Differentially permeable membrane

Note the similarity of the above formula to the ideal gas law and also that osmotic pressure is not dependent on particle charge. This equation was derived by van t Hoff Osmotic pressure is the basis of reverse osmosis, a process commonly used to purify water. The water to be purified is placed in a chamber and put under an amount of pressure greater than the osmotic pressure exerted by the water and the solutes dissolved in it. Part of the chamber opens to a differentially permeable membrane that lets water molecules through, but not the solute particles. The osmotic pressure of ocean water is about 27 atm. Reverse osmosis desalinators use pressures around 50 atm to produce fresh water from ocean salt water. 

Williams, P.D., Laska, D.A., Heim, R.A. and Rush, G.F. (1993). Differential toxicity of parenteral antibiotic drugs in renal cells (LLC-PK4) grown on permeable membrane filters. Toxicol. Methods 3(2) 130-141. 

The apparent permeability of 11 test compounds was measured in the presence and absence of human serum albumin in the donor compartment, and by solving the differential equations describing the kinetics of membrane permeability, membrane retention and protein binding, the authors were able to obtain the Kd. With the protein in solution rather than immobilized and without the need for mass balance or equilibrium conditions, this approach provides an attractive alternative to existing methods with the potential to be applied to an array of other soluble proteins. 

Cell A small cavity, compartment or locule also the structural and functional unit of plants and animals, consisting of a small mass of cytoplasm and a denser portion (the nucleus) and surrounded by a more or less differentiated semipermeable membrane often the cell secretes a permeable covering or cell wall around itself from which the term was first derived. 

New polymer membrane-based ISEs for nitrate and carbonate exhibit detection limits and selectivities that may be applicable for ocean measurements. In addition, a number of these ISEs can be used as internal transducers for the design of useful potentiometric gas sensors. For example, dissolved C02 can be detected potentiometrically by using either a glass membrane electrode or a polymer-based carbonate ISE, in conjunction with an appropriate reference electrode, behind an outer gas permeable membrane. Novel differential pC02 sensors based on two polymer membrane-type pH sensors have also been developed recently. 

J. Bernstein and A. Tchermak, Pflug. Arch. Ges. Physiol. 112 439 (1906). Differential permeability is the basis to membrane potentials. 

As outlined in Chapter 3, cell excitability can in part be determined by the maintenance of gradients of Na+, K+ and CP ions. Differential plasma membrane (PM) permeabilities to such ions and the gradients of ion concentration contribute to the transmembrane potential difference (t tm), which is typically about —0.1 volt (V) (inside with respect to the outside). In addition, the cytosolic free concentration of Ca2+ is extremely low (0.1 pM in resting cells and about 10 pM in excited cells) as compared to concentrations of Na+, CP and K+ of about 10, 10 and 100 mM, respectively, in the cytosol and about 100, 100 and 10 mM, respectively, in the extracellular milieu. These huge ion gradients are maintained through the operation of ion pumps such as the adenosine 5 -triphosphate (ATP)-energized Ca2+ pump (Ca2+-ATPase) and the Na+ and K+ pump (Na+, K+-ATPase). 

A bilayered composite skin equivalent has been developed with a viable dermis and epidermis. The epidermis is composed from cornified differentiated keratinocytes and a dermal matrix composed of a collagen lattice containing viable fibroblasts. Its cellular components assist with wound closure through stimulation of the wound bed. The outer layer of the differentiated bilayered skin equivalent, the stratum corneum, acts as a specialized vapor permeable membrane and protective outer barrier.f ... 

Whenever a solution is separated from a solvent by a membrane that is permeable only to solvent molecules (referred to as a semi-permeable membrane), there is a passage of solvent across the membrane into the solution. This is the phenomenon of osmosis. If the solution is totally confined by a semipermeable membrane and immersed in the solvent, then a pressure differential develops across the membrane, which is referred to as the osmotic pressure. Solvent passes through the membrane because of the inequality of the chemical potentials on either side of the membrane. Since the chemical potential of a solvent molecule in solution is less than that in pure solvent, solvent will spontaneously enter the solution until this inequality is removed. The equation which relates the osmotic pressure of the solution. If, to the solution concentration... 

Figure 3-1 shows an example of a voltaic cell. A zinc electrode is immersed in a solution of NaCl and a copper electrode in a solution of CuCl2,with a semi-permeable membrane separating the two solutions. If a wire connects the two electrodes, electrons flow spontaneously from the zinc electrode to the copper electrode because is a stronger oxidising agent than Zn(s). At the copper cathode, Cu in the solution is reduced to CU(s) by electrons that are the product of the simultaneous oxidation of Zn(s) to Zn at the zinc anode. The difference in oxidation potential of the two metals results in a differential of approximately 1.10 volts between the two electrodes (assuming equal concentrations of Cu and Zn ). Across the membrane, Cf ions must move toward or... 

Diclofop-methyl is a herbicide which, upon entry into the plant, undergoes minimal acropetal and basipetal transport (8). In our experiments transport to the roots or to the leaves of [14C] diclofop-methyl applied to the axils of two-leaved susceptible and resistant Lolium plants does not appear to differ. No data are presently available as to whether proplastids or chloroplasts from the two biotypes exhibit differential permeability to diclofop-methyl or to the active acid derivative diclofop. Similarly, there is no evidence for a differential capacity to convert diclofop-methyl to diclofop nor differential sequestration of the ester or the acid in some secondary compartment such as the vacuole or within membranes. 

The term selectively permeable or differentially permeable is used to describe biological membranes because they restrict passage of particles based both on size and charge. Even small ions, such as H, cannot pass freely across a cell membrane. 

Saponins of Gypsophila plant facilitate the release of intracellular K+ and lactate dehydrogenase in rat hepatocytes, suggesting that they destabilize the plasma membrane [127] by removing membrane lipids [128]. Furthermore, Gypsophila plant derived saponins induce differential permeability of the intracellular membrane of rat hepatocytes [129], Vaccaroid A, a triterpenoid saponin from Vaccaria segetalis [130], induces contractivity of rat uterus. 

Within individual pressure cells, there is a shift in the petroleum gradient across minor faults (see structure map in Fig. 3). The southwesterly cell shows a shallowing of the petroleum-water contact from 30/7a-P7 to 30/7a-8 to 30/7a-Pl, i.e. in a northeasterly direction. The data suggest that a pressure differential of ca. 10 psi is required for migration to occur across each fault and that the fault acts as a semi-permeable membrane. This pressure difference is referred to as the capillary pressure of the fault. Thus, despite the common aquifer, differences in pressru-e within the petroleum gradients from well to well indicate that petroleum from individual fault compartments will have to be produced separately. 

Nonintestinal Cell Lines. Madin Darby canine kidney cells (MDCK [50]) differentiate into columnar epithelial cells forming tight Junctions when cultured on semi-permeable membranes they are commonly applied to study cell growth regulation, metabolism, toxicity, and transport at the level of the distal renal tubule epithelia [51]. MDCK cells, like Caco-2 cells, are suitable for molecular permeability screening studies MDCK cells have an advantage over Caco-2 cells in that they do not need 3 weeks in culture before differentiation, but a disadvantage is that they do not express P-gp. 

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