Increased lung volume limits endurance of inspiratory muscles

We examined the influence of lung volume on the ability of normal subjects to sustain breathing against inspiratory resistive loading. Four normal subjects breathed on a closed circuit in which inspiration was loaded by a flow resistor. Subjects were assigned a series of breathing tasks over a range of pressures and flows. In each task there was a specified resistor and also targets for either mean esophageal or airway opening pressure, respiratory frequency, and duty cycle. Endurance was assessed as the length of time to failure of the assigned task. The prime experimental variable was lung volume, which was increased by approximately 1 liter during some tasks; 8 cmH2O continuous positive airway pressure was applied to increase lung volume without increasing elastic load. As previously shown (McCool et al.J. Appl. Physiol. 60: 299-303, 1986), for tasks that could be sustained for the same time, there was an inverse linear relationship of mean esophageal pressure with inspiratory flow rate. This trade-off of pressure and flow was apparent both with and without the increase of lung volume. Comparable tasks, however, could not be sustained as long at the higher lung volumes. This effect of volume on endurance was greater for tasks characterized by high inspiratory pressures and low flow rates than for tasks that could be sustained for the same time but that had lower inspiratory pressures and higher flow rates. This is probably due to the effects of shortening of the sarcomere on fatiguability. Increased lung volume, per se, may contribute to respiratory failure because of increased inspiratory muscle fatiguability by mechanisms independent of elastic load.     

Refining the role of phenology in regulating gross ecosystem productivity across European peatlands

The role of plant phenology as a regulator for gross ecosystem productivity (GEP) in peatlands is empirically not well constrained. This is because proxies to track vegetation development with daily coverage at the ecosystem scale have only recently become available and the lack of such data has hampered the disentangling of biotic and abiotic effects. This study aimed at unraveling the mechanisms that regulate the seasonal variation in GEP across a network of eight European peatlands. Therefore, we described phenology with canopy greenness derived from digital repeat photography and disentangled the effects of radiation, temperature and phenology on GEP with commonality analysis and structural equation modeling. The resulting relational network could not only delineate direct effects but also accounted for possible effect combinations such as interdependencies (mediation) and interactions (moderation). We found that peatland GEP was controlled by the same mechanisms across all sites: phenology constituted a key predictor for the seasonal variation in GEP and further acted as a distinct mediator for temperature and radiation effects on GEP. In particular, the effect of air temperature on GEP was fully mediated through phenology, implying that direct temperature effects representing the thermoregulation of photosynthesis were negligible. The tight coupling between temperature, phenology and GEP applied especially to high latitude and high altitude peatlands and during phenological transition phases. Our study highlights the importance of phenological effects when evaluating the future response of peatland GEP to climate change. Climate change will affect peatland GEP especially through changing temperature patterns during plant phenologically sensitive phases in high latitude and high altitude regions.     

Structure of frozen–hydrated triad junctions: A case study in motif searching inside tomograms

We used tomographic reconstructions of frozen–hydrated triad junctions to determine the structure of the macromolecular complex associated with calcium release from the sarcoplasmic reticulum (SR), during excitation–contraction coupling. Using a rapid motif search algorithm with a reference motif of the ryanodine receptor (RyR) provided by single-particle cryo-electron microscopy, 49 receptors were located in five tomograms. Following co-alignment of the receptors and division into quadrants centered on the 4-fold symmetry axis, the receptors were classified using multivariate statistics. Global and class averages reveal that the SR membrane in the vicinity of the receptor is highly curved, creating an open vestibule with a gap of 4 nm between the receptor pore and the calsequestrin layer in the SR lumen. The in-plane densities in the calsequestrin layer have paracrystalline order, consistent with the packing of calsequestrin dimers in the three-dimensional crystal structure. Faint densities (“tethers”) extend to the calsequestrin layer from densities in the SR membrane located 15 nm from the symmetry axis of the RyR. In a class average of RyRs with proximal transverse tubules (TT), a cytoplasmic density is observed near the receptor that could represent the most consistent location of tethers observed in tomograms between the SR and TT membranes.     

Angularis oculi vein blood flow modulates the magnitude but not the control of selective brain cooling in sheep

