Since leaf area index in crowded, self-thinning stands is independent of stand

density, the drag force per unit land can also be assumed to be independent of stand density, with only canopy height influencing the total toppling moment. Tree PND-1186 chemical structure stem dimensions and the self-thinning biomass can then be computed by further assuming that the risk of toppling over and stem maintenance per unit land area are independent of stand density, and that stem maintenance cost is a linear function of stem surface area and sapwood volume. These assumptions provide a novel way to understand tree allometry and lead to a self-thinning line relating tree biomass and stand density with a power between -3/2 and -2/3 depending on the ratio of maintenance of sapwood and stem surface. (C) 2010 Elsevier Ltd. All rights reserved.”
“Excessive neuronal iron has been proposed to contribute

to the pathology of several neurodegenerative diseases including Alzheimer’s and Parkinson’s diseases. This work characterized human neuroblastoma IMR-32 cells exposure to ferric ammonium citrate (FAC) as a model of neuronal iron overload and neurodegeneration. The consequences of FAC treatment on neuronal oxidative stress and on the modulation of the oxidant-sensitive transcription factors AP-1 and NF-kappa B were investigated. Incubation with FAC (150 mu M) resulted in a time ARS-1620 (3-72 h)-dependent increase in cellular iron content, and was associated with cell oxidant increase. FAC caused a time-dependent (3-48 h) increase in nuclear AP-1- and NF-kappa B-DNA binding. This was associated with the upstream activation of the mitogen activated kinases ERK1/2, p38 and JNK and of I kappa B alpha phosphorylation and degradation.

After 72 h incubation with FAC, cell viability was 40% lower than in controls. Iron overload caused apoptotic cell death. After 48-72 h of incubation with FAC, caspase 3 activity was increased, and chromatin condensation and nuclear fragmentation were observed. In summary, the exposure of IMR-32 cells to FAC is associated with increased oxidant selleck cell levels, activation of redox-sensitive signals, and apoptosis. (C) 2010 Elsevier Inc. All rights reserved.”
“A large amount of experimental data on the characteristics of the cardiac Na+/K+ pump have been accumulated, but it remains difficult to predict the quantitative contribution of the pump in an intact cell because most measurements have been made under non-physiological conditions. To extrapolate the experimental findings to intact cells, we have developed a comprehensive Na+/K+ pump model based on the thermodynamic framework (Smith and Crampin, 2004) of the Post-Albers reaction cycle combined with access channel mechanisms. The new model explains a variety of experimental results for the Na+/K+ pump current (I-NaK), including the dependency on the concentrations of Na+ and K+, the membrane potential and the free energy of ATP hydrolysis.