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111.
Winter is energetically challenging for small herbivores because of greater energy requirements for thermogenesis at a time when little energy is available. We formulated a model predicting optimal wintering body size, accounting for the scaling of both energy expenditure and assimilation to body size, and the trade-off between survival benefits of a large size and avoiding survival costs of foraging. The model predicts that if the energy cost of maintaining a given body mass differs between environments, animals should be smaller in the more demanding environments, and there should be a negative correlation between body mass and daily energy expenditure (DEE) across environments. In contrast, if animals adjust their energy intake according to variation in survival costs of foraging, there should be a positive correlation between body mass and DEE. Decreasing temperature always increases equilibrium DEE, but optimal body mass may either increase or decrease in colder climates depending on the exact effects of temperature on mass-specific survival and energy demands. Measuring DEE with doubly labeled water on wintering Microtus agrestis at four field sites, we found that DEE was highest at the sites where voles were smallest despite a positive correlation between DEE and body mass within sites. This suggests that variation in wintering body mass between sites was due to variation in food quality/availability and not adjustments in foraging activity to varying risks of predation. 相似文献
112.
Fang X Song Y Zemans R Hirsch J Matthay MA 《American journal of physiology. Lung cellular and molecular physiology》2004,287(1):L104-L110
Previous studies have used fluid-instilled lungs to measure net alveolar fluid transport in intact animal and human lungs. However, intact lung studies have two limitations: the contribution of different distal lung epithelial cells cannot be studied separately, and the surface area for fluid absorption can only be approximated. Therefore, we developed a method to measure net vectorial fluid transport in cultured rat alveolar type II cells using an air-liquid interface. The cells were seeded on 0.4-microm microporous inserts in a Transwell system. At 96 h, the transmembrane electrical resistance reached a peak level (1,530 +/- 115 Omega.cm(2)) with morphological evidence of tight junctions. We measured net fluid transport by placing 150 microl of culture medium containing 0.5 microCi of (131)I-albumin on the apical side of the polarized cells. Protein permeability across the cell monolayer, as measured by labeled albumin, was 1.17 +/- 0.34% over 24 h. The change in concentration of (131)I-albumin in the apical fluid was used to determine the net fluid transported across the monolayer over 12 and 24 h. The net basal fluid transport was 0.84 microl.cm(-2).h(-1). cAMP stimulation with forskolin and IBMX increased fluid transport by 96%. Amiloride inhibited both the basal and stimulated fluid transport. Ouabain inhibited basal fluid transport by 93%. The cultured cells retained alveolar type II-like features based on morphologic studies, including ultrastructural imaging. In conclusion, this novel in vitro system can be used to measure net vectorial fluid transport across cultured, polarized alveolar epithelial cells. 相似文献
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Wu Q Martin RJ Rino JG Jeyaseelan S Breed R Chu HW 《American journal of physiology. Lung cellular and molecular physiology》2007,292(5):L1064-L1072
The original hygiene hypothesis suggests that early childhood respiratory infections preceding allergen exposure may decrease the prevalence of allergic diseases. We have recently demonstrated that Mycoplasma pneumoniae infection preceding allergen exposure reduced allergic responses in mice. However, the molecular mechanisms underlying the protective role of M. pneumoniae in allergic responses, particularly airway mucin production, remain unclear. Wild-type and Toll-like receptor 2 (TLR2)-deficient mice with a respiratory M. pneumoniae infection preceding allergen (ovalbumin) challenge were utilized to determine the regulatory role of TLR2-IFN-gamma signaling pathway in airway mucin expression. Furthermore, air-liquid interface cultures of mouse primary tracheal epithelial cells were performed to examine the effects of IFN-gamma on mucin expression. In wild-type mice, M. pneumoniae infection preceding allergen challenge significantly reduced airway mucins but increased IFN-gamma. In sharp contrast, in TLR2-deficient mice, M. pneumoniae preceding allergen challenge resulted in increased mucin protein without a noticeable change of IFN-gamma. In cultured mouse primary tracheal epithelial cells, IFN-gamma was shown to directly inhibit mucin expression in a dose-dependent manner. Our study demonstrates for the first time that a respiratory M. pneumoniae infection preceding allergen challenge reduces airway epithelial mucin expression in part through TLR2-IFN-gamma signaling pathway. A bacterial infection in asthmatic subjects with weakened TLR2-IFN-gamma signaling may result in an exaggerated airway mucin production. 相似文献
117.
