Absence Of HCO3 Research Articles

Ion permeability profiles of renal paracellular channel-forming claudins.

Members of the claudin protein family are the major constituents of tight junction strands and determine the permeability properties of the paracellular pathway. In the kidney, each nephron segment expresses a distinct subset of claudins that form either barriers against paracellular solute transport or charge- and size-selective paracellular channels. It was the aim of the present study to determine and compare the permeation properties of these renal paracellular ion channel-forming claudins. MDCK II cells, in which the five major claudins had been knocked out (claudin quintupleKO), were stably transfected with individual mouse Cldn2, -4, -8, -10a, -10b, or -15, or with dog Cldn16 or -19, or with a combination of mouse Cldn4 and Cldn8, or dog Cldn16 and Cldn19. Permeation properties were investigated in the Ussing chamber and claudin interactions by FRET assays. Claudin-4 and -19 formed barriers against solute permeation. However, at low pH values and in the absence of HCO3 -, claudin-4 conveyed a weak chloride and nitrate permeability. Claudin-8 needed claudin-4 for assembly into TJ strands and abolished this anion preference. Claudin-2, -10a, -10b, -15, -16+19 formed highly permeable channels with distinctive permeation profiles for different monovalent and divalent anions or cations, but barriers against the permeation of ions of opposite charge and of the paracellular tracer fluorescein. Paracellular ion permeabilities along the nephron are strictly determined by claudin expression patterns. Paracellular channel-forming claudins are specific for certain ions and thus lower transepithelial resistance, yet form barriers against the transport of other solutes.

Reaction of FeaqII with Peroxymonosulfate and Peroxydisulfate in the Presence of Bicarbonate: Formation of FeaqIV and Carbonate Radical Anions.

Many advanced oxidation processes (AOPs) use Fenton-like reactions to degrade organic pollutants by activating peroxymonosulfate (HSO5-, PMS) or peroxydisulfate (S2O82-, PDS) with Fe(H2O)62+ (FeaqII). This paper presents results on the kinetics and mechanisms of reactions between FeaqII and PMS or PDS in the absence and presence of bicarbonate (HCO3-) at different pH. In the absence of HCO3-, FeaqIV, rather than the commonly assumed SO4•-, is the dominant oxidizing species. Multianalytical methods verified the selective conversion of dimethyl sulfoxide (DMSO) and phenyl methyl sulfoxide (PMSO) to dimethyl sulfone (DMSO2) and phenyl methyl sulfone (PMSO2), respectively, confirming the generation of FeaqIV by the FeaqII-PMS/PDS systems without HCO3-. Significantly, in the presence of environmentally relevant concentrations of HCO3-, a carbonate radical anion (CO3•-) becomes the dominant reactive species as confirmed by the electron paramagnetic resonance (EPR) analysis. The new findings suggest that the mechanisms of the persulfate-based Fenton-like reactions in natural environments might differ remarkably from those obtained in ideal conditions. Using sulfonamide antibiotics (sulfamethoxazole (SMX) and sulfadimethoxine (SDM)) as model contaminants, our study further demonstrated the different reactivities of FeaqIV and CO3•- in the FeaqII-PMS/PDS systems. The results shed significant light on advancing the persulfate-based AOPs to oxidize pollutants in natural water.

An Insight into the Bicarbonate Effect in Photosystem II through the Prism of the JIP Test

Photosystem II (PSII) is the unique pigment–protein complex that is capable of evolving molecular oxygen using solar energy. The activity of PSII determines the overall productivity of all oxygenic photosynthetic organisms. It is well known that the absence of HCO3− induces a drop in the activity of PSII. However, it is not yet clear what type of photochemical reaction, single turn-over or multiple turn-over, HCO3− is involved in. Kinetic parameters of this (these) involvement(s) are almost unexplored now. This work addresses these issues. Using the JIP test, being the perspective noninvasive method for measuring PSII activity in plants, this paper describes how HCO3− deficiency affects the electron transfer on the oxidizing as well as the reducing sides of PSII in thylakoids and in PSII preparations from the leaves of pea plants. HCO3− was found to be simultaneously involved both in single turn-over and in multiple turn-over events (“dynamical processes”). Moreover, the involvement of HCO3− in dynamical photochemical processes was revealed to be associated with both sides of PSII, being the rate limiting on the reducing side, which follows from obtained kinetic parameters. The involvement of HCO3− in dynamical processes as the constant exchangeable ligand is discussed for both the electron donor and acceptor sides of PSII.

