Permeability, of sodium

Neurotransmitters can be classified as excitatory or inhibitory, depending on the nature of the action they elicit. Stimulation of excitatory neurons causes a movement of ions that results in a depolarization of the postsynaptic membrane. These excitatory postsynaptic potentials (EPSP) are generated by the following (1) Stimulation of an excitatory neuron causes the release of neurotransmitter molecules, such as norepinephrine or acetylcholine, which bind to receptors on the postsynaptic cell membrane. This causes a transient increase in the permeability of sodium (Na+) ions. (2) The influx of Na+ causes a weak depolarization or excitatory postsynaptic potential (EPSP). (3) If the number of excitatory fibers stimulated increases, more excitatory neurotransmitter is released, finally causing the EPSP depolarization of the postsynaptic cell to pass a threshold, and an all-or-none action potential is generated. [Note The generation of a nerve impulse typically reflects the activation of synaptic receptors by thousands of excitatory neurotransmitter molecules released from many nerve fibers.] (See Figure 8.2 for an example of an excitatory pathway.)... 

Saxitoxins (see structure for Saxitoxin or SXT, CAS 35523-89-8, C10H17N7O4) are produced by Alex-andrium spp. (Gonyaulax) and several of the cyanobacteria. Heat-stable neurotoxic saxitoxins have a relaxant action on vascular smooth muscle. They inhibit the temporary permeability of sodium ion influx by binding I I with high affinity to a specific receptor site on the outside surface of the membrane... 

Fabra, M.J., Talens, P., Chiralt, A. Effeet of alginate and A-carrageenan on tensile properties and water vapour permeability of sodium easeinate-lipid based films. Carbohydr. Polym. 74(3), 419-426 (2008)... 

Valinomycin assists potassium ions to penetrate erythrocytes, mitochondria (Moore and Pressman, 1964), and bacterial plasma membranes (Harold and Baarda, 1967) but has little effect on the permeability of sodium, lithium, or hydrogen ions. Nonactin acts similarly, but monactin also slightly assists the permeability of sodium (Henderson, McGivan and Chappell, 1969). Valinomycin is active against cancer in mice (Carter, Sakurai and Umezawa, 1981). 

Studies on the permeability of sodium bentonite indicated that pure organic compounds can be detrimental to the liner s performance. Cracking was found to occur, when compounds such as alcohols (e.g. methanol) and ketones (e.g. acetone) were introduced in high concentrations. Strong acids (e.g. hydrofluoric and phosphoric acids) and bases (e.g. NaOH) can also be quite aggressive on soil minerals and cause variations of hydraulic conductivity. However, the problem posed by organic solvents is probably exaggerated in the case of domestic landfills, as these substances normally represent a minimal proportion of the components of leachate in domestic waste landfill sites. 

For waterproofing, sodium silicate concentrations below 30% are adequate concentrations between 35 and 70% are used for strength improvement. Grouts having 35 vol % or higher silicate resist deterioration on freeze—thaw or wet—dry cycles. Water permeability of sands can be reduced from 10 to 10 cm/s. Unconfined compressive strengths of stabilized sand can vary from 103 to 4130 kPa (15—600 psi) the normal range is between 690 and 1380 kPa. 

The poor efficiencies of coal-fired power plants in 1896 (2.6 percent on average compared with over forty percent one hundred years later) prompted W. W. Jacques to invent the high temperature (500°C to 600°C [900°F to 1100°F]) fuel cell, and then build a lOO-cell battery to produce electricity from coal combustion. The battery operated intermittently for six months, but with diminishing performance, the carbon dioxide generated and present in the air reacted with and consumed its molten potassium hydroxide electrolyte. In 1910, E. Bauer substituted molten salts (e.g., carbonates, silicates, and borates) and used molten silver as the oxygen electrode. Numerous molten salt batteiy systems have since evolved to handle peak loads in electric power plants, and for electric vehicle propulsion. Of particular note is the sodium and nickel chloride couple in a molten chloroalumi-nate salt electrolyte for electric vehicle propulsion. One special feature is the use of a semi-permeable aluminum oxide ceramic separator to prevent lithium ions from diffusing to the sodium electrode, but still allow the opposing flow of sodium ions. 

The permeability tests for alkali metal ions in the aqueous solution were also conducted. When an aqueous salt solution moves to cell 2 through the membrane from cell 1, the apparent diffusion coefficient of the salt D can be deduced from a relationship among the cell volumes Vj and V2, the solution concentration cx and c2, the thickness of membrane, and time t6 . In Table 12, permeabilities of potassium chloride and sodium chloride through the 67 membrane prepared by the casting polymerization technique from the monomer solution in THF or DMSO are compared with each other and with that the permeability through Visking dialyzer tubing. The... 

