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The regional impact of abrupt glacial climate variability remains poorly constrained for arid southwestern Asia, particularly winter dynamics during Marine Isotope Stage 3, due to limited paleoarchives in the Middle East. Here, we present continuous speleothem records of δ18O and δ13C with robust chronologies for southwestern and central Iran, spanning ∼50–30 ka. Stable‐isotope signals in the two stalagmites are generally uncorrelated and do not exhibit a consistent response to Greenland stadials or interstadials; however, both show a positive δ18O excursion that coincides with Heinrich event 4. We explore the potential mechanisms for intermittent coupling of speleothem δ18O across Iran through isotope‐enabled atmospheric modeling outputs, from which we utilize the spatial δ18O gradient as a proxy for wintertime westerly versus southerly jet strength. Our results suggest that during Heinrich event 4 and several Greenland stadials, stronger westerly winds enhanced Mediterranean moisture contributions to both sites and reduced aridity in southern Iran. Stalagmites are useful archives to reconstruct the climate of the past. In order to shed light on the past climate of western Asia and the response of this region to the rapid climate changes, here we present two stalagmites from central and southwestern Iran that span 50,000 to 30,000 yrs ago. Our findings suggest that during extreme cold events, the moisture originates mostly from the west, whereas out of these extraordinarily cold periods moisture comes mostly from the south. Continuous high‐resolution speleothem record of climatic change in southwestern and central Iran between 50 and 30 kaDecoupled responses of stable‐isotope gradients in central and southern Iran to glacial climate variability, except during Heinrich event 4Decreased impact of southerly moisture sources and reinforced westerlies during extreme cold events Continuous high‐resolution speleothem record of climatic change in southwestern and central Iran between 50 and 30 ka Decoupled responses of stable‐isotope gradients in central and southern Iran to glacial climate variability, except during Heinrich event 4 Decreased impact of southerly moisture sources and reinforced westerlies during extreme cold events

Abstract Disturbances in potassium homoeostasis presenting as low or high serum potassium are common, especially among hospitalised patients. Given the fact that untreated hypokalaemia or hyperkalaemia is associated with high [...]

Accurate geological modeling of subsurface structures with all available geophysical data is a challenging task in geo-exploration studies. Concern in precise modeling will increase by increasing geological complexity of subsurface structures such as salt dome. Integrating various sources of geophysical data will reduce uncertainty in geological modeling in complex media. In this study, we introduce an integrated strategy for more appropriate detection of salt boundary in seismic image, by applying the normalized full gradient (NFG) method, used in processing of potential field data. In the proposed strategy, we initially, analyzed sensitivity of the NFG parameters by derivation of a synthetic model. Parameter analysis and optimization showed dependency of geometrical properties of the geological target to the harmonic number in the NFG method. Afterwards, seismic traces were processed by the NFG method. Results showed increase in vertical resolution of seismic envelope compared to the result of the well-known Hilbert Transform. The proposed strategy was applied on a synthetic seismic data contains complex salt model. Results have shown that application of the proposed strategy produced higher resolution seismic image compared to the Hilbert Transform method. The method also was applied on a field seismic data with a complex salt dome from southwest of Kazakhstan. Seismic image obtained by the integration procedure could better exhibit body of the salt dome, as well as better interpretation of faults, layer boundary truncation, salt bottom and subsalt layers. Thus, it was concluded that the proposed strategy could be considered as an alternative to resolve some of ambiguities in geological interpretation of seismic data in complex geological settings.

