NH3 Transport Research Articles

Anatomy of Summertime Upslope Events in Northeastern Colorado: Ammonia (NH3) Transport to the Rocky Mountains.

The Transport and Transformation of Ammonia (TRANS2Am) airborne field campaign occurred over northeastern Colorado during the summers of 2021 and 2022. A subset of the TRANS2Am flights investigated easterly wind conditions capable of moving agricultural emissions of ammonia (NH3) through urban areas and into the Rocky Mountains. TRANS2Am captured 6 of these events, unveiling important commonalities. (1) NH3 enhancements are present over the mountains on summer afternoons when easterly winds are present in the foothills region. (2) The abundance of gas-phase NH3 is 1 and 2 orders of magnitude higher than particle-phase NH4+ over the mountains and major agricultural sources, respectively. (3) During thermally driven circulation periods, emissions from animal husbandry sources closer to the mountains likely contribute more to the NH3 observed over the mountains than sources located further east. (4) Transport of plumes from major animal husbandry sources in northeastern Colorado westward across the foothills requires ∼5 h. (5) Winds drive variability in the transport of NH3 into nearby mountain ecosystems, producing both direct plume transport and recirculation. A similar campaign in other seasons, including spring and autumn, when synoptic scale events can produce sustained upslope transport, would place these results in context.

Metal ionic liquid-based hybrid membranes for ammonia separation through moderate interaction sites and cooperative transport channels

The combination ionic liquids (ILs) with membranes is a potential method for direct NH3 separation. In particular, ILs can modulate the interactions with NH3 and construct pathways in membranes for preferential NH3 transport, which is expected to overcome the trade-off effect and achieve a desirable separation performance. In this work, four metal ILs (MILs) with different metal centres and hydrogen bond donating ability, including [2-Mim][Li(NTf2)2], [Eim][Li(NTf2)2], [Bmim]2[Co(NCS)4], and [Bim]2[Co(NCS)4], were incorporated into sulfonated block copolymers to prepare MIL-based hybrid membranes for NH3 separation. The investigation of structure–performance relationships suggested that the interaction sites and transport channels could be tuned by the MIL type, which greatly affects the NH3 separation performance of the membranes. The Nexar/2-Mim-Li-10 membrane exhibits NH3 permeability of 735.6 Barrer with NH3/N2 selectivity of 844.5 and NH3/H2 selectivity of 154.7, which is higher than other MIL-based hybrid membranes owing to self-assembled transport channels and moderate complexation. Increasing the MIL content and feed pressure significantly improved NH3 separation performance.

Multifunctional effect of copper in bimetallic Cu-M/Al2O3 catalysts (M = Fe, Co, and Ni) for NH3 decomposition

Ammonia is a promising hydrogen carrier, which can enhance energy transport efficiency when bulk NH3 is transported in a gas carrier vessel. At the end of the NH3 transport, the NH3 gas should be converted to H2 and N2 using NH3 decomposition catalyst, which has outstanding catalytic performance and low cost. The M/Al2O3 and Cu-M/Al2O3 catalysts (M = Fe, Co, and Ni) were test and characterized regarding catalytic NH3 decomposition because we expected the Cu addition could differently change the electronic structure and the desorption behaviors of active metal species. As our expectation, the added Cu modified the catalytic performance and characteristics, but these changes were different, depending on the kind of active metal species (Fe, Co, and Ni). The catalytic activity was improved for Fe/Al2O3 but worsened for Co/Al2O3 and Ni/Al2O3. In addition, the added Cu element acted as an electron donor in Cu-Fe/Al2O3 but as an electron acceptor in Cu-Co/Al2O3 and Cu-Ni/Al2O3 and influenced the desorption behaviors of the generated H and N atoms, particularly in the Cu-Fe/Al2O3, the added Cu alleviated the desorption behaviors of H and N atoms but suppress them in the Cu-Co/Al2O3 and Cu-Ni/Al2O3, which affected the catalytic performance of NH3 decomposition.