Study on the preparation of coal wastewater slurry from salt/alkali wastewater

Combining experimental research and simulation calculation, the effect of high-concentration salt/alkali wastewater on the preparation of coal wastewater slurry (CWWS) was studied. The research on the slurry-ability of CWWS shows that Na+ in NaCl will be electrically neutralized with the negative charge on the coal, the electrostatic repulsion of particles will decrease, and the viscosity will increase. In the presence of HCO3c, negative charge increases on coal particles, the apparent viscosity decreases by 42 mPa·s compared with the absence of HCO3−. In the CO32− systems, the pH is 8.25. Higher pH indicates that there are more OH−. Because CO32− is easy to combine with water to form a stable structure, and the strong polar effect of OH− is also easy to bind water molecules, forming a stable water molecule layer configuration on the coal, which hinders the adsorption of sodium lignosulfonate (SL), resulting in a decrease in steric hindrance effect, which is not conducive to the dispersion of particles. The molecular dynamics (MD) simulation results confirmed the existence of the neutralization of Na+ and the negative charge on coal in the NaCl system. The adsorption energies (Eadsorption) of each system were negative, indicating that the dispersant was easily adsorbed on the coal. However, in the CO32− system, the absolute value of Eadsorption was lower than that the pure water system, indicating that the presence of CO32− is not conducive to the adsorption of SL. The self-diffusion coefficient(D) of Na2CO3 system is lower than that of coal/water/SL system, NaCl system, and NaHCO3 system. It shows that the presence of CO32− can significantly reduce the migration rate of water molecules and is easy to bind water molecules. The presence of HCO3− is also easy to bind water molecules, but it is weaker than CO32−. The migration and diffusion rate of water molecules in the saline-alkali mixed system decrease. This may be mainly affected by CO32−, which easily binds water molecules on the coal surface and hinders the adsorption of SL.

Molecular mechanism underlying transport and allosteric inhibition of bicarbonate transporter SbtA

SbtA is a high-affinity, sodium-dependent bicarbonate transporter found in the cyanobacterial CO2-concentrating mechanism (CCM). SbtA forms a complex with SbtB, while SbtB allosterically regulates the transport activity of SbtA by binding with adenyl nucleotides. The underlying mechanism of transport and regulation of SbtA is largely unknown. In this study, we report the three-dimensional structures of the cyanobacterial Synechocystis sp. PCC 6803 SbtA-SbtB complex in both the presence and absence of HCO3- and/or AMP at 2.7 Å and 3.2 Å resolution. An analysis of the inward-facing state of the SbtA structure reveals the HCO3-/Na+ binding site, providing evidence for the functional unit as a trimer. A structural comparison found that SbtA adopts an elevator mechanism for bicarbonate transport. A structure-based analysis revealed that the allosteric inhibition of SbtA by SbtB occurs mainly through the T-loop of SbtB, which binds to both the core domain and the scaffold domain of SbtA and locks it in an inward-facing state. T-loop conformation is stabilized by the AMP molecules binding at the SbtB trimer interfaces and may be adjusted by other adenyl nucleotides. The unique regulatory mechanism of SbtA by SbtB makes it important to study inorganic carbon uptake systems in CCM, which can be used to modify photosynthesis in crops.

V-Type ATPase Mediates Airway Surface Liquid Acidification in Pig Small Airway Epithelial Cells.

In a newborn pig cystic fibrosis (CF) model, the ability of gland-containing airways to fight infection was affected by at least two major host-defense defects: impaired mucociliary transport and a lower airway surface liquid (ASL) pH. In the gland-containing airways, the ASL pH is balanced by CFTR (CF transmembrane conductance regulator) and ATP12A, which, respectively, control HCO3- transport and proton secretion. We found that, although porcine small airway tissue expressed lower amounts of ATP12A, the ASL of epithelial cultures from CF distal small airways (diameter < 200 μm) were nevertheless more acidic (compared with non-CF airways). Therefore, we hypothesized that gland-containing airways and small airways control acidification using distinct mechanisms. Our microarray data suggested that small airway epithelia mediate proton secretion via ATP6V0D2, an isoform of the V0 d subunit of the H+-translocating plasma membrane V-type ATPase. Immunofluorescence of small airways verified the expression of the V0 d2 subunit isoform at the apical surface of Muc5B+ secretory cells, but not ciliated cells. Inhibiting the V-type ATPase with bafilomycin A1 elevated the ASL pH of small airway cultures, in the presence or absence of HCO3-, and decreased ASL viscosity. These data suggest that, unlike large airways, which are acidified by ATP12A activity, small airways are acidified by V-type ATPase, thus identifying V-type ATPase as a novel therapeutic target for small airway diseases.