PurposeTo determine the proper time for traumatic cataract surgery after open globe injuries.SettingFarabi Eye Hospital, Tehran University of Medical Sciences, Tehran, Iran.DesignRandomized clinical trial.Patients and methodsIn a randomized clinical trial, 30 eyes with traumatic cataract after open globe injury with IOL implantation underwent early (in the first week after the trauma) and 30 eyes underwent late cataract surgery (from the first to second month after the trauma). We excluded patients who were under 12-year-old. All patients were visited at 1 week, 4 weeks, 12 weeks, and 6 months after surgery. In each visit, patients were examined regarding visual acuity, intraocular pressure (IOP), anterior chamber inflammation, IOL position, and posterior synechiae. In addition, posterior segment evaluation and fundoscopy were performed. Intraoperative complication including posterior capsular rupture, anterior vitrectomy, and zonulysis as well as the site of IOL implantation were documented and post-operative complications including raised IOP, anterior chamber inflammation, visual axis opacity, posterior synechiae, subluxation of IOL, and IOL pigment deposition were listed.ResultsBest-corrected visual acuity 6 months after surgery was not different between the two groups. Also in early cataract surgery group, the rate of posterior capsular rupture was not significantly higher than the late surgery group (P=0.069). On the other hand, zonulysis was significantly higher in the late procedure group (P=0.039). Other complications including anterior vitrectomy, raised IOP, anterior chamber inflammation, visual axis opacity, posterior synechiae, subluxation of IOL, and IOL pigment deposition were not different in the two groups.ConclusionsEarly and late traumatic cataract surgery and IOL implantation after open globe injuries, have no significant difference regarding the post-surgical BCVA and prominent intraoperative and post-operative complications.

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Nowadays artificial neural networks (ANNs) with strong ability have been applied widely for prediction of nonlinear phenomenon. In this work an optimized ANN with 7 inputs that consist of temperature, pressure, critical temperature, critical pressure, density, molecular weight and acentric factor has been used for solubility prediction of three disperse dyes in supercritical carbon dioxide (SC-CO2) and ethanol as co-solvent. It was shown how a multi-layer perceptron network can be trained to represent the solubility of disperse dyes in SC-CO2. Numeric Sensitivity Analysis and Garson equation were utilized to find out the degree of effectiveness of different input variables on the efficiency of the proposed model. Results showed that our proposed ANN model has correlation coefficient, Nash–Sutcliffe model efficiency coefficient and discrepancy ratio about 0.998, 0.992, and 1.053 respectively.

Study design:This is a clinical trial (phase 1).Objectives:The objective of this study was to asses the safety and feasibility of bone marrow mesenchymal stem cell (MSC) and Schwann cell (SC) co-injection through cerebral spinal fluid (CSF) for the treatment of patients with chronic spinal cord injury.Methods:Six subjects with complete spinal cord injury due to trauma according to International Standard of Neurological Classification for Spinal Cord Injury (ISNCSCI) developed by the American Spinal Injury Association were enrolled. They received autologous co-transplantation of MSC and SC through lumbar puncture. Neurological status of the patients was determined by ISNCSCI, as well as by assessment of functional status by Spinal Cord Independent Measure. Before and after cell transplantation, magnetic resonance imaging (MRI) was performed for all the patients. Before the procedure, all the patients underwent electromyography, urodynamic study (UDS) and MRI tractograghy. After transplantation, these assessments were performed in special cases when the patients reported any changes in motor function or any changes in urinary sensation.Results:Over the mean 30 months of follow-up, the radiological findings were unchanged without any evidence of neoplastic tissue overgrowth. American Spinal Injury Association class in one patient was changed from A to B, in addition to the improvement in indexes of UDS, especially bladder compliance, which was congruous with axonal regeneration detected in MRI tractography. No motor score improvement was observed among the patients.Conclusion:No adverse findings were detected at a mean of 30 months after autologous transplantation of the combination of MSCs and SCs through CSF. It may suggest the safety of this combination of cells for spinal cord regeneration.

