Second transmembrane domain modulates epithelial sodium channel gating in response to shear stress

Na(+) absorption and K(+) secretion in the distal segments of the nephron are modulated by the tubular flow rate. Epithelial Na(+) channels (ENaC), composed of α-, β-, and γ-subunits respond to laminar shear stress (LSS) with an increase in open probability. Higher vertebrates express a δ-ENaC subunit that is functionally related to the α-subunit, while sharing only 35% of sequence identity. We investigated the response of δβγ channels to LSS. Both the time course and magnitude of activation of δβγ channels by LSS were remarkably different from those of αβγ channels. ENaC subunits have similar topology, with an extracellular region connected by two transmembrane domains with intracellular N and C termini. To identify the specific domains that are responsible for the differences in the response to flow of αβγ and δβγ channels, we generated a series of α-δ chimeras and site-specific α-subunit mutants and examined parameters of activation by LSS. We found that specific sites in the region encompassing and just preceding the second transmembrane domain were responsible for the differences in the magnitude and time course of channel activation by LSS.     

Invasive knotweed modifies predator–prey interactions in the soil food web

Biological Invasions - Invasive plants often modify the structure of the community of native plants and animals, but their potential impact on the plant–soil interface is poorly studied. In...     

Effects of electrical muscle stimulation on oxygen consumption

Electrical muscle stimulation (EMS) devices are being marketed as weight/ fat loss devices throughout the world. Commercially available stimulators have the ability to evoke muscle contractions that may affect caloric expenditure while the device is being used. The aim of this study was to test the effects of two different EMS devices (Abtronic and Feminique) on oxygen consumption at rest. Subjects arrived for testing after an overnight fast, had the devices fitted, and then positioned supine with expired air measured to determine oxygen consumption. After a 10-minute acclimation period, oxygen consumption was measured for 20 minutes with the device switched off (resting) then 20 minutes with the device switched on (stimulated). There were no significant differences (p > 0.05) in oxygen consumption between the resting and stimulated periods with either the Abtronic (mean +/- SD; resting, 3.40 +/- 0.44; stimulated, 3.45 +/- 0.53 ml of O(2).kg(-1).min(-1)) or the Feminique (resting, 3.73 +/- 0.45; stimulated, 3.75 +/- 0.46 ml of O(2).kg(-1).min(-1)). In summary, the EMS devices tested had no effect on oxygen consumption during muscle stimulation.     

Gestational age‐dependent gene expression profiling of ATP‐binding cassette transporters in the healthy human placenta

The ATP‐binding cassette (ABC) transporters control placental transfer of several nutrients, steroids, immunological factors, chemicals, and drugs at the maternal‐fetal interface. We and others have demonstrated a gestational age‐dependent expression pattern of two ABC transporters, P‐glycoprotein and breast cancer resistance protein throughout pregnancy. However, no reports have comprehensively elucidated the expression pattern of all 50 ABC proteins, comparing first trimester and term human placentae. We hypothesized that placental ABC transporters are expressed in a gestational‐age dependent manner in normal human pregnancy. Using the TaqMan^® Human ABC Transporter Array, we assessed the mRNA expression of all 50 ABC transporters in first (first trimester, n = 8) and third trimester (term, n = 12) human placentae and validated the resulting expression of selected ABC transporters using qPCR, Western blot and immunohistochemistry. A distinct gene expression profile of 30 ABC transporters was observed comparing first trimester vs. term placentae. Using individual qPCR in selected genes, we validated the increased expression of ABCA1 (P < 0.01), ABCA6 (P < 0.001), ABCA9 (P < 0.001) and ABCC3 (P < 0.001), as well as the decreased expression of ABCB11 (P < 0.001) and ABCG4 (P < 0.01) with advancing gestation. One important lipid transporter, ABCA6, was selected to correlate protein abundance and characterize tissue localization. ABCA6 exhibited increased protein expression towards term and was predominantly localized to syncytiotrophoblast cells. In conclusion, expression patterns of placental ABC transporters change as a function of gestational age. These changes are likely fundamental to a healthy pregnancy given the critical role that these transporters play in the regulation of steroidogenesis, immunological responses, and placental barrier function and integrity.     

