Stress in membranes

J Ubl, H Murer, HA Kolb. Ion channels activated by osmotic and mechanical stress in membranes of opossum kidney cells. J Membrane Biol 104 223-232, 1988. 

Of the layers mentioned above, the thin films showing the widest range of stress are the PECVD oxides. The stress state of the oxide layers becomes important when such films are used as part of a membrane or as a passivation layer. Membranes that are under considerable compressive stress tend to buckle, severely changing their mechanical properties. In contrast, considerable tensile stress in membranes can lead to crack formation and fracture. The passivation properties of PECVD oxide layers, for example, towards humidity, depend sensitively on their composition, which, in turn, has a great influence on the stress. 

This chapter is a practical summary of how to create CFD models, and how to interpret results. A review of recent literature on PEM fuel cell modeling was presented. A fiill three-dimensional computational fluid d5mamics model of a PEM fuel cell with straight flow channels has been developed. This model provides valuable information about the transport phenomena inside the fuel eell such as reactant gas concentration distribution, liquid water saturation distribution, temperature distribution, potential distribution in the membrane and gas diffusion layers, activation overpotential distribution, diffusion overpotential distribution, and local current density distribution. In addition, the hygro and thermal stresses in membrane, which developed during the cell operation, were modeled and investigated. 

In addition to high permselectivity, the membrane must have low-elec trical resistance. That means it is conductive to counterions and does not unduly restrict their passage. Physical and chemical stabihty are also required. Membranes must be mechanically strong and robust, they must not swell or shrink appreciably as ionic strength changes, and they must not wrinkle or delorm under thermal stress. In the course of normal use, membranes may be expec ted to encounter the gamut of pH, so they should be stable from 0 < pH < 14 and in the presence of oxidants. 

Within the nervous system, ChEs were shown to be involved in membrane conductance and transmission of excitatory amino acids, learning and memory, neurite growth, neuritic translocation and acute stress reactions. Recent findings propose AChE s involvement in apoptosome formation [2]. 

Fujikawa, S. Miura, K. (1986). Plasma membrane ultrastructural changes caused by mechanical stress in the formation of extracellular ice as a primary cause of slow freezing injury in fhiit-bodies of basidiomycetes (Lyophyllum ulmarium [Fr.J KOhner). Cryobiol. 23,371-382. 

A molecular variation of plasma membrane has been reported by Puccia et al. Reduction of total lipids (XL) content and significant variations of triglyceride (TG) and phospholipids (PL) fractions were observed as a consequence of exposure of C. intestinalis ovaries to TBTCl solutions. In particular, an evident TG decrease and a PL increase were observed, which probably provoked an increment in membrane fluidity, because of the high concentration of long chain fatty acids and, as a consequence, PL. This could be a cell-adaptive standing mechanism toward the pollutants, as observed in Saccharomyces cerevisiae. Also the increase in the content of the polyunsaturated fatty acids (PUPA), important in the synthesis of compounds such as prostaglandin which are present in the ovary in a stress situation, was probably a consequence of a defense mechanism to the stress provoked by the presence of TBTCl. 

In both plant (e.g. [57]) and animal (e.g. [86]) cell systems, cellular respiration has been shown to be a more sensitive indicator of system response to hydro-dynamic stress than membrane integrity, suggesting that intracellular enzymes and/or organelles may be affected at stress levels lower than those required to cause membrane damage. 

In a wider context, alterations in membrane structure are generally associated with environmental stress. For example, it has been shown in the archaeon Methanococcoides burtonii that the degree of unsaturated lipids in cells grown at 4°C was higher than in cells grown at 23°C, and that the degree of unsaturation is specihc for each class of phospholipid (Nichols et al. 2004). 

Subjecting cells to oxidative stress can result in severe metabolic dysfunctions, including peroxidation of membrane lipids, depletion of nicotinamide nucleotides, rises in intracellular free Ca ions, cytoskeletal disruption and DNA damage. The latter is often measured as formation of single-strand breaks, double-strand breaks or chromosomal aberrations. Indeed, DNA damage has been almost invariably observed in a wide range of mammalian cell types exposed to oxidative stress in a number... 

This force is resisted by the normal component of the forces associated with the membrane stresses in the walls of the vessel (given by, force = stress x area)... 

The minimum wall thickness required to resist the hydrostatic pressure can be calculated from the equations for the membrane stresses in thin cylinders (Section 13.3.4) ... 

Calculate the maximum membrane stress in the wall of shells having the shapes listed below. The vessel walls are 2 mm thick and subject to an internal pressure of 5 bar. 

Haidekker MA, L Heureux N, Frangos JA (2000) Fluid shear stress increases membrane fluidity in endothelial cells a study with DCVJ fluorescence. Am J Physiol Heart Circ Physiol 278(4) H1401-H1406... 

Hydroxy-10,12-octadecadienoic acid, which is formed by the reduction of 9-HPODE, was identified in the erythrocyte membrane phospholipid of diabetic patients [83]. It was suggested that this compound was formed as a result of glucose-induced oxidative stress in the reaction of hydroxyl radicals with linoleic acid. 

Many chlorine producers are having to tolerate impurities originating from standard plastic materials used in membrane technology. Flot chlorine and hot anolyte emerging from the anodic compartment of the cell place tremendous stresses on these plastic construction materials. 

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