Anion Transport Properties Research Articles

Comparison of transport properties of monovalent anions through anion-exchange membranes

Transport properties of chloride, fluoride and nitrate ions through AFN, AMX, ACS, ACM anion-exchange membranes (from Tokuyama Soda) and MA-40 membrane (from the Institute of Plastic Materials, Moscow) have been investigated by studying electroconductivity, transport numbers and current–voltage characteristics. On the basis of the micro-heterogeneous model proposed by Nikonenko and Zabolotsky describing the microstructure of the membrane material, the volume fractions of the different phases and the electroconductivity of the joint-gel phase have been determined. Good correlations have been founded between the electroconductivity of the anion-exchange membranes (AEMs) and their structural properties. Recommendations are provided to determine which kind of membrane has to be selected for a given application. For all the membranes, increase of the counter-ion mass transfer is observed above the limiting current.

Preparation and transport properties of anion-exchange membranes containing viologen moieties as anion-exchange groups in the presence or absence of photoirradiation

Anion-exchange membranes containing viologen groups have been prepared from chloromethylstyrene and divinylbenzene copolymer membranes and 4,4′-bipyridine. The viologen moieties were reduced by photoirradiation to form radical monocations and biradicals in pure water and various salt solutions. As the viologen moiety was changed from a divalent to a monovalent cation and to an uncharged group upon photoirradiation, the transport numbers of sulfate, bromide, nitrate and fluoride ions, decreased relative to chloride ions. After oxidation of the reduced viologen group of the membranes with air, the transport properties of anions through the membrane became the same as before photoirradiation. The transport properties of the membranes changed reversibly between photoirradiation (reduced form) and oxidation of the reduced form. The decrease in the transport numbers of the various anions relative to chloride ions is due to a sieving effect because of the shrinkage of the polymer network due to a decrease in the charge density of the anion-exchange membranes. The decrease in the pore size of the membrane upon photoirradiation was also confirmed by the decrease in the permeability coefficient of a neutral molecule, urea.

Bicarbonate permeability of the outwardly rectifying anion channel

Single anion-selective channels have been studied in cultured human epithelial cells using the patch-clamp technique. Three cell types were used as models for different anion transport systems: (i) PANC-1, a cell line derived from the pancreatic duct, (ii) T84, a Cl-secreting colonic cell line, and (iii) primary cultures of sweat duct epithelium. Outwardly rectifying anion-selective channels were observed in all three preparations and were indistinguishable with respect to conductance, selectivity and gating. Striking similarities between HCO3- and Cl-secreting epithelia, and the high density of outward rectifiers in pancreatic cells prompted us to study HCO3 permeation through this channel. HCO3 permeability was significant when channels were bathed in symmetrical 150 mM HCO3 solutions, Cl-HCO3 mixtures, and under bi-ionic conditions with outwardly and inwardly directed HCO3 gradients. Permeability ratios (PHCO3/PCl) estimated from bi-ionic reversal potentials ranged from 0.50 to 0.64, although conductance ratios greater than 1.2 were observed with high extracellular pH. Chloride did not inhibit HCO3 permeation noticeably but rather had a small stimulatory effect when present on the opposite side of the membrane. The prevalence of outward rectifiers in PANC-1 and their permeability to bicarbonate suggests the channel may have a dual role in HCO3 secretion; to allow Cl recycling at the apical membrane and to mediate some of the HCO3 flux. Defective modulation of this channel in cystic fibrosis might provide a common basis for dysfunction in epithelia having very different anion transport properties (e.g., HCO3 secretion, Cl secretion and Cl absorption.

Interatomic potential and phonon frequencies in α and β phases of lead fluoride

Reports an interatomic potential for lead fluoride which is based on the shell model of lattice dynamics. The potential provides a good description of the experimentally determined dispersion curves in the beta (cubic) phase, the measured Raman frequencies in the alpha -phase and the formation energy of anion Frenkel defects in this solid. The authors suggest the use of this potential for studying other anion transport properties in PbF2.

New approaches for the reconstitution and functional assay of membrane transport proteins. Application to the anion transporter of human erythrocytes

The human red blood cell anion transport protein, band 3, was isolated and reconstituted into lipid vesicles. The main feature of the new reconstitution is the replacement of native lipids and of solubilizing detergent by externally added lipids, while band 3 protein is immobilized on a gel matrix. The vesicles formed upon detergent removal and sonication are unilamellar and sealed, and band 3 protein is the major polypeptide detectable in them. The method consists of: (a) solubilization of alkali-treated red blood cell membranes by Triton X-100; (b) binding of glycophorin and band 3 protein to diethylaminoethyl (DEAE)-cellulose in Triton X-100 solution, followed by high ionic strength elution; (c) band 3 protein complexation to organomercurial Sepharose; (d) exchange of the Triton X-100 with the dialyzable detergent octylglucopyranoside, while band 3 protein is complexed to the column; (e) elution of band 3 by cysteine (5 mM) in the presence of octylglucopyranoside; (f) addition of lipids (asolectin or egg phosphatidylcholine) to the protein-detergent suspension; and (g) dialysis of the mixture against 1% bovine serum albumin to remove the detergent completely. The vesicles were assayed for anion transport capacity by a novel procedure which is based on the fluorescent substrate N-(2- aminoethylsulfonate)7- nitrobenz-2- oxa-1,3- diazole (NBD-taurine) and on anti-NBD-antibodies as quenchers of extravesicular NBD-taurine fluorescence. Efflux of NBD-taurine from vesicles was monitored in a continuous mode as a decrease in intravesicular fluorescence. The band 3-mediated flux was approx. 50% inhibitable by externally added disulfonic stilbenes, indicating the random distribution of band 3 protein in reconstituted vesicles. Both the specific transfer rate (i.e., nmol substrate/mg protein per min) of band 3 and its energy of activation ( E a ) in the artificial lipid milieu were similar to those obtained with the native system. Glycophorin incorporation into this milieu had no significant effect on the associated anion transport properties.

