Membrane permeability differentiation at the lipid divide

One of the deepest branches in the tree of life separates the Archaea from the Bacteria. These prokaryotic groups have distinct cellular systems including fundamentally different phospholipid membrane bilayers. This dichotomy has been termed the lipid divide and is assumed to bestow different biophysical and biochemical characteristics on each cell type. Classic experiments suggest that bacterial membranes are more permeable, yet systematic analysis based on direct measurements is absent. Here we develop a new approach for assessing the membrane permeability of cell-sized unilamellar vesicles, consisting of an aqueous medium enclosed by a single lipid bilayer. Comparing the permeability of twenty metabolites demonstrates that archaeal-type membranes are permeable to a range of compounds useful for core metabolic networks, including amino acids, sugars, and nucleobases. Surprisingly, permeability is much lower in bacterial-type membranes, in contradiction to current orthodoxy. We then show that archaeal permeability traits are specifically linked to both the methyl branches present on the archaeal phospholipid tails and the ether link between the tails and the head group. To explore this result further, we compare the abundance of transporter-encoding families present on genomes sampled from across the prokaryotic tree of life. Interestingly, archaea have a reduced repertoire of transporter gene families, consistent with an increased dependency on membrane permeation for a subset of metabolites. Taken together, these results demonstrate that the lipid divide demarcates a clear difference in permeability function with implications for understanding some of the earliest transitions in cell and protocell evolution.

Thrombomodulin is essential for maintaining quiescence in vascular endothelial cells

Thrombomodulin (TM) is a thrombin receptor on endothelial cells that is involved in promoting activation of the anticoagulant protein C pathway during blood coagulation. TM also exerts protective anti-inflammatory properties through a poorly understood mechanism. In this study, we investigated the importance of TM signaling to cellular functions by deleting it from endothelial cells by CRISPR-Cas9 technology and analyzed the resultant phenotype of TM-deficient (TM−/−) cells. Deficiency of TM in endothelial cells resulted in increased basal permeability and hyperpermeability when stimulated by thrombin and TNF-α. The loss of the basal barrier permeability function was accompanied by increased tyrosine phosphorylation of VE-cadherin and reduced polymerization of F-actin filaments at cellular junctions. A significant increase in basal NF-κB signaling and expression of inflammatory cell adhesion molecules was observed in TM−/− cells that resulted in enhanced adhesion of leukocytes to TM−/− cells in flow chamber experiments. There was also a marked increase in expression, storage, and release of the von Willebrand factor (VWF) and decreased storage and release of angiopoietin-2 in TM−/− cells. In a flow chamber assay, isolated platelets adhered to TM−/− cells, forming characteristic VWF–platelet strings. Increased VWF levels and inflammatory foci were also observed in the lungs of tamoxifen-treated ERcre-TMf/f mice. Reexpression of the TM construct in TM−/− cells, but not treatment with soluble TM, normalized the cellular phenotype. Based on these results, we postulate cell-bound TM endows a quiescent cellular phenotype by tightly regulating expression of procoagulant, proinflammatory, and angiogenic molecules in vascular endothelial cells.

Evaluating the Air Permeability Properties of Summer Cooling Towels

Air permeability is one of the thermal comfort properties of clothing and fabrics. This study evaluated the air permeability properties of summer cooling towels of different brands available in the market, “Perfect Fitness”, “N-rit” and “Cooldyxm” and an anonymous ice towel. The air permeability function of the cooling towels was evaluated instrumentally. Other than the air permeability property, other fabric specification such as fiber composition, fabric type, fabric weight, fabric thickness, yarn linearity and fabric density were measured. Some specifications were found to have good statistical correlation with the air permeability. Based on the experimental results and statistical analysis, the sample of Perfect Fitness was found to have the poorest cooling effect, whereas N-rit, Cooldyxm and Ice Towel samples had comparable air permeability properties. The best performance of air permeability was seen in N-rit sample. The underlying reason could be ascribed to the fabric structure and thickness. This study can provide some information for choosing cooling towel for practical use.