Two-phase flow visualization in direct ammonia fuel cells

In this work, the two-phase flow occurring in a direct ammonia fuel cell is visualized to understand the interactions between the complex physico-chemical processes involving in fuel cells. Experimental observations indicate that the appearance, growth, coalescence, detachment and sweeping processes of nitrogen bubbles occur periodically. Besides, the effect of operating conditions on the behavior of two-phase flow as well as cell performance is explored. Experimental results demonstrate that numerous nitrogen gas slugs are generated in the anode flow channel when the fuel flow rate is lower than 1.0 mL min−1, which seriously blocks the transport of NH3 and OH− to the anode catalyst layer. At an operating temperature of 95 °C, the flow channels are almost completely occupied by gases (a mixture of ammonia, nitrogen, and water), even under open-circuit conditions (a mixture of ammonia and water). In addition, the effects of using parallel and serpentine flow fields on the behaviour and flow patterns of two-phase flows are explored. Experimental results reveal that the parallel flow field is prone to clogging local flow channels by slugs. Moreover, the removal frequency of bubbles in the parallel design is significantly slower than that in the serpentine one.

Functional Characterization of an Ammonia Transporter RhBG Mutation Identified in Diabetic Kidney Disease Patients

Metabolic acidosis is a major complication of CKD (chronic kidney disease) and DKD (diabetic kidney disease). The kidney responds to metabolic acidosis by eliminating acid, primarily by producing and excreting NH4+ in the urine. Two Rh glycoproteins, RhBG and RhCG, expressed in the collecting duct are directly involved in NH3/NH4+transport. We previously determined that RhBG transports both NH4+ and NH3 across the basolateral membrane of intercalated cells. Impaired NH3/NH4+ production and/or transport may be a factor in increasing acid load and worsening kidney disease. In type 2 diabetes, net endogenous acid production is significantly elevated, and the proportion of acid excreted as NH4+ is decreased even after accounting for diet and renal function. This is significant given that the association between acidosis and faster decline in GFR is now well established. In DKD, impaired NH4+ excretion as a potential risk factor for progression of kidney disease remains poorly understood. Specifically, the genetic risk factors contributing to DKD are unclear. Hypothesis: Defined RhBG variant(s) linked to DKD cause impaired NH3/NH4+ transport that may contribute to DKD development and progression. Methods: We conducted whole-exome sequencing (WES) analysis using data from A therosclerosis R isk i n C ommunities (ARIC) study and the C hronic R enal I nsuffciency C ohort (CRIC) study. We selected DKD patients with the most rapid GFR decline and compared them with: 1) subjects without kidney disease (healthy control); 2) diabetic patients without CKD (DM control); 3) CKD patients without diabetes (CKD control). This approach will identify single nucleotide variants (SNVs) of RhBG associated with DKD. This will also determine if the detected variants contribute to the development of kidney disease per se and whether they contribute to the development of diabetes and/or fast GFR decline. To study function, we expressed RhBG variants (and wild-type RhBG) in Xenopus oocytes by microinjecting oocytes with the respective mRNA. The effect of defined SNV of RhBG on NH3/NH4+ transport was assessed from measurements of changes in intracellular pH (pHi), membrane potential (Vm), whole cell currents (I) or surface pH (pHs) induced by exposing the oocytes to bath solutions containing NH4Cl or methyl ammonium chloride (MA/MA+). Results: We identified an SNV, rs3748569 (minor allele frequency MAF > 0.05), that was significantly associated with DKD. Significance was determined compared to DM control (OR=1.38, p=0.0026) and healthy control (OR=1.26, p=0.01). This variant has also been predicted to be deleterious by 4 bioinformatic tools. Our electrophysiological measurements showed that the resultant amino acid switch, G315R, completely inhibited transport of NH3 and NH4+ (p<0.001) and the transport of MA and MA+ (p<0.0001), compared with RhBG-WT. Conclusions: WES results suggest that this naturally occurring RhBG mutation, G315R, contributes to DKD occurrence. This effect is through the development of kidney disease and less likely due to development of diabetes. It is therefore likely a general CKD risk factor. Inhibition of NH3/NH4+ transport by this mutation is a contributing factor to its deleterious effect. This work provides experimental validation of computational predictions concerning CKD and diabetes. NIH-U54 GM104940, Paul Teschan Research, NIH-R01, Carol Lavin Bernick, Tulane institutional. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Estimation of ammonia deposition to forest ecosystems in Scotland and Sri Lanka using wind-controlled NH3 enhancement experiments

