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Chronic kidney disease progression can be predicted based on the degree of tubular atrophy, which is the result of proximal tubule apoptosis. The [Na.sup.+]/[H.sup.+] exchanger NHE1 regulates proximal tubule cell survival through interaction with phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2], but pathophysiologic triggers for NHE1 inactivation are unknown. Because glomerular injury permits proximal tubule luminal exposure and reabsorption of fatty acid/albumin complexes, we hypothesized that accumulation of amphipathic, longchain acyl-CoA (LC-CoA) metabolites stimulates lipoapoptosis by competing with the structurally similar PI(4,5)P2 for NHE1 binding. Kidneys from mouse models of progressive, albuminuric kidney disease exhibited increased fatty acids, LC-CoAs, and caspase-2--dependent proximal tubule lipoapoptosis. LC-CoAs and the cytosolic domain of NHE1 directly interacted, with an affinity comparable to that of the PI(4,5)P2-NHE1 interaction, and competing LC-CoAs disrupted binding of the NHE1 cytosolic tail to PI(4,5)P2. Inhibition of LC-CoA catabolism reduced NHE1 activity and enhanced apoptosis, whereas inhibition of proximal tubule LC-CoA generation preserved NHE1 activity and protected against apoptosis. Our data indicate that albuminuria/lipiduria enhances lipotoxin delivery to the proximal tubule and accumulation of LC-CoAs contributes to tubular atrophy by severing the NHE1-PI(4,5)P2 interaction, thereby lowering the apoptotic threshold. Furthermore, these data suggest that NHE1 functions as a metabolic sensor for lipotoxicity., Introduction Over 26 million people in the US suffer from chronic kidney diseases, approximately half of whom have diabetic nephropathy (DN) as the etiology (1). Most forms of chronic kidney [...]

This article reports the preparation of new anion exchange composite fibers (AECFs). These AECFs were prepared by simple stirring of polyacrylonitrile (PAN) and silica gel in different stoichiometric ratios. The physicochemical characterization of the prepared AECFs was characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction analysis, thermogravimetric analysis (TGA, differential thermal analysis, and differential thermal gravimetry), and elemental analysis (CHNS/O). Ion-exchange behavior was also observed. The results indicate that addition of silica gel affects the structure and properties of the composite fibers. The addition of silica gel also changes the thermal stability of PAN-silica gel AECFs. The ion-exchange capacity of the resulting AECFs was found to be 1.98 mequiv/g. POLYM. ENG. SCI., 53:2027-2033, 2013. © 2013 Society of Plastics Engineers, INTRODUCTION Organic--inorganic ion-exchange composite materials have the advantages of light weight, flexibility, and mechanical stability because of organic polymer, whereas inorganic part provides thermal stability and inorganic matrices of co-ions [...]

A method for the preparation of a bipolar ion-exchange surface was proposed; it consists in the dynamic arrangement of the nanoparticles of an ion-exchanger modifier in the macropores of a matrix ion exchanger of opposite polarity and the retention of these nanoparticles by Coulomb forces. The NACATEX analytical cation-exchange column with the separating surface of a new type was prepared, which is suitable for the separation of the mixtures of alkaline element and ammonium ions and also calcium and magnesium ions. Keywords: ion chromatography, bipolar ion exchanges, macroporous matrix ion exchanger, nanoparticles, ion-exchanger modifier DOI: 10.1134/S1061934813050079, Ion chromatography is widely used for the analysis of the complex solutions of various electrolytes. The analytical column, which is a high-tech product with finely tuned characteristics, is the main [...]

A polyelectrolyte has been prepared, as a potential proton exchange polymer, by grafting acrylic acid/acrylamide (AAc/AAm) and acrylic acid/acrylonitrile (AAc/AN) comonomers onto a low-density polyethylene film via gamma irradiation. The developed polymers were characterized by evaluating their physico-chemical properties such as ion exchange capacity (IEC) and electrical conductivity as functions of grafting yield. The grafted film at different compositions was characterized by Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy. IEC of the grafted film at grafting % 191 and monomer concentration ratio 50:50 for (LDPE-g-AAc/AAm) was found to be more than that for (LDPE-g-AAc/AN). The electrical conductivity was found to be greatly affected by the comonomer composition, were it increased as the degree of grafting increased for all grafted films. After alkaline treatment with 3% KOH (3% potassium hydroxide), the electrical conductivity of the grafted films found to be increased. The presence of potassium as counter ion maximized the electrical conductivity of the grafted films. The electrical conductivity of Cu-membrane complexes was higher than that of both Co (cobalt) and Ni (Nickel) complexes. It has been indicated that, the electrical conductivity increased by increasing both Cu ion content and temperature. POLYM. ENG. SCI., 53:792-799, 2013. © 2012 Society of Plastics Engineers, INTRODUCTION The modification of polymers has received much attention recently. Among the methods of modification of polymers, grafting is one of the promising methods. Modification or introduction of new characteristics [...]

Calcium ions ([Ca.sup.2+]) have an important role as secondary messengers in numerous signal transduction processes (1-4), and cells invest much energy in controlling and maintaining a steep gradient between intracellular [...]

Sodium titanates and peroxotitanates are inorganic ion-exchangers that exhibit strong affinities for a wide range of metals. These materials serve as effective ion-exchangers in strongly alkaline, neutral, and weakly acidic solutions. One of the sodium titanates, referred to as monosodium titanate, is currently used at the Savannah River Site in a batch-contact process to separate [sup.90]Sr and alpha-emitting radioisotopes from high-level nuclear waste solutions. The titanates can be incorporated into porous supporting matrices that allow deployment in a flow-through filter or column configuration. Recent studies indicate that the titanates may also be a suitable platform to either remove or deliver metals under physiological conditions., Introduction Over the last 30 years, a number of titanium-based substances have been developed that serve as effective ion exchangers in chemical separations. For example, monosodium titanate (MST) (1) and [...]

Fen--bog succession is accompanied by strong increases of carbon accumulation rates. We tested the prevailing hypothesis that living Sphagna have extraordinarily high cation exchange capacity (CEC) and therefore acidify their environment by exchanging tissue-bound protons for basic cations in soil water. As Sphagnum invasion in a peatland usually coincides with succession from a brown moss-dominated alkaline fen to an acidic bog, the CEC of Sphagna is widely believed to play an important role in this acidification process. However, Sphagnum CEC has never been compared explicitly to that of a wide range of other bryophyte taxa. Whether high CEC directly leads to the ability to acidify the environment in situ also remains to be tested. We screened 20 predominant subarctic bryophyte species, including fen brown mosses and bog Sphagna for CEC, in situ soil water acidification capacity (AC), and peat acid neutralizing capacity (ANC). All these bryophyte species possessed substantial CEC, which was remarkably similar for brown mosses and Sphagna. This refutes the commonly accepted idea of living Sphagnum CEC being responsible for peatland acidification, as Sphagnum's ecological predecessors, brown mosses, can do the same job. Sphagnum AC was several times higher than that of other bryophytes, suggesting that CE (cation exchange) sites of Sphagna in situ are not saturated with basic cations, probably due to the virtual absence of these cations in the bog water. Together, these results suggest that Sphagna can not realize their CEC in bogs, while fen mosses can do so in fens. The fen peat ANC was 65% higher than bog ANC, indicating that acidity released by brown mosses in the CE process was neutralized, maintaining an alkaline environment. We propose two successional pathways indicating boundaries for a fen bog shift with respect to bryophyte CEC. In neither of them is Sphagnum CE an important factor. We conclude that living Sphagnum CEC does not play any considerable role in the fen--bog shift. Alternatively, we propose that exclusively indirect effects of Sphagnum expansion such as peat accumulation and subsequent blocking of upward alkaline soil water transport are keys to the fen bog succession and therefore for bog-associated carbon accumulation. Key words: acidification; acidity; acid neutralizing capacity; bog; brown moss; bryophyte; carbon cycling; CEC (cation exchange capacity); fen, moss; Sphagnum spp.; succession.