Exploring the Intracellular‐pH Sensitivity of the Electrogenic Sodium Bicarbonate Cotransporter NBCe1‐B when Co‐expressed with its Cytosolic Binding Partner IRBIT

The electrogenic Na/HCO3 cotransporter (NBCe1), by transferring HCO3− across the cell plasma membrane, plays a major role in regulating intracellular pH (pHi)—a parameter that must be maintained within a tight range to support normal physiological functions. In addition, NBCe1 mediates HCO3− movement across epithelial cells. Because of its role in pHi regulation, we ask whether the activity of this transporter depends on pHi. Recently, we addressed this question by investigating the pHi‐dependence of NBCe1‐A, the variant of NBCe1 that is most abundant in the kidney. Surprisingly, we found that, when expressed in oocytes, the activity of NBCe1‐A is not pHi sensitive in the pH range of 6.70–7.50 (Occhipinti and Boron, 2019 FASEB J, 33 (1): 544.2). Here, we extend the above study to NBCe1‐B, the variant of NBCe1 that is more widespread, but especially abundant in the pancreas. Because the activity of NBCe1‐B is naturally low when expressed by itself, we investigate the pHi‐dependence of NBCe1‐B when co‐expressed with its cytosolic binding partner IRBIT [inositol trisphosphate (IP3)‐receptor binding protein released with IP3], which is known to relieve autoinhibition by binding to the NH2‐terminus. As done previously, we employ ion‐sensitive microelectrodes and two‐electrode voltage clamping to record pHi and NBCe1‐conductance (GNBC) on Xenopus oocytes injected with either H2O (control) or cRNA encoding NBCe1‐B with IRBIT or super‐IRBIT (which lacks the PP1 binding motif). Again, we use out‐of‐equilibrium (OOE) CO2/HCO3− solutions to control pHi as we vary bulk extracellular [CO2] ([CO2]o) and keep [Na+]o, pHo, and [HCO3−]o constant. After exposing oocytes to ND96 (free of CO2 and HCO3−) and obtaining a first set of current‐voltage recordings (IV#1), we switch the superfusate to a “pure” HCO3− OOE solution (0% CO2/33 mM HCO3−/pH 7.50). In the case of NBCe1‐expressing oocytes, exposure to “pure” HCO3− leads to the entry of HCO3− into the cell, thereby raising pHi. Once pHi reaches ~7.50, we take a second set of current‐voltage recordings (IV#2). We then switch the bath solution to an OOE solution containing either 2.5% CO2 or 20% CO2 and, once pHi has reached its nadir (lower in the case of 20% CO2), take a third set of current‐voltage recordings (IV#3). For each experiment, we compute GNBC as the slope of the I‐V curve in the presence of HCO3− minus the slope of the I‐V curve in the absence of HCO3− (i.e., in ND96). We compute GNBC between −20 and +20 mV, where the net NBCe1‐mediated HCO3− flux is strongly inward. To account for variability in protein expression levels, we normalize GNBC from IV#3 to GNBC from IV#2. Analysis of normalized GNBC reveals that the activity of NBCe1‐B, whether co‐expressed with IRBIT or with super‐IRBIT, does not change between pHi ~6.60 (20% CO2, apparent [HCO3−]i = 16.6 mM) and ~7.60 (0% CO2, apparent [HCO3−]i = 0 mM). Assuming that NBCe1‐B is insensitive to CO2 and (while operating in the inward direction) insensitive to [HCO3−]i, we reach the surprising conclusion that NBCe1‐B—when activated by IRBIT or super‐IRBIT—is independent of pHi.Support or Funding InformationSupported by NIH K01‐DK107787 to RO and NIH R01‐DK113197, ONR N00014‐15‐1‐2060, ONR N00014‐16‐1‐2535 to WFB

Effects of HCO3- on Degradation of Toxic Contaminants of Emerging Concern by UV/NO3.

This study investigated the significant influence of HCO3- on the degradation of contaminants of emerging concern (CECs) during nitrate photolysis at 254 nm for water reuse applications. The second-order rate constants for the reactions between selected contaminants with carbonate radical (CO3•-) were determined at pH 8.8 and T = 20 °C: estrone ((5.3 ± 1.1) × 108 M-1 s-1), bisphenol A ((2.8 ± 0.2) × 108 M-1 s-1), 17α-ethynylestradiol ((1.6 ± 0.3) × 108 M-1 s-1), triclosan ((4.2 ± 1.4) × 107 M-1 s-1), diclofenac ((2.7 ± 0.7) × 107 M-1 s-1), atrazine ((5.7 ± 0.1) × 106 M-1 s-1), carbamazepine ((4.2 ± 0.01) × 106 M-1 s-1), and ibuprofen ((1.2 ± 1.1) × 106 M-1 s-1). Contributions from UV, reactive nitrogen species (RNS), hydroxyl radical (•OH), and CO3•- to the CEC decomposition in UV/NO3- in the presence and absence of HCO3- were investigated. In addition, possible transformation products and degradation pathways of triclosan, diclofenac, bisphenol A, and estrone in UV/NO3-/HCO3- were proposed based on the mass (MS) and MS2 spectra. Significant reduction in the cytotoxicity of bisphenol A was observed after the treatment with UV/NO3-/HCO3-.