N-triethyl chitosan (TEC) has recently been proven to be an efficient polymer for improving transport of hydrophilicdrugs. Thus, in order to evaluate its gene delivery efficiency, TEC is assembled with Enhanced Green fluorescenceprotein plasmid DNA (pEGFP) at different polymer to plasmid (N/P) ratios to form TEC/pEGFP nanoparticles.Photon correlation spectroscopy is used to evaluate nanoparticles size and zeta potential. The transfection efficiency andcytotoxicity in gene delivery to AsPC-1 cells (human pancreatic cancer cells) are evaluated via fluorescence microscopy,flow cytometry and MTT assay. Also parameters such as cancer cells' mean fluorescence intensity (MFI) and cell sizechanges after transfection are assayed. The results indicate that the incorporation of pEGFP in TEC can form chargednanoparticles at N/P ratios from 10 to 40. Increasing the N/P ratio increases transfection efficiency, MFI, cell size and cytotoxicity.At N/P ratio of 10, transfection increased up to 11.12 fold with the least cytotoxicity. Considering that mathematicalmodels can be used to understand and predict consequences associated with nanomedicine, the relation betweenTEC /pDNA nanoparticles charge ratio, cell transfection and toxicity was evaluated for the first time with interpolationpolynomial method.

Aim To supporting growth and functional differentiation of adult stem cells into hepatocytes in a well-controlled manner, we performed differentiation of human bone marrow mesenchymal stem cells (hBMSCs) to hepatocytes-like cells on a constructed 3-dimensional (3D) nanofibrous biocompatible scaffold.Methods After characterization of the hBMSCs isolated from human bone marrow, the performance of the cells seeded and their proliferation on the scaffold was evaluated by scanning electron microscopy (SEM) and 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Different approaches such as immunocytochemistry, reverse transcriptase polymerase chain reaction (RT-PCR), and biochemical assays were used to estimate the ability of hBMSC-derived cells to express hepatocyte-specific markers.Results Scanning electron micrographs and MTT analysis revealed the cells were able to expand and remained biologically and metabolically active for 21 days. Immunocytochemical analysis of albumin and a-fetoprotein showing the accumulation of these markers in differentiated cells was confirmed by RT-PCR. Additional markers such as cytochrome P450 3A4, cytokeratin-18, and cytokeratin-19 detected by RT-PCR showed progressive expression during 3 weeks of differentiation on 3D scaffold. The hepatocyte-like cells displayed several characteristics of metabolic functions as judged by production of albumin, urea, transferrin, serum glutamic pyruvic transaminase (SGPT), and serum oxaloacetate aminotransferase (SGOT). Levels of above-mentioned markers, except SGOT in differentiated cells on scaffold, were found to be significantly greater than in the 2D culture system (p<0.05).Conclusion Overall data suggest that the engineered nanofibrous scaffold is a conductive matrix for functional hBMSC-derived hepatocyte-like cells and is promising for maintenance of hepatocytes suitable for implantation.

Activated carbon is widely used in various processes as an inexpensive and effective adsorbent. The adsorption properties of activated carbon vary with the feed materials used and the method of activation. The use of an inexpensive material and performing a suitable production method may help to generate a low cost product. Agricultural wastes could be considered as suitable raw materials for the production of activated carbon. In this work, activated carbon was produced by chemical activation with phosphoric acid of agricultural wastes such as bagasse, hard shells of apricot stones, almond, walnut and hazelnut shells. The effects of various preparation variables on both yield and quality of the prepared carbon were studied. The results showed that the selection of final activation temperature, heating rate, activation time and impregnation rate of the chemical agent was important in determining the quality of activated carbon obtained. The surface area and ash content of the activated carbon produced were compared to those of imported commercial samples. According to the results obtained, activated carbon from the hard shells of apricot stones have the best adsorption properties and the highest surface area. This activated carbon could be used in the separation of metal ions from wastewaters.

In the present study, based on a biomimetic approach, novel 3D nanofibrous hybrid scaffolds consisting of poly(e-caprolactone), polyvinyl alcohol), and chitosan were developed via a multi-jet electrospinning method. The influence of chemical, physical, and structural properties of the scaffolds on the differentiation of mesenchymal stem cells into osteoblasts, and the proliferation of the differentiated cells were investigated. Osteogenically induced cultures revealed that cells were well-attached, penetrated into the construct and were uniformly distributed. The expression of early and late phenotypic markers of osteoblastic differentiation was upregulated in the constructs cultured in osteogenic medium.