A coupled acoustic-gravity field is efficient for entrapping a particle at the position determined by its acoustic properties rather than its size. This field has been applied to the dynamic observation of ion-exchange reactions occurring in a single resin bead. The replacement of counterions in an ion-exchange resin induces changes in its acoustic properties, such as density and compressibility. Therefore, we can visually trace the advancement of an ion-exchange reaction as a time change in the levitation position of a resin bead entrapped in the field. Cation-exchange reactions occurring in resin beads with diameters of 40-120 [micro]m are typically completed within 100-200 s. Ion-exchange equilibrium or kinetics is often evaluated with off-line chemical analyses, which require a batch amount of ion exchangers. Measurements with a single resin particle allow us to evaluate ion-exchange dynamics and kinetics of ions including those that are difficult to measure by usual off-line analyses. The diffusion properties of ions in resins have been successfully evaluated from the time change in the levitation positions of resin beads. 10.1021/ac100275p

Nephrogenic dopamine is a potent natriuretic paracrine/autocrine hormone that is central for mammalian sodium homeostasis. In the renal proximal tubule, dopamine induces natriuresis partly via inhibition of the sodium/ proton exchanger NHE3. The signal transduction pathways and mechanisms by which dopamine inhibits NHE3 are complex and incompletely understood. This manuscript describes the role of the serine/ threonine protein phosphatase 2A (PP2A) in the regulation of NHE3 by dopamine. The PP2A regulatory subunit B56[delta] (coded by the Ppp2r5d gene) directly associates with more than one region of the carboxy-terminal hydrophilic putative cytoplasmic domain of NHE3 (NHE3-cyto), as demonstrated by yeast-two-hybrid, coimmunoprecipitation, blot overlay, and in vitro pull-down assays. Phosphorylated NHE3-cyto is a substrate for purified PP2A in an in vitro dephosphorylation reaction. In cultured renal cells, inhibition of PP2A by either okadaic acid or by overexpression of the simian virus 40 (SV40) small T antigen blocks the ability of dopamine to inhibit NHE3 activity and to reduce surface NHE3 protein. Dopamine-induced NHE3 redistribution is also blocked by okadaic acid ex vivo in rat kidney cortical slices. These studies demonstrate that PP2A is an integral and critical participant in the signal transduction pathway between dopamine receptor activation and NHE3 inhibition. natriuresis; sodium transport; signal transduction do: 10.1152/ajprenal.00708.2009.

Protein phosphorylation is one of the most biologically relevant and ubiquitous post-translational modifications. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) is a powerful tool for the analysis of protein phosphorylation by detection of phosphopeptides in phosphoprotein digest. Enrichment of phosphopeptides by immobilized metal ion affinity chromatography (IMAC) or metal oxide affinity chromatography (MOAC) followed with MALDI analysis is the common approach. However, the pH for loading and elution of phosphopeptides is incompatible with protein digestion as well as the preparation of the MALDI matrix solution. Therefore, some pretreatment steps, such as pH adjustment and desalting, are required, which make the approach tedious and insensitive. In this study, a strong anion-exchange (SAX) capillary monolith was prepared to enrich phosphopeptides from protein digest for MALDI-TOF MS analysis. It was found that phosphopeptides could be specifically retained on the SAX column at high pH around 8 and could be eluted by 5% formic acid. Thus, the protein digests without any pretreatment could be loaded onto the SAX column under basic pH condition; after removing nonphosphopeptides by washing, the bound phosphopeptides could be eluted directly onto a MALDI target and analyzed by MALDI-TOF MS. This approach significantly simplified the analytical procedures and reduced the sample loss. Because of the excellent MALDI MS compatible procedure and the microscale SAX column, a detection limit as low as 50 amol for the analysis of phosphopeptides from [beta]-casein digest was achieved. To circumvent the inconvenience of the sample loading, a now simple sample introducing method based on capillary action was proposed, which further reduced the detection limit to 10 amol. 10.1021/ac902907w

Small RNA molecules are effective regulators of gene expression, and the expression signature of one subgroup of small RNA, the microRNA (miRNA), has been linked to disease development and progression. Therefore, detection of small RNA in biological samples will greatly improve the understanding of their functions and render effective tools to researchers for cellular process control and disease prevention. To solve the challenges in detecting the low-abundance and short strand-length of small RNA molecules, we designed a ligation-assisted binding assay and applied the cation exchange-based fluorescence amplification (CXFluoAmp) method developed in our group for detection. Nonfluorescent, ionic nanocrystals (NCs) of CdSe were conjugated to detection probes and immobilized onto the array surface via ligation with the target small RNA, miR21, which bound to the capture probe complimentarily. Each binding event induced by one target miR21 molecule was then amplified by the release of thousands of [Cd.sup.2+] from one NC. The free [Cd.sup.2+] immediately turned on the fluorescence of thousands of fluorogenic Rhod-5N molecules. With such a powerful signal amplification strategy, our assay achieved a limit of detection (LOD) of 35 fM and signals were detectible with analyte concentrations spanning over 7 orders of magnitude. We also identified the differential expression of miR21 in total RNA extracts from healthy breast tissue and diseased cells. Furthermore, our detection scheme demonstrated good specificity in small RNA detection, because significant signal intensity could be observed from small RNAs with one or two nucleotides difference in sequences. Thus, our assay has great application potential for disease diagnosis relying on miRNA biomarkers, or in small RNA expression profiling for now target discovery and functional study. 10.1021/ac901983s

In this manuscript, we provide a theoretical rationalization of the mechanisms that control double H2 addition to an unsaturated 14 e cationic Ir(III) complex to yield a dihydride Ir(III) complex. Further, we also present two mechanisms that can explain the experimentally observed incorporation of deuterium into the tert-Butyl ([sup.t.Bu]) groups of the N-heterocyclic I[sup.t.Bu] ligands. Key words: homogeneous catalysis, hydrogenation, deuteration, N-heterocyclic carbene, density functional calculations. Dans ce travail, on rapporte une rationalisation theorique des mecanismes qui controlent la double addition de [H.sub.2] sur le complexe cationique insature de Ir(III) conduisant a la formation d'un dihydrure complexe de Ir(III). De plus, on presente deux mecanismes qui pourraient expliquer l'incorporation observee experimentalement de deuterium dans les groupes tert-butyles des ligands I[sup.t.Bu] de l'heterocycle azote. Mots-cles: catalyse homogene, hydrogenation, deuteration, carbene N-heterocyclique, calculs de la fonctionnelle de la densite. [Traduit par la Redaction], Introduction Coordinatively unsaturated transition-metal complexes containing hydride ligands are of remarkable interest because of their potential role in catalysis. (1-6) Due to their unsaturated nature, the structural characterization and a [...]