Formation and detection of oxidant-generated tryptophan dimers in peptides and proteins

Free radicals are produced during physiological processes including metabolism and the immune response, as well as on exposure to multiple external stimuli. Many radicals react rapidly with proteins resulting in side-chain modification, backbone fragmentation, aggregation, and changes in structure and function. Due to its low oxidation potential, the indole ring of tryptophan (Trp) is a major target, with this resulting in the formation of indolyl radicals (Trp•). These undergo multiple reactions including ring opening and dimerization which can result in protein aggregation. The factors that govern Trp• dimerization, the rate constants for these reactions and the exact nature of the products are not fully elucidated. In this study, second-order rate constants were determined for Trp• dimerization in Trp-containing peptides to be 2–6 × 108M−1s−1 by pulse radiolysis. Peptide charge and molecular mass correlated negatively with these rate constants. Exposure of Trp-containing peptides to steady-state radiolysis in the presence of NaN3 resulted in consumption of the parent peptide, and detection by LC-MS of up to 4 different isomeric Trp-Trp cross-links. Similar species were detected with other oxidants, including CO3•- (from the HCO3- -dependent peroxidase activity of bovine superoxide dismutase) and peroxynitrous acid (ONOOH) in the presence or absence of HCO3-. Trp-Trp species were also isolated and detected after alkaline hydrolysis of the oxidized peptides and proteins. These studies demonstrate that Trp• formed on peptides and proteins undergo rapid recombination reactions to form Trp-Trp cross-linked species. These products may serve as markers of radical-mediated protein damage, and represent an additional pathway to protein aggregation in cellular dysfunction and disease.

262 - Potential Involvement of Peroxymonocarbonate and SOD in the Oxidation of the Anticancer Drug Metabolite, 6-Mercaptopurine

Introduction 6-mercaptopurine (6MP), an immunosuppressive and cytotoxic metabolite of azathioprine, is used therapeutically in the treatment of many inflammatory and immunological diseases. 6MP is known to undergo metabolism through oxidation by xanthine oxidase, S-methylation via thiopurine methyltransferase, and can be metabolized to form 6-thioguanine, which is believed to be the active metabolite. At sites of inflammation, reactive oxygen species (ROS) are generated, including H2O2 that inactivates superoxide dismutase. In the presence of HCO3-, peroxymonocarbonate (HCO4–) can potentially be produced, which enhances the oxidation potential of H2O2. H2O2 can also produce CO3●– through SOD peroxidase activity. Thiols have been shown to be oxidized by HCO4– or CO3●– but no studies have investigated the effect on 6MP. Hypothesis HCO4– and CO3●– will oxidize 6-mercaptopurine at the sulfur atom, and SOD peroxidase activity will act as a catalyst. Methods and Results UV-Vis spectrometry was used at room temperature to monitor the spectral changes (200 – 500 nm) using 20 µM 6MP and other purine analogs including its parent drug, azathioprine, and related metabolites including 6-methyl-MP, 6-thioguanine, 6-thioxanthine, and 6-thiouric acid. Reactions were run in 0.1 M KPO4 buffer pH 7.4 containing 250 µM DTPA, and were initiated by the addition of 25 mM HCO3– and 1 mM H2O2. The most prominent changes were observed with 6MP and 6-thioguanine; less changes were observed with 6-thioxanthine and 6-thiouric acid. Oxidation of 6MP by H2O2 was observed in the absence of HCO3– but was significantly enhanced using 12.5 and 25 mM HCO3–. The reactions were analyzed by high resolution LC/MS and were compared with reactions that contained SOD to catalyze SOD peroxidase activity. 6MP was detected at its expected m/z (151.0086, C5H4N4S) and the major product peak found corresponded to an m/z of 182.9981 (C5H4N4O2S), representing a sulfoxide product. SOD inclusion in these reactions produced the same products but with only 30 min incubation time vs. 24 h without SOD. The reaction of CO3●– with 6-MP was confirmed by EPR and spectrometric measurements. SOD activity was significantly enhanced by 6-MP but not azathioprine and the CO3●– radicals were scavenged by only 6-MP. 6MP was oxidized by H2O2/HCO3– and treated with HEK293 and HepG2 cells. 6MP-sulfoxide was significantly less cytotoxicity to both cell lines compared to unadulterated 6MP. Conclusions Exposure of 6MP to H2O2/HCO3– with and without SOD significantly enhanced its oxidation, and led to the formation of a 6MP-sulfoxide, which loses its cytotoxic activity and consequently ameliorates SOD activity.