Activated carbon can be produced from a large variety of raw materials, basically by two methods, physical and chemical activation or a combination of both. The adsorption properties of activated carbon vary with the feed materials used and the way of activation. Production cost may be lowered by choosing a cheap raw material and performing a suitable production process. Agricultural and forestry residues, or generally, biomass residue wastes could be used as suitable raw materials for the production of activated carbon. In the present work, different agricultural residues such as hard shells of apricot stones, almond, walnut and hazelnut shells, rice hulls and residues of liquorices were used as precursors. The activation was performed using phosphoric acid under the same conditions. The results showed that at the selected experimental conditions, the type of biomass as well as the final activation temperature, heating rate and impregnation rate of the chemical agent had the greatest influence on the quality of activated carbon. The quality of activated carbon was evaluated in terms of the iodine number reflecting the surface area. According to the results, activated carbon from the hard shells of apricot stones had the best adsorption properties and the largest surface area.

The effect of chemical reagent (H3PO4, KOH, and NaOH), temperature (400 °C, 475 °C, 550 °C), and impregnation ratio (100 %, 150 %, 200 %) was investigated on the specific surface area and iodine uptake of the carbons produced from almond, walnut, and pistachio‐nut shells and date stones. The effect of mesh size and holding time was also studied in the case of almond shell. While the alkali activation of the precursors resulted in such fine powders that purifying them of contaminants was almost impossible, the acid activation of the raw materials produced carbons with high iodine numbers (about 1000 mg I2/g carbon). To further characterize their porosity, the almond‐based carbons underwent BET measurements, with the results showing comparatively high surface areas (about 1400 m2/g). The carbons were rather mesoporous, and thus more suitable for liquid applications, which was confirmed by using the carbons in chromium (VI) uptake in another study [1].

Extraction of AuIIIions by an emulsion liquid membrane (ELM) system with methyl isobutyl ketone (MIBK) as the mobile carrier and also liquid‐liquid extraction of AuIIIfrom aqueous solutions have been studied. Experiments on the transport of the gold ions in a liquid‐liquid extraction system and stripping of the extracted ions from the organic phase as well as the extraction by a three‐phase W/O/W emulsion liquid membrane system have been performed. The results showed that even when the distribution coefficient of the diffusing species in the phases is small, the extraction by emulsion liquid membranes would be an effective process. A first‐order extraction rate was proposed and examined for the extraction system.

A Quantitative structure-property relationship analysis had been applied to a set of gemini surfactants which were of special interest because of their roles in environmental samples. Modeling of the critical micelle concentrations (CMC) of 94 gemini surfactants as a function of their theoretically-derived descriptors (i.e. topological indices) was established by means of multiple linear regression (MLR) and partial least squares (PLS) regression methods. The genetic algorithm was used to find a set of descriptors that resulted in the best-fitted models. The results showed that both MLR (with 9 selected descriptors) and PLS (with 20 selected descriptors) methods could model the relationship between CMC of gemini surfactants and their topological descriptors perfectly. However, better results obtained by PLS regression. The stability and validity of models were tested by cross-validation technique and by prediction of the response values for the prediction set. The average relative error of prediction for the best MLR and PLS models, was equal to 2.94 and 0.36, respectively. Also, the respective squares of correlation coefficients of these models were 0.979 and 0.985.

Summary: This protocol describes the use of the pH-sensitive, intracellularly trapped dye 2′,7′-bis (2-carboxyethyl), 5 (and -6) carboxyfluorescein (BCECF), to characterize the pH regulating mechanisms in cultured human kidney proximal tubule cells. This is a reliable method for intracellular pH measurements and is applicable to single cells, cell suspensions, and confluent cultures.

