Osmotic water

The dehvery port can be sized sufficiently large that the back pressure is negligibly small. Equation 4 then reduces to equation 5, where k represents the osmotic water permeabihty of the membrane and S represents the solubihty of the dmg at saturated concentration. 

Cells are normally kept at osmotic (water activity) equilibrium by the action of the Na-pump. Inhibition of the pump with the specific Na -K -ATPase inhibitor, ouabain, causes cell swelling as does inhibition of it by hypothermia. The intracellular environment contains a high concentration of K (100 to 120 mM, in most mammalian cells), lower concentrations of Na (about 10 to 30 mM), and high... 

In view of the universal role of the area postrema (AP) in emesis among animal species, including man [54], an analysis of this structure in terms of receptors, neurotransmitters and neurophysiological responses is indicated. The AP has also been implicated in several other functions (cardiovascular, caloric intake, osmotic water balance) unrelated to emesis [55], The reader is referred to general and comprehensive references on this neuronal structure [36, 37, 56],... 

McGann, L.E., Kinetics of osmotic water movement in chontrocites isolated from articular cartilage and application to cryopreservation, /. Orthopedic Res., 6,109,1988. 

Nafion absorbs MeOH more selectively than water, and the MeOH diffusion flow is higher than the osmotic water flow in Nafion membranes. Diffusion coefficients of Nafion 117 determined by different techniques have been reported. Ren et al. measured MeOH diffusion coefficients in Nafion 117 membranes exposed to 1.0 M MeOH solutions using pulsed field gradient (PPG) NMR techniques. The MeOH self-diffusion coefficient was 6 x 10 cm S and roughly independent of concentration over the range of 0.5-8.0 M at 30°C. A similar diffusion coefficient was obtained for Nafion 117 at 22°C by Hietala, Maunu, and Sundholm with the same technique. Kauranen and Skou determined the MeOH diffusion coefficient of 4.9 x 10 cm for Nafion... 

The simple water charmel models can explain the ionomer peak and the small-angle upturn in the scattering data of fhe unoriented samples as well as of the oriented films. Interestingly, the helical structure of backbone segments is responsible for fhe sfabilify of fhe long cylindrical charmels. The self-diffusion behavior of wafer and protons in Nation is well described by the water channel model. The existence of parallel wide channels af high wafer uptake favors large hydrodynamic confributions to electro-osmotic water transport and hydraulic permeation. 

It is our hypothesis that the presence of large amounts of K" " in the cell is a major determining factor in ozone injury at the cellular level. The alteration of K+ permeability (coupled with an inhibition of the mechanism for regaining the lost K" ") causes a large loss of K" " (down an electro-chemical potential gradient) followed by a rapid loss of osmotic water. 

It is ultimately this loss of osmotic water which leads to... 

In conclusion, it is our view that K+ plays a dominant role in maintaining a favorable plant cell water status and that the deleterious effects of ozone occur primarily due to disruption of this normal ionic balance. We currently visualize the following scheme of ozone damage (a) ozone attack of an SH group or fatty acid residue (b) permeability changes of the membrane leading to loss of both K" " and osmotic water (c) inhibition or loss of K" " pump activity for reacquisition of lost K+ (d) loss of a critical level of ion and (e) gross disruption of cellular metabolism. 

Fig. 3 Aquaporin deletion reduces osmotic water permeability in lung, but does not impair active fluid absorption, a AQP expression in epithelia and endothelia in nasopharyngeal cavity, upper and lower airways, and alveoli, b Osmotically driven water transport across the airspace/capillary barrier in perfused lungs from wildtype and indicated AQP null mice. Note the remarkable slowing of osmotic equilibration in mice lacking AQPl or AQP5. c Alveolar fluid clearance measured from the increased concentration of a volume marker 15 min after instillation of isosmolar fluid at 37°C. Where indicated, fluid absorption was inhibited by amiloride or stimulated by isoproterenol. From Bat et al. (1999) and Ma et al. (2000a)...

The contribution of free salt ions to the electric conductivity may therefore be negligible and only the adsorbed countercharge of cations will then contribute to electric conduction. The derived values of ke enable the prediction of the electro-osmotic water flux by active application of an electric potential gradient. Thus, at 0.01 M NaCl in the compacted bentonite, a gradient of 1 V/m will, in the absence of a hydraulic pressure gradient, cause a water flux of the order of 10 10 m/s. 

Robertson, J.C., and J.R. Hazel (1999). Influence of temperature and membrane lipid composition on the osmotic water permeability of teleost gills. Physiol. Biochem. Zool. 72 623-632. 

