Bicarbonate Flux Research Articles

In-field carbon dioxide removal via weathering of crushed basalt applied to acidic tropical agricultural soil

Enhanced weathering (EW) of silicate rocks such as basalt provides a potential carbon dioxide removal (CDR) technology for combatting climate change. Modelling and mesocosm studies suggest significant CDR via EW but there are few field studies. This study aimed to directly measure in-field CDR via EW of basalt applied to sugarcane on acidic (pH 5.8, 0–0.25 m) Ultisol in tropical northeastern Australia, where weathering potential is high. Coarsely crushed basalt produced as a byproduct of gravel manufacture (<5 mm) was applied annually from 2018 to 2022 at 0 or 50 t ha−1 a−1, incorporated into the soil in 2018 but not in subsequent years. Measurements in 2022 show increased soil pH and extractable Mg and Si at 0–0.25 m depth, indicating significant weathering of the basalt, but showed no increase in crop yield. Soil inorganic carbon content and bicarbonate (HCO3−) flux to deep drainage (1.25 m depth) were measured to quantify CDR in the 2022–2023 wet season (i.e. one year). Soil inorganic carbon was below detection limits. Mean HCO3− flux was 3.15 kmol ha−1 a−1 (±0.40) in the basalt-treated plots and 2.56 kmol ha−1 a−1 (±0.18) in the untreated plots but the difference (0.59 kmol ha−1 a−1 or 0.026 t CO2 ha−1 a−1) was not significant (p = 0.082). Most weathering of the basalt was attributed to acids stronger than carbonic acid. These were, in decreasing order of contribution, surface-bound protons (inherent soil acidity), nitric acid (from nitrification), organic acids, and acids associated with cation uptake by plants. These results indicate in-field CDR via EW of basalt is low where soil and regolith pH is well below the pKa1 of 6.4 for H2CO3. However, increased soil pH, and the consumption of strong acids by weathering will eventually lead to reduced CO2 emission from soil or evasion from rivers, with continued basalt addition.

Genome-scale community modelling elucidates the metabolic interaction in Indian type-2 diabetic gut microbiota

Type-2 diabetes (T2D) is a rapidly growing multifactorial metabolic disorder that induces the onset of various diseases in the human body. The compositional and metabolic shift of the gut microbiota is a crucial factor behind T2D. Hence, gaining insight into the metabolic profile of the gut microbiota is essential for revealing their role in regulating the metabolism of T2D patients. Here, we have focused on the genome-scale community metabolic model reconstruction of crucial T2D-associated gut microbes. The model-based analysis of biochemical flux in T2D and healthy gut conditions showed distinct biochemical signatures and diverse metabolic interactions in the microbial community. The metabolic interactions encompass cross-feeding of short-chain fatty acids, amino acids, and vitamins among individual microbes within the community. In T2D conditions, a reduction in the metabolic flux of acetate, butyrate, vitamin B5, and bicarbonate was observed in the microbial community model, which can impact carbohydrate metabolism. The decline in butyrate levels is correlated with both insulin resistance and diminished glucose metabolism in T2D patients. Compared to the healthy gut, an overall reduction in glucose consumption and SCFA production flux was estimated in the T2D gut environment. Moreover, the decreased consumption profiles of branch chain amino acids (BCAAs) and aromatic amino acids (AAAs) in the T2D gut microbiota can be a distinct biomarker for T2D. Hence, the flux-level analysis of the microbial community model can provide insights into the metabolic reprogramming in diabetic gut microbiomes, which may be helpful in personalized therapeutics and diet design against T2D.

Multiple Regulatory Signals and Components in the Modulation of Bicarbonate Transporters.

Bicarbonate transporters are responsible for the appropriate flux of bicarbonate across the plasma membrane to perform various fundamental cellular functions. The functions of bicarbonate transporters, including pH regulation, cell migration, and inflammation, are highlighted in various cellular systems, encompassing their participation in both physiological and pathological processes. In this review, we focused on recently identified modulatory signaling components that regulate the expression and activity of bicarbonate transporters. Moreover, we addressed recent advances in our understanding of cooperative systems of bicarbonate transporters and channelopathies. This current review aims to provide a new, in-depth understanding of numerous human diseases associated with the dysfunction of bicarbonate transporters.