Grassland harvesting alters ant community trophic structure: An isotopic study in tallgrass prairies

Disturbances have long been recognized as important forces for structuring natural communities but their effects on trophic structure are not well understood, particularly in terrestrial systems. This is in part because quantifying trophic linkages is a challenge, especially for small organisms with cryptic feeding behaviors such as insects, and often relies on conducting labor‐intensive feeding trials or extensive observations in the field. In this study, we used stable isotopes of carbon and nitrogen to examine how disturbance (annual biomass harvesting) in tallgrass prairies affected the trophic position, trophic range, and niche space of ants, a widespread grassland consumer. We hypothesized that biomass harvest would remove important food and nesting resources of insects thus affecting ant feeding relationships and trophic structure. We found shifts in the feeding relationships inferred by isotopic signatures with harvest. In particular, these shifts suggest that ants within harvest sites utilized resources at lower trophic levels (possibly plant‐based resources or herbivores), expanded trophic breadth, and occupied different niche spaces. Shifts in resource use following harvest could be due to harvest‐mediated changes in both the plant and arthropod communities that might affect the strength of competition or alter plant nitrogen availability. Because shifts in resource use alter the flow of nutrients across the food web, disturbance effects on ants could have ecosystem‐level consequences through nutrient cycling.     

Defective CD4<Superscript>+</Superscript>CD25<Superscript>+</Superscript>regulatory T cell functioning in collagen-induced arthritis: an important factor in pathogenesis,counter-regulated by endogenous IFN-γ

Mice with a deficiency in IFN-γ or IFN-γ receptor (IFN-γR) are more susceptible to collagen-induced arthritis (CIA), an experimental autoimmune disease that relies on the use of complete Freund's adjuvant (CFA). Here we report that the heightened susceptibility of IFN-γR knock-out (KO) mice is associated with a functional impairment of CD4⁺CD25⁺ T_reg cells. Treatment of wild-type mice with depleting anti-CD25 antibody after CFA-assisted immunisation with collagen type II (CII) significantly accelerated the onset of arthritis and increased the severity of CIA. This is an indication of a role of T_reg cells in the effector phase of CIA. IFN-γR deficiency did not affect the number of CD4⁺CD25⁺ T cells in the central and peripheral lymphoid tissues. In addition, CD4⁺CD25⁺ T cells isolated from naive IFN-γR KO mice had a normal potential to suppress T cell proliferation in vitro. However, after immunisation with CII in CFA, the suppressive activity of CD4⁺CD25⁺ T cells became significantly more impaired in IFN-γR-deficient mice. Moreover, expression of the mRNA for Foxp3, a highly specific marker for T_reg cells, was lower. We further demonstrated that the effect of endogenous IFN-γ, which accounts for more suppressive activity in wild-type mice, concerns both T_reg cells and accessory cells. Our results demonstrate that the decrease in T_reg cell activity in CIA is counter-regulated by endogenous IFN-γ.     

Physicochemical and mechanical characterization of galactomannan from Mimosa scabrella: Effect of drying method

The galactomannan from Mimosa scabrella Bentham was extracted on a pilot plant scale and dried either by vacuum oven (GVO) or by spray-drier (GSD) to evaluate the effect of the drying technique on the powder quality and its applicability as excipient in solid dosage forms. The analysis by high performance size exclusion chromatography (HPSEC) coupled to multiangle laser light scattering (MALLS) suggests that both products behave as semi-flexible polymers, although the GSD showed more aggregation at molecular level (～10%) and higher chain stiffness (Lp 9.1 nm). TG and DSC analysis showed weight loss event with peak at 299.7 and 311.9 °C to GVO and GSD, respectively, as well and higher ash content for GSD sample, in both inert and oxidant atmosphere. The X-ray diffraction confirmed the amorphous nature of both galactomannans although GVO showed high crystallinity. The GSD showed lower density (1.009 g/cm³), higher cohesiveness (repose angle 35.5°, compressibility 32.2% and absence of flow), smaller and more spherical particles than GVO sample, both with high polydispersion. As vacuum oven-drying resulted in a like fibrous material, spray-drying appears as an alternative method easy to extrapolate in industry, requiring a glidant incorporation to improve the powder flowability.