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Conductive Pathways (conductive + pathway)
Selected AbstractsWater relations of baobab trees (Adansonia spp.PLANT CELL & ENVIRONMENT, Issue 6 2006L.) during the rainy season: does stem water buffer daily water deficits? ABSTRACT Baobab trees are often cited in the literature as water-storing trees, yet few studies have examined this assumption. We assessed the role of stored water in buffering daily water deficits in two species of baobabs (Adansonia rubrostipa Jum. and H. Perrier and Adansonia za Baill.) in a tropical dry forest in Madagascar. We found no lag in the daily onset of sap flow between the base and the crown of the tree. Some night-time sap flow occurred, but this was more consistent with a pattern of seasonal stem water replenishment than with diurnal usage. Intrinsic capacitance of both leaf and stem tissue (0.07,0.08 and 1.1,1.43 MPa,1, respectively) was high, yet the amount of water that could be withdrawn before turgor loss was small because midday leaf and stem water potentials (WPs) were near the turgor-loss points. Stomatal conductance was high in the daytime but then declined rapidly, suggesting an embolism-avoidance strategy. Although the xylem of distal branches was relatively vulnerable to cavitation (P50: 1.1,1.7 MPa), tight stomatal control and minimum WPs near ,1.0 MPa maintained native embolism levels at 30,65%. Stem morphology and anatomy restrict water movement between storage tissues and the conductive pathway, making stored-water usage more appropriate to longer-term water deficits than as a buffer against daily water deficits. [source] Purinergic regulation of the epithelial Na+ channelCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2009Lauren M O'Mullane Summary 1. The epithelial Na+ channel (ENaC) is a major conductive pathway that transports Na+ across the apical membrane of the distal nephron, the respiratory tract, the distal colon and the ducts of exocrine glands. The ENaC is regulated by hormonal and humoral factors, including extracellular nucleotides that are available from the epithelial cells themselves. 2. Extracellular nucleotides, via the P2Y2 receptors (P2Y2Rs) at the basolateral and apical membrane of the epithelia, trigger signalling systems that inhibit the activity of the ENaC and activate Ca2+ -dependent Cl, secretion. 3. Recent data from our laboratory suggest that stimulation of the P2Y2Rs at the basolateral membrane inhibits ENaC activity by a signalling mechanism that involves G,, subunits freed from a pertussis toxin (PTX)-sensitive G-protein and phospholipase C (PLC) ,4. A similar signalling mechanism is also partially responsible for inhibition of the ENaC during activation of apical P2Y2Rs. 4. Stimulation of apical P2Y2Rs also activates an additional signalling mechanism that inhibits the ENaC and involves the activated G, subunit of a PTX-insensitive G-protein and activation of an unidentified PLC. The effect of this PTX-insensitive system requires the activity of the basolateral Na+/K+/2Cl, cotransporter. [source] Microstructural Engineering of Hydroxyapatite Membranes to Enhance Proton ConductivityADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Dongxia Liu Abstract A new approach to enhancing proton conductivity of ceramics is demonstrated by aligning proton conductive pathways and eliminating resistive grain boundaries. Hydroxyapatite (HAP) membranes are synthesized by multistage crystallization onto palladium. The synthesis involves three steps: electrochemical deposition of HAP seeds, secondary hydrothermal crystallization onto the seed layer to promote c -axis growth normal to the substrate, and tertiary hydrothermal crystallization to promote a- axis growth to fill the gaps between the aligned crystals. The c -axis alignment with crystal domains spanning the membrane thickness significantly enhances proton conduction since protons are primarily transported along the c -axes of HAP crystals. The novel HAP membranes display proton conductivity almost four orders of magnitude higher than traditional sintered HAP ceramics. The HAP membranes on palladium hydrogen membrane substrates hold promise for use in intermediate-temperature fuel cells, chemical sensors, and other devices. The synthesis approach presented may also be applied to other ion-conducting membrane materials to enhance transport properties. [source] Localized electrical current propagation in anisotropically perturbed atmospheresINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 1 2010T. I. ZohdiArticle first published online: 29 MAR 2010 Abstract The trajectory of free atmospheric electrical currents, such as lightning and sparks, is strongly influenced by microscale events that occur at the current front. In particular, highly conductive pathways can occur at the free surface front due to dielectric breakdown. The specific directions of the local pathways are minutely perturbed, due to the gaseous, disordered, nature of the media at the small scale. This results in highly conductive, anisotropically perturbed, continuum-level properties at the electrical current front. In this work, a model is developed to investigate the role of the resulting anisotropically perturbed conductivity at the propagation front on the overall trajectory of free atmospheric electrical currents. The approach is to relate the electrical current velocity to the local anisotropic conductivity at the propagation front and the surrounding electric field. The conductive anisotropy is decomposed into an isotropic ,base state' and an anisotropic perturbation. The current trajectory is shown to be governed by a set of non-linear differential equations, for which a numerical solution scheme is developed. The difference between paths taken through anisotropically perturbed and isotropic