Evolutionary history of the groundwater system in the Pearl River Delta (China) during the Holocene

Abstract Coastal groundwater reservoirs are sensitive to the complicated evolution of marine transgressions and regressions in river delta regions. We integrated hydrogeological investigation and hydrogeochemical data with numerical modeling to assess the evolution of the groundwater system in the Pearl River Delta’s aquifer system (in southeastern China). We studied the effects of flow dynamics and redox conditions on the biogeochemical processes of nutrients in the regional groundwater flow systems in response to the transient states related to variable paleoprecipitation and seawater salinity decline from the late Pleistocene to the Holocene. The results from paleo-hydrogeological reconstruction of the aquifer-aquitard system showed that the saline groundwater formed by paleo-seawater intrusion was still present in the old marine aquitard and affected groundwater salinity and chemicals in the adjacent aquifers, while most of the groundwater in the shallow young marine aquitard has been freshened by infiltrated old/fresh rainwater. Consequently, total ammonium and carbon stored in the Pearl River Delta were estimated to be (1.91 ± 1.13) × 107 mol m–1 and (5.74 ± 4.05) × 107 mol m–1, respectively, and the ammonium and bicarbonate fluxes derived from groundwater discharge to the sea were calculated as (90.6 ± 55.9) mol m–1 yr–1 and (301.02 ± 196.23) mol m–1 yr–1, respectively. If the buried ammonium in the delta is released to the sea, it would be equivalent to nearly 205 ± 123 yr of Pearl River fluvial loading. These findings suggest that the chemicals trapped in the deltaic aquifer system during the Holocene could contribute to future ocean eutrophication and acidification.

The rs12532734 Polymorphism Near the Solute Carrier 26A3 Gene Locus Is Associated With Gallstone Disease in Children.

Gallstones are increasingly frequent in children. In this candidate gene study, we genotyped 5 gene variants ( ANO1 , SPTLC3 , TMEM147 , TNRC6B , rs12532734) from a recent gallstone genome-wide association study (GWAS) in a cohort of 214 children with gallstones and 172 gallstone-free adult controls. In total, 138 genotyped children presented with symptomatic gallstone disease, 47 underwent cholecystectomy, and 126 received ursodeoxycholic acid (UDCA) as therapy for stones. Among 5 tested variants, the rs12532734 polymorphism modulated the gallstone risk in the studied cohort. Its genotype distribution significantly ( P = 0.025) departed from the Hardy-Weinberg equilibrium among cases, and the common allele was associated with increased odds of developing gallstones at young age (OR = 1.69, P = 0.014). SLC26A3 is the nearest gene to rs12532734 and is involved in the transepithelial bicarbonate and chloride transport. The association of rs12532734 with pediatric gallstones is a novel finding warranting further investigations also with regard to biliary bicarbonate flux and bile composition.

Effects of Epiphytic Biofilm Activity on the Photosynthetic Activity, pH and Inorganic Carbon Microenvironment of Seagrass Leaves (Zostera marina L.)

Epiphytic biofilms on seagrass leaves can lead to extreme microenvironmental conditions for the encapsulated leaf limiting both its photosynthesis and respiration. Yet, little is known about how the biological activity of the biofilm itself changes the seagrass phyllosphere microenvironment and dynamics. We used microsensors to measure O2 concentrations and pH gradients and calculate fluxes of O2, CO2 and bicarbonate (HCO3−) around seagrass leaves (Z. marina L.) covered with artificial, inactive biofilms and natural epiphytic biofilms. A sterilized seawater-agar matrix was used to make an artificial “inactive” biofilm on seagrass leaves with the same thickness as the natural leaf epiphytic biofilm, which impeded turbulent exchange of gases but did not have microbial activity. We compared the concentration profiles and fluxes of O2 and inorganic carbon of the “active” and “inactive” biofilm to investigate the effect of microbial activity and molecular diffusion in seagrass leaf biofilms. In light, the O2 flux of leaves with inactive biofilm was only 31% of the leaves with active biofilm, indicating that the photosynthesis of the microbial community in the biofilm makes up the majority of O2 production in the leaf microenvironment. During darkness, the O2 concentration profiles and O2 fluxes were almost identical in the “active” and “inactive” biofilms. The pH profiles showed the same trend with an increase in pH of ~1.0 in the “active” biofilms and ~0.3 pH units in the “inactive” biofilms in the light, and both showing a decrease of ~0.3 pH units in darkness compared to the bulk seawater. Our measurements thus demonstrate strong photosynthesis in the epiphyte layer driving phyllosphere basification and inorganic carbon limitation. The calculated CO2 concentration on the leaf surface decreased to 0.09 μmol L-1 in the epiphytic biofilm in the light compared to leaf surface CO2 concentrations of 13.8 μmol L-1 on bare seagrass leaves, and the CO2 influxes were only 3.0% and 5.4% of O2 effluxes for leaves with “active” and “inactive” biofilm, respectively. Calculations also showed that HCO3− influxes in light accounted for 91-97% of the total inorganic carbon influx to the seagrass leaf, although the HCO3− utilization via CO2 concentration mechanisms is energy-consuming. Besides increasing mass transfer impedance, leaf epiphytic biofilm activity thus strongly affects the seagrass leaf microenvironment in the light by inducing higher O2 concentration and pH, increasing CO2 limitation and reducing the leaf photosynthetic efficiency.

