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951.
The effect of locomotor activity on respiration rate was studiedin the food-deprived copepod Calanus euxinus tethered to a forcesensor. The power generated by mouth appendages during cruisinglocomotion, with a frequency of 40 Hz, accounted for 0.026 and0.0031 W for metabolic and mechanical processes, respectively.To overcome total hydrodynamic drag during foraging with a meanswimming speed of 3.2 cm s1, the copepods need 0.4 x103 W, equating to 1.3% of total metabolism. The lossesof mechanical energy for body propulsion amounted to 1.3 x 103W, whilst the cost of feeding current generation run up to 1.8x 103 W, or 58% of the total. Changing of locomotor activityand respiration rate during feeding was examined separatelyin tethered and free-swimming copepods. At algal concentrationof 300 µg C L1, the magnitude of specific dynamicaction (SDA) averaged 1.2 ± 0.44 nL O2 µg C1h1 in copepodites V and females, with similar movingactivity before and during feeding. The contribution of SDAinto total metabolism varied from 23 to 85% in C. euxinus withlow activity level and constituted only 10% in active animals.In starved copepods, with low locomotor activity, feeding eventsstimulated the increase in frequency and total duration of locomotionwhich resulted in elevated energy expenditure enhancing theapparent SDA. 相似文献
952.
An analytical approach for the mechanical interaction of the self-expanding Cardiocoil stent with the stenosed artery is presented. The damage factor as the contact stress at the stent-artery interface is determined. The stent is considered as an elastic helical rod having a nonlinear pressure-displacement dependence, while the artery is modeled by an elastic cylindrical shell. An influence of a moderate relative thickness of the shell is estimated. The equations for both the stent and the artery are presented in the stent-associated helical coordinates. The computational efficiency of the model enabled to carry out a parametric study of the damage factor. Comparative examinations are conducted for the stents made of the helical rods with circular and rectangular cross sections. It was found, in particular, that, under same other conditions, the damage factor for the stent with a circular cross section may be two times larger than that for a rectangular one. 相似文献
953.
Chichirau A Flueraru M Chepelev LL Wright JS Willmore WG Durst T Hussain HH Charron M 《Free radical biology & medicine》2005,38(3):344-355
ortho-Hydroxyphenols (catechols) form a common structural unit in naturally occurring antioxidants such as polyphenols. They also show pro-oxidant characteristics which depend on their particular structure. Here we examined the acetylated versions of three catechols and a naphthalenediol for cytotoxicity to adrenal PC12-AC cells. We found that the three catechols H1 (a p-methoxycatechol), H2 (a catechol analog of alpha-tocopherol), and H4 (a dioxymethylene-substituted catechol) strongly upregulate glutathione (GSH) in 24 h, whereas 1,4-dipropyl-2,3-naphthalenediol (DPND) does not. Upregulation of GSH is primarily caused by oxidative stress in the form of hydrogen peroxide generation, and both GSH upregulation and the rate of H(2)O(2) generation correlate well with the cytotoxicity. The major source of H(2)O(2) is autoxidation in the extracellular space, which results from transport of the (deacetylated) hydroquinone form outside the cell, rather than internal redox cycling. DPND is much less cytotoxic than any of the catechols. We show that this is because it cannot form a naphthoquinone due to the energy penalty associated with the loss of aromaticity in the benzene ring adjacent to the diol functional group. The relevance of these results to the design of antioxidants is discussed. 相似文献
954.
The genus Rhodococcus is a very diverse group of bacteria that possesses the ability to degrade a large number of organic compounds, including some of the most difficult compounds with regard to recalcitrance and toxicity. They achieve this through their capacity to acquire a remarkable range of diverse catabolic genes and their robust cellular physiology. Rhodococcus appear to have adopted a strategy of hyper-recombination associated with a large genome. Notably, they harbour large linear plasmids that contribute to their catabolic diversity by acting as 'mass storage' for a large number of catabolic genes. In addition, there is increasing evidence that multiple pathways and gene homologues are present that further increase the catabolic versatility and efficiency of Rhodococcus. 相似文献
955.
The pattern of catecholaminergic innervation of the dentate gyrus (DG) of the hippocampus, particularly the relatively dense and selective noradrenergic input, creates favourable conditions for real-time monitoring of noradrenaline (NA) release following stimulation of the locus coeruleus (LC) by in vivo voltammetry. Two electrochemically active species with different temporal characteristics were registered in the DG following electrical stimulation of the LC. Several approaches, including testing of anatomical and pharmacological specificity, coating of microelectrodes with Nafion and use of fast cyclic voltammetry, were used to verify the characteristics of electrochemical responses. The first sharp peak that appeared immediately during stimulation was definitely associated with NA overflow. The second late peak was possibly attributable to ascorbic acid. We examined the characteristics of alpha-2 adrenoceptor regulation of NA release in the DG, and showed for the first time that noradrenergic terminals resemble dopaminergic terminals in their mechanisms of increasing the refilling rate of the readily releasable pool following stimulation repeated at short intervals. Amperometric registration of NA in the DG was complicated by interference with electrical activity of hippocampus. This interference could be used, after appropriate filtration, for simultaneous recording from the same microelectrode of NA release and electrical activity of the hippocampus. 相似文献
956.
