Organic cations, permeability

Fig. 7.14. Effective permeability (Peflr) of cimetidine in human jejunum at two clinically relevant luminal concentrations. A reasonable fa value for cimetidine has been estimated to 75% [90, 91]. Cimetidine may be a substrate for both P-gp and/or organic cation transporters (OCNT1 and OCNT2) [82, 92], This investigation was performed to determine...

The ion movement can be controlled by ion exchange or ion transfer membranes, thin sheets of cross-linked organic polymers with ion exchange properties—for example, sulfonated polystyrene-divinylbenzene polymers. Both cation-permeable and anion-permeable membranes are available and have been described (3, 9). To achieve demineralization, these membranes are spaced alternately between a cathode and an anode which introduce direct current. The compartment between each pair of membranes is filled with a saline water. The resulting ion motion is controlled by the membranes, so that one set of compartments—for example, the even-numbered compartments—lose ions and the odd-numbered compartments gain ions. The product from the ion-losing cells is collected and comprises electrically demineralized water. 

Figure 9.14 The effective permeabilities (Pefr, different clinically relevant concentrations to mean SD) of cimetidine in human jejunum at investigate saturation in any carrier-mediated two clinically relevant luminal concentrations. transport across the intestinal epithelium. No The rate and extent of intestinal absorption of difference in Pefr values between the two cimetidine have been widely discussed, and Fa concentrations was noted, and, togetherwith the for this drug has been estimated at around observation that human permeability in vivo is 75% [90, 91], It has been reported that cimetidine similar to permeability in the Caco-2 model (with is a substrate for both P-gp and/or organic cation low expression of carrier proteins), this suggests transporters (OCNT1 and OCNT2) [82, 92], We that passive diffusion is the dominant determined the human jejunal in vivo Pe - at two mechanism even for cimetidine [82],...

The Calu-3 human submucosal gland cell line forms polarized cell monolayers with tight junctions, produces mucus, and develops apical cilia when grown at an air interface. Transport studies can be performed after 10-14 days in culture, and it has been shown that Calu-3 cells express P-gp and actively transport amino acids, nucleosides, and dipeptide analogs organic anions, organic cations, polyamines, and efflux pump substrates are not actively transported.43,51,53-56 Because Calu-3 cells are not subject to the influence of multiple in vivo cell types, the expression of carrier proteins and enzymes may not reflect in vivo levels. Nevertheless, values obtained in Calu-3 permeability studies correlate well with those obtained from primary cultured rabbit tracheal epithelial cells and in vivo rat lung absorption studies.54 Mannitol permeation in Calu-3 cells is about 10 times less than that in vivo, but this is the same ratio difference between Caco-2 cells and in vivo intestinal epithelium.51... 

Henderson R, Wang J (1972) Solubilization of a specific tetrodotoxin binding component from garfish olfactory nerve membrane. Biochemistry 11 4565-4569 Hille B (1967) A pharmacological analysis of the ionic channels in nerve. Thesis, Rockefeller University. University Microfilms International, Ann Arbor, no 689584 Hille B (1971) The permeability of the sodium channel to organic cations in myelinated nerve. J Gen Physiol 58 599-619... 

More commonly, permselective membranes create a differential in the transport rate of different species. The permeability differences may be based on physical size, solubility differences, or specific interactions between the polymer and the diffusing species. Permselective membranes are used in a variety of functions, such as diffusion barriers and membranes for interference removal. A commonly used permselective membrane is Nafion which demonstrates an extremely high affinity for organic cations, reasonable affinity for inorganic cations, and almost completely excludes both organic and inorganic anions [16]. 

In a study of the effects of organic mercurials on the cation permeability of human red blood cells, Knauf and Rothstein (1971) found that the rate of uptake of PCMBS was diminished by 50% in cells exposed to SITS (4-acetamido-4 -isothiocyano-stilbene 2,2 -disulfonic acid), so that the total uptake could be divided into roughly equal SITS-sensitive and SITS-insensitive components. If the chloride in the bathing solution was replaced with either sulfate or phosphate, the SITS-sensitive component of PCMBS uptake was virtually unchanged whereas the SITS-insensitive component was substantially reduced. One interpretation of these results is that PCMBS enters by two routes, one the anion transporter that serves as a route for anionic complexes, and the other the lipid layer that permits the permeation of a neutral Cl complex of PCMBS, the latter perhaps being less abundant in the anion substituted media. Alternatively, a cationic form of the mercurial could permeate via some other membrane protein. 

Organic components of the catholyte were found to decompose anodically and, hence, it was necessary to use a separator. Alter considerable difficulties, a cation-permeable membrane was identified as suitable in the electrolysis conditions. The process, however, predated the developments in modern pcrfluorinated membranes (Chapter 3) and for many years the performance of the membrane was a problem. Indeed, this factor deten in l iranage-... 

A similar trend was observed in the body sections of these two cores, as shown in Figure 11. However the plugging was less severe in the body section of the core, which was only 0.45 in. from Che core face. It is worth mentioning that the body section of the treated core had a brine, permeability of 16 md before the treatment its brine permeability increased to 45 md after the treatment with 1 wt% hexylammonium chloride. Possibly the treatment with hexylammonium ion could help explain this permeability increase since it has been reported that organic cations help prevent clay swelling and dispersion in sandstone cores. ... 

Hille, B., 1971, The permeability of the sodium channel to organic cations in myelinated nerve, /. Gen. Physiol. 58 599. 

Dobrovinskaya OR, Muniz J, Pottosin II (1999b) Asymmetric block of the plant vacuolar Ca permeable channel by organic cations. Eur Biophys J 28 552-563 Drouin H, Hermann A (1994) Intracellular action of spermine on neuronal Ca and K currents. Eur J Neurosci 6 412-419... 

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