Cyanobacterial weathering in warming periglacial sediments: Implications for nutrient cycling and potential biosignatures

AbstractThe cryosphere hosts a widespread microbial community, yet microbial influences on silicate weathering have been historically neglected in cold‐arid deserts. Here we investigate bioweathering by a cold‐tolerant cyanobacteria (Leptolyngbya glacialis) via laboratory experiments using glaciofluvial drift sediments at 12°C, analogous to predicted future permafrost surface temperatures. Our results show threefold enhanced Si weathering rates in pre‐weathered, mixed‐lithology Antarctic biotic reactors compared to abiotic controls, indicating the significant influence of microbial life on weathering. Although biotic and abiotic weathering rates are similar in Icelandic sediments, neo‐formed clay and Fe‐(oxy)hydroxide minerals observed in association with biofilms in biotic reactors are common on Icelandic mafic minerals, similar to features observed in unprocessed Antarctic drifts. This suggests that microbes enhance weathering in systems where they must scavenge for nutrients that are not easily liberated via abiotic pathways; potential biosignatures may form in nutrient‐rich systems as well. In both sediment types we also observed up to fourfold higher bicarbonate concentrations in biotic reactors relative to abiotic reactors, indicating that, as warming occurs, psychrotolerant biota will enhance bicarbonate flux to the oceans, thus stimulating carbonate deposition and providing a negative feedback to increasing atmospheric CO2.

Is CFTR an exchanger?: Regulation of HCO3−Transport and extracellular pH by CFTR

The disease, cystic fibrosis, is caused by the malfunction of the cystic fibrosis transmembrane conductance regulator. Expression of functional CFTR may normally regulate extracellular pH via control of bicarbonate efflux. Reports also suggest that the CFTR may be a Cl-/HCO3- exchanger. If true, this could be very important for treatment of CF given the airway host defense system is quite sensitive to pH, and acidic pH been found to increase mucus viscosity. We compared evidentiary support of four possible models of CFTR's role in the transport of bicarbonate: 1) CFTR as a Cl-channel that permits bicarbonate conductance, 2) CFTR as an anion Cl-/HCO3- exchanger (AE), 3.) CFTR as both a Cl-channel and an AE, and 4.) CFTR as a Cl-channel that allows for transport of bicarbonate and regulates an independent AE. The effect of stimulators and inhibitors of CFTR and AEs were evaluated via iodide efflux and studies of extracellular pH. This data, as well as that published by others, suggest that while CFTR may support and regulate bicarbonate flux it is unlikely it directly performs Cl-/HCO3- anion exchange.

Paracellular bicarbonate flux across human cystic fibrosis airway epithelia tempers changes in airway surface liquid pH