Ammonia (NH3) pollution has emerged as a major cause of concern as atmospheric concentrations continue to increase globally. Environmentally damaging NH3 levels are expected to severely affect sensitive and economically important organisms, but evidence is lacking in many parts of the world. We describe the design and operation of a wind-controlled NH3 enhancement system to assess effects on forests in two contrasting climates. We established structurally identical NH3 enhancement systems in a temperate birch woodland in the UK and a tropical sub-montane forest in central Sri Lanka, both simulating real-world NH3 pollution conditions. Vertical and horizontal NH3 concentrations were monitored at two different time scales to understand NH3 transport within the forest canopies. We applied a bi-directional resistance model with four canopy layers to calculate net deposition fluxes. At both sites, NH3 concentrations and deposition were found to decrease exponentially with distance away from the source, consistent with expectations. Conversely, we found differences in vertical mixing of NH3 between the two experiments, with more vertically uniform NH3 concentrations in the dense and multi-layered sub-montane forest canopy in Sri Lanka. Monthly NH3 concentrations downwind of the source ranged from 3 to 29 μg m−3 at the UK site and 2–47 μg m−3 at the Sri Lankan site, compared with background values of 0.63 and 0.35 μg m−3, respectively. The total calculated NH3 dry deposition flux to all the canopy layers along the NH3 transects ranged from 12 to 162 kg N ha−1 yr−1 in the UK and 16–426 kg N ha−1 yr−1 in Sri Lanka, representative of conditions in the vicinity of a range of common NH3 sources. This multi-layer model is applicable for identifying the fate of NH3 in forest ecosystems where the gas enters the canopy laterally through the trunk space and exposes the understorey to high NH3 levels. In both study sites, we found that cuticular deposition was the dominant flux in the vegetation layers, with a smaller contribution from stomatal uptake. The new facilities are now allowing the first ever field comparison of NH3 impacts on forest ecosystems, with special focus on lichen bio-indicators, which will provide vital evidence to inform NH3 critical levels and associated nitrogen policy development in South Asia.

Mathematical model and experiment investigation on electrodialysis separation process of LiBr from NH3-H2O-LiBr ternary solution in ammonia absorption refrigeration system

The utilization of NH3-H2O-LiBr ternary working fluid is effective to improve the COP of the ammonia absorption refrigeration system (AARS). However, LiBr impairs the absorption of NH3 in the absorber and consequently limits the COP promotion. To address this limitation, electrodialysis (ED) is introduced into AARS to reduce the LiBr concentration in the absorber because it has been widely applied in ion separation from industrial waste solutions. In this study, a simulation model for the NH3-H2O-LiBr ternary solution ED separation process was developed based on the overall mass transfer equation. Experiments were conducted to measure and verify the coefficients in the model. The results showed that the NH3 transport was hard to be separated by ED. For the LiBr, the overall transport number and the overall electro-osmotic permeability were −3.49 × 10−3 kg min−1 A−1 and -1.33 × 10−4 L min−1 A−1. The overall diffusion permeability, overall osmosis permeability, and average resistance were dependent on the LiBr concentrations in the solutions. Moreover, the influences of ED parameters on the LiBr separation were studied using the model and the energy efficiency was applied to evaluate the separation performance. The energy efficiencies were 0.0325 and 0.323 when the membrane pair exceeded 10 and the membrane effective area (Aeff) surpassed 0.0325 m2. The energy efficiency increased with the decrease of current density and the increase of LiBr concentration difference between the two solutions. Moreover, an effective method was built to obtain a set of suitable ED parameters that meet high ED energy efficiency and the LiBr separation requirements in AARS.

Beyond equilibrium ammonia synthesis in a membrane and heat exchange integrated microreactor: A modeling study

Ammonia (NH3) synthesis is modeled in a micro–structured membrane reactor (MR) comprising reaction, cooling and NH3 separation functions in the same volume. The proposed MR involves permeate and reaction channels segregated by layers of zirconia supported ZnCl2 immobilized molten–salt (IMS) membrane selective to NH3 transport. While H2 + N2 is fed to reaction channels washcoated with an iron–based catalyst, permeate channels host N2 as the sweep gas which also regulates reaction temperature. The in–situ cooled MR is modeled by considering mass, momentum and energy conservation in the fluid phases of the reaction and permeate channels, reaction in the catalyst layer and NH3 transport across the membrane, whose thermal stability limit of 623 K is set as the maximum reactor temperature. Upon N2 sweep dosing equal to 50 × the molar H2 + N2 input at H2/N2 = 3, 613 K, 50 bar and 1.5 × 103 m3 kgcat–1 s−1, MR can deliver ∼47 % N2 conversion which exceeds 40 and 13.5 % of the pertinent thermodynamic barrier and the membraneless case, respectively. Despite the exothermic heat release, co–current partitioning of the streams ensures operability below 623 K. Increasing space velocity and H2/N2 ratio, and decreasing inlet temperature and pressure inhibit reactor performance. Using molar sweep–to–reactive mixture ratios < 50 is penalized by the violation of the specified maximum temperature. Membrane integration can improve NH3 production by ∼3.5 times per unit amount of H2O consumed in its electrocatalytic conversion to H2.

