Characterization of Newly Formed and Aged Granules in the Neurohypophysis

Neurosecretory granules from the rat and bovine neurohypophysis were isolated and some of their biochemical and biophysical properties studied. Neurosecretory granules (NSG) from rat neurohypophysis were labeled, in vivo, with [35S]cysteine and isolated on isoosmotic gradients. Whereas 1 day after labeling most of the radioactivity was found in the lower part of the gradient, 35 days later the isotope was also located in the lighter NSG-containing fraction. Different analytical procedures showed that the lighter fraction, both in bovine and rat NSG, contain more subpopulations of neurophysin-like material than the heavier fraction. The first material to be released during stimulation of secretion, in vivo or in vitro, is mobilized from the heavy NSG. Isolation of rat NSG, at different times during and after dehydration of the animals, reveals that the newly synthesized material is found in the heavy NSG-containing fraction. Furthermore, the results indicate that the newly synthesized NSG are more resistant to lysis than the lighter granules. The results are discussed in relation to the maturation and degradation processes of the granule content and to the functional state of the NSG.     

Decomposition Patterns of Foliar Litter and Deadwood in Managed and Unmanaged Stands: A 13-Year Experiment in Boreal Mixedwoods

Litter decomposition is a major driver of carbon (C) and nitrogen (N) cycles in forest ecosystems and has major implications for C sequestration and nutrient availability. However, empirical information regarding long-term decomposition rates of foliage and wood remains rare. In this study, we assessed long-term C and N dynamics (12–13 years) during decomposition of foliage and wood for three boreal tree species, under a range of harvesting intensities and slash treatments. We used model selection based on the second-order Akaike’s Information Criterion to determine which decomposition model had the most support. The double-exponential model provided a good fit to C mass loss for foliage of trembling aspen, white spruce, and balsam fir, as well as aspen wood. These litters underwent a rapid initial phase of leaching and mineralisation, followed by a slow decomposition. In contrast, for spruce and fir wood, the single-exponential model had the most support. The long-term average decay rate of wood was faster than that of foliage for aspen, but not of conifers. However, we found no evidence that fir and spruce wood decomposed at slower rates than the recalcitrant fraction of their foliage. The critical C:N ratios, at which net N mineralisation began, were higher for wood than for foliage. Long-term decay rates following clear-cutting were either similar or faster than those observed in control stands, depending on litter material, tree species, and slash treatment. The critical C:N ratios were reached later and decreased for all conifer litters following stem-only clear-cutting, indicating increased N retention in harvested sites with high slash loads. Partial harvesting had weak effects on C and N dynamics of decaying litters. A comprehensive understanding of the long-term patterns and controls of C and N dynamics following forest disturbance would improve our ability to forecast the implications of forest harvesting for C sequestration and nutrient availability.     

Photoaffinity spin-labeling of the Ca2+ ATPase in sarcoplasmic reticulum : Evidence for oligomeric structure

A spin labeled fatty acid (16-doxylstearic acid) was linked to a photochemical reacting group (azido derivative). When the molecule is introduced, at a low concentration, into rabbit sarcoplasmic reticulum membranes, the spectrum before illumination is identical to the spectrum obtained with the corresponding spin labeled fatty acid. After illumination, a large immobilized components is seen. It corresponds to about 70% of the ESR signal of the effectively bound label, at room temperature. The fraction of immobilized component varies with temperature, from 100% at 0°C to 50% at 35°C. Addition of a small amount of detergent (dodecyl octaethylene glycol monoether), under non solubilizing conditions, decreases the fraction of signal due to a strongly immobilized probe. A possible interpretation is that the immobilized signal reflects protein bound spin labels trapped in Ca²⁺ ATPase oligomers, which are partially dissociated by detergent addition or temperature increase.     

Functional Effects of Adiponectin on Endothelial Progenitor Cells

Adiponectin is an adipokine whose plasma levels are inversely correlated to metabolic syndrome components. Adiponectin protects against atherosclerosis and decreases risks in myocardial infarction. Endothelial progenitor cells (EPCs) are a heterogeneous population of circulating cells involved in vascular repair and neovascularization. EPCs number is reduced in patients with cardiovascular disease. We hypothesize that the positive effects of adiponectin against atherosclerosis are explained in part by its interactions with EPCs. Cells were obtained from healthy volunteers' blood by mononuclear cell isolation and plating on collagen‐coated dishes. Three sub‐populations of EPCs were identified and characterized using flow cytometry. EPCs' expression of adiponectin receptors, AdipoR1, and AdipoR2 was evaluated by quantitative PCR. The effects of recombinant adiponectin on EPCs' susceptibility to apoptosis were assessed. Finally, expression of neutrophil elastase by EPCs and activity of this enzyme on adiponectin processing were assessed. Quantitative PCR analysis of EPCs mRNAs showed that AdipoR1 mRNA is expressed at higher levels than AdipoR2. Expression of AdipoR1 protein was confirmed by western blot. Adiponectin significantly increased survival of two sub‐populations of EPCs in conditions of serum deprivation. Such effect could not be demonstrated in the third EPCs sub‐population. We also demonstrated that EPCs, particularly one sub‐population, express neutrophil elastase. Neutrophil elastase activity was confirmed in EPCs' conditioned media. Adiponectin protects some EPCs sub‐populations against apoptosis and therefore could modulate EPCs ability to induce repair of vascular damage. Neutrophil elastase activity of EPCs could locally modulate adiponectin activity by its involvement in the generation of the globular form of adiponectin.