Key points Cl− and HCO3 − had similar paracellular permeabilities in human airway epithelia.PCl/PNa of airway epithelia was unaltered by pH 7.4 vs. pH 6.0 solutions.Under basal conditions, calculated paracellular HCO3 − flux was secretory.Cytokines that increased airway surface liquid pH decreased or reversed paracellular HCO3 − flux.HCO3 − flux through the paracellular pathway may counterbalance effects of cellular H+ and HCO3 − secretion. Airway epithelia control the pH of airway surface liquid (ASL), thereby optimizing respiratory defences. Active H+ and HCO3 − secretion by airway epithelial cells produce an ASL that is acidic compared with the interstitial space. The paracellular pathway could provide a route for passive HCO3 − flux that also modifies ASL pH. However, there is limited information about paracellular HCO3 − flux, and it remains uncertain whether an acidic pH produced by loss of cystic fibrosis transmembrane conductance regulator anion channels or proinflammatory cytokines might alter the paracellular pathway function. To investigate paracellular HCO3 − transport, we studied differentiated primary cultures of human cystic fibrosis (CF) and non‐CF airway epithelia. The paracellular pathway was pH‐insensitive at pH 6.0 vs. pH 7.4 and was equally permeable to Cl− and HCO3 −. Under basal conditions at pH ∼6.6, calculated paracellular HCO3 − flux was weakly secretory. Treating epithelia with IL‐17 plus TNFα alkalinized ASL pH to ∼7.0, increased paracellular HCO3 − permeability, and paracellular HCO3 − flux was negligible. Applying IL‐13 increased ASL pH to ∼7.4 without altering paracellular HCO3 − permeability, and calculated paracellular HCO3 − flux was absorptive. These results suggest that HCO3 − flux through the paracellular pathway counterbalances, in part, changes in the ASL pH produced via cellular mechanisms. As the pH of ASL increases towards that of basolateral liquid, paracellular HCO3 − flux becomes absorptive, tempering the alkaline pH generated by transcellular HCO3 − secretion.

Revisiting groundwater carbon fluxes to the ocean with implications for the carbon cycle

Abstract Compared with riverine systems, the influence of groundwater on the global carbon cycle has remained underexplored. Here, we provide a new estimate of the bicarbonate fluxes from fresh groundwater to the ocean by coupling a statistical and hydrological analysis of groundwater and river samples across the contiguous United States with a study of global groundwater characteristics. We find that the mean concentration ([]) in groundwaters exceeds that in surface rivers by a factor of 2–3 throughout the contiguous United States. Based on estimates of fresh groundwater discharge to the ocean and scaling up our estimated mean [] in groundwaters from the United States and around the world, we arrived at a mean global flux from groundwaters ranging from 7.4 × 1012 (25th percentile)–1.8 × 1013 mol/yr (75th percentile) to 2.8 × 1013–8.3 × 1013 mol/yr, which is 22%–237% of the global flux from river systems, respectively. We also estimated that the global carbon flux derived from subsurface silicate weathering could be comparable to 32%–351% that from surficial silicate weathering, depending on groundwater discharge rates. Despite large uncertainties due to data limitation, this study highlights that groundwater weathering could be an important carbon sink in both the short- and long-term carbon cycle. Therefore, additional work on groundwaters is needed to develop a well-constrained view of the global carbon cycle.

Modeling of Performance Loss and pH Gradients in Hydroxide Exchange Membrane Fuel Cells Exposed to Carbon Dioxide