The [Ca.sup.2+]-independent phospholipase [A.sub.2] VI ([iPLA.sub.2]-VI) and the [Na.sup.+][H.sup.+] exchanger isoform l (NHE1) are highly pH-sensitive proteins that exert both protective and detrimental effects in cardiac ischemia-reperfusion. Here, we investigated the role of extracellular pH ([pH.sub.o]) in ischemia-reperfusion injury and death and in regulation and function of [iPLA.sub.2]-VI and NHE1 under these conditions. HL-1 cardiomyocytes were exposed to simulated ischemia (SI; 0.5% [O.sub.2], 8 mM [K.sup.+], and 20 mM lactate) at [pH.sub.o] 6.0 and 7.4, with or without 4 or 8 h of reperfusion (SI/R). Cytochrome c release and caspase-3 activation were reduced after acidic compared with neutral SI, whereas necrotic death, estimated as glucose-6-phosphate dehydrogenase release, was similar in the two conditions. Inhibition of [iPLA.sub.2]-VI activity by bromoenol lactone (BEL) elicited cardiomyocyte necrosis during normoxia and after acidic, yet not after neutral, SI. The isoform-selective enantiomers R- and S-BEL both mimicked the effect of racemic BEL after acidic SI. In contrast, inhibition of NHE activity by EIPA had no significant effect on necrosis after SI. Both neutral and acidic SI were associated with a reversible loss of F-actin and cortactin integrity. Inhibition of [iPLA.sub.2]-VI disrupted F-actin, cortactin, and mitochondrial integrity, whereas inhibition of NHE slightly reduced stress fiber content, [iPLA.sub.2]-VIA and NHE1 mRNA levels were reduced during SI and upregulated in a [pH.sub.o]-dependent manner during SI/R. This also affected the subcellular localization of [iPLA.sub.2]-VIA. Thus, the mode of cell death and the roles and regulation of [iPLA.sub.2]-VI and NHE1 are at least in part determined by the [pH.sub.o] during SI. In addition to having clinically relevant implications, these findings can in part explain the contradictory results obtained from previous studies of [iPLA.sub.2]-VIA and NHE1 during cardiac I/R. cytoskeleton; cell death; extracellular pH; NHE1; [iPLA.sub.2]; EIPA; necrosis

Amino acid transporters at the surface of cells are in an ideal location to relay nutritional information, as well as nutrients themselves, to the cell interior. These transporters are able to modulate signaling downstream of intracellular amino acid receptors by regulating intracellular amino acid concentrations through processes of coupled transport. The concept of dual-function amino acid transporter/receptor (or 'transceptor') proteins is well established in primitive eukaryotes such as yeast, where detection of extracellular amino acid deficiency leads to upregulation of proteins involved in biosynthesis and transport of the deficient amino acid(s). The evolution of the 'extracellular milieu' and nutrient-regulated endocrine controls in higher eukaryotes, alongside their frequent inability to synthesize all proteinaceous amino acids (and, hence, the requirement for indispensable amino acids in their diet), appears to have lessened the priority of extracellular amino acid sensing as a stimulus for metabolic signals. Nevertheless, recent studies of amino acid transporters in flies and mammalian cell lines have revealed perhaps unanticipated 'echoes' of these transceptor functions, which are revealed by cellular stresses (notably starvation) or gene modification/silencing. APC-transporter superfamily members, including slimfast, path, and SNAT2 all appear capable of sensing and signaling amino acid availability to the target of rapamycin (TOR) pathway, possibly through PI 3-kinase-dependent mechanisms. We hypothesize (by extrapolation from knowledge of the yeast Ssyl transceptor) that, at least for SNAT2, the transceptor discriminates between extracellular and intracellular amino acid stimuli when evoking a signal. SNAT2; mammalian target of rapamycin; GCN2; transporters; receptors

Phospholemman (PLM) belongs to the FXYD family of small ion transport regulators. When phosphorylated at [Ser.sup.68], PLM inhibits cardiac [Na.sup.+]/[Ca.sup.2+] exchanger (NCX1). We previously demonstrated that the cytoplasmic tail of PLM interacts with the proximal intracellular loop (residues 218-358), but not the transmembrane (residues 1-217 and 765-938) or [Ca.sup.2+]-binding (residues 371-508) domains, of NCX1. In this study, we used intact [Na.sup.+]/[Ca.sup.2+] exchanger with various deletions in the intracellular loop to map the interaction sites with PLM. We first demonstrated by Western blotting and confocal immunofluorescence microscopy that wild-type (WT) NCX1 and its deletion mutants were expressed in transfected HEK-293 cells. Cotransfection with PLM and NCX1 (or its deletion mutants) in HEK-293 cells did not decrease expression of NCX1 (or its deletion mutants). Coexpression of PLM with WT NCX1 inhibited NCX1 current ([I.sub.NaCa]). Deletion of residues 240-679, 265-373, 250-300, or 300-373 from WT NCX1 resulted in loss of inhibition of [I.sub.NaCa] by PLM. Inhibition of [I.sub.NaCa] by PLM was preserved when residues 229-237, 270-300, 328-330, or 330-373 were deleted from the intracellular loop of NCX1. These results suggest that PLM mediated inhibition of [I.sub.NaCa] by interacting with two distinct regions (residues 238-270 and 300-328) of NCX1. Indeed, [I.sub.NaCa] measured in mutants lacking residues 238-270, 300-328, or 238270 + 300-328 was not affected by PLM. Ghitathione S-transferase pull-down assays confirmed that PLM bound to fragments corresponding to residues 218-371, 218-320, 218-270, 238-371, and 300-373, but not to fragments encompassing residues 250-300 and 371-508 of NCX1, indicating that residues 218-270 and 300-373 physically associated with PLM. Finally, acute regulation of [I.sub.NaCa] by PLM phosphorylation observed with WT NCX1 was absent in 250300 deletion mutant but preserved in 229-237 deletion mutant. We conclude that PLM mediates its inhibition of NCX1 by interacting with residues 238-270 and 300-328. FXYD1; ion transport; sodium-calcium exchange

