patterns of genetic variation can provide key insights into how and where new species form. We quantified the population genetic structure of a protobranch bivalve, Neilonella salicensis, along a depth gradient (2200–3800 m) in the western North Atlantic using both nuclear (28S and calmodulin intron) and mitochondrial (cytochrome c oxidase subunit I) loci. A sharp genetic break occurred for each locus between populations above 2800 m and below 3200 m, defining two distinct clades with no nuclear or mitochondrial haplotypes shared between depth regimes. Bayesian phylogenetic analyses provided strong support for two clades, separated by depth, within N. salicensis. Although no morphological divergence was apparent, we suggest that the depth‐related population genetic and phylogenetic divergence is indicative of a cryptic species. The frequent occurrence of various stages of divergence associated with species formation along bathymetric gradients suggests that depth, and the environmental gradients that attend changes in depth, probably play a fundamental role in the diversification of marine organisms, especially in deep water. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 113 , 897–913. 相似文献
67.
Purification and Na+ uptake by human placental microvillus membrane vesicles prepared by three different methods 总被引:2,自引:0,他引:2
Three methods were used to prepare microvillus membrane vesicles from each of six human placentas. Two of these incorporated an agitation stage to preferentially remove microvilli and either Ca2+ (Method 1) or Mg2+ (Method 2) aggregation of non-microvillus membrane. The third method involved homogenisation of the tissue followed by Mg2+ aggregation of non-microvillus membrane (Method 3). Enrichment of alkaline phosphatase activity (27.6 +/- 1.9, 25.3 +/- 2.7) and ouabain binding (5.9 +/- 2.6, 5.3 +/- 2.2, respectively) was similar in vesicles prepared by Methods 1 and 2, respectively. Method 3 vesicles showed a significantly (P less than 0.01) lower alkaline phosphatase enrichment (18.1 +/- 1.2), but ouabain binding enrichment (6.3 +/- 1.3) was not different and vesicle protein recovery (mg/g placenta) was 5-fold greater. Na+ uptake in the presence of an outwardly directed proton gradient was significantly inhibited in all microvillus membrane vesicles by amiloride (0.5 mM). However, the amiloride sensitive component of Na+ uptake was 3-6-fold greater in Method 3 vesicles than in Method 1 and 2 vesicles, and showed overshoot above equilibrium in the former but not the latter. Further experiments using the pH sensitive dye, 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein suggested that the proton gradient dissipated faster from Method 1 than from Method 3 vesicles. Thus methodological differences can have a marked effect on transport processes in microvillus membrane vesicles prepared from the human placenta. 相似文献
68.
Douglas S. Glazier 《Functional ecology》2009,23(5):963-968
1. Metabolic rate is conventionally assumed to scale with body mass to the 3/4-power, independently of the metabolic level of the organisms being considered. However, recent analyses in a variety of animals and plants indicate that the power (log–log slope) of this relationship varies significantly with metabolic level, ranging from c . 2/3 to 1.
2. Here I show that the scaling slopes of rates of respiration and growth are related to the metabolic level of a variety of unicellular organisms, as similarly occurs for respiration rates in multicellular organisms.
3. The recently proposed 'metabolic-level boundaries hypothesis' provides insight into these effects of metabolic level. As predicted, the scaling slopes for resting (endogenous) respiration rate in prokaryotes, algae and protozoans are negatively related to metabolic level; and in protozoans, the scaling slope increases with starvation. Also as predicted, the scaling slopes of growth rate in algae and protozoans are negatively related to growth level. Unexpectedly, opposite effects of starvation on the metabolic scaling slopes of unicellular prokaryotes (compared to that of eukaryotes) may be a spurious result of respiration measurements that did not adequately consider the effects of rapid cell multiplication in prokaryotes with extremely short generation times.
4. Analyses of both unicellular and multicellular organisms show that there is no universal metabolic scaling relationship, and that variation in metabolic scaling relationships is systematically and possibly universally related to metabolic level. 相似文献
2. Here I show that the scaling slopes of rates of respiration and growth are related to the metabolic level of a variety of unicellular organisms, as similarly occurs for respiration rates in multicellular organisms.
3. The recently proposed 'metabolic-level boundaries hypothesis' provides insight into these effects of metabolic level. As predicted, the scaling slopes for resting (endogenous) respiration rate in prokaryotes, algae and protozoans are negatively related to metabolic level; and in protozoans, the scaling slope increases with starvation. Also as predicted, the scaling slopes of growth rate in algae and protozoans are negatively related to growth level. Unexpectedly, opposite effects of starvation on the metabolic scaling slopes of unicellular prokaryotes (compared to that of eukaryotes) may be a spurious result of respiration measurements that did not adequately consider the effects of rapid cell multiplication in prokaryotes with extremely short generation times.
4. Analyses of both unicellular and multicellular organisms show that there is no universal metabolic scaling relationship, and that variation in metabolic scaling relationships is systematically and possibly universally related to metabolic level. 相似文献
69.
Nikodem J. Popławski Ubirajara Agero J. Scott Gens Maciej Swat James A. Glazier Alexander R. A. Anderson 《Bulletin of mathematical biology》2009,71(5):1189-1227
We study the interface morphology of a 2D simulation of an avascular tumor composed of identical cells growing in an homogeneous
healthy tissue matrix (TM), in order to understand the origin of the morphological changes often observed during real tumor growth. We use the Glazier–Graner–Hogeweg
model, which treats tumor cells as extended, deformable objects, to study the effects of two parameters: a dimensionless diffusion-limitation
parameter defined as the ratio of the tumor consumption rate to the substrate transport rate, and the tumor-TM surface tension.
We model TM as a nondiffusing field, neglecting the TM pressure and haptotactic repulsion acting on a real growing tumor;
thus, our model is appropriate for studying tumors with highly motile cells, e.g., gliomas. We show that the diffusion-limitation
parameter determines whether the growing tumor develops a smooth (noninvasive) or fingered (invasive) interface, and that
the sensitivity of tumor morphology to tumor-TM surface tension increases with the size of the dimensionless diffusion-limitation
parameter. For large diffusion-limitation parameters, we find a transition (missed in previous work) between dendritic structures,
produced when tumor-TM surface tension is high, and seaweed-like structures, produced when tumor-TM surface tension is low.
This observation leads to a direct analogy between the mathematics and dynamics of tumors and those observed in nonbiological
directional solidification. Our results are also consistent with the biological observation that hypoxia promotes invasive
growth of tumor cells by inducing higher levels of receptors for scatter factors that weaken cell-cell adhesion and increase
cell motility. These findings suggest that tumor morphology may have value in predicting the efficiency of antiangiogenic
therapy in individual patients. 相似文献
70.
Niels de Fine Olivarius Volkert Siersma Anni BS Nielsen Lars J Hansen Lotte Rosenvinge Carl Erik Mogensen 《BMC endocrine disorders》2010,10(1):1-12