Membrane, leaky

Each polyion pair which yielded a stable membrane was removed from the receiving bath and treated. In general, quintuple washings with an excess (50 ml) of PBS were required to remove all traces of the polymeric reagents. The PBS also simulated the osmotic pressure which the capsule, and mammalian cells, would encounter in vivo. For several polyanion-polycation systems the membranes which were produced were not sufficiently strong to survive the rinsings. Leaky membranes and the complete collapse of the capsule were two common failures. 

Neuronal plasticity is an essential component of neuronal adaptability and there is increasing evidence that this is primarily a biochemical rather than a morphological process. The neuron is not a fixed entity in terms of the quantity of transmitter it releases, and transmitters which are co-localized in a nerve terminal may be differentially secreted under different conditions. This, together with the repeated firing of some neurons that appear to have "leaky" membranes, may underlie the rhythmicity of neuronal activity within the brain. 

To understand how this might work, it is important to recognize that serotonergic and noradrenergic neuromodulatory neurons tend to fire spontaneously unless they are inhibited. This is because they are pacemaker cells whose leaky membranes depolarize on their own. As a consequence, they are reliable suppliers of their modulatory molecules unless they are inhibited. But these cells also have another remarkable property they self-regulate by means of direct feedback inhibition via recurrent collateral offshoots from their axons. These recurrent collaterals contact the cell bodies via autoreceptors that are often inhibitory. 

K+-ATPase is the primary source of the membrane potential for most eukaryotic cells and is said to be electrogenic. Because the cell membrane is somewhat permeable to K+, outward diffusion of K+ through the "leaky" membrane along its concentration gradient helps to maintain the membrane potential as does inward leakage of CP. At the same time, Na+ diffuses inward, aided by the membrane potential. Even though the permeability of Na+ is low, a steady state is reached at which the rate of passive inward diffusion of cations just balances the membrane potential set up by the active transport. 

If the electrode response is sluggish, first check/replace the membrane since most 02 electrode problems are due to dirty or leaky membranes. Remove the cell plug and rinse the cell thoroughly with distilled water using a plastic disposable pipet to avoid the risk of damage to the membrane. 

Mechanism of Action. Amphotericin B appears to work by binding to specific steroidlike lipids (sterols) located in the cell membrane of susceptible fungi.7 This binding causes increased permeability in the cell membrane, leading to a leaky membrane and loss of cellular components. 

A two-color dot plot (Fig. 8.23) of cells stained with propidium iodide and annexin V FITC will indicate cells in three of the four quadrants. Unstained cells are alive and well and are the double negatives they neither express phosphatidylserine on their surface nor take up propidium iodide through leaky membranes. Cells that stain just with annexin V are apoptotic they have begun to express phosphatidylserine on their surface, but have not yet gone through the process that leads to permeabilization of their cytoplasmic membrane. Cells that stain both with propidium iodide and annexin V are necrotic (that is, dead) they take up propidium iodide and also stain with annexin Y. With a permeable cell, the flow cytometer cannot tell us whether the annexin V is on the outside of the membrane (because the cells have gone through apoptosis before membrane permeabilization) or on the inside of the membrane (because the cells have died by the necrotic pathway without apoptosis). 

Else, P.L., and A.J. Hulbert (1987). Evolution of mammalian endothermic metabolism leaky membranes as a source of heat. Am. J. Physiol. 253 (Regulatory Integrative Comp. Physiol. 22) R1-R7. 

Hulbert, A.J., and P.L. Else (1990). The cellular basis of endothermic metabolism A role for leaky membranes News Physiol. Sci. 5 25-28. 

If the normalized salt rejection is low or the normalized permeate flow is high, the integrity of the membrane may be in question. The vacuum decay test is a direct test for the integrity of a spiral wound RO membrane module. The test is best used to identify leaks within the membrane modules rather than leaks due to chemical attack. The test requires the isolation of an individual membrane module or the entire pressure vessel. A vacuum is then pulled on the membrane(s) and the rate of decay in pressure is observed. A decay of greater than 100 millibar per minute is indicative of a leaky membrane. Refer to ASTM Standards D39235 and D69086 for a more detailed review of the technique. 