CO2 quality control in Oxy-fuel technology for CCS: SO2 removal by the caustic scrubber in Callide Oxy-fuel Project

Flue gas from Oxy-fuel combustion is enriched with CO2 and SO2. SO2 has significant impacts throughout the system. This paper primarily focuses on the operation characteristics of caustic scrubber for the removal of SO2 in Callide Oxy-fuel Project.Both gas and liquid sampling and analysis were carried out for the caustic scrubber which comprises two spray columns, the initial Quencher followed by the low pressure (LP) scrubber. Dynamic changes of gas and liquid species in two scrubbers have been obtained and several conclusions can be drawn.From gas analysis, it can be concluded that the Quencher had high capture efficiencies for SO2 (97%) and NO2 (77%), and low capture efficiencies for NO (32%). The Quencher captured most of the SO2 and NO2; the LP scrubber captured a limited amount of SO2 (1%) and NO2 (4%). Therefore, the LP scrubber is not a necessary component for capturing SO2.Liquid analysis gave consistent results with gas analysis in that the Quencher (0.011–0.037M) contained a 100 times higher concentration of Total S than that (0.0001–0.0006M) in the LP scrubber. The Total S existed in the form of S(IV) and S(VI) in the Quencher, and only in the form of S(VI) in the LP scrubber. The S(VI) ratio of 11% in the Quencher agreed with the reported 2–15% oxidation.SO2 concentration in gas phase can be correlated well with Total S in liquid, but not the effective ratio of Na+. Mass balance between gas and liquid Total S can be achieved.The long term storage of liquid samples is accompanied by pH changes and desorption of CO2 with exposure to the atmosphere. The final pH depends on the presence of HCO3−. In the presence of HCO3− in liquids, the final pH is around 8; in the absence of HCO3−, the final pH is around 4. The increase in pH to 8 is explained by desorption of CO2. The amount of CO2 desorbed is around 0.0614% of the amount of CO2 in the CPU.

Cholecystokinin receptors regulate sperm protein tyrosine phosphorylation via uptake of HCO3-.

Cholecystokinin (CCK), a peptide hormone and a neurotransmitter, was detected in mature sperm two decades ago. However, the exact role of CCK and the types of CCK receptors (now termed CCK1 and CCK2) in sperm have not been identified. Here, we find that CCK1 and CCK2 receptors are immunolocalized to the acrosomal region of mature sperm. The antagonist of CCK1 or CCK2 receptor strongly activated the soluble adenylyl cyclase/cAMP/protein kinase A signaling pathway that drives sperm capacitation-associated protein tyrosine phosphorylation in dose- and time-dependent manners. But these actions of stimulation were abolished when sperm were incubated in the medium in the absence of HCO3-. Further investigation demonstrated that the inhibitor of CCK1 or CCK2 receptor could accelerate the uptake of HCO3- and significantly elevate the intracellular pH of sperm. Interestingly, the synthetic octapeptide of CCK (CCK8) showed the same action and mechanism as antagonists of CCK receptors. Moreover, CCK8 and the antagonist of CCK1 or CCK2 receptor were also able to accelerate human sperm capacitation-associated protein tyrosine phosphorylation by stimulating the influx of HCO3-. Thus, the present results suggest that CCK and its receptors may regulate sperm capacitation-associated protein tyrosine phosphorylation by modulating the uptake of HCO3-.

The Functional Complex Composed of the Sodium/Bicarbonate Cotransporter and the Soluble Adenylate Cyclase (sAC) Modulates Basal Cardiac Contractility