Hydroxide exchange membrane fuel cells (HEMFCs) have been attracting significant interest due to recent advancements in membrane stability and performance, as well as cost advantages of materials enabled by the alkaline environment1. A critical challenge for HEMFCs is mitigating performance loss upon exposure to carbon dioxide, which is caused by carbonate and bicarbonate formation in the polymer electrolyte. The presence of carbonate and bicarbonate reduces conductivity of the membrane and induces concentration overpotential through pH gradients. Therefore, transport of carbonate and bicarbonate in alkaline polymer electrolytes is a critically important issue for the future of HEMFCs. Modeling can provide crucial insight into the magnitude of the carbon dioxide poisoning effect and possibilities for performance improvement. As an initial investigation, we have created a 1-D model of carbonate transport through the thickness of the membrane electrode assembly (MEA) based on dilute solution theory. The model considers the kinetics of CO2 hydration and dehydration by both the carbonic acid and alkaline reactions2, CO2 + H2O ↔ H2CO3 [1a]H2CO3 + OH- ↔ H2O + HCO3 - [1b]CO2 + OH- ↔ HCO3 - [2] Additionally, the acid-base equilibrium between carbonate, bicarbonate, and hydroxide, HCO3 - + OH- ↔ CO3 2- + H2O [3] is considered. The model is used to predict the pH profile through the MEA and quantify the effects of temperatures, flow rates, and CO2concentration on HEMFC performance. Figure 1 shows the pH profile in the anode, membrane, and cathode for the case of O2 with 400 ppm CO2 as the oxidant. At open circuit, the pH is lower at the cathode than at the anode due to the difference in CO2 partial pressure, although the gradient is small. Once current is applied, the ionic potential gradient drives bicarbonate and carbonate towards the anode, and the pH gradient reverses. At moderate and high current densities, nearly all CO2is removed from the cathode gas stream and electrochemically pumped into the anode gas stream. The electrochemical pumping of carbonate and bicarbonate towards the anode lowers the anode pH until the rate of CO2 dehydration balances the flux of CO2 through the membrane. Carbonate and bicarbonate carry both CO2 and charge simultaneously. When the CO2flux through the membrane is small relative to the current density, the current is carried either by hydroxide ions or by counterbalanced fluxes of carbonate and bicarbonate. A large pH gradient is required to drive the counterbalancing diffusion of bicarbonate from anode to cathode. At high pH, charge transport shifts from the carbonate-bicarbonate shuttle to hydroxide ions, and the pH gradient flattens. In Figure 1, these dynamics are illustrated by the steep pH gradient from ca. 10-12, and the much flatter gradient above a pH of 12. Figure 2 shows the effect of 400 ppm carbon dioxide on MEA performance for varying reactant flowrates. Increasing the cathode flowrate increases the amount of CO2 electrochemically pumped into the anode gas stream. Reducing the anode flowrate provides less dilution for the pumped CO2, increasing the anode partial pressure of CO2. Both of these factors force the anode pH lower to accelerate CO2 dehydration, leading to larger pH gradients and reduced performance. Even at the high operating temperature of 95 °C, the introduction of 400 ppm CO2into the cathode gas stream can cause roughly 0.2 V of performance loss.

Temperature versus hydrologic controls of chemical weathering fluxes from United States forests

Chemical weathering is a dominant control on modern inland water chemistry and global element budgets over geologic time scales. Due to its central role in the earth's biogeochemistry it remains an intense area of interest. Understanding the controls on chemical weathering is difficult because it has many drivers with overlapping temporal and spatial signals. Of particular interest is the relationship between chemical weathering fluxes and global temperatures due to a negative feedback loop where warmer temperatures leads to more chemical weathering and its associated atmospheric CO2 consumption (Berner et al., 1983). Recently it has been proposed that this negative feedback loop is indirect where the acceleration of the hydrologic cycle by increased global temperatures leads to higher chemical weathering and atmospheric CO2 consumption (Maher and Chamberlain, 2014). Here, fluxes of all major cations and anions are calculated for 150 forested watersheds smaller than 500km2 in order to explore controls on chemical weathering from United States forests. Relationships between watershed hydrology, ion ratios and pH are reported that explain a large amount of across site variation in bicarbonate fluxes. Furthermore, across all watersheds ~32% of the cation flux is not balanced by bicarbonate but by sulfate. Paired alkalinity, temperature and discharge data are used to determine a temperature sensitivity of chemical weathering across 51 forested watersheds with a minimum of 70 measurements. The temperature sensitivity of bicarbonate fluxes is absent at low flow conditions because long residence times leads to chemical equilibrium and transport limitation. As discharge increases and residence time decreases, the temperature sensitivity of chemical weathering is released from transport limitation. The temperature sensitivity then increases with discharge until it levels off at high discharges as the system becomes reaction limited. Records of daily discharge, watershed discharge to flux relationships, and the temperature sensitivity are then used to estimate how chemical fluxes would change with a 20% increase in discharge, and 10° increase in temperature global change scenario. Not surprisingly it is found that increased discharge leads to higher weathering fluxes. Interestingly, wetter years have a higher temperature sensitivity due to a release of the temperature sensitivity from transport limitation. This coupled with a strong direct temperature effect leads to an approximately equal response from temperature and increased discharge using this scenario of global change. Thus periods of time and regions that are subject to both warm and wet conditions may have a particularly strong control on weathering fluxes.

Sources of protons and a role for bicarbonate in inhibitory feedback from horizontal cells to cones in Ambystoma tigrinum retina.