Table 12. Permeability of potassium chloride and sodium chloride through poly(tetrahydro-pyran-2,6-diyliminocarbonyl) membrane in aqueous solution at 25 °C70 ...

The term chlor-alkali refers to those products obtained from the commercial electrolysis of aqueous sodium chloride. These are chlorine, sodium hydroxide, and sodium carbonate. The first two are produced simultaneously during the electrolysis while the latter is included because it is also produced in small quantities and shares many of the end uses of sodium hydroxide. Perfluorinated ionomer membranes are permeable to sodium ions but not the chloride ions, and hence they are useful for these electrolytic cells. The arrangement of a typical membrane cell is shown in Figure 10.2. 

The GSH reductase inhibitor l,3-bis(2-chloroethyl)-l-nitrosourea (BCNU) also promotes corneal swelling in the isolated cornea. The addition of GSH prevents the action of BCNU as the cornea needs a constant supply of NADPH for maintaining adequate concentrations of reduced glutathione for the detoxification of hydrogen peroxide. It has been shown that hydrogen peroxide and BCNU primarily affect the permeability of the endothelial cells rather than the active processes transporting sodium and chloride ions across the membrane (Riley, 1985). 

Using liposomes made from phospholipids as models of membrane barriers, Chakrabarti and Deamer [417] characterized the permeabilities of several amino acids and simple ions. Phosphate, sodium and potassium ions displayed effective permeabilities 0.1-1.0 x 10 12 cm/s. Hydrophilic amino acids permeated membranes with coefficients 5.1-5.7 x 10 12 cm/s. More lipophilic amino acids indicated values of 250 -10 x 10-12 cm/s. The investigators proposed that the extremely low permeability rates observed for the polar molecules must be controlled by bilayer fluctuations and transient defects, rather than normal partitioning behavior and Born energy barriers. More recently, similar magnitude values of permeabilities were measured for a series of enkephalin peptides [418]. 

Yamashita et al. [82] added up to 10 mM taurocholic acid, cholic acid (cmc 2.5 mM), or sodium laurel sulfate (SLS low ionic strength cmc 8.2 mM) to the donating solutions in Caco-2 assays. The two bile acids did not interfere in the transport of dexamethasone. However, SLS caused the Caco-2 cell junctions to become leakier, even at the sub-CMC 1 mM level. Also, the permeability of dexamethasone decreased at 10 mM SLS. 

Calcium bentonite, as though more permeable than sodium bentonite, has also been used for soil blends. Approximately twice as much calcium bentonite typically is needed however, to achieve a hydraulic conductivity comparable with that of sodium bentonite. One problem with using sodium bentonite, however, is its vulnerability to attack by chemicals and waste leachates, a problem that will be discussed later. 

Since calcium bentonite, typically, is 100-1000 times more permeable than sodium bentonite, the introduction of this permeating liquid could change hydraulic conductivity substantially. 

Morimoto et al. [33] demonstrated that the ocular absorption of hydrophilic compounds over a wide range of molecular weights could be increased by 2 and 10 mM sodium taurocholate and sodium taurodeoxycholate in a dose-dependent manner. The compounds were glutathione (307 Da), 6-carboxyfluorescein (376 Da), FTTC-dextran (4 kDa), and insulin (5.7 kDa). Of the two bile salts, sodium taurodeoxycholate was more effective. At 10 mM, this bile salt increased the permeability of 6-carboxyfluorescein from 0.02% to 11%, glutathione from 0.08% to 6%, FITC-dextran from 0% to 0.07%, and insulin from 0.06% to 3.8%. Sodium taurocholate, on the other hand, increased the permeability to 0.13%, 0.38%, 0.0011%, and 0.14%, respectively. Taurodeoxycholate was more effective than taurocholate in the nasal epithelium as well [202], This difference in activities can possibly be attributed to their micelle-forming capability, which is higher for taurodeoxycholate, a dihydroxy bile salt [190],... 

DM Maurice. (1951). The permeability to sodium ions of the living rabbit cornea. J Physiol 112 367-391. 

H Yasuda, CE Lamaze, LD Ikenberry. Permeability of solutes through hydrated polymer membranes I. Diffusion of sodium chloride. Makromol Chem 118 196-206, 1968. 

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