In addition to the adenylate cyclase (AC) associated to the plasma membrane, a new source of cyclic AMP (cAMP) was identified, the soluble AC (sAC). However, the physiological function of sAC in the heart is unknown. The cardiac Na+/HCO3- cotransporter (NBC) promotes the cellular co-influx of HCO3- and Na+. Since sAC is a HCO3--dependent enzyme, we aimed to investigate the potential impact of the relationship between the activity of NBC and sAC on cAMP-dependent cardiac contractility. Rat ventricular myocytes were loaded with Fura-2 or Fluo-3 in order to measure Ca2+ transient amplitude (CaT) by epifluorescence or Ca2+ sparks frequency (CaSF) by confocal microscopy, respectively. Sarcomere shortening as contractility index was measured simultaneously with epifluorescence. The NBC blocker S0859 (10μM) induced a negative inotropic effect (NIE) in the presence of HCO3- (Control: 19.1±3.2% vs. S0859: 14.6±2.6%; n=9, P<0.05) which was associated with a decrease of 18.5±2.6% in CaT. S0859 failed to induce a NIE in the absence of HCO3-. The selective inhibitor of sAC, KH7 (1μM) decreased contractility (Control: 15.7±0.7% vs. KH7: 11.3±0.9%, n=5, P<0.05) and CaT (15.7±4.9%) only in HCO3-. KH7 also prevented the NIE of S0859 (KH7+S0859: 11.1±0.9%, n=5). Since cAMP activates the kinase PKA, which in turn increases Ca2+ release through sarcoplasmic reticulum RyR channels, CaSF was measured as an index of RyR open probability. The increase in CaSF observed when field stimulation frequency was increased from 0.5 to 3 Hz (Control variation ratio: 1.23±0.1) was reversed in the presence of S0859 (0.62±0.2, n=5, P<0.05) only when HCO3- was present in the extracellular medium. In summary, these results demonstrate for the first time that the complex NBC-sAC plays a relevant role in Ca2+ management and basal cardiac contractility.

Degradation of bisphenol A by UV/H2O2 oxidation in aqueous solution containing nitrate and alkalinity

The goal of the present study was to investigate the effect of nitrate and bicarbonate on the removal of bisphenol A (BPA) by conducting bench-scale UV/H2O2 operations under a variety of reaction time and initial concentrations of H2O2, NO3--N and HCO3-. Although 100% removal efficiency of BPA was observed in 2 min in the absence of HCO3-, only 76.4 and 67.0% removal was achieved in the presence of 65 and 159 mg L−1HCO3-, respectively. In the presence of 5 mg L−1 of NO3--N and 65 mg L−1 of HCO3-, the BPA removal efficiency was 87 and 76.5%, respectively. In the presence of both NO3- and HCO3-, 51.2% of BPA was removed. It was reduced to approximately 50% less than both are absent. The efficiency of BPA removal depends not only on nitrate but also on bicarbonate in aqueous solution. The scavenging effect of bicarbonate was more noticeable than nitrate. The effect was about 33% under same conducted test conditions. The scavenging effect on BPA removal was largest when there were both nitrate and bicarbonate in aqueous solution. The efficiency of BPA was almost halved by them.

Adsorption and desorption of arsenic to aquifer sediment on the Red River floodplain at Nam Du, Vietnam

The adsorption of arsenic onto aquifer sediment from the Red River floodplain, Vietnam, was determined in a series of batch experiments. Due to water supply pumping, river water infiltrates into the aquifer at the field site and has leached the uppermost aquifer sediments. The leached sediments remain anoxic but contain little reactive arsenic and iron, and are used in our experiments. The adsorption and desorption experiments were carried out by addition or removal of arsenic from the aqueous phase in sediment suspensions under strictly anoxic conditions. Also the effects of HCO3, Fe(II), PO4 and Si on arsenic adsorption were explored. The results show much stronger adsorption of As(V) as compared to As(III), full reversibility for As(III) adsorption and less so for As(V). The presence or absence of HCO3 did not influence arsenic adsorption. Fe(II) enhanced As(V) sorption but did not influence the adsorption of As(III) in any way. During simultaneous adsorption of As(III) and Fe(II), As(III) was found to be fully desorbable while Fe(II) was completely irreversibly adsorbed and clearly the two sorption processes are uncoupled. Phosphate was the only solute that significantly could displace As(III) from the sediment surface. Compiling literature data on arsenic adsorption to aquifer sediment in Vietnam and Bangladesh revealed As(III) isotherms to be almost identical regardless of the nature of the sediment or the site of sampling. In contrast, there was a large variation in As(V) adsorption isotherms between studies. A tentative conclusion is that As(III) and As(V) are not adsorbing onto the same sediment surface sites. The adsorption behavior of arsenic onto aquifer sediments and synthetic Fe-oxides is compared. Particularly, the much stronger adsorption of As(V) than of As(III) onto Red River as well as on most Bangladesh aquifer sediments, indicates that the perception that arsenic, phosphate and other species compete for the same surface sites of iron oxides in sediments with properties similar to those of, for example a synthetic goethite, probably is not correct. A simple two-component Langmuir adsorption model was constructed to quantitatively describe the reactive transport of As(III) and PO4 in the aquifer.