To investigate the role of the angularis oculi vein (AOV) in selective brain cooling (SBC), we measured brain and carotid blood temperatures in six adult female Dorper sheep. Halfway through the study, a section of the AOV, just caudal to its junction with the dorsal nasal vein, was extirpated on both sides. Before and after AOV surgery, the sheep were housed outdoors at 21-22°C and were exposed in a climatic chamber to daytime heat (40°C) and water deprivation for 5 days. In sheep outdoors, SBC was significantly lower after the AOV had been cut, with its 24-h mean reduced from 0.25 to 0.01°C (t(5) = 3.06, P = 0.03). Carotid blood temperature also was lower (by 0.28°C) at all times of day (t(5) = 3.68, P = 0.01), but the pattern of brain temperature was unchanged. The mean threshold temperature for SBC was not different before (38.85 ± 0.28°C) and after (38.85 ± 0.39°C) AOV surgery (t(5) =0.00, P = 1.00), but above the threshold, SBC magnitude was about twofold less after surgery. SBC after AOV surgery also was less during heat exposure and water deprivation. However, SBC increased progressively by the same magnitude (0.4°C) over the period of water deprivation, and return of drinking water led to rapid cessation of SBC in sheep before and after AOV surgery. We conclude that the AOV is not the only conduit for venous drainage contributing to SBC in sheep and that, contrary to widely held opinion, control of SBC does not involve changes in the vasomotor state of the AOV.     

Retrofit implementation of Zernike phase plate imaging for cryo-TEM

In-focus phase-plate imaging is particularly beneficial for cryo-TEM because it offers a substantial overall increase in image contrast, without an electron dose penalty, and it simplifies image interpretation. We show how phase-plate cryo-TEM can be implemented with an appropriate existing TEM, and provide a basic practical introduction to use of thin-film (carbon) phase plates. We point out potential pitfalls of phase-plate operation, and discuss solutions. We provide information on evaluating a particular TEM for its suitability.     

Glasshouse vs field experiments: do they yield ecologically similar results for assessing N impacts on peat mosses?

? Peat bogs have accumulated more atmospheric carbon (C) than any other terrestrial ecosystem today. Most of this C is associated with peat moss (Sphagnum) litter. Atmospheric nitrogen (N) deposition can decrease Sphagnum production, compromising the C sequestration capacity of peat bogs. The mechanisms underlying the reduced production are uncertain, necessitating multifactorial experiments. ? We investigated whether glasshouse experiments are reliable proxies for field experiments for assessing interactions between N deposition and environment as controls on Sphagnum N concentration and production. We performed a meta-analysis over 115 glasshouse experiments and 107 field experiments. ? We found that glasshouse and field experiments gave similar qualitative and quantitative estimates of changes in Sphagnum N concentration in response to N application. However, glasshouse-based estimates of changes in production--even qualitative assessments-- diverged from field experiments owing to a stronger N effect on production response in absence of vascular plants in the glasshouse, and a weaker N effect on production response in presence of vascular plants compared to field experiments. ? Thus, although we need glasshouse experiments to study how interacting environmental factors affect the response of Sphagnum to increased N deposition, we need field experiments to properly quantify these effects.     

CD95 ligand (CD95L) immunohistochemistry: a critical study on 12 antibodies

In recent years, some studies on the expression of CD95(Fas/APO-1) ligand (CD95L) in tissues or cells raised concerns about the specificity of the antibodies used. We therefore tested 12 CD95L antibodies for their reliability in immunocyto/histochemistry by (i) staining CD95L-transfected and control CV-1/EBNA cells and (ii) comparing staining patterns in immunohistochemically labeled tissue sections with the localization of CD95L+ cells in in situ hybridization. While G247-4, NOK-1, NOK-2, 4H9, and MIKE-1 stained CD95L-transfected cells and did not significantly bind to controls, G247-4 was the only antibody giving satisfying signals in tissue sections perfectly matching the distribution of CD95L+ cells by in situ hybridization. MAb 33, C-20, and N-20 comparably stained both transfected and control cells and showed considerable background or falsely positive staining in sections. MIKE-2, 8B8, A11, and 4A5 did not or only very faintly bind to either cells and, thus, were not tested on sections. We conclude that G247-4 is the only tested antibody that is recommendable for immunohistochemistry.     

Potential for ammonia recapture by farm woodlands: design and application of a new experimental facility

There has been increasing pressure on farmers in Europe to reduce the emissions of ammonia from their land. Due to the current financial climate in which farmers have to operate, it is important to identify ammonia control measures that can be adopted with minimum cost. The planting of trees around farmland and buildings has been identified as a potentially effective and low-cost measure to enhance ammonia recapture at a farm level and reduce long-range atmospheric transport. This work assesses experimentally what fraction of ammonia farm woodlands could potentially remove from the atmosphere. We constructed an experimental facility in southern Scotland to simulate a woodland shelterbelt planted in proximity to a small poultry unit. By measuring horizontal and vertical ammonia concentration profiles within the woodland, and comparing this to the concentration of an inert tracer (SF6) we estimate the depletion of ammonia due to dry deposition to the woodland canopy. Together with measurements of mean ammonia concentrations and throughfall fluxes of nitrogen, this information is used to provide a first estimate of the fraction of emitted ammonia that is recaptured by the woodland canopy. Analysis of these data give a lower limit of recapture of emitted ammonia, at the experimental facility, of 3%. By careful design of shelterbelt woodlands this figure could be significantly higher.