Poliovirus escape from RNA interference: short interfering RNA-target recognition and implications for therapeutic approaches 总被引:17,自引:0,他引:17
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Short interfering RNAs (siRNAs) directed against poliovirus and other viruses effectively inhibit viral replication. Although RNA interference (RNAi) may provide the basis for specific antiviral therapies, the limitations of RNAi antiviral strategies are ill defined. Here, we show that poliovirus readily escapes highly effective siRNAs through unique point mutations within the targeted regions. Competitive analysis of the escape mutants provides insights into the basis of siRNA recognition. The RNAi machinery can tolerate mismatches but is exquisitely sensitive to mutations within the central region and the 3' end of the target sequence. Indeed, specific mutations in the target sequence resulting in G:U mismatches are sufficient for the virus to escape siRNA inhibition. However, using a pool of siRNAs to simultaneously target multiple sites in the viral genome prevents the emergence of resistant viruses. Our study uncovers the elegant precision of target recognition by the RNAi machinery and provides the basis for the development of effective RNAi-based therapies that prevent viral escape. 相似文献
957.
A new susceptibility locus for autosomal dominant pancreatic cancer maps to chromosome 4q32-34 总被引:4,自引:0,他引:4
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Eberle MA Pfützer R Pogue-Geile KL Bronner MP Crispin D Kimmey MB Duerr RH Kruglyak L Whitcomb DC Brentnall TA 《American journal of human genetics》2002,70(4):1044-1048
Pancreatic cancer is the fifth leading cause of cancer death in the United States. Nearly every person diagnosed with pancreatic cancer will die from it, usually in <6 mo. Familial clustering of pancreatic cancers is commonly recognized, with an autosomal dominant inheritance pattern in approximately 10% of all cases. However, the late age at disease onset and rapid demise of affected individuals markedly hamper collection of biological samples. We report a genetic linkage scan of family X with an autosomal dominant pancreatic cancer with early onset and high penetrance. For the study of this family, we have developed an endoscopic surveillance program that allows the early detection of cancer and its precursor, before family members have died of the disease. In a genomewide screening of 373 microsatellite markers, we found significant linkage (maximum LOD score 4.56 in two-point analysis and 5.36 in three-point analysis) on chromosome 4q32-34, providing evidence for a major locus for pancreatic cancer. 相似文献
958.
In the presence of Zn(CN)(2), benzylated 2-thio-2-S-(p-tolyl)pyranosyl chlorides (2) generated in situ from tri-O-benzyl-D-glucal and p-TolSCl, smoothly react with thiophene, 2-methylthiophene, furan, 2-methylfuran, and N-methylpyrrole to give heteroaryl 2-thio-2-S-(p-tolyl)-C-beta-D-glucopyranosylic compounds (C-glycosides) in good yields. Upon treatment with SnCl(4), the reaction of chlorides 2 with thiophene or 1,4-dimethoxybenzene provides the corresponding benzylated C-beta-D-glucofuranosylic derivatives. Under the same conditions, the use of 2-methylthiophene, furan, 2-methylfuran, or N-methylpyrrole yields (2S,3R,4R,5S)-1,3,4-tribenzyloxy-6,6-diheteroaryl-5-(p-tolylthio)-2-hexanoles. Treatment of 2 and mesitylene with AgBF(4) yielded 1,6-anhydro-3,4-di-O-benzyl-2-thio-2-S-(p-tolyl)-beta-D-glucose. 相似文献
959.
A novel approach to the analysis of an equilibrium two-step peptide-protein binding is developed and applied to the experimental data. The first step of the process is the release of an endogenous peptide from a binding groove and the second is the binding of an added peptide. The method developed enables us to determine consequently the maximum protein occupancy level (protein-binding capacity), the dissociation constant of an endogenous peptide, and the dissociation constant of a binding (antigenic) peptide. It is shown and confirmed by experimental data that the value of an equilibrium dissociation constant of a binding peptide could be much less than the experimental value of ED(50) (concentration of added peptide required to bind half of the protein), but not equal to that commonly assumed for major histocompatibility complex (MHC)-peptide binding. The model considered gives a clear understanding of why some peptides may be good binders to MHC protein in vitro, but do not exhibit anticipated activity on the cellular level and vice versa. 相似文献
960.
Korochkin LI Alexandrova MA Pavlova GV Bashkirov VN Revischin AV Alexenko OA Evgen'ev MB 《Tsitologiia》2002,44(8):803-806
Drosophila neuroectodermal embryonic cells were transplanted into the occipital brain region of adult rats. The first series of experiments used a transgenic strain expressing lacZ to detect the presence of Drosophila cells. The second series used a strain carrying a is lethal (ts403) in the X chromosome; this mutation strongly inhibits the synthesis of heat shock proteins (hsps) and their transport into the nuclei. Immunostaining reveals a strong induction of hsp70 in the xenografts in the first series of experiments, in which no glial scar was detectable. By contrast, where the ts mutation was xenotransplanted, the condition of xenografts was worse, and a glial scar was readily evident between the xenograft and host tissue. 相似文献