In the vertebrate retina, photoreceptors influence the signalling of neighbouring photoreceptors through lateral-inhibitory interactions mediated by horizontal cells (HCs). These interactions create antagonistic centre-surround receptive fields important for detecting edges and generating chromatically opponent responses in colour vision. The mechanisms responsible for inhibitory feedback from HCs involve changes in synaptic cleft pH that modulate photoreceptor calcium currents. However, the sources of synaptic protons involved in feedback and the mechanisms for their removal from the cleft when HCs hyperpolarize to light remain unknown. Our results indicate that Na+ -H+ exchangers are the principal source of synaptic cleft protons involved in HC feedback but that synaptic cleft alkalization during light-evoked hyperpolarization of HCs also involves changes in bicarbonate transport across the HC membrane. In addition to delineating processes that establish lateral inhibition in the retina, these results contribute to other evidence showing the key role for pH in regulating synaptic signalling throughout the nervous system. Lateral-inhibitory feedback from horizontal cells (HCs) to photoreceptors involves changes in synaptic cleft pH accompanying light-evoked changes in HC membrane potential. We analysed HC to cone feedback by studying surround-evoked light responses of cones and by obtaining paired whole cell recordings from cones and HCs in salamander retina. We tested three potential sources for synaptic cleft protons: (1) generation by extracellular carbonic anhydrase (CA), (2) release from acidic synaptic vesicles and (3) Na+ /H+ exchangers (NHEs). Neither antagonizing extracellular CA nor blocking loading of protons into synaptic vesicles eliminated feedback. However, feedback was eliminated when extracellular Na+ was replaced with choline and significantly reduced by an NHE inhibitor, cariporide. Depriving NHEs of intracellular protons by buffering HC cytosol with a pH 9.2 pipette solution eliminated feedback, whereas alkalinizing the cone cytosol did not, suggesting that HCs are a major source for protons in feedback. We also examined mechanisms for changing synaptic cleft pH in response to changes in HC membrane potential. Increasing the trans-membrane proton gradient by lowering the extracellular pH from 7.8 to 7.4 to 7.1 strengthened feedback. While maintaining constant extracellular pH with 1mm HEPES, removal of bicarbonate abolished feedback. Elevating intracellular bicarbonate levels within HCs prevented this loss of feedback. A bicarbonate transport inhibitor, 4,4'-diisothiocyano-2,2'-stilbenedisulfonic acid (DIDS), also blocked feedback. Together, these results suggest that NHEs are the primary source of extracellular protons in HC feedback but that changes in cleft pH accompanying changes in HC membrane voltage also require bicarbonate flux across the HC membrane.

Snowball Earth ocean chemistry driven by extensive ridge volcanism during Rodinia breakup

During Neoproterozoic Snowball Earth glaciations, the oceans gained massive amounts of alkalinity, culminating in the deposition of massive cap carbonates on deglaciation. Changes in terrestrial runoff associated with both breakup of the Rodinia supercontinent and deglaciation can explain some, but not all of the requisite changes in ocean chemistry. Submarine volcanism along shallow ridges formed during supercontinent breakup results in the formation of large volumes of glassy hyaloclastite, which readily alters to palagonite. Here we estimate fluxes of calcium, magnesium, phosphorus, silica and bicarbonate associated with these shallow-ridge processes, and argue that extensive submarine volcanism during the breakup of Rodinia made an important contribution to changes in ocean chemistry during Snowball Earth glaciations. We use Monte Carlo simulations to show that widespread hyaloclastite alteration under near-global sea-ice cover could lead to Ca2+ and Mg2+ supersaturation over the course of the glaciation that is sufficient to explain the volume of cap carbonates deposited. Furthermore, our conservative estimates of phosphorus release are sufficient to explain the observed P:Fe ratios in sedimentary iron formations from this time. This large phosphorus release may have fuelled primary productivity, which in turn would have contributed to atmospheric O2 rises that followed Snowball Earth episodes. The Cryogenian Snowball Earth glaciations were followed by the deposition of massive cap carbonates. Geochemical modelling suggests that shallow-ridge volcanism supplied much of the alkalinity and cations that fuelled this deposition.

Modeling non-linear kinetics of hyperpolarized [1-(13)C] pyruvate in the crystalloid-perfused rat heart.