Recent calorimetric measurements of the solvation enthalpies of some dipeptide analogs confirm our earlier prediction that the principle of group additivity is not valid for the interaction of the peptide group with water. We examine the consequences for understanding the properties of peptide solvation. A major consequence is that the current value of the peptide-solvation enthalpy, which is a basic parameter in analyzing the energetics of protein folding, is seriously wrong. Electrostatic calculations of solvation-free energies provide an estimate of the size and nature of the error. Peptide hydrogen exchange rates provide an experimental approach for testing the accuracy of the solvation-free energies of peptide groups found by electrostatic calculations. These calculations emphasize that ignoring electrostatic interactions with neighboring NHCO groups should be a major source of error. Results in 1972 for peptide hydrogen exchange rates demonstrate that peptide-solvation-free energies are strongly affected by adjoining NHCO groups. In the past, the effect of adjoining peptide groups on the exchange rate of a peptide NH proton was treated as an inductive effect. The effect can be calculated, however, by an electrostatic model with fixed partial charges and a continuum solvent. group additivity | peptide solvation | peptide hydrogen exchange

The selectivities of the K-Ca and K-Mg cation exchange reactions were studied in batch experiments carried out with 7 Chilean saline sandy soils with low organic matter (OM) content, and rich in quartz and halite, by using the experimental Gaines and Thomas procedure and the semi-empirical Rothmund-Kornfeld approach. The soils present high reactivity to the exchange process in terms of CEC and a preference order from the surface for the cation of K > Ca > Mg. In addition, the existence of different types of exchange sites was determined; some were specific for determined cations and others presented free competition. The proposed exchange reaction for both equilibria was thermodynamically possible and the studied cations presented a decreasing mobility order K > Ca > Mg, which follows the increasing order of hydrated ionic radii. As for the Rothmund-Kornfeld semi-empirical approach, it can be employed on soils classified as Aridisol due to good fit with the experimental data. On the other hand, the Gaines and Thomas approach is only experimentally applicable since poses some restrictions concerning to salinity and carbonate contents in the studied soils. Additional keywords: exchange equilibria, saline soils, thermodynamic models., Introduction Soils affected by salts located in the north of Chile, which extends from 17°30' to 21°39'S and from 68°25'W to the Pacific Ocean, with dry weather and little rainfall [...]

We describe the steady-state function of the ubiquitous mammalian Na/H exchanger (NHE) 1 isoform in voltage-clamped Chinese hamster ovary cells, as well as other cells, using oscillating pH-sensitive microelectrodes to quantify proton fluxes via extracellular pH gradients. Giant excised patches could not be used as gigaseal formation disrupts NHE activity within the patch. We first analyzed forward transport at an extracellular pH of 8.2 with no cytoplasmic Na (i.e., nearly zero-trans). The extracellular Na concentration dependence is sigmoidal at a cytoplasmic pH of 6.8 with a Hill coefficient of 1.8. In contrast, at a cytoplasmic pH of 6.0, the Hill coefficient is

The cation exchange capacity (CEC) of soils depends on the amount and composition not only of clay minerals but also of soil organic matter (SOM). While the CEC of soil clay minerals has been intensively studied, little is known about the CEC of organic matter (OM) fractions, in particular those obtained with newly developed SOM extraction techniques. The objective of this study was to develop and test a method to quantitatively determine the CEC of extracted OM fractions and to relate CEC(OM) to OM functional groups possibly responsible for sorption of cations. Water- and pyrophosphate-soluble OM fractions were sequentially extracted from differently managed arable soils of two well-known long-term field experiments. The CEC of a freeze-dried pyrophosphate-soluble OM fraction [OM(PY)] (0.03 g) mixed with quartz sand (4.97 g) was determined by applying the standard percolation method. The chemical composition of OM(PY) was analyzed by Fourier-transform infrared (FTIR) spectroscopy. For all plots except those fertilized with farmyard manure, the sorption properties of the OM(PY) fraction were found to be site specific and to reflect soil and crop rotation effects. The relative contribution of the CEC of OM(PY) to the CEC of the soil (0.8-11.6%) is dependent on soil C content and extractability. For all plots, however, the relative contents of carboxylic functional groups in OM(PY) determined with FTIR spectroscopy was found to be linearly related to the CEC of the OM(PY), similar to pure organic substances. This relationship indicates the usefulness of CEC determination on OM(PY) fractions. The results suggest that the relative contents ofcarboxylic functional groups in OM(PY) reflect long-term effects of femlization and crop rotation on the sorption properties of the SOM. Abbreviations: BL, Bad Lauchstadt; CEC, cation exchange capacity; FTIR, Fourier-transform infrared; FYM, farmyard manure; HL, Halle; LFE, long-term field experiment; OM, organic matter; OMC, organo-mineral complexes; OM(PY), pyrophosphate-soluble organic matter fraction; R1, 4-yr crop rotation at Bad Lauchstadt; R2, 8-yr crop rotation at Bad Lauchstadt; SOC, soil organic carbon; SOM, soil organic manet.

Bobuleseu IA, Dubree M, Zhang J, McLeroy P, Moe OW. Effect of renal lipid accumulation on proximal tubule [Na.sup.+]/[H.sup.+] exchange and ammonium secretion. Am J Physiol Renal Physiol 294: F1315-F1322, 2008. First published April 16, 2008; doi:10.1152/ajprenal.00550.2007.--Patients with metabolic syndrome have increased risk of uric acid nephrolithiasis due to lower urinary pH and impaired ammonium excretion. The pathophysiology underlying these urinary changes is unknown. We used two animal models and a cell culture model to study whether the alteration in renal acidification is associated with renal fat infiltration (steatosis). Compared with pair-fed lean control rats, Zucker diabetic fatty rats have higher renal triglyceride content, decreased urinary ammonium and pH, and lower levels of brush border membrane Na+/H+ exchanger-3 (NHE3), a major mediator of ammonium excretion. High-fat feeding in Sprague-Dawley rats results in transient lowering of urinary ammonium and pH, with all parameters returning to normal when the animals resumed eating normal chow. This is consistent with an absence of diet-induced renal steatosis in these animals. To examine the direct effect of fat accumulation, we incubated opossum kidney (OKP) cells with a mixture of long-chain fatty acids and found accumulation of intracellular lipids with concomitant dose-dependent decrease in NHE3 activity, surface biotin-accessible NHE3 protein, and ammonium secretion. A lower dose of fatty acids that leads to intracellular lipid accumulation but does not change baseline NHE3 is sufficient to abolish the stimulation of NHE3 by insulin and to partially block the stimulation of NHE3 by glucocorticoid hormones; acid regulation of NHE3 in lipid-loaded OKP cells is not affected. These findings suggest that renal steatosis decreases ammonium secretion in the proximal tubule, in part by reducing NHE3 activity and by impairing the regulation of NHE3 by specific agonists. [Na.sup.+]/[H.sup.+] exchanger-3; free fatty acids; lipotoxicity; Zucker diabetic fatty rat; metabolic syndrome

A partial cation-exchange method is described in which the lability is considered for synthesizing PbSe/CdSe core/shell nanocrystal quantum dots (NQDs). The NQDs have undergone additional shell growth in order to produce PbSe/CdSe/ZnS core/shell NQDs that have represented initial steps toward bright, biocompatible near-infrared optical labels.