Robust methods to estimate large-strain consolidation parameters from column experiments

New approaches are proposed for robustly determining the compressibility and permeability functions for large-strain consolidation (LSC), using limited measurements from one-dimensional tests, such as column or centrifuge experiments. These new methods are developed from several new findings reported in this paper, including (i) new analytical solutions that relate parameters of compressibility functions to the final density profile, (ii) analytical proof of the independence of the shape of the settlement curve from the parameter M, where the permeability or hydraulic conductivity k is given by MeP, e is void ratio, and M and P are material-related constants; and (iii) that when the same k function is employed, for the case of one-dimensional settlement, the optimal values of M and P are located on a unique straight line in the P–lnM space. The third finding was determined from optimization analysis of thousands of LSC simulations. Using different combinations of these new findings, three new methods are developed to estimate the permeability function. The efficiency, robustness, and accuracy of the three methods are investigated by their application to four column tests from the literature. The simplest of the three methods requires only two LSC analyses plus several hand-calculations, demonstrating strong potential for practical use.

Estimating the configuration of the subglacial drainage system under a mountain glacier in St. Elias Mountains, Yukon

<p>Numerous studies have documented that water at the ice-bed interface can affect ice flow dynamics of both, mountain glaciers and the Greenland ice sheet. Water at the bed is routed through a complex network of conduits that form a subglacial drainage system. The subglacial drainage system evolves over the melt season in response to the changes in the meltwater supply. However, it is challenging to study due to the inaccessibility of the glacier bed. We use an extensive near-bed water pressure data set from an ablation zone of a small, polythermal, mountain glacier in St. Elias Mountains, Yukon.  Pressure sensors, that exhibit common diurnal variations, are considered to be connected to a hydraulically active drainage system. </p><p>We use a simplified two-dimensional continuum version of the subglacial drainage model with an additional assumption that changes in drainage configuration are negligible over a short time period. Spatially varying permeability function is used as a proxy for the subglacial drainage configuration, assuming that the areas of high (low) permeability correspond to the areas that are connected (disconnected) to a hydraulically active system.  In order to study the evolution of the subglacial drainage system over the melt season, we divide the melt season in a series of short time periods. We then use the inverse model to estimate the permeability function for each of these time periods. Continuity is ensured by using, respectively, the final pressure distribution and the estimated permeability function of the previous period, as the initial condition and the a priori estimate for the consequent time period.</p>

Influence of Degree of Compaction on Unsaturated Hydraulic Properties of a Compacted Completely Decomposed Granite

It is crucial to understand hydraulic properties, i.e., soil-water characteristic curve (SWCC) and unsaturated permeability function (UPF), of completely decomposed granite (CDG) for relevant engineering projects in southeastern China. Previous studies mainly focused on SWCCs of CDG, whereas UPFs of CDG have not yet been well understood. In this study, the effects of the degree of compaction (DOC) on SWCCs and UPFs of CDG were investigated based on experiments where suction range was from 0 to 500 kPa. The microstructure of soil specimens was then analyzed by mercury intrusion porosimetry (MIP). Furthermore, the UPFs of CDG under different values of DOC were calculated using four prediction models and compared with experimental data. Results showed that the pore volume of specimens at higher DOC was smaller than that at lower DOC, and there were more macropores observed in specimens at lower DOC. Meanwhile, it was found that increasing compaction effort produced negligible influence on the volume of micropores. When the suction was less than 100 kPa, the permeability was reduced with the increase in DOC, due to the decrease of macropore volume. However, the influence of DOC on SWCCs and UPFs became marginal when the suction exceeded 100 kPa. The Fredlund and Xing model provided the best prediction of UPF among the four models when suction was smaller than air entry value (AEV). It is suggested that these models could be improved to capture UPFs at higher suctions than AEV by considering suction-induced volume contraction.