Search

Excessive sodium intake is associated with nephrolithiasis, but the impact of sodium-deficient (SD) diets is unknown. Hence, we investigated the effects of short- and long-term SD diets on the expression of renal aquaporins and sodium transporters, and thus calcium oxalate (CaOx) crystal formation in hyperoxaluria rats. In a short-term sodium balance study, six male rats received drinking water and six received 0.75% ethylene glycol (EG) to induce hyperoxaluria. After a 30-day period of feeding on normal chow, both groups were treated with a normal-sodium diet for 5 days, followed by a sodium-free diet for the next 5 days. In a long-term SD study (42 days), four groups, induced with EG or not, were treated with normal-sodium water and sodium-free drinking water, alternately. Short-term sodium restriction in EG rats reversed the daily positive sodium balance, but progressively caused a negative cumulative water balance. In the long-term study, the abundant levels of of Na/H exchanger, thiazide-sensitive Na-Cl cotransporter, Na-K-ATPase, and aquaporins-1 from SD + EG rats were markedly reduced, corresponding to a decrease in Uosm, as compared to SD rats. Increased urine calcium, AP(CaOx)index, and renal CaOx deposition were also noted in SD + EG rats. Although the SD treatment reduced sodium excretion, it also increased urinary calcium and impaired renal function, ultimately causing the formation of more CaOx crystals. [ABSTRACT FROM AUTHOR]

To control net sodium (Na+) uptake, Arabidopsis plants utilize the plasma membrane (PM) Na+/H+ antiporter SOS1 to achieve Na+ efflux at the root and Na+ loading into the xylem, and the channel-like HKT1;1 protein that mediates the reverse flux of Na+ unloading off the xylem. Together, these opposing transport systems govern the partition of Na+ within the plant yet they must be finely co-regulated to prevent a futile cycle of xylem loading and unloading. Here, we show that the Arabidopsis SOS3 protein acts as the molecular switch governing these Na+ fluxes by favoring the recruitment of SOS1 to the PM and its subsequent activation by the SOS2/SOS3 kinase complex under salt stress, while commanding HKT1;1 protein degradation upon acute sodic stress. SOS3 achieves this role by direct and SOS2-independent binding to previously unrecognized functional domains of SOS1 and HKT1;1. These results indicate that roots first retain moderate amounts of salts to facilitate osmoregulation, yet when sodicity exceeds a set point, SOS3-dependent HKT1;1 degradation switches the balance toward Na+ export out of the root. Thus, SOS3 functionally links and co-regulates the two major Na+ transport systems operating in vascular plants controlling plant tolerance to salinity. [ABSTRACT FROM AUTHOR]

Members of the family Prevotellaceae are Gram-negative, obligate anaerobic bacteria found in animal and human microbiota. In Prevotella bryantii, the Na+-translocating NADH:quinone oxidoreductase (NQR) and quinol:fumarate reductase (QFR) interact using menaquinone as electron carrier, catalyzing NADH:fumarate oxidoreduction. P. bryantii NQR establishes a sodium-motive force, whereas P. bryantii QFR does not contribute to membrane energization. To elucidate the possible mode of function, we present 3D structural models of NQR and QFR from P. bryantii to predict cofactor-binding sites, electron transfer routes and interaction with substrates. Molecular docking reveals the proposed mode of menaquinone binding to the quinone site of subunit NqrB of P. bryantii NQR. A comparison of the 3D model of P. bryantii QFR with experimentally determined structures suggests alternative pathways for transmembrane proton transport in this type of QFR. Our findings are relevant for NADH-dependent succinate formation in anaerobic bacteria which operate both NQR and QFR. [ABSTRACT FROM AUTHOR]

Soil salinity severely limits crop yields and quality. Plants have evolved several strategies to mitigate the adverse effects of salinity, including redistribution and compartmentalization of toxic ions using ion-specific transporters. However, the mechanisms underlying the regulation of these ion transporters have not been fully elucidated. Loss-of-function mutants of OsHKT2;1, which is involved in sodium uptake, exhibit strong salt stress-resistant phenotypes. In this study, OsHKT2;1 was identified as a transcriptional target of the type-B response regulator OsRR22. Loss-of-function osrr22 mutants showed resilience to salt stress, and OsRR22-overexpression plants were sensitive to salt stress. OsRR22 was found to activate the expression of OsHKT2;1 by directly binding to the promoter region of OsHKT2;1 via a consensus cis-element of type-B response regulators. Moreover, rice DELLA protein OsSLR1 directly interacted with OsRR22 and functioned as a transcriptional co-activator. This study has uncovered a novel transcriptional regulatory mechanism by which a type-B response regulator controls sodium transport under salinity stress. [ABSTRACT FROM AUTHOR]

PurposeThe epithelium lining the ocular surface, which includes corneal and conjunctival epithelia, expresses the prosecretory chloride channel cystic fibrosis transmembrane conductance regulator (CFTR) and the proabsorptive epithelial sodium channel (ENaC). Here, methodology was established to measure the millivolt (mV) potential differences at the ocular surface, called ocular surface potential difference (OSPD), in human subjects produced by ion transport.MethodsOSPD was measured in human subjects in which a fluid-filled measuring electrode contacted a fluid pool created by eversion of the lateral lower eyelid, with a reference electrode placed subcutaneously in the forearm. Through the use of a high-impedance voltmeter, OSPD was measured continuously over 10 to 15 minutes in response to a series of perfusate fluid exchanges.ResultsBaseline OSPD (± SEM) in six normal human subjects was -21.3 ± 3.6 mV. OSPD depolarized by 1.7 ± 0.6 mV following the addition of the ENaC inhibitor amiloride, hyperpolarized by 6.8 ± 1.5 mV with a zero chloride solution, and further hyperpolarized by 15.9 ± 1.6 mV following CFTR activation by isoproterenol. The isoproterenol-induced hyperpolarization was absent in two cystic fibrosis subjects lacking functional CFTR. OSPD measurement produced minimal epithelial injury.ConclusionsOur results establish the feasibility and safety of OSPD measurement in humans and demonstrate robust CFTR activity, albeit minimal ENaC activity, at the ocular surface. OSPD measurement may be broadly applicable to investigate fluid transport mechanisms and test drug candidates to treat ocular surface disorders.Translational relevanceTo the best of our knowledge, this is the first measurement of the electrical potential generated by the ocular surface epithelium in human subjects, offering a new approach to study ocular surface function and health.