In this article, we report the family of robust layered sulfides [K.sub.2x][Mn.sub.x][Sn.sub.3-x][S.sub.6] (x = 0.5-0.95) (KMS-1). These materials feature hexagonal [[[Mn.sub.x][Sn.sub.3-x] [S.sub.6]].sup.2x-] slabs of the [Cdl.sub.2] type and contain highly mobile [K.sup.+] ions in their interlayer space that are easily exchangeable with other cations and particularly strontium. KMS-1 display outstanding preference for strontium ions in highly alkaline solutions containing extremely large excess of sodium cations as well as in acidic environment where most alternative adsorbents with oxygen ligands are nearly inactive. The implication of these results is that simple layered sulfides should be considered for the efficient remediation of certain nuclear wastes. chalcogenide | environmental remediation | ion exchange | layered materials | nuclear waste

In this study, predictive quantitative structure-property relationship (QSPR) models that employed a support vector machine regression algorithm and a set of novel pH-dependent descriptors were employed for the prediction of protein chromatographic behavior at any pH. The calculated pH-dependent descriptors were based on protein crystal structures and sequence information and represent charge and electrostatic potential properties on the protein surfaces. With this set of pH-dependent descriptors, proteins at different pH were treated as distinct molecules, thus enabling the generation of integrated QSPR models, which allow the prediction of chromatographic behavior of test set proteins across a wide range of mobile-phase pH conditions. The predictions from these integrated QSPR models in general showed good agreement with the experimental results. For proof of concept, the steric mass action adsorption isotherm parameters of a binary test set of proteins (lysozyme and aprotinin) at a pH not employed in the training set were predicted from the integrated QSPR models. Further, the predicted parameters were used in a macroscopic transport model to simulate the chromatographic separation of this binary protein mixture at this new pH. The simulated column behavior of these proteins showed good agreement with experimental results. The use of pH-dependent descriptors in this multiscale modeling approach now enables the prediction of various modes of protein chromatography at any mobile-phase pH, which may have significant implications for downstream bioprocessing.

Although inhibition of the sarcolemmal (SL) [Na.sup.+]-[K.sup.+]-ATPase is known to cause an increase in the intracellular concentration of [Ca.sup.2+] ([[[Ca.sup.2+]].sub.i]) by stimulating the SL [Na.sup.+]/[Ca.sup.2+] exchanger (NCX), the involvement of other SL sites in inducing this increase in [[[Ca.sup.2+]].sub.i] is not fully understood. Isolated rat cardiomyoeytes were treated with or without different agents that modify [Ca.sup.2+] movements by affecting various SL sites and were then exposed to ouabain. Ouabain was observed to increase the basal levels of both [[[Ca.sup.2+]].sub.i] and intracellular [Na.sup.+] concentration ([[[Na.sup.+]].sub.i]) as well as to augment the KCl-induced increases in both [[[Ca.sup.2+]].sub.i] and [[[Na.sup.+]].sub.i] in a concentration-dependent manner. The ouabain-induced changes in [[[Na.sup.+]].sub.i] and [[[Ca.sup.2+]].sub.i] were attenuated by treatment with inhibitors of SL [Na.sup.+]/[H.sup.+] exchanger and SL [Na.sup.+] channels. Both the ouabain-induced increase in basal [[[Ca.sup.2+]].sub.i] and augmentation of the KCl response were markedly decreased when cardiomyocytes were exposed to 0-10 mM [Na.sup.+]. Inhibitors of SL NCX depressed but decreasing extracellular [Na.sup.+] from 105-35 mM augmented the ouabain-induced increase in basal [[[Ca.sup.2+]].sub.i] and the KCl response. Not only was the increase in [[[Ca.sup.2+]].sub.i] by ouabain dependent on the extracellular [Ca.sup.2+] concentration, but it was also attenuated by inhibitors of SL L-type [Ca.sup.2+] channels and store-operated [Ca.sup.2+] channels (SOC). Unlike the SL L-type [Ca.sup.2+]-channel blocker, the blockers of SL [Na.sup.+] channel and SL SOC, when used in combination with SL NCX inhibitor, showed additive effects in reducing the ouabain-induced increase in basal [[[Ca.sup.2+]].sub.i]. These results support the view that in addition to SL NCX, SL L-type [Ca.sup.2+] channels and SL SOC may be involved in raising [[[Ca.sup.2+]].sub.i] on inhibition of the SL [Na.sup.+]-[K.sup.+]-ATPase by ouabain. Furthermore, both SL [Na.sup.+]/[H.sup.+] exchanger and [Na.sup.+] channels play a critical role in the ouabain-induced [Ca.sup.2+] increase in cardiomyocytes. sodium-calcium exchanger; sodium-hydrogen exchanger; sarcolemreal [Ca.sup.2+] transport doi:10.1152/ajpheart.01414.2006

A floating-type probe and its driving circuit are developed by using the nonlinear characteristics of the probe sheath and the plasma density is measured in inductively coupled plasmas. The analysis has shown that floating-type probe with high probe operating frequency is not affected by the contaminant deposition on the probe tip, hence it can be applied to plasma diagnostics for processing plasmas such as deposition or etching plasmas.

The nature of the chemical interactions between organic species and mineral surfaces and interlayers has significant implications for many geochemical processes and for medical and materials applications, but the molecular-scale characteristics of such interactions are poorly understood. Here we describe an experimental investigation of citrate-hydrotalcite (HT) that is designed to investigate the structural environments and dynamical behavior of carboxylic species interacting with the protonated surfaces of positively charged materials such as layered double hydroxides (LDHs). X-ray diffraction, compositional analysis, and thermal analysis confirm successful intercalation of trivalent citrate anions into the interlayers of the Mg/Al hydrotalcite using an ion-exchange method. The basal spacing changes from 8.9 [Angstrom] at relative humidity (R.H.) = 0% to 11.3 [Angstrom] at R.H. = 75%, to 18.9 [Angstrom] at 100% R.H., consistent with reorientation of the citrate from parallel to the hydroxide layers at low water contents to perpendicular to them at higher water contents. At the largest water contents, the citrate may lose contact with one of the hydroxide layers, in contrast to the behavior of LDHs containing small, inorganic species. The similarity of the [sup.13]C nuclear magnetic resonance (NMR) chemical shifts for citrate-HT and sodium citrate solution demonstrates the absence of grafting (covalent bond formation) between the citrate molecules and the metal hydroxide layers, and the dominance of Coulombic and H-bond interactions in stabilizing the structure. Decreasing [sup.13]C NMR peak widths, decreasing signal/noise ratios in the [sup.1]H-[sup.13]C CPMAS NMR spectra, and increasing basal spacing with increasing R.H. are consistent with increasing dynamical disorder of the interlayer citrate sites in a progressively more water-rich interlayer. Keywords: Citrate- HT, ion-exchange, XRD, thermal analysis, [sup.1]H-[sup.13]C CPMAS NMR

A strategy for increasing the efficiency of infrared multi-photon dissociation (IRMPD) in a quadrupole ion trap (QIT) is described. IR-active ligands ORALs) are incorporated into noncovalent complexes of the type [[M.sup.2+](analyte) IRAL].sup.+], where M is a transition metal such as copper or cobalt and IRAL is an auxiliary ligand with an IR-active phosphonate functional group. The complexes are formed via self-assembly in solution directly prior to ESI-MS analysis. We demonstrate this new IRMPD approach for the structural characterization of flavonoids. The fragment ions obtained by IRMPD are similar to those obtained by CAD and allow facile isomer differentiation of flavonoids. Fourier transform infrared absorption attenuated total reflectance (FTIR-ATR) and energy-variable CAD experiments indicate that the high IRMPD efficiencies stem from the very large IR absorptivities of the IR-active ligands.

