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101.
The antagonist potencies of methylnaloxone and naloxone were measured for morphine in the isolated guinea pig ileum by the pA2 method and a potency ratio determined. A second potency ratio was determined by comparing the concentration of each antagonist required to produce abstinence-like contractures of ileal tissues from morphine-treated guinea pigs. If the latter response required penetration of the cell membrane lipid bilayer, one would expect methylnaloxone, a quaternary amine, to be significantly less potent than naloxone. Comparison of potency ratios for methylnaloxone and naloxone did not support this hypothesis. 相似文献
102.
Vegetation and water velocity effects on patterns of sediment deposition were tested by monitoring sedimentation rates in dense cattail, open water, and transitional vegetation zones at distances of 5, 10, and 20 m from the inflows of two experimental wetland basins at the Des Plaines River Wetlands Demonstration Project, northeastern Illinois, USA. One basin received a high hydrologic load (up to 50 cm/wk) and one basin received a low load (up to 6 cm/wk). Sediment deposition rates within 20 m of the inflows reached 3300 g dry wt m−2 day−1 in the high-load basin and 700 g dry wt m−2 day−1 in the low-load basin. Vegetation patterns did not have a significant effect (P > 0.05) on sediment deposition rates in the high-load basin, whereas water velocity effects on rates of sedimentation were significant (P < 0.01) in three of four periods of monitoring. In the low-load basin, vegetation effects were significant (P < 0.01) during the entire period of investigation. Experimental research at this scale aids in the assessment of design criteria for constructed wetlands. 相似文献
103.
104.
Radioiodinated derivatives of the metabolically stable enkephalin analogues, [DAla2,Leu5]- and [DAla2,DLeu5]-enkephalin, have been prepared. Such derivatives show sterospecific binding to receptors in brain homogenates and some neuroblastoma cell lines such as NG108-15 and N4TG1. The relative effects of levorphanol and dextrorphan and Na+ and Mn++ ions on enkephalin binding in brain and cells indicate that the iodinated derivatives are interacting with opiate receptors. Levorphanol is considerably more potent in displacing specifically bound enkephalin than dextrorphan. Sodium ions at physiological concentrations decrease enkephalin binding whereas manganese ions enhance it. Unlabelled monoiodo derivatives retain high potency in the guinea-pig ileum, mouse vas deferens and receptor binding assays. Unlabelled diiodo derivatives show far lower potency in these assays. It is concluded that radio-iodinated derivatives containing one iodine per molecule retain high affinity for the opiate receptor but diiodo derivatives do not. 相似文献
105.
A comparison of rat brain and liver β-hydroxybutyrate dehydrogenase (EC 1.1.1.30) has revealed that significant differences exist between the enzymes with regard to their kinetic and physical properties. In contrast to the liver enzyme, brain β-hydroxybutyrate dehydrogenase is rapidly inactivated at 46° and is unstable when stored at ?20°. The brain dehydrogenase was found to have a larger Km (apparent) for the 3-acetylpyridine analog of NAD+, and a greater energy of activation in the direction of β-hydroxybutyrate oxidation than the liver enzyme. In the reverse direction, the brain and liver dehydrogenase exhibit substrate inhibition by NADH (0.22 mM and 0.36 mM, respectively). The brain and liver β-hydroxybutyrate dehydrogenase did not differ significantly with regard to the Michaelis-Menten constants measured for NAD+ and β-hydroxybutyrate. The Km constants of brain β-hydroxybutyrate dehydrogenase for acetoacetate (0.39 mM) and NADH (0.05 mM) were lower than those determined for the liver enzyme, acetoacetate (0.73 mM) and NADH (0.35 mM) respectively. These results suggest that the β-hydroxybutyrate dehydrogenase from rat brain and liver are isozymic variants. 相似文献
106.
107.