Ammonia recovery from municipal wastewater using hybrid NaOH closed-loop membrane contactor and ion exchange system

Water scarcity is affected by population growth and increasing nutrients pollution. This study evaluated the integration of ion exchange-natural activated clinoptilolite zeolite (IEX-NZ) and hollow-fibre liquid–liquid membrane contactor (HF-LLMC) as an innovative and sustainable hybrid technology for ammonia recovery from treated urban wastewaters. The process is based on NaOH closed-loop process to i) ensure the extracted concentration of ammonia from the loaded zeolites and ii) enhance the transport of NH3 through the HF-LLMC. Regeneration of the IEX-NZ provided recoveries up to around 92% using 8% NaOH solution with concentration factors between 30 and 60 and a residual ammonium stream below 1 mg NH4+-N/L. Recovery of NH3 from NaOH solutions was carried out by HF-LLMCs using two different membrane chemistries: polypropylene (PP) and poly (4-methyl-1-pentene) (PMP) (>95%). A 1-D model was developed and used to describe the time evolution of NH3 concentration during the recovery process, to determine its mass transfer coefficient (9.5·107 m3/m2·s) and to quantify the undesired water co-transport (5.0·105 m3/m2·s). In addition, the model was used to analyse the influence of operational parameters on the membrane's permeability to maximise the concentration of the ammonium salts recovered as fertilisers. In this case, the 1-D algorithm was used to identify the needed stages to achieve residual levels of NH3 on the treated streams that promoted the NaOH closed-loop recycling to secure economic feasibility.

Metal-Organic Framework Materials for Production and Distribution of Ammonia.

The efficient production of ammonia (NH3) from dinitrogen (N2) and water (H2O) using renewable energy is an important step on the roadmap to the ammonia economy. The productivity of this conversion hinges on the design and development of new active catalysts. In the wide scope of materials that have been examined as catalysts for the photo- and electro-driven reduction of N2 to NH3, functional metal-organic framework (MOF) catalysts exhibit unique properties and appealing features. By elucidating their structural and spectroscopic properties and linking this to the observed activity of MOF-based catalysts, valuable information can be gathered to inspire new generations of advanced catalysts to produce green NH3. NH3 is also a surrogate for the hydrogen (H2) economy, and the potential application of MOFs for the practical and effective capture, safe storage, and transport of NH3 is also discussed. This Perspective analyzes the contribution that MOFs can make toward the ammonia economy.

Ammonia Cycling and Emerging Secondary Aerosols from Arable Agriculture: A European and Irish Perspective

Ammonia (NH3) is a naturally occurring, highly reactive and soluble alkaline trace gas, originating from both natural and anthropogenic sources. It is present throughout the biosphere, yet plays a complicated role in atmospheric acid–base reactions resulting in the formation of inorganic secondary inorganic aerosols (SIAs). While the general mechanisms are recognised, factors controlling the reactions leading to SIA formation are less explored. This review summarises the current knowledge of NH3 sources, emission and deposition processes and atmospheric reactions leading to the formation of SIA. Brief summaries of NH3 and SIA long-range transport and trans-boundary pollution, a discussion of precursor species to SIAs (other than NH3), abiotic and biotic controls and state-of-the-art methods of measurement and modelling of pollutants are also included. In Ireland, NH3 concentrations remained below National and European Union limits, until 2016 when a rise in emissions was seen due to agricultural expansion. However, due to a lack of continuous monitoring, source and receptor relationships are difficult to establish, including the appointment of precursor gases and aerosols to source regions and industries. Additionally, the lack of continuous monitoring leads to over- and underestimations of precursor gases present, resulting in inaccuracies of the estimated importance of NH3 as a precursor gas for SIA. These gaps in data can hinder the accuracy and precision of forecasting models. Deposition measurements and the modelling of NH3 present another challenge. Direct source measurements are required for the parameterization of bi-directional fluxes; however, high-quality data inputs can be limited by local micrometeorological conditions, or the types of instrumentation used. Long-term measurements remain challenging for both aerosols and precursor gases over larger areas or arduous terrains.