Span surfactant niosomes have been dispersed in oil-in-water emulsions to yield a vesicle in a water-in-oil system, v/w/o, using the same surfactant that was used to make niosomes [152]. The release of CF from these systems followed the trend v/w/odifference between the v/w/o and w/o formulations was minimal. The release of CF encapsulated within these niosomes was influenced by the emulsion oil following the trend, isopropyl myristate>octane>hexadecane and by the nature of the surfactant, following the trend span 20>span 40>span 60. Span 80 v/w/o systems had a rather faster release rate due to the unsaturation in the oleyl alkyl chain, which leads to the formation of a more leaky membrane. 

Datta, R., et al. Generalized model for the transport of gases in porous, non-porous, and leaky membranes. I. Application to single gases, J. Membr. Sci., 75, 245, 1992. 

This expression shows that fuel utilization levels as high as 90% can be achieved even when the membrane is quite leaky to fuel, that is, when /crossover /cell=o is quite large. For example, with /crossover /cen=o as high as 50% of the cell current density targeted, operation at /ceii//iim,an = 0-85 enables, according to Eq. (62), rj i as high as 93% with the leaky membrane. 

As a consequence of the passage of solvent, say water, through the membrane, solute is carried to the membrane surface, and the concentration at the membrane surface tends to be higher than in the bulk of the liquid. This phenomenon is called concentration polarization. Several deleterious effects arise from concentration polarization, one of which is the local increase in osmotic pressure due to the increased solute concentration at the membrane. The result is that the solvent flux is decreased because the effective driving pressure is reduced. Another effect is an increase in the solute concentration in the product, for with real leaky membranes the flux of solute across the membrane is proportional to the difference in solute concentration on both sides. The extent of concentration polarization depends on the hydrodynamics and geometry of the system, with increased flow speed of the solution past the membrane tending to reduce the effect. 

It is of interest not only to perforate vesicle membranes but also to destroy them after they have served their purpose as transport vehicles, in particular for DNA. Natural vesicles, so-called endosomes, contain about 50% cholesterol. The disruption of such cholesterol-containing lipid bilayers by Triton XI00 or sodium deoxycholate, examples of artificial and natural detergents, results in a leaky membrane at low concentration and in a catastrophic rupture process above the cmc of the amphiphiles. Vesicles made of fluid phospholipid bilayers devoid of cholesterol showed only leakiness under the same conditions. Amphiphiles with a carboxylate end group and a very bulky hydrophobic end (e.g., with two tert. butyl groups) disrupt membranes at pH 5 and have no effect above pH 7 (harpoons). For an example, see Figure 6.5.3. 

For an ideal semi-permeable membrane, all solutes are reflected by the membrane and only water molecules can pass through the membrane. However, shale exhibits a non-ideal semi-permeable ( leaky ) membrane behaviour to water-based solutions because... 

Another concept is the preparation of responsive polymersome membranes, which are further cross-linked for stabilization. This concept allows for preservation of the general polymersome capsule structure upon switching polarity but leads to a more leaky membrane structure, resulting in enhanced membrane transport (Fig. 6.5).This can be achieved by incorporating pH-sensitive blocks, for example, in photo-cross-linkable polymersomes. The membrane of the vesicle is then formed spontaneously as double layer at suitable pH from the block copolymer containing the photo-cross-linkable units and is subsequently cross-linked in the collapsed state. Upon acidification, the nonpolar blocks are protonated and transformed into a polar block. Therefore, the polymersome would like to disintegrate but is linked by chemical bonds, and... 

The chemical gradient of H+ protons and OH hydroxyls embedded in the rocks is suspiciously similar to the gradient used by all cells to make ATP. Carbon chains naturally coat the walls of the chamber, reactions could use the stored energy to increase complexity, and, who knows One fine day a self-sustaining carbon bubble could venture out from its rocky nursery and make a living in the wide ocean. Lane and Martin s story even works with suboptimal, leaky membranes that tighten up over time. 

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