Hyperpolarized 13C MR measurements have the potential to display non‐linear kinetics. We have developed an approach to describe possible non‐first‐order kinetics of hyperpolarized [1‐13C] pyruvate employing a system of differential equations that agrees with the principle of conservation of mass of the hyperpolarized signal. Simultaneous fitting to a second‐order model for conversion of [1‐13C] pyruvate to bicarbonate, lactate and alanine was well described in the isolated rat heart perfused with Krebs buffer containing glucose as sole energy substrate, or glucose supplemented with pyruvate. Second‐order modeling yielded significantly improved fits of pyruvate–bicarbonate kinetics compared with the more traditionally used first‐order model and suggested time‐dependent decreases in pyruvate–bicarbonate flux. Second‐order modeling gave time‐dependent changes in forward and reverse reaction kinetics of pyruvate–lactate exchange and pyruvate–alanine exchange in both groups of hearts during the infusion of pyruvate; however, the fits were not significantly improved with respect to a traditional first‐order model. The mechanism giving rise to second‐order pyruvate dehydrogenase (PDH) kinetics was explored experimentally using surface fluorescence measurements of nicotinamide adenine dinucleotide reduced form (NADH) performed under the same conditions, demonstrating a significant increase of NADH during pyruvate infusion. This suggests a simultaneous depletion of available mitochondrial NAD+ (the cofactor for PDH), consistent with the non‐linear nature of the kinetics. NADH levels returned to baseline following cessation of the pyruvate infusion, suggesting this to be a transient effect. © 2016 The Authors. NMR in Biomedicine published by John Wiley & Sons Ltd.

Distinct α-intercalated cell morphology and its modification by acidosis define regions of the collecting duct.

During metabolic acidosis, the cortical collecting duct (CCD) of the rabbit reverses the polarity of bicarbonate flux from net secretion to net absorption, and this is accomplished by increasing the proton secretory rate by α-intercalated cells (ICs) and decreasing bicarbonate secretion by β-ICs. To better characterize dynamic changes in H(+)-secreting α-ICs, we examined their morphology in collecting ducts microdissected from kidneys of normal, acidotic, and recovering rabbits. α-ICs in defined axial regions varied in number and basolateral anion exchanger (AE)1 morphology, which likely reflects their relative activity and function along the collecting duct. Upon transition from CCD to outer medullary collecting duct from the outer stripe to the inner stripe, the number of α-ICs increases from 11.0 ± 1.2 to 15.4 ± 1.11 and to 32.0 ± 1.3 cells/200 μm, respectively. In the CCD, the basolateral structure defined by AE1 typically exhibited a pyramidal or conical shape, whereas in the medulla the morphology was elongated and shallow, resulting in a more rectangular shape. Furthermore, acidosis reversibly induced α-ICs in the CCD to acquire a more rectangular morphology concomitant with a transition from diffusely cytoplasmic to increased basolateral surface distribution of AE1 and apical polarization of B1-V-ATPase. The latter results are consistent with the supposition that morphological adaptation from the pyramidal to rectangular shape reflects a transition toward a more "active" configuration. In addition, α-ICs in the outer medullary collecting duct from the outer stripe exhibited cellular morphology strikingly similar to dendritic cells that may reflect a newly defined ancillary function in immune defense of the kidney.

High altitude may alter oxygen availability and renal metabolism in diabetics as measured by hyperpolarized [1-13C]pyruvate magnetic resonance imaging

The kidneys account for about 10% of the whole body oxygen consumption, whereas only 0.5% of the total body mass. It is known that intrarenal hypoxia is present in several diseases associated with development of kidney disease, including diabetes, and when renal blood flow is unaffected. The importance of deranged oxygen metabolism is further supported by deterioration of kidney function in patients with diabetes living at high altitude. Thus, we argue that reduced oxygen availability alters renal energy metabolism. Here, we introduce a novel magnetic resonance imaging (MRI) approach to monitor metabolic changes associated with diabetes and oxygen availability. Streptozotocin diabetic and control rats were given reduced, normal, or increased inspired oxygen in order to alter tissue oxygenation. The effects on kidney oxygen metabolism were studied using hyperpolarized [1-(13)C]pyruvate MRI. Reduced inspired oxygen did not alter renal metabolism in the control group. Reduced oxygen availability in the diabetic kidney altered energy metabolism by increasing lactate and alanine formation by 23% and 34%, respectively, whereas the bicarbonate flux was unchanged. Thus, the increased prevalence and severity of nephropathy in patients with diabetes at high altitudes may originate from the increased sensitivity toward inspired oxygen. This increased lactate production shifts the metabolic routs toward hypoxic pathways.