The combination of active drug, preservative, and vehicle usually results in a hypotonic formulation (< 290 mOsm). Simple or complex salts, buffering agents, or certain sugars are often added to adjust osmolarity of the solution to the desired value. An osmolarity of 290 mOsm is equivalent to 0.9% saline, and this is the value sought for most ophthalmic and intravenous medications.The ocular tear film has a wide tolerance for variation in osmotic pressure. However, increasing tonicity above that of the tears causes immediate dilution by osmotic water movement from the eyelids and eye. Hypotonic solutions are sometimes used to treat dry eye conditions and to reduce tear osmolarity from abnormally high values. 

Effects on the bile flow due to osmotic water movement... 

A theoretical approach to calculate the burst time from an osmotically active spherical capsule, which depended on the initial radius, wall thickness, osmotic pressure of the contents, and the material of the capsule, has been presented. This approach assumed that the spherical core increases in size upon osmotic water influx, leading to an elongation of the membrane until a certain yield stress is reached to rupture it. The rate of volume increase was described by the following equation ... 

Hepatic Bile Formation. Carrier-mediated active transport of bile acids across the canalicular surface generates osmotic water flow that is a major factor regulating bile formation and secretion. Transport of these organic anions also influences secretion of the remainder of the major components of bile, such as bilirubin, cholesterol, and phospholipids. There is no secretion of the latter two compounds in the absence of bile acid secretion. The influence of bile acid... 

Kreuer et al. [25] investigated the membrane properties, including water sorption, transport (proton conductivity, electro-osmotic water drag and water diffusion), microstructure and viscoelasticity of the short-side-chain (SSC) perfluorosulfonic acid ionomers (PFSA, Dow 840 and Dow 1150) with different lEC-values. The data were compared to those for Nafion 117, and the implications for using such ionomers as separator materials in direct methanol and hydrogen fuel cells discussed. Tire major advantages of PFSA membranes were seen to be (i) a high proton conductivity. 

The variation of current efficiency with solution concentration in the chlor-alkali environment is an added complicating feature of these membranes behavior. Kruissink (9) has performed elaborate calculations to yield the effect of electro-osmotic water transport on permselectivity, in classical terms. Results suggest that the minimum seen in t a+ (at lower NaOH concentrations than used here)... 

At low current density the degree of sodium ion hydration is small— about two water molecules for every sodium ion. The ratio /H2o//Na remains steady until about 0.3 amps cm"2 then rises with increasing current density. The dependence of cation transport number (5,6) and electro-osmotic water fluxes (7,8) on current density have been reported previously. In these cases the dependence of fluxes on current density can be explained by solution polarization phenomena alone. 

The same experiment was carried out several times with different pieces of Nafion 390 cut from a large sheet all data showed similar trends in current efficiency and electro-osmotic water with increasing current density. However, results from each membrane were nonidentical, presumably because of macroscopic inhomogeneities. 

Although the liver is commonly identified with its primary role of drug metabolism, one of the main functions of the liver is the formation of bile. BUe forms in the canaliculus between adjacent hepatocytes following active secretion bUe acids and other components (phospholipids, bilirubin, cholesterol) across the canalicular membrane. These components are either synthesized by the liver or transported into the hepatocyte across the sinusoidal membrane. Bile acid secretion stimulates osmotic water flow across the canalicular membrane. The resulting bile drains into branches of intrahepatic bile ductules that converge to the common hepatic bUe duct. In humans, 500 to 600 ml of bile is produced daily. 

Diffusion of solvent through the ion exchange membrane is called osmosis, which is caused by a difference in the chemical potential of the solvent across the membrane. Solvent is transported from the dilute solution to the concentrated and osmotic water is proportional to the osmotic pressure between the two solutions, II, which is expressed as follows (aw and 5W activities of solvent in the solution and in the membrane phase),... 

When a direct current passes through an ion exchange membrane immersed in electrolyte solution, counter-ions are transported through the membrane, accompanied by water molecules, which is the electro-osmotic water. Because the liquid in a membrane pore has the same charge as the counter-ion, the liquid moves in... 

Dj is proportional to the fixed ion concentration of the membrane and inversely proportional to the specific flow resistance and specific conductivity. Also, Df is independent of membrane thickness. Figure 2.6 shows the change in electro-osmotic water transport with the fixed ion concentration of an anion exchange membrane measured with 0.5 N sodium chloride solution.25 Dj decreases with increasing fixed ion concentration. The specific conductance of the membrane increases and the water content of the membrane decreases (po increases) with increasing fixed ion concentration of the membrane. The electro-osmotic behavior through the membrane is not simply explained from this experimental data. 

Figure 2.6 Change in electro-osmotic water coefficient with fixed ion concentration of an anion exchange membrane. Measured in 0.50 N sodium chloride solution using an anion exchange membrane (v = fit, v volume flux ft electro-osmotic water coefficient I current density t period).

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