Abstract.: Na+/H+ exchanger isoforms NHE-2 and NHE-3 demonstrate distinct tissue expression patterns in renal epithelial cells. NHE-2 is predominantly expressed in the inner medulla whereas NHE-3 is highly expressed in the proximal tubule cells. The purpose of the current experiments was to study the characteristics of NHE-2 upon its own expression in cultured proximal tubule cells, LLC-PK1. Toward this end, LLC-PK1 cells were subjected to six cycles of proton suicide. The mutant cells, when grown to confluence and assayed for Na+/H+ exchanger by 22Na+ influx, showed significant reduction in NHE activity as compared to the parent cells (10.4 nmole/mg prot/4 min in parent cells vs. 1.8 in mutant cells, P < 0.001, n= 4). This remaining exchanger activity was mostly mediated via NHE-3 as shown by inhibition of the Na influx following PKC stimulation (65% with PMA vs. 100% without PMA. P < 0.05, n= 4). The mutant cells were transiently transfected with a pCMV/NHE-2 expression vector using calcium phosphate precipitation method. Northern blot analysis showed the expression of a 3.4 kb transcript only in the transfected cells. The expression peaked at 48 hr and diminished by 96 hr. The exchanger activity at 48 hr after transfection was mostly due to NHE-3 (as shown by inhibition in the presence of PMA) but was significantly lower than in sham transfected cells (1.2 nmoles/mg prot. in NHE-2-transfected and 2.1 in sham-transfected, P < 0.05, n= 4). At 60 hr after transfection, the cells exhibited PMA-stimulated Na influx (>28%) indicating functional expression of NHE-2. Increasing the osmolality of the media to 510 mOsm/l stimulated the Na+/H+ exchanger in NHE-2 transfected cells but inhibited the exchanger activity in sham transfected cells. In conclusion, NHE-2 appears as a 3.4 kb transcript in transfected LLC-PK1 cells and functional expression of NHE-2 is preceded by inhibition of endogenous NHE-3 activity. The NHE-2 is stimulated by hypertonicity, indicating a likely role for this isoform in cell volume regulation.

Functional properties of a cloned human kidney Na+:HCO3- cotransporter (NBC-1) were studied in cultured HEK-293 cells that were transiently transfected with NBC-1 cDNA. The Na+:HCO3- cotransporter activity was assayed as the Na+ and HCO3-dependent pHi recovery from intracellular acidosis with the use of the pH-sensitive dye 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein. In acid-loaded cells and in the presence of amiloride (to block Na+/H+ exchange), switching to a Na+-containing solution (115 mM) resulted in rapid pHi recovery only in the presence of HCO3-. This recovery was completely abolished by 300 microM 4, 4'-diisothiocyanostilbene-2,2'-disulfonic acid. Replacing the Na+ with Li+ (115 mM) caused significant HCO3--dependent, DIDS-sensitive pHi recovery from intracellular acidosis, with Li+ showing lower affinity than Na+. Potassium (K+) had no affinity for the Na+:HCO3- cotransporter. The Na+-dependent HCO3- cotransport was abolished in the presence of 0.2 mM harmaline. The Na+:HCO3- cotransporter could also function in Na+:OH- cotransport mode, although only at high external pH (7.8). Based on functional similarities with the mammalian kidney experiments, we propose that NBC-1 is the proximal tubule Na+:HCO3- cotransporter.

Several modes of HCO3- transport occur in the kidney, including Na+-independent Cl/HCO3- exchange (mediated by the AE family of Cl-/HCO3- exchangers), sodium-dependent Cl-/HCO3- exchange, and Na+:HCO3- cotransport. The functional similarities between the Na+-coupled HCO3- transporters and the AE isoforms (i.e. transport of HCO3- and sensitivity to inhibition by 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid) suggested a strategy for cloning the other transporters based on structural similarity with the AE family. An expressed sequence tag encoding part of a protein that is related to the known anion exchangers was identified in the GenBankTM expressed sequence tag data base and used to design an oligonucleotide probe. This probe was used to screen a human kidney cDNA library. Several clones were identified, isolated, and sequenced. Two overlapping cDNA clones were spliced together to form a 7.6-kilobase cDNA that contained the entire coding region of a novel protein. Based on the deduced amino acid sequence, the cDNA encodes a protein with a Mr of 116,040. The protein has 29% identity with human brain AE3. Northern blot analysis reveals that the 7.6-kilobase mRNA is highly expressed in kidney and pancreas, with detectable levels in brain. Functional studies in transiently transfected HEK-293 cells demonstrate that the cloned transporter mediates Na+:HCO3- cotransport.