Black Carbon (BC) may significantly affect nutrient retention and play a key role in a wide range of biogeochemical processes in soils, especially for nutrient cycling. Anthrosols from the Brazilian Amazon (ages between 600 and 8700 yr BP) with high contents of biomass-derived BC had greater potential cation exchange capacity (CEC measured at pH 7) per unit organic C than adjacent soils with low BC contents. Synchrotron-based near edge X-ray absorption fine structure (NEXAFS) spectroscopy coupled with scanning transmission X-ray microscopy (STXM) techniques explained the source of the higher surface charge of BC compared with non-BC by mapping cross-sectional areas of BC particles with diameters of 10 to 50 [micro]m for C forms. The largest cross-sectional areas consisted of highly aromatic or only slightly oxidized organic C most likely originating from the BC itself with a characteristic peak at 286.1 eV, which could not be found in humic substance extracts, bacteria or fungi. Oxidation significantly increased from the core of BC particles to their surfaces as shown by the ratio of carboxyl-C/aromatic-C. Spotted and non-continuous distribution patterns of highly oxidized C functional groups with distinctly different chemical signatures on BC particle surfaces (peak shift at 286.1 eV to a higher energy of 286.7 eV) indicated that non-BC may be adsorbed on the surfaces of BC particles creating highly oxidized surface. As a consequence of both oxidation of the BC particles themselves and adsorption of organic matter to BC surfaces, the charge density (potential CEC per unit surface area) was greater in BC-rich Anthrosols than adjacent soils. Additionally, a high specific surface area was attributable to the presence of BC, which may contribute to the high CEC found in soils that are rich in BC.

A new 'grafting from' strategy based on surface-initiated atom transfer radical polymerization (ATRP) was first used for the preparation of a polymer-based ion-exchange support for HPLC. The most important property of the proposed method is to be applicable for the synthesis of any type of ion exchanger in both the strong and the weak forms. Monodisperse, porous poly(glycidyl methacrylateco-ethylene dimethacrylate), poly(GMA-co-EDM) particles 5.8 [micro]m in size were synthesized by 'modified seeded polymerization'. Poly(dihydroxypropyl methacrylate-coethylene dimethacrylate), poly(DHPM-co-EDM) particles were then obtained by the acidic hydrolysis of poly(GMAco-EDM) particles. The ATRP initiator, 3-(2-bromoisobutyramido)propyl(triethoxy)silane was covalently attached onto poly(DHPM-co-EDM) particles via the reaction between triethoxysilane and diol groups. In the next stage, the selected monomer carrying strong cation exchanger groups, 3-sulfopropyl methacrylate (SPM), was polymerized on the initiator-immobilized particles via surfaceinitiated ATRP. The degree of polymerization of SPM (i.e., length of polyionic ligand) on the particles was precisely controlled by adjusting ATRP conditions. Poly(SPM)-grafted poly(DHPM-co-EDM) particles obtained with different ATRP formulations were tried as chromatographic packing in the separation of proteins by ion-exchange chromatography. The proteins were successfully separated with higher column yields with respect to the previously proposed materials. The plate heights between 100 and 150 [micro]m were achieved with the column packed with the particles carrying the shortest poly(SPM) chains. The plate height showed no significant increase with increasing flow rate in the range of 0.5-16 cm/min.

A systematic study of thermal silver ion exchange used for the fabrication of optical channel waveguides is reported in a single-alkali glass. The diffusion equilibrium and diffusion dynamics are experimentally studied, and the concentration-dependent diffusion coefficients are determined. The relationship between the fabrication conditions, i.e., time, temperature, and melt concentration, and the induced waveguide refractive index profile is established. It is demonstrated that the diffusion equation can be solved, without use of any free parameters, to predict the refractive index profiles of both planar and channel waveguides. A 1.6 cm diameter integrated optic ring resonator, with a propagation loss of 0.1 dB/cm, is fabricated in a glass by thermal silver ion exchange. The induced refractive index profile is related to the optical characteristics of the functional device. OCIS codes: 130.2790. 130.3130, 230.3120, 230.7380, 230.7390.

The transport of ions across the membranes of cells and organelles is a prerequisite for many of life's processes. Transport often involves very precise selectivity for specific ions. Recently, atomic-resolution structures have been determined for channels or pumps that are selective for sodium, potassium, calcium, and chloride: four of the most abundant ions in biology. From these structures we can begin to understand the principles of selective ion transport in terms of the architecture and detailed chemistry of the ion conduction pathways., The flow of ions across the cell membrane is essential to many of life's processes. Ion pumps build gradients across the membrane, which are then used as an energy source [...]

A new approach for the carbon-specific determination of humic-like substances (HULIS) in atmospheric aerosols is presented. The method is based on a two-step isolation procedure of HULIS and the determination of HULIS carbon with a dissolved organic carbon analyzer. In the first step, a C18 solid-phase extraction is performed to separate HULIS from inorganic and hydrophilic organic sample constituents in aqueous sample solutions. The second isolation step is conducted on a strong anion exchanger to separate HULIS from remaining carbonaceous compounds. This ion chromatographic separation step including the subsequent on-line detection of HULIS carbon was performed fully automated to avoid the risk of sample contamination and to enhance the reproducibility of the method. With a 5-mL sample volume, a limit of detection of 1.0 mg C/L was obtained; this corresponds to an absolute amount of 5 [micro]g of HULIS carbon. The reproducibility of the method given as the relative standard deviation was 4.3% (n = 10). The method was applied for the determination of water-soluble HULIS in airborne particulate matter. PM10 concentrations at an urban site in Vienna, Austria, ranged from around 0.1 to 1.8 [micro]g of C/[m.sup.3] (n = 49); the fraction of water-soluble HULIS in OC was 12.1 [+ or -] 7.2% (n = 49).

