Anion transporter

The Anion Transporter of Erythrocytes Also Operates by Facilitated Diffusion... 

FIGURE 10.7 A model for the arrangement of the anion transport protein in the membrane, based on hydropathy analysis. 

The gradients of H, Na, and other cations and anions established by ATPases and other energy sources can be used for secondary active transport of various substrates. The best-understood systems use Na or gradients to transport amino acids and sugars in certain cells. Many of these systems operate as symports, with the ion and the transported amino acid or sugar moving in the same direction (that is, into the cell). In antiport processes, the ion and the other transported species move in opposite directions. (For example, the anion transporter of erythrocytes is an antiport.) Proton symport proteins are used by E. coU and other bacteria to accumulate lactose, arabinose, ribose, and a variety of amino acids. E. coli also possesses Na -symport systems for melibiose as well as for glutamate and other amino acids. 

Mass transport measurements have shown that cation transport predominates in FeO (Fe ) and Fej04 (Fe, Fe ), whereas anion transport predominates in FejOj (0 ). This leads to the well-accepted growth scheme for multi-layered scale growth on iron shown in Fig. 7.3, with the governing equations for individual layer growth being ... 

Cellular defense mechanisms against toxins (A multistep mechanism for elimination of toxic metabolites and xenobiotics. It involves various transport, oxidation, and conjugation steps.) are usually divided into several steps as it is visualized on Fig. 3. Organic anion transporting proteins (OATPs) are responsible for the cellular uptake of endogenous compounds and... 

MDR-ABC Transporters. Figure 3 Detoxification cellular mechanisms. X, toxic compound X-OH, oxidized toxic compound GS-X, conjugated toxic compound OATP, organic anion transporting proteins CYPs, cytochromes GSH, glutathion UDPGIcUA, Uridine 5-diphosphoglucuronic acid PAPs, 3-phosphoadenylylsulfate. 

Gall bladder Various oral cystographic agents, e.g., iopanoic acid Telepaque etc. Anion transport Urich K, Speck U (1991) Biliary excretion of contrast media. Progr Pharmacol Clin Pharmacol 8 307-322... 

Bile ducts Various intravenous cholegraphic agents, e.g., iodipamide Biligrafin Anion transport Lin SK et al (1977) Iodipamide kinetics Capacity-limited biliary excretion with simultaneous pseudo-first-order renal excretion. J Pharm Sci 66 1670-1674... 

Sasaki M, Suzuki H, Aoki J, Ito K, Meier PJ and Sugiyama Y. Prediction of in vivo biliary clearance from the in vitro transcellular transport of organic anions across a double-transfected Madin-Darby canine kidney II monolayer expressing both rat organic anion transporting polypeptide 4 and multidrug resistance associated protein 2. Mol Pharmacol 2004 66 450-9. 

Wright SH and Dantzler WH. Molecular and cellular physiology of renal organic cation and anion transport. Physiol Rev 2004 84 987-1049. 

Tamai I, Nezu J, Uchino H, Sai Y, Oku A, Shimane M, et al. Molecular identification and characterization of novel members of the human organic anion transporter (OATP) family. Biochem Biophys Res Commun 2000 273 251-60. 

Chang C, Pang KS, Swaan PW, Ekins S. Comparative pharmacophore modeling of organic anion transporting polypeptides a meta-analysis of rat Oatplal and human OATPIBI. J Pharmacol Exp Ther 2005 314 533-41. 

Yarim M, Moro S, Huber R, Meier PJ, Kaseda C, Kashima T, et al. Application of QSAR analysis to organic anion transporting polypeptide la5 (Oatpla5) substrates. Bioorg Med Chem 2005 13 463-71. 

Heijn, M., Oude Elferink, R. and Jansen, P. (1992). ATP-dependent multispecific organic anion transport system in rat erythrocyte membrane vesicles. Am. J. Physiol. 262, 104-110. 

FIG. 2 Model explaining the ability of tenidap to lower intracellular pH. Step 1 drug dissociation dictated by its pK value Step 2 entry of the conjugate acid of tenidap into the cell by diffusion, followed by reestablishment of the acid-base equilibrium Step 3 transport of tenidap anion out of the cell, activated by an anion transporter. (Reprinted from Ref. 107.)... 

Inhibition of anion transport in Nation was attributed to the inhomogeneous structure of the ion exchange sites in the polymer network (Gierke cluster network model). It was found that Nation contains (even in... 

Radiotracer techniques involving lsO in the anodization process are used with subsequent neutron activation analysis84 or SIMS.85 Another method involves implantation of inert ion markers into the surface layer of the sample prior to anodization and examination of the position of the markers after the oxide film has grown to a certain thickness.86 Assuming immobility of the inert species, the ratio of the cation to the anion transport number, t+/, should be equal to the ratio of the outer to the inner layer thickness. Numerous experimental determinations72,87 suggest t+ and f to be 0.4 and 0.6, respectively. 

C. C. Paulusma, R. P. Oude Elferink et al. Drug export activity of the human canalicular multispecific organic anion transporter in polarized kidney MDCK cells expressing cMOAT (MRP2) cDNA, J. Clin. Invest. 1998, 101, 1310-1319... 

In cell lines, the organic anion transporters (OAT and OATP) have been identified and cloned into cells of kidney origin such as LLC-PK1, MDCK, HK-2, and Caco-2 [129]. The most well-known uptake transporters, which transport the substrate over the membrane into the organism are the amino acid- [35, 42, 139] and oligopeptide-carriers (PepTl and PepT2) [139-142]. These two transporter families are abundantly expressed in the small intestine of most animals, and can therefore be involved in the absorption process of pharmaceutical drugs. The PepTl is expressed in the cell lines Caco-2 and HT-29 [140-142]. 

Fig.n.2. Human duodenal expression variability of nucleoside, organic cation ion, and anion transporters (unpublished data). Shaded box indicates 25-75% of expression range, the line within the box marks the median, and error bars indicate 10-90% of expression range. ENT2, equilibrative nucleoside transporter CNT1, concentrative pyrimidine nucleoside transporter CNT2, concentrative purine nucleoside transporter ... 

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