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排序方式: 共有766条查询结果,搜索用时 15 毫秒
71.
72.
Koch LG Green CL Lee AD Hornyak JE Cicila GT Britton SL 《American journal of physiology. Regulatory, integrative and comparative physiology》2005,288(2):R466-R472
An inverse relationship between initial level of physical capacity and the magnitude of response to training is termed the principle of initial value. We tested the operation of this principle under experimental conditions of minimal genetic and environmental variation. Inbred rat strains previously identified as genetic models of low [Copenhagen (COP)] and high [Dark Agouti (DA)] intrinsic (untrained) exercise capacity were trained for 8 wk on a treadmill using two disparate protocols: 1) a relative mode where each rat exercised daily according to its initial capacity, and 2) an absolute mode where both strains received the same amount of training independent of initial capacity. Response to exercise was the change in running capacity as estimated by meters run to exhaustion before and after training. When trained with the relative mode, COP rats gained 88 m (+21%; NS) whereas DA rats increased distance run by 228 m (+36%; P < 0.001). When each strain trained with the same absolute amount of training, the COP strain showed essentially no change (-6 m, -2%) and the DA strain gained 325 m (+49%; P < 0.009). Differences in response to exercise between the COP and DA could not be explained by body mass differences, oxidative enzyme activity (citrate synthase or ATP), or spontaneous behavioral activity. Our data demonstrate that genetic factors causative of high response to exercise are not uniquely associated with genetic factors for low intrinsic capacity and thus are not in accord with the principle of initial value. 相似文献
73.
74.
Photobiomodulation directly benefits primary neurons functionally inactivated by toxins: role of cytochrome c oxidase 总被引:9,自引:0,他引:9
Wong-Riley MT Liang HL Eells JT Chance B Henry MM Buchmann E Kane M Whelan HT 《The Journal of biological chemistry》2005,280(6):4761-4771
Far red and near infrared (NIR) light promotes wound healing, but the mechanism is poorly understood. Our previous studies using 670 nm light-emitting diode (LED) arrays suggest that cytochrome c oxidase, a photoacceptor in the NIR range, plays an important role in therapeutic photobiomodulation. If this is true, then an irreversible inhibitor of cytochrome c oxidase, potassium cyanide (KCN), should compete with LED and reduce its beneficial effects. This hypothesis was tested on primary cultured neurons. LED treatment partially restored enzyme activity blocked by 10-100 microm KCN. It significantly reduced neuronal cell death induced by 300 microm KCN from 83.6 to 43.5%. However, at 1-100 mm KCN, the protective effects of LED decreased, and neuronal deaths increased. LED significantly restored neuronal ATP content only at 10 microm KCN but not at higher concentrations of KCN tested. Pretreatment with LED enhanced efficacy of LED during exposure to 10 or 100 microm KCN but did not restore enzyme activity to control levels. In contrast, LED was able to completely reverse the detrimental effect of tetrodotoxin, which only indirectly down-regulated enzyme levels. Among the wavelengths tested (670, 728, 770, 830, and 880 nm), the most effective ones (830 nm, 670 nm) paralleled the NIR absorption spectrum of oxidized cytochrome c oxidase, whereas the least effective wavelength, 728 nm, did not. The results are consistent with our hypothesis that the mechanism of photobiomodulation involves the up-regulation of cytochrome c oxidase, leading to increased energy metabolism in neurons functionally inactivated by toxins. 相似文献
75.
76.
Saunders BM Tran S Ruuls S Sedgwick JD Briscoe H Britton WJ 《Journal of immunology (Baltimore, Md. : 1950)》2005,174(8):4852-4859
TNF is critical for immunity against Mycobacterium tuberculosis infection; however, the relative contributions of the soluble and transmembrane forms of TNF in this immunity are unknown. Using memTNF mice, which express only the transmembrane form of TNF, we have addressed this question. Wild-type (WT), TNF-/-, and transmembrane TNF (memTNF) mice were infected with M. tuberculosis by aerosol. TNF-/- mice developed overwhelming infection with extensive pulmonary necrosis and died after only 33 days. memTNF mice, like WT mice, contained bacterial growth for over 16 wk, developed an Ag-specific T cell response, and initially displayed compact granulomas, comprised of both lymphocytes and macrophages. Expression of mRNA for the chemokines CXCL10, CCL3, CCL5, and CCL7 was comparable in both WT and memTNF mice. As the infection progressed, however, the pulmonary lesions in memTNF mice became larger and more diffuse, with increased neutrophil accumulation and necrosis. This was accompanied by increased influx of activated memory T cells into the lungs of memTNF mice. Eventually, these mice succumbed to infection with a mean time to death of 170 days. The expression of memTNF on T cells is functionally important because the transfer of T cells from memTNF, but not TNF-/- mice, into either RAG-/- or TNF-/- mice conferred the same survival advantage on the M. tuberculosis-infected recipient mice, as the transfer of WT T cells. Therefore, memTNF, in the absence of soluble TNF, is sufficient to control acute, but not chronic, M. tuberculosis infection, in part through its expression on T cells. 相似文献
77.