The effects of a new, potent, and selective inhibitor of the [Na.sup.+] /[Ca.sup.2+] exchange, SEA-0400 (SEA), on steady-state outward (forward exchange), inward (reverse exchange), and [Ca.sup.2+]/[Ca.sup.2+] transport exchange modes were studied in internally dialyzed squid giant axons from both the extra- and intracellular sides. Inhibition by SEA takes place preferentially from the intracellular side of the membrane. Its inhibition has the following characteristics: it increases synergic intracellular [Na.sup.+] ([Na.sup.+.sub.i]) + intracellular [H.sup.+] ([H.sup.+.sub.i]) reactivation, is antagonized by ATP and intracellular alkalinization, and is enhanced by intracellular acidification even in the absence of [Na.sup.+]. Inhibition by SEA is still present even after 1 h of its removal from the experimental solutions, whereas removal of the cointeracting agents of inhibition, [Na.sup.+.sub.i] and [H.sup.+.sub.i], even in the continuous presence of SEA, releases inhibition, indicating that SEA facilitates the reversible attachment of the natural [H.sup.+.sub.i] and [Na.sup.+.sub.i] synergic inhibitors. On the basis of a recent model of squid [Na.sup.+]/[Ca.sup.2] exchange regulation (DiPolo R and Beauge L. J Physiol 539:791-803, 2002), we suggest that SEA acts on the [H.sup.+.sub.i] + [Na.sup.+.sub.i] inactivation process and can interact with the [Na.sup.+]-free and [Na.sup.+]--bound protonized carrier. Protection by ATP concurs with the antagonism of the nucleotide by [H.sup.+.sub.i] + [Na.sup.+.sub.i] synergic inhibition. ionic-metabolic interactions

Abstract: The influence of masking agents (acetate, thiosulfate, tartrate, and iodide ions thiourea and ethylenediaminetetraacetic acid (EDTA)) in a dithizone solution on the complexation of Hg(II), Pd(II), and Ag(I) ions on the solid phase of the fibrous anion exchanger filled with AV-17 was studied. Mercury, palladium, and silver were adsorbed as chloride complexes. The possibility of the simultaneous group determination of the three elements and the selective determination of palladium in the presence of mercury and silver by measuring the diffuse reflection coefficient at two wavelengths (580 and 680 nm, respectively) was demonstrated. A mixture of dithizone with EDTA, acetate, iodide, or thiosulfate can be used for masking concomitant elements. The reaction of palladium with dithizone on the solid phase can be used for the test determination of palladium with the detection limit 0.01 mg/L. Article History: Registration Date: 07/10/2004

Measurements of Cu or other trace elements in soils are rarely available in sufficient abundance to permit accurate mapping of large areas, in contrast, information is more widely available for major soil characteristics, such as cation-exchange capacity (CEC). Using data for soils of northern North Dakota, we compared four geostatistical methods as predictors of soil Cu: ordinary kriging (OK), ordinary kriging combined with regression (OKR), ordinary cokriging (OCK), and standardized ordinary cokriging (SCK). Ordinary kriging utilized data for soil Cu only, whereas the other three methods made use of CEC, which served as a secondary variable to improve the prediction and mapping of soil Cu. Quantitative predictions of soil Cu were tested by partitioning 619 sites of Cu into a training set of 310 sites, which was used to build models, and a testing set of 309 sites, which was reserved to test predictions derived from the training set. All three of the methods utilizing CEC data improved predictions substantially in comparison to OK. A larger data set containing data for soil Cu, CEC, or both was compiled from several comparable sources to prepare maps of Cu in soils of the 18 counties of northern North Dakota. These maps, based on data for 1002 sites within northern North Dakota, were quite similar for the three kriging methods which used data for both Cu and CEC, but different from the map derived from OK. Thus, the differences among the maps for soil Cu were consistent with our conclusion that the prediction of soil Cu was substantially improved by the use of CEC as an auxiliary variable.

ABSTRACT This paper discusses the application of a novel polyacrylate-based ion-exchange material for the removal of Pb ions from water. Preliminary testing includes the establishment of the operating pH range, [...]

Cation- and anion-exchange capacities (CEC and AEC) of variable-charge soils are often expressed as a function of pH and the electrolyte concentration. A difficulty following this formulation is that changes in pH with time and space must be computed precisely if ion transport is to be predicted. In this paper, an alternative formulation of CEC and AEC is presented in which pH does not appear explicitly. The formulation is based on the notion that, unless [H.sup.+] or O[H.sup.-] is added, changes in the total cation adsorption, [Q.sub.cat] (= CEC), and the total anion adsorption, [Q.sub.an] (= AEC), in response to a change in the total electrolyte concentration, C, are nearly equivalent. This means that the net surface charge remains virtually constant and leads to an equation that relates d[[H.sup.+]]/dC to partial derivatives of [Q.sub.cat] and [Q.sub.an] with respect to [[H.sup.+]] and C. Using this relation, we show that, if the exchange capacities are expressed by [Q.sub.cat] = [k.sub.cat][[[H.sup.+]].sup.-acat][C.sup.bcat] and [Q.sub.an] = [k.sub.an][[H.sup.+].sup.-aan] [C.sup.ban] the change in [Q.sub.cat] (or [Q.sub.an]) with C in a soil saturated with monovalent ions is described by an ordinary differential equation which does not contain pH as a variable. The [Q.sub.cat]-C relations predicted by solving the equation closely agreed with those by the conventional method in which pH-dependent adsorption, mass balance, and electroneutrality equations were solved simultaneously. The advantage of this approach is that once the adsorption parameters are known, the transport equation for [H.sup.+] need not be solved in predicting transport of electrolyte ions in soil.

The metabolism, flagellar beating, and acrosome reaction of spermatozoa are regulated by ion flux across the plasma membrane. As is true of most cells, swimming sperm maintain intracellular [Ca.sup.2+] concentrations at submicromolar levels. Here we describe a [K.sup.+]-dependent [Na.sup.+]/[Ca.sup.2+] exchanger (suNCKX) from sea urchin sperm. The suNCKX is phylogenetically related to other NCKXs, which use high relative intracellular [K.sup.+], and high relative extracellular [Na.sup.+], to couple the efflux of 1 [Ca.sup.2+] and 1 [K.sup.+] to the influx of 4 [Na.sup.+]. The 652-aa suNCKX shares structural topology with other NCKX proteins, and has two protein kinase A sites and a His-rich region in its cytoplasmic loop. The suNCKX is encoded by a single gene, which is highly expressed in testes. The suNCKX activity of whole sperm shows [Na.sup.+] and [K.sup.+] dependence, and like other NCKXs can run in reverse exchange mode. An inhibitor blocks the suNCKX activity and sperm motility, suNCKX localizes to the plasma membrane over the sperm flagellum. The suNCKX may play a major role in keeping [Ca.sup.2+] low in swimming sperm. sperm motility | ion exchangers | fertilization | flagellar ion exchange

This paper presents the results of experiments to evaluate the potential for using a resin-in-pulp process to remove lead contamination from soil. These experiments examined the kinetics and equilibrium partitioning of lead, lead carbonate, lead oxide, and lead sulfate in resin-soil-acetate buffer systems. The results show the trade-offs to be made among the amount of resin used, the number of contacting stages that may be needed to meet a target final soil concentration, the contact time, the solution pH, and the solution acetate concentration. DOI: 10.1061/(ASCE)0733-9372(2002)128:5(416) CE Database keywords: Lead; Soil pollution; Abatement and removal; Ion exchanges; Resins.