Activity-dependent hyperpolarization of EGABA is absent in cutaneous DRG neurons from inflamed rats

A shift in GABAA signaling from inhibition to excitation in primary afferent neurons appears to contribute to the inflammation-induced increase in afferent input to the CNS. An activity-dependent depolarization of the GABAA current equilibrium potential (EGABA) has been described in CNS neurons which drives a shift in GABAA signaling from inhibition to excitation. The purpose of the present study was to determine if such an activity-dependent depolarization of EGABA occurs in primary afferents and whether the depolarization is amplified with persistent inflammation. Acutely dissociated retrogradely labeled cutaneous dorsal root ganglion (DRG) neurons from naïve and inflamed rats were studied with gramicidin perforated patch recording. Rather than a depolarization, 200 action potentials delivered at 2Hz resulted in a ∼10mV hyperpolarization of EGABA in cutaneous neurons from naïve rats. No such hyperpolarization was observed in neurons from inflamed rats. The shift in EGABA was not blocked by 10μM bumetanide. Furthermore, because activity-dependent hyperpolarization of EGABA was fully manifest in the absence of HCO3− in the bath solution, this shift was not dependent on a change in HCO3−–Cl− exchanger activity, despite evidence of HCO3−–Cl− exchangers in DRG neurons that may contribute to the establishment of EGABA in the presence of HCO3−. While the mechanism underlying the activity-dependent hyperpolarization of EGABA has yet to be identified, because this mechanism appears to function as a form of feedback inhibition, facilitating GABA-mediated inhibition of afferent activity, it may serve as a novel target for the treatment of inflammatory pain.

Bicarbonate blocks iron translocation from cotyledons inducing iron stress responses in Citrus roots

The effect of bicarbonate ion (HCO3−) on the mobilization of iron (Fe) reserves from cotyledons to roots during early growth of citrus seedlings and its influence on the components of the iron acquisition system were studied. Monoembryonic seeds of Citrus limon (L.) were germinated “in vitro” on two iron-deprived media, supplemented or not with 10mM HCO3− (−Fe+Bic and −Fe, respectively). After 21d of culture, Fe concentration in seedling organs was measured, as well as gene expression and enzymatic activities. Finally, the effect of Fe resupply on the above responses was tested in the presence and absence of HCO3− (+Fe+Bic or +Fe, respectively). −Fe+Bic seedlings exhibited lower Fe concentration in shoots and roots than −Fe ones but higher in cotyledons, associated to a significative inhibition of NRAMP3 expression. HCO3− upregulated Strategy I related genes (FRO1, FRO2, HA1 and IRT1) and FC-R and H+-ATPase activities in roots of Fe-starved seedlings. PEPC1 expression and PEPCase activity were also increased. When −Fe+Bic pre-treated seedlings were transferred to Fe-containing media for 15d, Fe content in shoots and roots increased, although to a lower extent in the +Fe+Bic medium. Consequently, the above-described root responses became markedly repressed, however, this effect was less pronounced in +Fe+Bic seedlings. In conclusion, it appears that HCO3− prevents Fe translocation from cotyledons to shoot and root, therefore reducing their Fe levels. This triggers Fe-stress responses in the root, enhancing the expression of genes related with Fe uptake and the corresponding enzymatic activities.

Lactate-H+Transport Is a Significant Component of the In Vivo Corneal Endothelial Pump

To confirm the expression of monocarboxylate transporters (MCT) 1, 2, and 4 in rabbit CE and to test the hypothesis that cellular buffering contributed by HCO₃⁻, NBCe1, and carbonic anhydrase (CA) activity facilitates lactate-H⁺ efflux thereby controlling corneal hydration in vivo. MCT1-4 expression of rabbit endothelium was examined by Western blotting and immunofluorescence staining. Lactate-induced acidification (LIA) was measured in perfused CE in the presence and absence of HCO₃⁻ and acetazolamide (ACTZ) using tissue treated with siRNA specific to MCT1, 2, and 4. Corneal thickness and lactate concentration were measured in New Zealand White rabbits treated with the topical CA inhibitor Azopt, and from eyes that were injected intracamerally with ouabain, disodium 4,4'-diisothiocyanatostilbene-2,2'-disulfonate (DIDS), and shRNA specific to the 1Na⁺:2HCO₃⁻ cotransporter NBCe1. MCT1 and MCT4 are localized to the lateral membrane, while MCT2 is apical. Cell pH measurements showed LIA in response to 40 mM lactate in bicarbonate free (BF) Ringer's that was inhibited by niflumic acid and by MCT siRNA knockdown, and significantly reduced in the presence of HCO₃⁻. Lactate-dependent proton flux in vitro was not significantly greater in the presence of HCO₃⁻ or reduced by ACTZ. However, when active transport, NBCe1, or CA activity was disrupted in vivo, corneal edema ensued and was associated with significant corneal lactate accumulation. MCT1, 2, and 4 are expressed in rabbit CE on both the apical and basolateral surfaces and function to transport lactate-H⁺. Lactate-H⁺ flux is facilitated by active transport, HCO₃⁻ transport and CA activity, disruption of which causes corneal edema in vivo and indicates that facilitation of lactate efflux is a component of the endothelial pump.

