Plasma membrane, permeability permeation

In situ perfusion studies assess absorption as lumenal clearance or membrane permeability and provide for isolation of solute transport at the level of the intestinal tissue. Controlled input of drug concentration, perfusion pH, osmolality, composition, and flow rate combined with intestinal region selection allow for separation of aqueous resistance and water transport effects on solute tissue permeation. This system provides for solute sampling from GI lumenal and plasma (mesenteric and systemic) compartments. A sensitive assay can separate metabolic from transport contributions. 

The lipid bilayer arrangement of the plasma membrane renders it selectively permeable. Uncharged or nonpolar molecules, such as oxygen, carbon dioxide, and fatty acids, are lipid soluble and may permeate through the membrane quite readily. Charged or polar molecules, such as glucose, proteins, and ions, are water soluble and impermeable, unable to cross the membrane unassisted. These substances require protein channels or carrier molecules to enter or leave the cell. 

Plant cells have several internal compartments separated by plasma membranes. The main compartments controlling the ionic relations of the cell are the cytosol and vacuole. The vacuole occupies more than 90% of the cell volnme and so contains the bnlk of the ions. Many different ions permeate the membranes, bnt in general K+, Na+ and Cr have the greatest concentrations and permeabilities. Studies of ion relations in plant cells have led to the following conclnsions ... 

Ethidium bromide is not able to permeate the plasma membrane, and only penetrates non-viable cells that have lost the selective permeability of the membrane. It can intercalate the bases of double-stranded DNA molecules, emitting an orange fluorescent light. Ethidium bromide also forms weak complexes with RNA, resulting in red fluorescence. Thus, non-viable cells will present a strong orange fluorescence, since ethidium... 

In the case of the PDMS gas, the membrane permeability of CO2 decreased, but the selectivity of CO2 over CH4 was found to be remarkably improved irrespective of the plasma gas used (NH3, Ar, Nj, O2). The nitrogen plasma treatment seemed to give better selectivity than the ammonia plasma (Matsuyama et al. 1995). The NH3 and N2 plasma treatment of the dense PE (Nakata and Kumazawa 2006) and PP (Teramae and Kumazawa 2007) membranes increased both the permeation coefficient for CO2 and the ideal separation factor for CO2 relative to N2. The effects of both plasma gases are very similar. 

A great deal of attention has been directed to the anaerobic fermentation by yeasts, notably Saccharomyces cerevisiae in its various forms (top and bottom brewers and bakers yeast). This has been industrially important, and the subspherical cells, about 6-8 /n in diameter, are produced under standard conditions. They can be brought into suspension with little or no clumping. They are then suitable for tests of the permeation through the surface of the suspended cells. From the discussion on pages 9-13, it follows that permeation can be treated either as the diffusion into spheres, where there is no semipermeable plasma membrane, or as the unidimensional diffusion through a relatively thin, slightly permeable membrane, with substantial complete diffusion of permeant. Since there is every reason to assume the latter case, the former case is considered unimportant. 

In fermentation no oxygen is used, so that there is no question as to permeability to oxygen. Glucose, provided in the medium, must permeate the yeast cell before metabolism starts. Metabolism, probably by means of several steps leads to the liberation of carbon dioxide presumably by decarboxylation. To be measured, this carbon dioxide must pass out through the plasma membrane and be freed as a gas from the medium (see Nord and Weichherz, 64). The very great permeability to carbon dioxide of all or most of all the studied types of plasma membrane leads to the conclusion that this step has no measurable influence. The liberation of carbon dioxide from even saturated solutions has been thought to require the use of special methods, such as the addition of large amounts of citric acid as Meyerhof advocates (53). Further study of this step is desirable. 

If calculations are made which correlate carbon dioxide production in the relatively steady state of fermentation with rate of permeation by glucose, it can be concluded tentatively that the rate of fermentation is regulated by a permeability of plausible magnitude. This seems to be a reasonable conclusion, i.e., that, as fast as glucose arrives by diffusion through the plasma membrane, it flows through several steps toward the final product. 

Table 34.3 H2 Permeation Rates and Permeability Ratio of H2/CH4 for Plasma Polymers of Butyronitrile Deposited on Silicone-Carbonate-Coated Polysulfone Porous Membranes...

Pulsate flows were applied to mineral microfiltrations membranes during apple juice filtration [36] illustrating the advantage of this method to enhance permeability compared to steady flow regime. With carefully chosen pulsations permeate flux increased up to 45% at 1 Hz pulsation frequency. Moreover well defined pulsations decreased the hydraulic power dissipated in the retentate per unit volume by up to 30%. In an other work on cross-flow filtration of plasma from blood [37] permeate flux increase was also observed when pressure and flow pulsations at 1 Hz are superimposed on the retentate. 

Polybutadiene/polycarbonate membranes with a pp-ethylenediamine layer had an increased gas permeability (in comparison with the unmodified one) due to surface etching. Their selectivity was closely connected with the chemical composition of the top layer. A high nitrogen content was required for high O2 selectivity (Ruaan et al. 1998). The presence of the amine groups on the membrane surface also enhanced the capacity for CO2/CH4 separation. The plasma-polymerized diisopropylamine on the surface of the composite membrane—porous polyimide (support)/ silicone (skin)— made the separation coefficient as high as 17 for a permeation rate of 4.5 X cmVcm sec cmHg (Matsuyama et al. 1994). 

However, the grafted layer is apparently extremely thin, since no changes were detected in DSC thermograms. The CO2 permeation test indicated that the plasma-modified membrane exhibited a greatly enhanced permeability (144Barrer at 25 °C). 

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