78.
B Walsh R B Hooks J E Hornyak L G Koch S L Britton M C Hogan 《Journal of applied physiology》2006,100(6):1765-1769
Qualitative and quantitative measures of mitochondrial function were performed in rats selectively bred 15 generations for intrinsic aerobic high running capacity (HCR; n = 8) or low running capacity (LCR; n=8). As estimated from a speed-ramped treadmill exercise test to exhaustion (15 degrees slope; initial velocity of 10 m/min, increased 1 m/min every 2 min), HCR rats ran 10 times further (2,375+/-80 m) compared with LCR rats (238+/-12 m). Fiber bundles were obtained from the soleus and chemically permeabilized. Respiration was measured 1) in the absence of ADP, 2) in the presence of a submaximally stimulating concentration of ADP (0.1 mM ADP, with and without 20 mM creatine), and 3) in the presence of a maximally stimulating concentration of ADP (2 mM). Although non-ADP-stimulated and maximally ADP-stimulated rates of respiration were 13% higher in HCR compared with LCR, the difference was not statistically significant (P>0.05). Despite a similar rate of respiration in the presence of 0.1 mM ADP, HCR rats demonstrated a higher rate of respiration in the presence of 0.1 mM ADP+20 mM creatine (HCR 33% higher vs. LCR, P<0.05). Thus mitochondria from HCR rats exhibit enhanced mitochondrial sensitivity to creatine (i.e., the ability of creatine to decrease the Km for ADP). We propose that increased respiratory sensitivity to ADP in the presence of creatine can effectively increase muscle sensitivity to ADP during exercise (when creatine is increased) and may be, in part, a contributing factor for the increased running capacity in HCR rats. 相似文献
79.
Ericson PG Anderson CL Britton T Elzanowski A Johansson US Källersjö M Ohlson JI Parsons TJ Zuccon D Mayr G 《Biology letters》2006,2(4):543-547
Patterns of diversification and timing of evolution within Neoaves, which includes almost 95% of all bird species, are virtually unknown. On the other hand, molecular data consistently indicate a Cretaceous origin of many neoavian lineages and the fossil record seems to support an Early Tertiary diversification. Here, we present the first well-resolved molecular phylogeny for Neoaves, together with divergence time estimates calibrated with a large number of stratigraphically and phylogenetically well-documented fossils. Our study defines several well-supported clades within Neoaves. The calibration results suggest that Neoaves, after an initial split from Galloanseres in Mid-Cretaceous, diversified around or soon after the K/T boundary. Our results thus do not contradict palaeontological data and show that there is no solid molecular evidence for an extensive pre-Tertiary radiation of Neoaves. 相似文献
80.
Multiple GTPases participate in the assembly of the large ribosomal subunit in Bacillus subtilis
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Schaefer L Uicker WC Wicker-Planquart C Foucher AE Jault JM Britton RA 《Journal of bacteriology》2006,188(23):8252-8258
GTPases have been demonstrated to be necessary for the proper assembly of the ribosome in bacteria and eukaryotes. Here, we show that the essential GTPases YphC and YsxC are required for large ribosomal subunit biogenesis in Bacillus subtilis. Sucrose density gradient centrifugation of large ribosomal subunits isolated from YphC-depleted cells and YsxC-depleted cells indicates that they are similar to the 45S intermediate previously identified in RbgA-depleted cells. The sedimentation of the large-subunit intermediate isolated from YphC-depleted cells was identical to the intermediate found in RbgA-depleted cells, while the intermediate isolated from YsxC-depleted cells sedimented slightly slower than 45S, suggesting that it is a novel intermediate. Analysis of the protein composition of the large-subunit intermediates isolated from either YphC-depleted cells or YsxC-depleted cells indicated that L16 and L36 are missing. Purified YphC and YsxC are able to interact with the ribosome in vitro, supporting a direct role for these two proteins in the assembly of the 50S subunit. Our results indicate that, as has been demonstrated for Saccharomyces cerevisiae ribosome biogenesis, bacterial 50S ribosome assembly requires the function of multiple essential GTPases. 相似文献