The effects of dopant cation-oxygen vacancy complexes on the anion transport properties of non-stoichiometric fluorite oxides

We have calculated the effect of association of dopant cations and oxygen vacancies on the concentration of vacancies free to become charge carriers in anion deficient oxides. The calculations show that even with only modest association energies the vacancies stay bound to the cations even at high temperatures. The consequences of this effect are discussed for fast anion transport in oxides.

PAH transport in rock crab urinary bladder. II. Luminal and serosal steps.

To characterize the organic anion transport properties of the luminal (1) and serosal (s) membranes of crab urinary bladder, initial (10 min) fluxes (J) and tissue accumulations (Ac) of 10 microM PAH were measured in the absence and presence of 1 mM BCG (nontransported, high-affinity competitor). Control bladders exhibited net reabsorptive transport with a mean Jl leads to s/Js leads to 1 of about 7; concentrative transport of p-aminohippuric acid (PAH) occurred only across the luminal cell (c) membrane. With luminal PAH, luminal bromocresol green (BCG) reduced Jl leads to c, Jc leads to s, and Ac by about 85%; serosal BCG reduced Jc leads to s, increased Ac but had no effect on Jl leads to c. With serosal PAH, serosal BCG reduced Js leads to c, Jc leads to l, and Ac; luminal BCG had no effects on either fluxes or tissue accumulation. When bladder sheets were loaded with radiolabeled PAH, mounted in a chamber, and exposed to flowing crab Ringer solution on both sides, Jc leads to s was nearly twice as large as Jc leads to l; BCG significantly reduced Jc leads to s but not Jc leads to l. With unlabeled PAH in the efflux media, Jc leads to s was increased. The data are consistent with a model featuring an inwardly directed pump at the luminal membrane, a facilitated carrier at the serosal membrane, and nonmediated pathways at both membranes.

A study of anion transport in bismuth based oxide systems by electrical conductivity and secondary ion mass spectroscopy (SIMS)

The anion transport properties of the γ-Bi2O3 (sillenite) structure compounds MOX.− 6Bi2O3 with M = Si and Pb have been determined by electrical conductivity and oxygen self diffusion measurements. The differences in transport properties seen are related to the nature of the M cation.

Alterations in chloride transport during differentiation of Friend virus‐transformed cells

Friend erythroleukemic cells can be induced by a variety of agents to synthesize hemoglobin and to exhibit other characteristics suggesting erythroid maturation. Upon induction of hemoglobin synthesis with dimethylsulfoxide (DMSO), the chloride flux in Friend cells gradually increases, until after five days of exposure to DMSO (when the hemoglobin content of the cells approaches that of the mature erythrocyte) the flux is three times the value in non-induced cells. A similar flux increase is observed in the presence of a different type of inducer, hypoxanthine, but no increase in flux is seen in the mutant cell line, TG-13, which does not synthesize hemoglobin after DMSO treatment. Thus, the flux increase seems to be associate d with the induction process, rather than being a direct effect of the inducing agent. After DMSO treatment, the sulphate flux decreases and the chloride/sulphate selectivity increases, aswould be expected if the cells were becoming more like red cells. On the other hand, the sensitivity of the chloride flux to the inhibitor, furosemide, and to temperature is the same in the induced as in the non-induced Friend cells, and different from that of the mature red cell. Thus, the anion transport properties of the induced Friend cell are different from those of both the non-induced Friend cell and the mature erythrocyte. Either the system in the induced cell represents an intermediate stage in the development of the mature red cell characteristics, or else the maturation of transport function in the Friend cell differs from that in normal erythrocyte precursors.

The interaction of the anionic fluorescence probe, 1-anilinonaphthalene-8-sulfonate, with hepatocytes and hepatoma tissue culture cells

The fluorescence probe 1-anilinonaphthalene-8-sulfonate (ANS) has been used to characterize the anion transport properties of normal hepatocytes and hepatoma tissue culture cells. Incubation of hepatocytes in the presence of ANS (20 μM) resulted in a 35-fold enhancement of fluorescence and a 50 nm blue shift. The time course of this process is biphasic. A rapid initial fluorescence enhancement suggests ANS binding to the plasma membrane, and a slower component reflects the uptake of ANS into intracellular compartments. Analysis of ANS uptake showed this latter process to be saturable, with a K m of 10 μM, to be temperature dependent and to occur only in viable cells. The above observations suggest a carrier-mediated anion transport mechanism. Incubation of hepatoma tissue culture cells with ANS (20 μM) gave a fluorescence emission spectrum similar to that obtained from purified plasma membranes. The kinetics of this interaction only exhibited a rapid initial binding of ANS. The second slow component was now absent, suggesting that ANS transport by the malignant cell system was greatly reduced. Transport of ANS could, however, be stimulated in the presence of the local anesthetic tetracaine. The observed transport was now saturable, temperature dependent, and as in normal hepatocytes, required viable cells, again indicating a carrier-mediated transport system. These studies suggest a significant alteration in membrane function in hepatoma tissue culture cells resulting in a major defect in anion transport.