NH3 spatiotemporal variability over Paris, Mexico City, and Toronto, and its link to PM2.5 during pollution events

Abstract. Megacities can experience high levels of fine particulate matter (PM2.5) pollution linked to ammonia (NH3) mainly emitted from agricultural activities. Here, we investigate such pollution in the cities of Paris, Mexico, and Toronto, each of which have distinct emission sources, agricultural regulations, and topography. Ten years of measurements from the infrared atmospheric sounding interferometer (IASI) are used to assess the spatiotemporal NH3 variability over and around the three cities. In Europe and North America, we determine that temperature is associated with the increase in NH3 atmospheric concentrations with a coefficient of determination (r2) of 0.8 over agricultural areas. The variety of the NH3 sources (industry and agricultural) and the weaker temperature seasonal cycle in southern North America induce a lower correlation factor (r2=0.5). The three regions are subject to long-range transport of NH3, as shown using HYSPLIT cluster back trajectories. The highest NH3 concentrations measured at the city scale are associated with air masses coming from the surrounding and north/northeast regions of Paris, the south/southwest areas of Toronto, and the southeast/southwest zones of Mexico City. Using NH3 and PM2.5 measurements derived from IASI and surface observations from 2008 to 2017, annually frequent pollution events are identified in the three cities. Wind roses reveal statistical patterns during these pollution events with dominant northeast/southwest directions in Paris and Mexico City, and the transboundary transport of pollutants from the United States in Toronto. To check how well chemistry transport models perform during pollution events, we evaluate simulations made using the GEOS-Chem model for March 2011. In these simulations we find that NH3 concentrations are underestimated overall, though day-to-day variability is well represented. PM2.5 is generally underestimated over Paris and Mexico City, but overestimated over Toronto.

Is fertilization the dominant source of ammonia in the urban atmosphere?

It was previously believed that ammonia (NH3) has a short residence time in the atmosphere and cannot be transported far from its sources. In late March, however, this study observed a severe NH3 episode in urban Beijing when fertilizer was intensively applied on the North China Plain, with the highest hourly concentrations of 66.9 μg m-3 throughout the year. The stable nitrogen isotopic composition of NH3 (δ15N-NH3) during this episode (-37.0 to -20.0‰) fell in the range of endmembers of fertilizer and livestock, suggesting the long-range transport of NH3 from agricultural to urban regions. Based on a Bayesian isotope mixing model, the contribution of agriculture (fertilization) to urban NH3 concentrations was apportioned as 43.5% (26.0%) on polluted days. However, these contributions were reduced to 29.1% (12.8%) when nitrogen isotope fractionation between NH3 and ammonium was considered. In contrast to the limited contribution of agricultural sources, we found that nonagricultural emissions, particularly vehicles, dominate the source of NH3 in urban Beijing, even during the fertilization period. This finding indicated that nonagricultural sources should be considered when designing a control strategy for NH3 to reduce haze pollution in the urban atmosphere.

Recovery of Nutrients from Residual Streams Using Ion-Exchange Membranes: Current State, Bottlenecks, Fundamentals and Innovations.

The review describes the place of membrane methods in solving the problem of the recovery and re-use of biogenic elements (nutrients), primarily trivalent nitrogen NIII and pentavalent phosphorus PV, to provide the sustainable development of mankind. Methods for the recovery of NH4+ − NH3 and phosphates from natural sources and waste products of humans and animals, as well as industrial streams, are classified. Particular attention is paid to the possibilities of using membrane processes for the transition to a circular economy in the field of nutrients. The possibilities of different methods, already developed or under development, are evaluated, primarily those that use ion-exchange membranes. Electromembrane methods take a special place including capacitive deionization and electrodialysis applied for recovery, separation, concentration, and reagent-free pH shift of solutions. This review is distinguished by the fact that it summarizes not only the successes, but also the “bottlenecks” of ion-exchange membrane-based processes. Modern views on the mechanisms of NH4+ − NH3 and phosphate transport in ion-exchange membranes in the presence and in the absence of an electric field are discussed. The innovations to enhance the performance of electromembrane separation processes for phosphate and ammonium recovery are considered.