media is analytically bounded and quantified numerically as a function of the magnitude of the anisotropic perturbation. The analysis and numerical experiments indicate that, in a statistical sense, the difference in the paths taken in anisotropically perturbed and isotropic media depends quasilinearly on the perturbation magnitude. Copyright © 2010 John Wiley & Sons, Ltd. [source] Regulatory Mechanisms and Physiological Relevance of a Voltage-Gated H+ Channel in Murine Osteoclasts: Phorbol Myristate Acetate Induces Cell Acidosis and the Channel Activation,JOURNAL OF BONE AND MINERAL RESEARCH, Issue 11 2003Hiroyuki Mori Abstract The voltage-gated H+ channel is a powerful H+ extruding mechanism of osteoclasts, but its functional roles and regulatory mechanisms remain unclear. Electrophysiological recordings revealed that the H+ channel operated on activation of protein kinase C together with cell acidosis. Introduction: H+ is a key signaling ion in bone resorption. In addition to H+ pumps and exchangers, osteoclasts are equipped with H+ conductive pathways to compensate rapidly for pH imbalance. The H+ channel is distinct in its strong H+ extrusion ability and voltage-dependent gatings. Methods: To investigate how and when the H+ channel is available in functional osteoclasts, the effects of phorbol 12-myristate 13-acetate (PMA), an activator for protein kinase C, on the H+ channel were examined in murine osteoclasts generated in the presence of soluble RANKL (sRANKL) and macrophage-colony stimulating factor (M-CSF). Results and Conclusions: Whole cell recordings clearly showed that the H+ current was enhanced by increasing the pH gradient across the plasma membrane (,pH), indicating that the H+ channel changed its activity by sensing ,pH. The reversal potential (Vrev) was a valuable tool for the real-time monitoring of ,pH in clamped cells. In the permeabilized patch, PMA (10 nM-1.6 ,M) increased the current density and the activation rate, slowed decay of tail currents, and shifted the threshold toward more negative voltages. In addition, PMA caused a negative shift of Vrev, suggesting that intracellular acidification occurred. The PMA-induced cell acidosis was confirmed using a fluorescent pH indicator (BCECF), which recovered quickly in a K+ -rich alkaline solution, probably through the activated H+ channel. Both cell acidosis and activation of the H+ channel by PMA were inhibited by staurosporine. In ,80% of cells, the PMA-induced augmentation in the current activity remained after compensating for the ,pH changes, implying that both ,pH-dependent and -independent mechanisms mediated the channel activation. Activation of the H+ channel shifted the membrane potential toward Vrev. These data suggest that the H+ channel may contribute to regulation of the pH environments and the membrane potential in osteoclasts activated by protein kinase C. [source] Evidence for two conductive pathways in P2X7 receptor: differences in modulation and selectivityJOURNAL OF NEUROCHEMISTRY, Issue 3 2010Susanna Alloisio J. Neurochem. (2010) 113, 796,806. Abstract The P2X7 receptor (P2X7R) is an ATP-gated cation channel whose biophysical properties remain to be unravelled unequivocally. Its activity is modulated by divalent cations and organic messengers such as arachidonic acid (AA). In this study, we analysed the differential modulation of magnesium (Mg2+) and AA on P2X7R by measuring whole-cell currents and intracellular Ca2+ ([Ca2+]i) and Na+ ([Na+]i) dynamics in HEK293 cells stably expressing full-length P2X7R and in cells endowed with the P2X7R variant lacking the entire C-terminus tail (trP2X7R), which is thought to control the pore activation. AA induced a robust potentiation of the P2X7R- and trP2X7R-mediated [Ca2+]i rise but did not affect the ionic currents in both conditions. Extracellular Mg2+ reduced the P2X7R- and trP2X7R-mediated [Ca2+]i rise in a dose-dependent manner through a competitive mechanism. The modulation of the magnitude of the P2X7R-mediated ionic current and [Na+]i rise were strongly dependent on Mg2+ concentration but occurred in a non-competitive manner. In contrast, in cells expressing the trP2X7R, the small ionic currents and [Na+]i signals were totally insensitive to Mg2+. Collectively, these results support the tenet of a functional structure of P2X7R possessing at least two distinct conductive pathways one for Ca2+ and another for monovalent ions, with the latter which depends on the presence of the receptor C-terminus. [source] Effects of carbon fillers in thermally conductive polypropylene based resins,POLYMER COMPOSITES, Issue 3 2010Julia A. King The thermal conductivity of insulating polymers can be increased by adding conductive fillers. One potential market for these thermally conductive resins is for fuel cell bipolar plates. In this study, varying amounts of three different carbon fillers (carbon black, synthetic graphite particles, and carbon nanotubes) were added to polypropylene. The effects of single fillers and combinations of the different fillers were studied via a factorial design. Each single filler caused a statistically significant increase in composite through-plane thermal conductivity at the 95% confidence level, with synthetic graphite causing the largest increase. All of the composites containing combinations of the different fillers caused a statistically significant increase in composite through-plane thermal conductivity. It is possible that thermally conductive pathways are formed that ,link' these carbon fillers, which results in increased composite thermal conductivity. Composites containing 80 wt% synthetic graphite had an in-plane thermal conductivity of 28.0 W/m·K, which is desired for bipolar plates (>20 W/m·K). POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers [source] | ||||||||||||||||