Nitrogen and phosphorus are the primary nutrients that affect water quality in streams in the midwestern USA and high concentrations
of these nutrients tend to increase algal biomass. However, how nutrients interact with physical controls in regulating algal
biomass is not well known in agricultural streams. Eighteen streams in east-central Illinois (USA) were sampled during June
and September 2003 to analyze factors possibly regulating algal biomass. Additionally, two shaded and two non-shaded sites
in the Embarras River in east-central Illinois were sampled intensively from June to December 2003. Both sestonic and periphytic
chlorophyll-a (chl-a) were analyzed, and periphytic chl-a was assessed on natural substrata and unglazed ceramic tiles. Although high concentrations of nutrients were found in these
streams (mean total P = 0.09–0.122 mg l−1 and mean NO3-N=4.4–8.4 mg l−1), concentrations of sestonic chl-a were low among all sites and both sampling periods (<18 mg m−3, median values of 5 and 3 in June and September, respectively). Filamentous algae were an important component of the algal
communities in streams with stable substrata. Periphytic chl-a was generally not related to the concentration of N or P in the water column, and in non-shaded streams periphyton appeared
at times to be light-limited due to turbid water. Turbidity was found to be an important factor controlling chl-a on ceramic tiles across the 18 sites and for the Embarras River sites; chl-a decreased exponentially in concentration (132–0 mg m−2) as turbidity increased from 4 to 39 NTU (r
2 = 0.80). In general, the interaction between hydrology and light (turbidity) likely controlled algal biomass in these nutrient-rich,
agricultural streams. 相似文献
108.
Habitat fragmentation has been cited as one of the critical reasons for biodiversity loss. Establishing connected nature reserve networks is an effective way to reduce habit fragmentation. However, the resources devoted to nature reserves have always been scarce. Therefore it is important to allocate our scarce resources in an optimal way. The optimal design of a reserve network which is effective both ecologically and economically has become an important research topic in the reserve design literature. The problem of optimal selection of a subset from a larger group of potential habitat sites is solved using either heuristic or formal optimization methods. The heuristic methods, although flexible and computationally fast, can not guarantee the solution is optimal therefore may lead to scarce resources being used in an ineffective way. The formal optimization methods, on the other hand, guarantees the solution is optimal, but it has been argued that it would be difficult to model site selection process using optimization models, especially when spatial attributes of the reserve have to be taken into account. This paper presents a linear integer programming model for the design of a minimal connected reserve network using a graph theory approach. A connected tree is determined corresponding to a connected reserve. Computational performance of the model is tested using datasets randomly generated by the software GAMS. Results show that the model can solve a connected reserve design problem which includes 100 potential sites and 30 species in a reasonable period of time. As an empirical application, the model is applied to the protection of endangered and threatened bird species in the Cache River basin area in Illinois, US. Two connected reserve networks are determined for 13 bird species. 相似文献
109.
Cells were grown as primary monolayer cultures from kidney cortex of guinea pigs (nonhibernators), hamsters and ground squirrels (both hibernating species). When plates of cells were placed at 5 °C, cells of guinea pigs lost 37% of their K+ in 2 h and those of the hibernator lost about 10%.Uptake of 42K into the cells exhibited a simple, single exponential time course at both temperatures. Unidirectional efflux of K+ was equal to K+ influx in all cultures at 37 °C and, within limits of error, in hibernator cells at 5 °C. Efflux was 3- to 5-fold greater than influx in guinea pig cells at 5 °C.After 2 h in the cold the ouabain-sensitive K+ influx remaining (7–15% of that at 37 °C) was about the same in the cells of the 3 species. Cells from active hamsters and from hibernating ground squirrels, however, exhibited significantly greater pump activity after 45 min in the cold (19 and 14%, respectively). The stimulation of K+ influx by increasing [K+]o did not show an increase in Km+ at 5 °C in cells of guinea pigs and ground squirrels. Lowering [K+]c and/or raising [Na+]c by treatment in low- and high-K+ media caused only slight stimulation of K+ influx, except in cells of ground squirrels at 5 °C in which the stimulation was at least 11-times greater than at 37 °C or in cells of guinea pigs at either temperature.This altered kinetic response of K+ transport to cytoplasmic ion stimulation with cooling accounted for about one-third of the improved regulation of K+ at 5 °C in ground squirrel cells; the other two-thirds was attributable to a greater decrease in K+ leak with cooling. The inhibition of active transport by cold in all 3 species was much less severe than that previously seen in any (Na+ + K+)-ATPase of mammalian cells. 相似文献
110.