Reactive Transport of NH4+ in the Hyporheic Zone from the Ground Water to the Surface Water

Nowadays, ammonia nitrogen (NH4+) pollution gets more and more attention in drinking water sources. This study investigated the main behavior of biogeochemical NH4+ from groundwater to surface water in a hyporheic zone (HZ) sediment from a reservoir. The experiments were conducted using synthetic groundwater to investigate ammonium transformation. The results indicated that ammonium concentration decreased, apparently resulting from the influence of microbial oxidation and ion exchange with Ca2+, Mg2+, K+, and Na+. However, all the ammonium in the sediment was oxidized, then the adsorbed NH4+ became bioavailable by being released back when NH4+ concentration decreased in the aqueous phase. The results showed NH4+ behavior in a HZ where the aerobic and anaerobic environments frequently exchange, with different hydrological conditions controlled by a strong coupling between microbial activities, geochemistry, hydrology, and ion exchange.

Techno-environmental assessment of small-scale Haber-Bosch and plasma-assisted ammonia supply chains

Haber-Bosch (HB) process, the main method for ammonia (NH3) production, contributes to near 2% of the global carbon emissions because the hydrogen input is obtained from fossil sources. NH3 production is concentrated in a few countries, adding emissions due to global distribution. Distributed plants next to farmers and fed by renewable energy can reduce these impacts, as well as NH3 storage, shortage risks, and price volatility. Distributed plants cannot reach low NH3 production costs as centralised plants, but they can be promoted by the environmental benefits of its products lifecycles. Therefore, life cycle assessments of NH3 production pathways and specific modelling for NH3 transport in Australia were performed, from cradle-to-site, to identify the influence of storage, transport, and energy sources in their environmental profiles. The carbon footprint of centralised production was up to 2.96 kg.CO2-eq/kg.NH3, from which 29.3% corresponded to transport. Local production demonstrated substantial avoided transport impacts and that CO2-eq can reach reductions over 100% when including co-product credits such as oxygen and carbon black. Local plants using electrolysers to supply mini-HB loops obtained rates of 0.12, −0.52, and −1.57 kg.CO2-eq/kg.NH3 using electricity from solar, wind, and biogas (other than manure) sources, respectively. The alternative using high temperature plasma reactor instead of electrolyser obtained its best rate of −0.65 kg.CO2-eq/kg using biogas different from manure. At farm electrolyser-based plants using novel non-thermal plasma reactors, considering potential energy yields and simplified NH3 separation technology, could reach a rate of −1.07 kg.CO2-eq/kg.NH3, using solar energy. Among the assessed pathways, the most notable impact was on freshwater eutrophication in the electrolyser-based plants generating reductions up to 290%, due to oxygen credits. Despite these results, the use of solar energy raises concerns on land use and terrestrial ecotoxicity due to the area needed for solar farms and the manufacture of their components.

Insights into the Na+-dependent transport in SLC4 proteins from a cryo-EM structure of the NDCBE transporter and computational modelling

SLC4 transporters are involved in transport of Cl-, HCO3-, CO32-, Na+, H+, and NH3 through the membrane and are key for pH maintenance and ion homeostasis in the body. Despite their high sequence identity, the members of the family demonstrate an array of transport modes - Na+-dependent or independent transport, H+ and NH3 transport, Na+-anion symport, anion exchange and combinations thereof. Two structures of SLC4 transporters, the human anion exchanger 1 (AE1) and the human sodium carbonate electrogenic symporter 1 (NBCe1), have been previously resolved in their outward facing (OF) open state by X-Ray and cryo-EM, and putative binding sites have been determined from functional mutagenesis and computational modelling.

Effects of butyrate\u2212 on ruminal Ca2+ transport: evidence for the involvement of apically expressed TRPV3 and TRPV4 channels