Ivan Birukou Rachel L. Schweers John S. Olson 《The Journal of biological chemistry》2010,285(12):8840-8854
The role of the distal histidine in regulating ligand binding to adult human hemoglobin (HbA) was re-examined systematically by preparing His(E7) to Gly, Ala, Leu, Gln, Phe, and Trp mutants of both Hb subunits. Rate constants for O2, CO, and NO binding were measured using rapid mixing and laser photolysis experiments designed to minimize autoxidation of the unstable apolar E7 mutants. Replacing His(E7) with Gly, Ala, Leu, or Phe causes 20–500-fold increases in the rates of O2 dissociation from either Hb subunit, demonstrating unambiguously that the native His(E7) imidazole side chain forms a strong hydrogen bond with bound O2 in both the α and β chains (ΔGHis(E7)H-bond ≈ −8 kJ/mol). As the size of the E7 amino acid is increased from Gly to Phe, decreases in kO2′, kNO′, and calculated bimolecular rates of CO entry (kentry′) are observed. Replacing His(E7) with Trp causes further decreases in kO2′, kNO′, and kentry′ to 1–2 μm−1 s−1 in β subunits, whereas ligand rebinding to αTrp(E7) subunits after photolysis is markedly biphasic, with fast kO2′, kCO′, and kNO′ values ≈150 μm−1 s−1 and slow rate constants ≈0.1 to 1 μm−1 s−1. Rapid bimolecular rebinding to an open α subunit conformation occurs immediately after photolysis of the αTrp(E7) mutant at high ligand concentrations. However, at equilibrium the closed αTrp(E7) side chain inhibits the rate of ligand binding >200-fold. These data suggest strongly that the E7 side chain functions as a gate for ligand entry in both HbA subunits. 相似文献
118.
Clarke MB Wright R Irwin D Bose S Van Rheen Z Birari R Stenmark KR McCord JM Nozik-Grayck E 《Free radical biology & medicine》2010,49(12):2032-2039
Delivery of recombinant superoxide dismutase to the lung is limited by its short half-life and poor tissue penetration. We hypothesized that a chimeric protein, SOD2/3, containing the enzymatic domain of manganese superoxide dismutase (SOD2) and the heparan-binding domain of extracellular superoxide dismutase (SOD3), would allow for the delivery of more sustained lung and pulmonary vascular antioxidant activity compared to SOD2. We administered SOD2/3 to rats by intratracheal (i.t.), intraperitoneal (i.p.), or intravenous (i.v.) routes and evaluated the presence, localization, and activity of lung SOD2/3 1 day later using Western blot, immunohistochemistry, and SOD activity gels. The effect of i.t. SOD2/3 on the pulmonary and systemic circulation was studied in vivo in chronically catheterized rats exposed to acute hypoxia. Active SOD2/3 was detected in lung 1 day after i.t. administration but not detected after i.p. or i.v. SOD2/3 administration or i.t. SOD2. The physiologic response to acute hypoxia, vasoconstriction in the pulmonary circulation and vasodilation in the systemic circulation, was enhanced in rats treated 1 day earlier with i.t. SOD2/3. These findings indicate that i.t. administration of SOD2/3 effectively delivers sustained enzyme activity to the lung as well as pulmonary circulation and has a longer tissue half-life compared to native SOD2. Further testing in models of chronic lung or pulmonary vascular diseases mediated by excess superoxide should consider the longer tissue half-life of SOD2/3 as well as its potential systemic vascular effects. 相似文献
119.
EF-G-independent reactivity of a pre-translocation-state ribosome complex with the aminoacyl tRNA substrate puromycin supports an intermediate (hybrid) state of tRNA binding 总被引:3,自引:0,他引:3 下载免费PDF全文
Following peptide-bond formation, the mRNA:tRNA complex must be translocated within the ribosomal cavity before the next aminoacyl tRNA can be accommodated in the A site. Previous studies suggested that following peptide-bond formation and prior to EF-G recognition, the tRNAs occupy an intermediate (hybrid) state of binding where the acceptor ends of the tRNAs are shifted to their next sites of occupancy (the E and P sites) on the large ribosomal subunit, but where their anticodon ends (and associated mRNA) remain fixed in their prepeptidyl transferase binding states (the P and A sites) on the small subunit. Here we show that pre-translocation-state ribosomes carrying a dipeptidyl-tRNA substrate efficiently react with the minimal A-site substrate puromycin and that following this reaction, the pre-translocation-state bound deacylated tRNA:mRNA complex remains untranslocated. These data establish that pre-translocation-state ribosomes must sample or reside in an intermediate state of tRNA binding independent of the action of EF-G. 相似文献
120.
Williams TM Medina F Badano I Hazan RB Hutchinson J Muller WJ Chopra NG Scherer PE Pestell RG Lisanti MP 《The Journal of biological chemistry》2004,279(49):51630-51646