This study examines the effects of acute in vitro acid-base disorders on Na+/H+ and H+-ATPase transporters in rabbit kidney proximal tubules (PT). PT suspensions were incubated in solutions with varying acid base conditions for 45 min and utilized for brush border membrane (BBM) vesicles preparation. BBM vesicles were studied for Na+/H+ exchange activity (assayed by 22Na+ influx) or abundance (using NHE-3 specific antibody) and H+-ATPase transporter abundance (using antibody against the 31 kDa subunit). The Na+/ H+ exchanger activity increased by 55% in metabolic acidosis (pH 6.5, HCO3-3 mm) and decreased by 41% in metabolic alkalosis (pH 8.0, HCO3-90 mm). The abundance of NHE-3 remained constant in acidic, control, and alkalotic groups. H+-ATPase abundance, however, decreased in metabolic acidosis and increased in metabolic alkalosis by 57% and 42%, respectively. In PT suspensions incubated in isohydric conditions (pH 7.4), Na+/H+ exchanger activity increased by 29% in high HCO3-group (HCO3-96 mm) and decreased by 16% in the low HCO3-groups (HCO3-7mm. The NHE-3 abundance remained constant in high, normal, and low [HCO3-] tubules. The abundance of H+-ATPase, however, increased by 82% in high [HCO3-] and decreased by 77% in the low [HCO3-] tubules. In PT suspensions incubated in varying pCO2 and constant [HCO3-], Na+/H+ exchanger activity increased by 35% in high pCO2 (20% pCO2, respiratory acidosis) and decreased by 32% in low pCO2 (1.5% pCO2, respiratory alkalosis) tubules. The NHE-3 abundance remained unchanged in high, normal, and low pCO2 tubules. However, the H+-ATPase abundance increased by 74% in high pCO2 and decreased by 69% in low pCO2 tubules.

Cadherins are recognized as the principal mediators of homotypic cellular recognition and play a demonstrated role in the morphogenic direction of tissue development. We report here the identification of a structurally unique, kidney-specific member of the cadherin multigene family (Ksp-cadherin). cDNA cloning and molecular analysis of the 130-kDa protein confirmed that it was novel and indicated that it most closely resembled members of the LI-cadherin/HPT-1 cadherin subgroup. The predicted protein possesses the definitive cadherin-specific sequence motifs LDRE, DXND, and DXD in well conserved sequential arrangement, and the characteristic cysteine residues found in the last ectodomains of almost all known cadherins. Like LI-cadherin and HPT-1, Ksp-cadherin lacks the prosequence and HAV adhesion recognition sequence typical of most classical cadherins, and possesses a truncated cytoplasmic domain (18-22 amino acids). When expressed in a transient Vaccinia/T7 expression system, Ksp-cadherin displayed the classic calcium sensitivity to trypsin proteolysis that is observed in all cadherins. Immunolocalization studies and Northern analysis indicated that expression of Ksp-cadherin was kidney-specific and limited to the basolateral membranes of renal tubular epithelial cells. In summary, we have identified and cloned a novel, kidney-specific member of the cadherin multigene family that we propose be designated Ksp-cadherin.