The ruminal epithelium absorbs large quantities of NH4+ and Ca2+. A role for TRPV3 has emerged, but data on TRPV4 are lacking. Furthermore, short-chain fatty acids (SCFA) stimulate ruminal Ca2+ and NH4+ uptake in vivo and in vitro, but the pathway is unclear. Sequencing of the bovine homologue (bTRPV4) revealed 96.79% homology to human TRPV4. Two commercial antibodies were tested using HEK-293 cells overexpressing bTRPV4, which in ruminal protein detected a weak band at the expected ~ 100 kDa and several bands ≤ 60 kDa. Immunofluorescence imaging revealed staining of the apical membrane of the stratum granulosum for bTRPV3 and bTRPV4, with cytosolic staining in other layers of the ruminal epithelium. A similar expression pattern was observed in a multilayered ruminal cell culture which developed resistances of > 700 Ω · cm2 with expression of zonula occludens-1 and claudin-4. In Ussing chambers, 2-APB and the TRPV4 agonist GSK1016790A stimulated the short-circuit current across native bovine ruminal epithelia. In whole-cell patch-clamp recordings on HEK-293 cells, bTRPV4 was shown to be permeable to NH4+, K+, and Na+ and highly sensitive to GSK1016790A, while effects of butyrate− were insignificant. Conversely, bTRPV3 was strongly stimulated by 2-APB and by butyrate− (pH 6.4 > pH 7.4), but not by GSK1016790A. Fluorescence calcium imaging experiments suggest that butyrate− stimulates both bTRPV3 and bTRPV4. While expression of bTRPV4 appears to be weaker, both channels are candidates for the ruminal transport of NH4+ and Ca2+. Stimulation by SCFA may involve cytosolic acidification (bTRPV3) and cell swelling (bTRPV4).

Beyond Ca2+ signalling: the role of TRPV3 in the transport of NH4+

Mutations of TRPV3 lead to severe dermal hyperkeratosis in Olmsted syndrome, but whether the mutants are trafficked to the cell membrane or not is controversial. Even less is known about TRPV3 function in intestinal epithelia, although research on ruminants and pigs suggests an involvement in the uptake of NH4+. It was the purpose of this study to measure the permeability of the human homologue (hTRPV3) to NH4+, to localize hTRPV3 in human skin equivalents, and to investigate trafficking of the Olmsted mutant G573S. Immunoblotting and immunostaining verified the successful expression of hTRPV3 in HEK-293 cells and Xenopus oocytes with trafficking to the cell membrane. Human skin equivalents showed distinct staining of the apical membrane of the top layer of keratinocytes with cytosolic staining in the middle layers. Experiments with pH-sensitive microelectrodes on Xenopus oocytes demonstrated that acidification by NH4+ was significantly greater when hTRPV3 was expressed. Single-channel measurements showed larger conductances in overexpressing Xenopus oocytes than in controls. In whole-cell experiments on HEK-293 cells, both enantiomers of menthol stimulated influx of NH4+ in hTRPV3 expressing cells, but not in controls. Expression of the mutant G573S greatly reduced cell viability with partial rescue via ruthenium red. Immunofluorescence confirmed cytosolic expression, with membrane staining observed in a very small number of cells. We suggest that expression of TRPV3 by epithelia may have implications not just for Ca2+ signalling, but also for nitrogen metabolism. Models suggesting how influx of NH4+ via TRPV3 might stimulate skin cornification or intestinal NH4+ transport are discussed.

Physiological Characteristics and Transcriptomic Dissection in Two Root Segments with Contrasting Net Fluxes of Ammonium and Nitrate of Poplar Under Low Nitrogen Availability

To investigate physiological and transcriptomic regulation mechanisms underlying the distinct net fluxes of NH4+ and NO3- in different root segments of Populus species under low nitrogen (N) conditions, we used saplings of Populus × canescens supplied with either 500 (normal N) or 50 (low N) μM NH4NO3. The net fluxes of NH4+ and NO3-, the concentrations of NH4+, amino acids and organic acids and the enzymatic activities of nitrite reductase (NiR) and glutamine synthetase (GS) in root segment II (SII, 35-70 mm to the apex) were lower than those in root segment I (SI, 0-35 mm to the apex). The net NH4+ influxes and the concentrations of organic acids were elevated, whereas the concentrations of NH4+ and NO3- and the activities of NiR and GS were reduced in SI and SII in response to low N. A number of genes were significantly differentially expressed in SII vs SI and in both segments grown under low vs normal N conditions, and these genes were mainly involved in the transport of NH4+ and NO3-, N metabolism and adenosine triphosphate synthesis. Moreover, the hub gene coexpression networks were dissected and correlated with N physiological processes in SI and SII under normal and low N conditions. These results suggest that the hub gene coexpression networks play pivotal roles in regulating N uptake and assimilation, amino acid metabolism and the levels of organic acids from the tricarboxylic acid cycle in the two root segments of poplars in acclimation to low N availability.