Younger Dryas – early Holocene transition in the south‐eastern Iberian Peninsula: insights from land snail shell middens

ABSTRACTThe land snail Sphincterochila candidissima from archeological records in Villena (SE Spain) was studied isotopically to estimate the Younger Dryas (YD)–early Holocene transition in the western Mediterranean. Live‐collected individuals exhibited body (−21.8 ± 1.6‰) and shell (−5.8 ± 1.4‰) δ13C values typical of a C3 plant diet, probably combined with carbonate ingestion. Calculations of a carbon flux balance‐mixing model suggest that living specimens experienced similar metabolic rates, with comparable ratio of input and output fluxes of bicarbonate from the snail hemolymph. All fossil shells showed comparable δ13C values among each other, but values were ∼2‰ higher than living specimens. This may be explained by higher water stress at the YD–Holocene transition or by the Suess effect. Shell δ18O values averaged +1.3 ± 0.8‰ for living individuals, −0.5 ± 0.8‰ for Holocene (8.4–10.2 cal ka BP) specimens and +0.4 ± 0.6‰ for YD (12.0–12.4 cal ka BP) snails. An oxygen flux balance‐mixing model suggests that YD shells precipitated during relative humidity (RH) values of ∼79–82%, after which RH increased gradually reaching maximum values of ∼87–88% at ∼8.4–8.6 cal ka BP and, from there, RH eventually declined to present values of ∼82%. Comparisons with other snail data suggest that the xerophilous Sphincterochila records different environmental signatures fro other contemporaneous taxa.

Fluvial transport of carbon along the river‐to‐ocean continuum and its potential impacts on a brackish water food web in the Iwaki River watershed, northern Japan

AbstractRiverine transport of dissolved inorganic carbon (DIC) from land to the ocean is an important carbon flux that influences the carbon budget at the watershed scale. However, the dynamics of DIC in an entire river network has remained unknown, especially in mountainous Japanese watersheds. We examined the effects of watershed land use and geology on the transports of inorganic carbon as well as weathered silica (Si) and calcium (Ca) in the Iwaki River system where agricultural and residential areas have developed in the middle and lower parts of the watershed. The concentration and stable carbon isotope ratios (δ13C) of DIC showed the longitudinal increase of 13C‐depleted inorganic carbon along the river. As a result, most streams and rivers were supersaturated in dissolved CO2 that will eventually be emitted to the atmosphere. The possible origin of 13C‐depleted carbon is CO2 derived from the decomposition of organic matter in agricultural and urban landscapes, as well as from in‐stream respiration. In addition, agricultural and urban areas, respectively, exported the large amount of dissolved Si and Ca to the rivers, suggesting that CO2 increased by respiration accelerates the chemical weathering of silicate and carbonate materials in soils, river sediments, and/or urban infrastructure. Furthermore, riverine bicarbonate flux is likely to enter shell carbonates of Corbicula japonica, an aragonitic bivalve, in the downstream brackish lake (Lake Jusan). These results revealed that the flux of DIC from the human‐dominated watersheds is a key to understanding the carbon dynamics and food‐web structure along the land‐to‐river‐to‐ocean continuum.

Inorganic carbon speciation and fluxes in the Congo River

Seasonal variations in inorganic carbon chemistry and associated fluxes from the Congo River were investigated at Brazzaville‐Kinshasa. Small seasonal variation in dissolved inorganic carbon (DIC) was found in contrast with discharge‐correlated changes in pH, total alkalinity (TA), carbonate species, and dissolved organic carbon (DOC). DIC was almost always greater than TA due to the importance of CO2*, the sum of dissolved CO2 and carbonic acid, as a result of low pH. Organic acids in DOC contributed 11–61% of TA and had a strong titration effect on water pH and carbonate speciation. The CO2* and bicarbonate fluxes accounted for ~57% and 43% of the DIC flux, respectively. Congo River surface water released CO2 at a rate of ~109 mol m−2 yr−1. The basin‐wide DIC yield was ~8.84 × 104 mol km−2 yr−1. The discharge normalized DIC flux to the ocean amounted to 3.11 × 1011 mol yr−1. The DOC titration effect on the inorganic carbon system may also be important on a global scale for regulating carbon fluxes in rivers.