Potassium depletion is involved in the pathophysiology of metabolic alkalosis. In the present study, the expression of renal acid-base transporters that are involved in HCO3- reabsorption was studied in potassium depletion. Rats fed potassium-deficient (KD) diet developed significant hypokalemia at 14 days (serum K+ 1.9 +/- 0.2 in KD vs. 4.2 +/- 0.2 meq/l in control, P < 0.01) but not at 6 days (3.8 +/- 0.3 in KD vs. 4.1 +/- 0.3 meq/l in control, P > 0.05). Kidney mRNA for colonic H(+)-K(+)-adenosinetriphosphatase (H(+)-K(+)-ATPase, cHKA) increased by approximately 3- and 11-fold at 6 and 14 days of KD diet, respectively, indicating that increased expression preceded the onset of hypokalemia. The expression of Na+/H+ exchanger 3 (NHE-3) mRNA and its cognate protein remained unchanged at 6 and 14 days of KD diet. The mRNA levels for NHE-1, NHE-2, and NHE-4 also remained unchanged at 6 and 14 days of KD diet. Hypophysectomized (HPX) rats fed KD diet for 14 days developed similar hypokalemia. However, the expression of cHKA mRNA in the kidney was decreased by approximately 80% in potassium-depleted (HPX+KD) rats (P < 0.01 vs. KD only). Hypophysectomy did not affect the mRNA levels for either gastric H(+)-K(+)-ATPase (gHKA) or NHE isoforms in KD animals. Thus potassium depletion increases expression of cHKA in the kidney but not that of gHKA or NHE isoforms. The signal for this increase appears to precede hypokalemia. Furthermore, the data suggest that pituitary hormone(s) plays an important and novel role in the regulation of cHKA.

The exit of HCO3−across the basolateral membrane of the proximal tubule cell occurs via the electrogenic cotransport of 3 eq of base per Na+. We have used basolateral membrane vesicles isolated from rabbit renal cortex to identify the ionic species transported via this pathway. Media of varying pH and pCO2 were employed to evaluate the independent effects of HCO3−and CO32−on 22Na transport. Na+ uptake was stimulated when [CO32−] was increased at constant [HCO3−], indicating the existence of a transport site for CO32−. In the presence of HCO3−, Na+ influx was stimulated more than 3-fold by an inward SO32−gradient. SO32−-stimulated Na+ influx was stilbene-sensitive, confirming that it occurs via the Na+-HCO3−cotransport system. Na+-SO32−cotransport was demonstrated and found to have a 1:1 stoichiometry. Increasing [CO32−] at constant [HCO3−] reduced the stimulation of Na+ influx by SO32−, suggesting competition between SO32−and CO32−at a common divalent anion site. Additional divalent anions that were tested, such as SO42−, oxalate2-, and HPO4(2-), did not interact at this site. SO32−stimulation of Na+ influx was absolutely HCO3−(-)dependent and was increased as a function of [HCO3−], indicating the presence of a separate HCO3−site. Lastly, we tested whether Na+ interacts via ion pair formation with CO32−or binds to a distinct site. Na+, which has lower affinity than Li+ for ion pair formation with CO32−, was found to have > 5-fold higher affinity than Li+for the Na+-HCO3−cotransport system. Moreover, when its inhibition was studied as a function of [Na+], harmaline was found to be a competitive inhibitor of Na+ influx, indicating the existence of a distinct cation site. Our data are compatible with a model in which base transport across the basolateral membrane of the proximal tubule cell takes place via 1:1:1 cotransport of CO32−, HCO3−, and Na+on distinct sites.

Due to carbon dioxide role in global warming, low CO2 emission limits have been established in recent years. This has led to a variety of studies on CO2 removal approaches. In this study, a VSA cycle consisting of two packed beds is considered for CO2 removal from flue gas. An atmospheric stream containing 20 CO2 and 80 N2 is fed to the beds at 50degC. Two adsorbents, namely Zeolite 13X and activated carbon were selected to compare their performance. Due to the monolayer adsorption of CO2 and N2 on these adsorbents, the Toth isotherm was used for equilibrium adsorption estimation. A quasi-second order model was considered for the mass transfer rate prediction due to low CO2 concentration. The modeling results showed that the average absolute deviation for equilibrium adsorption capacity prediction was 2, and the CO2 breakthrough time curve was predicted with less than 2.5 deviation. Based on the results, the VSA cycle time for zeolite 13X bed will be 3.5 times of the activated carbon bed. Another advantage of Zeolite 13X is that in each process cycle, 80 of adsorbent will be used, while only 74 of activated carbon in beds is used. The advantage of activated carbon bed is its better regeneration capability, since the activated carbon will be regenerated 5 more than zeolite 13X at a vacuum pressure of 0.02bar.

GASTROENTEROLOGY 1999;117:276-277