Using the pH-sensitive fluorescent dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein acetoxymethyl ester, we examined the effects of hyperosmotic mannitol on basolateral [Na.sup.+]/[H.sup.+] exchange (NHE) activity in isolated nonperfused proximal tubule S2 segments from mice lacking both the mdr1a and mdr1b genes (KO) and wild-type mice (WT). All experiments were performed in C[O.sub.2]/HC[O.sup.-.sub.3]-free HEPES solutions. Osmolality of the peritubular solution was raised from 300 to 500 mosmol/kg[H.sub.2]O by the addition of mannitol. NHE activity was assessed by [Na.sup.+]-dependent acid extrusion rates ([J.sub.H]) after an acid load with N[H.sub.4]Cl prepulse. Under isosmotic conditions, [J.sub.H] values at a wide intracellular pH (p[H.sub.i]) range of 6.20-6.90 were not different between the two groups. In WT mice, hyperosmotic mannitol had no effect on [J.sub.H] at the wide p[H.sub.i] range. In contrast, in KO mice, hyperosmotic mannitol increased [J.sub.H] at a p[H.sub.i] range of 6.20-6.45 and shifted the [J.sub.H]-p[H.sub.i] relationship by 0.15 pH units in the alkaline direction. In KO mice, hyperosmotic mannitol caused an increase in maximal velocity without changing the Michaelis-Menten constant for peritubular [Na.sup.+]. Exposure of cells from WT mice to the hyperosmotic mannitol solution including the P-gp inhibitor cyclosporin A increased [J.sub.H] (at [pH.sub.i] 6.30) to an extent similar to that in cells from KO mice exposed to hyperosmotic mannitol alone. In KO mice, staurosporine and calphostin C inhibited the hyperosmotic mannitol-induced increase in [J.sub.H]. The stimulatory effect of hyperosmotic mannitol on [J.sub.H] was mimicked by addition to the isosmotic control solution, including phorbol 12-myristate 13-acetate (PMA; the PKC activator). In WT mice, hyperosmotic mannitol with PMA increased [J.sub.H]. We conclude that, in the absence of P-gp activity, hyperosmotic mannitol activates basolateral NHE via protein kinase C, whereas in the presence of P-gp activity, it does not. isolated nonperfused tubule; regulatory volume increase; intracellular pH measurement; sodium-hydrogen exchange

Acute hypertension rapidly decreases proximal tubule (PT) [Na.sup.+] reabsorption, facilitated by a redistribution of PT [Na.sup.+]/[H.sup.+] exchangers (NHE3) out of the apical brush border, increasing NaCl at the macula densa, the signal for autoregulation of renal blood flow and GFR. This study aimed to determine whether NHE3 activity per transporter decreases during acute hypertension and the time dependence of the response. Blood pressure was elevated by 50-60 mmHg in male Sprague-Dawley rats for 5 or 30 min by constricting arteries. Renal cortical membranes were fractionated by density gradient centrifugation. NHE3 transport activity was assayed as the rate of appearance of acridine orange (AO) from AO-loaded vesicles in response to an inwardly directed [Na.sup.+] gradient. After 5-min hypertension, 20% of total NHE3 protein, assayed by immunoblot, redistributed from low-density apical membranes to middensity membranes enriched in intermicrovillar cleft markers; by 30 min, a similar percentage shifted to heavier density membranes containing markers of endosomes. NHE3 activity shifted to higher density membranes along with NHE3 protein, that is, no change in activity/transporter during acute hypertension. Confocal analysis of NHE3 distribution also verified removal from apical microvilli and appearance in subapical vesicles. We conclude that the decrease in renal PT [Na.sup.+] transport during acute hypertension is mediated by removal of transport-competent NHE3 from the apical brush border to subapical and internal reserves. kidney; acridine orange; tubuloglomerular feedback; sodium transport; blood pressure; sodium-hydrogen exchanger

In this paper, a novel approach is described for the a priori prediction of protein retention in ion exchange systems. Quantitative structure retention relationship (QSRR) models based on a genetic algorithm/partial least squares approach were developed using experimental chromatographic data in concert with molecular descriptors computed using protein crystal structures. The resulting QSRR models were well-correlated, with cross-validated [r.sup.2] values of 0.938 and 0.907, and the predictive power of these models was demonstrated using proteins not included in the derivation of the models. Importantly, these models were able to predict selectivity reversals observed with two different stationary phase materials. To our knowledge, this is the first published example of predictive QSRR models of protein retention based on crystal structure data.

Prediction of gas and ion diffusion in unsaturated soils has been obstructed by the inability to independently measure tortuosity parameters. Analogies between transport processes are often suggested to assess these nonmeasurable parameters. However, it is unclear whether these analogies are valid in unsaturated soils. Therefore, to obtain a more fundamental insight into the differences between ion and gas diffusion in an unsaturated sandy soil a different approach than current empirical models is required. In this study, fitted tortuosity parameter values of analogy-based models describing the gas diffusion coefficient and bulk soil electrical conductivity (ion diffusion) of a sandy soil are compared. Gas diffusion in unsaturated soil is most affected by connectivity in contrast to electrical conductivity that is among other factors primarily determined by tortuosity. Measured gas diffusion and electrical conductivity are also compared with lattice-Boltzmann simulated gas and ion diffusion as a function of water content in a thin section (two dimensional) of a sandy soil. Results of the lattice-Boltzmann simulations are in qualitative agreement with measured diffusional ratios and support the findings with the analogy-based models. Lattice-Boltzmann simulations may be a valuable tool to overcome empirism of current models and increase our insight in transport properties of unsaturated soils in the coming years.

Thermodynamic modeling of the ion exchange equilibria has been approached in two ways, the deprotonation of quinolic resin P-127 and iminodiacetic resin Amberlite IRC-718. Hogfeldt's three-parameter model can be usefully explored to describe the ion exchange performance.

This study examines the effects on stable and radioactive (137)Cs+ and (89)(Sr)2+ by the ion exchange properties of a titanium silicate designated (M)2(Ti)2(O)3(SiO)4-n(H)2O (M=H, Na). The study, which was conducted by the Department of Chemistry, Texas A and M University, found that the sodium titanium silicate was an efficient Cs+ ion exchange in alkaline, neutral and acid media, as well as being an efficient Sr(2)+ ion exchanger in alkaline and neutral media.

A method for improving the porosity of the solid state Na2Zn3(Fe(CN)6)2.9H2O is described. The formation of Na2Zn3(Re6Se8(CN)6)2.24H20 is presented with reference to its enhanced capacity for ion-exchange.