Potassium permeation

The striking compartmentalization of potassium in intracellular fluid, and of sodium in extracellular fluid, is a condition which is established and maintained by active transport across all plasma membranes. In the absence of active transport pumps, cotransporters and conductance channels, a directional, selective, rapid and regulated movement of potassium (or sodium) through the cell membranes would be impossible. The major molecular pathways of potassium permeation through plasma membranes are Na, K- ATPase, H-K-ATPase, Na-2C1-K-transporter, and potassium conductance channels (Peterson 1997). 

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]. 

Rona and Schmuckler [410] used gel permeation chromatography to separate lithium from Dead Sea brine. The elements emerged from the column in the order potassium, sodium, lithium, magnesium, and calcium and it was possible to separate a lithium-rich fraction also containing some potassium and sodium but no calcium and magnesium. 

If the pore-mechanism applies, the rate of permeation should be related to the probability at which pores of sufficient size and depth appear in the bilayer. The correlation is given by the semi-empirical model of Hamilton and Kaler [150], which predicts a much stronger dependence on the thickness d of the membrane than the solubility-diffusion model (proportional to exp(-d) instead of the 1 Id dependence given in equation (14)). This has been confirmed for potassium by experiments with bilayers composed of lipids with different hydrocarbon chain lengths [148], The sensitivity to the solute size, however, is in the model of Hamilton and Kaler much less pronounced than in the solubility-diffusion model. 

Paula, S., Volkov, A. G., van Hoek, A. N., Haines, T. H. and Deamer, D. W. (1996). Permeation of protons, potassium ions, and small polar solutes through phospholipid bilayers as a function of membrane thickness, Biophys. J., 70, 339-348. 

The potassium chloride and potassium sulphate system was studied. The results of tests carried out (Table 11.2) showed that the recovery levels of potassium chloride permeate were excellent at the higher operating temperatures, with almost perfect rejection of potassium sulphate. The SRS skid could be designed for use in the caustic potash industry and recover potassium chloride from effluent purges. 

Table 19.1 Composition of various buffer systems possibly eligible for combined dissolution and permeation testing. Concentrations may vary from reference to reference. Composition of FaSSIF and FeSSIF is shown as reported by Galia et al. [3] in the meantime, several publications denoted a change from potassium to sodium as the main cation [91] or others changes. Abbreviations are given in the text. 

Even in this case, the use of a hybrid process combining NF, IE, and ED appears to improve the economics and performance of the tartaric stabilization of wines. For instance, Ferrarini (2001) proposed to split raw wine into a retentate and permeate by NF. The permeate, being richer in minerals, was processed by using in sequence cationic and anionic exchange resins and ED to reduce its potassium, calcium, and tartrate ion contents. By recombining the de-ashed permeate with the NF retentate, Ferrarini (2001) asserted to obtain a stabilized wine retaining almost all the flavor and aroma compounds originally present in raw wine. 

The simplest of these functions is that of a permeability barrier that limits free diffusion of solutes between the cytoplasm and external environment. Although such barriers are essential for cellular life to exist, there must also be a mechanism by which selective permeation allows specific solutes to cross the membrane. In contemporary cells, such processes are carried out by transmembrane proteins that act as channels and transporters. Examples include the proteins that facilitate the transport of glucose and amino acids into the cell, channels that allow potassium and sodium ions to permeate the membrane, and active transport of ions by enzymes that use ATP as an energy source. 

Types of explosives containing large amounts of ammonium nitrate. The oldest of these explosives (see Roburit, Favier Explosives) contain no nitroglycerine they consist of ammonium nitrate, often with some potassium nitrate, and aromatic di- and trinitro prod-nets. Their disadvantages are low sensitiveness and defective propagation. Later improved ammonium nitrate explosives contain small amounts of nitroglycerine. The nitroglycerine permeates the pulverent... 

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