Regulation of anion transport across the uterine epithelium ofGallus domesticus

For egg shell production, cations, primarily Ca(2+), and anions, primarily HCO(3)(-), must be secreted across the uterine epithelium. Because alterations of HCO(3)(-) transport influence Ca(2+) secretion, the present study was performed to gain insight into the regulation of anion transport (i.e., chloride and HCO(3)(-) transport) across the egg shell gland of the domestic chicken. To this purpose, unstripped uterus epithelia were mounted in modified Ussing chambers and electrogenic [i.e., short circuit current (I(sc))] and electroneutral anion transport were measured. Stimulating adenylate cyclases by forskolin, thereby enhancing the intracellular cyclic adenosine monophosphate( )(cAMP) concentration, evoked 2 patterns of I(sc) responses. Under HCO(3)(-)-buffered conditions, some of the tissues (3/8) showed an increase of I(sc), whereas in others (5/8) a decrease of I(sc) was observed in the presence of the drug. The I(sc) increase existed in HCO(3)(-) secretion because under HCO(3)(-)-free conditions forskolin stimulated only an I(sc) decrease. In addition, methazolamide, a blocker of carboanhydrases, significantly reduced baseline I(sc). The forskolin-induced decrease of I(sc) presented a Cl(-) absorption. In the absence of HCO(3)(-), forskolin yielded only an I(sc) decrease and the transepithelial flux of (36)Cl(-) was reduced. In the presence of mucosal 5-nitro-2-(3-phenylpropylamino) benzoic acid, a nonselective blocker of chloride channels, forskolin-induced I(sc) decrease was inhibited. In addition to cAMP, the regulatory influence of neurons or prostaglandins on baseline I(sc) and anion transport was investigated. Neither tetrodotoxin, a blocker of neuronal Na(+) conductances, electrical field stimulation, nor indomethacin, a blocker of cyclooxygenases, influenced the baseline I(sc) or anion transport. In summary, these data show effects of forskolin (i.e., cAMP) on anion transport across the egg shell gland of the domestic chicken: HCO(3)(-) secretion (supporting Ca(2+) mineralizing of the egg shell) and Cl(-) absorption. Neurons or prostaglandins did not influence the anion transport.

Soluble adenylyl cyclase mediates bicarbonate-dependent corneal endothelial cell protection

Cyclic AMP produced from membrane receptor complex bound adenylyl cyclases is protective in corneal endothelial cells (CEC). CEC also express soluble adenylyl cyclase (sAC), which is localized throughout the cytoplasm. When activated by HCO(3)(-), cAMP concentration ([cAMP]) increases by ∼50%. Here we ask if cAMP produced from sAC is also protective. We examined the effects of HCO(3)(-), pH, phosphodiesterase 4 inhibition by rolipram, sAC inhibition by 2HE (2-hydroxyestradiol), and sAC small interfering RNA (siRNA) knockdown on basal and staurosporine-mediated apoptosis. HCO(3)(-) (40 mM) or 50 μM rolipram raised [cAMP] to similar levels and protected endothelial cells by 50% relative to a HCO(3)(-)-free control, whereas 2HE, which decreased [cAMP] by 40%, and H89 (PKA inhibitor) doubled the apoptotic rate. sAC expression was reduced by two-thirds in the absence of HCO(3)(-) and was reduced to 15% of control by sAC siRNA. Protection by HCO(3)(-) was eliminated in siRNA-treated cells. Similarly, caspase-3 activity and cytochrome c release were reduced by HCO(3)(-) and enhanced by 2HE or siRNA. Analysis of percent annexin V+ cells as a function of [cAMP] revealed an inverse, nonlinear relation, suggesting a protective threshold [cAMP] of 10 pmol/mg protein. Relative levels of phosphorylated cAMP response element binding protein and phosphorylated Bcl-2 were decreased in CEC treated with 2HE or siRNA, suggesting that HCO(3)(-)-dependent endogenous sAC activity can mobilize antiapoptotic signal transduction. Overall, our data suggest a new role for sAC in endogenous cellular protection.