Dynamic changes in aquaporin gene expression occur during seed germination. One example is the ~30-fold increase in Arabidopsis thaliana PIP2;1 transcripts within 24 h of seed imbibition. To investigate whether AtPIP2;1 can influence seed germination wild-type Columbia-0, single (Atpip2;1) and double (Atpip2;1-Atpip2;2) loss-of-function mutants, along with transgenic 2x35S::AtPIP2;1 over-expressing (OE) lines and null-segregant controls, were examined. The various genotypes were germinated in control and saline (75 mM NaCl treatment) conditions and tested for germination efficiency, imbibed seed maximum cross sectional (MCS) area, imbibed seed mass, and seed Na+ and K+ content. Seed lacking functional AtPIP2;1 and/or AtPIP2;2 proteins or constitutively over-expressing AtPIP2;1 , had delayed germination in saline conditions relative to wild-type and null-segregant seed, respectively. Exposure to saline germination conditions resulted in Atpip2;1 mutants having greater imbibed seed mass and less accumulated Na+ than wild-type, whereas lines over-expressing AtPIP2;1 had reduced imbibed seed mass and greater seed K+ content than null-segregant control seed. The results imply a role for AtPIP2;1 in seed germination processes, whether directly through its capacity for water and ion transport or H2O2 signalling, or indirectly through potentially triggering dynamic differential regulation of other aquaporins expressed during germination. Future research will aid in dissecting the aquaporin functions influencing germination and may lead to novel solutions for optimising germination in sub-optimal conditions, such as saline soils. This study explored the role of Arabidopsis thaliana plasma membrane intrinsic protein (AtPIP2;1) in seed germination. Seed from plants varying in their relative abundance of AtPIP2;1 differed in the timing of germination in saline conditions relative to seed from wild-type plants. Wild-type seed germinated faster in saline conditions than the seed which had lost AtPIP2;1 function and the seed with a greater abundance of AtPIP2;1. [ABSTRACT FROM AUTHOR]

The article in Experimental Physiology explores the impact of exercise and digoxin administration on the regulation of sodium-potassium ATPase (NKA) pump in skeletal muscle. The study found that exercise had a more pronounced effect on NKA subunits compared to digoxin, with total beta subunit mRNA expression being impacted by digoxin supplementation. While the findings suggest potential benefits of combining digoxin with exercise in enhancing ion transport, further research is needed to understand the implications of digoxin-induced pathways like autophagy and apoptosis on muscle protein regulation. Overall, the study contributes to the understanding of NKA gene and protein regulation in skeletal muscle contraction, benefiting a wide audience interested in exercise physiology. [Extracted from the article]

Intracellular Ca2+ concentrations are strictly controlled by plasma membrane transporters, the endoplasmic reticulum, and mitochondria, in which Ca2+ uptake is mediated by the mitochondrial calcium uniporter complex (MCUc), while efflux occurs mainly through the mitochondrial Na+/Ca2+ exchanger (NCLX). RNAseq database repository searches led us to identify the Nclx transcript as highly enriched in astrocytes when compared with neurons. To assess the role of NCLX in mouse primary culture astrocytes, we inhibited its function both pharmacologically or genetically. This resulted in re‐shaping of cytosolic Ca2+ signaling and a metabolic shift that increased glycolytic flux and lactate secretion in a Ca2+‐dependent manner. Interestingly, in vivo genetic deletion of NCLX in hippocampal astrocytes improved cognitive performance in behavioral tasks, whereas hippocampal neuron‐specific deletion of NCLX impaired cognitive performance. These results unveil a role for NCLX as a novel modulator of astrocytic glucose metabolism, impacting on cognition. [ABSTRACT FROM AUTHOR]

HAK family transporters primarily function as K + transporters and play major roles in K + uptake and translocation in plants, whereas several HAK transporters exhibit Na + transport activity. OsHAK2, a rice HAK transporter, was shown to mediate Na + transport in Escherichia coli in a previous study. In this study, we investigated whether OsHAK2 is involved in Na + transport in the rice plant. Overexpression of OsHAK2 increased Na + translocation from the roots to the shoots of transgenic rice. It also increased both root and whole-plant Na + content, and enhanced shoot length under low Na + and K + conditions. Meanwhile, OsHAK2 overexpression increased salt sensitivity under a long-term salt stress condition, indicating that OsHAK2 is not involved in salt tolerance, unlike in the case of ZmHAK4 in maize. These results suggest that OsHAK2 is permeable to Na + and contributes to shoot growth in rice plants under low Na + and K + conditions. [ABSTRACT FROM AUTHOR]

Through its classic ATP‐dependent ion‐pumping function, basolateral Na/K‐ATPase (NKA) generates the Na+ gradient that drives apical Na+ reabsorption in the renal proximal tubule (RPT), primarily through the Na+/H+ exchanger (NHE3). Accordingly, activation of NKA‐mediated ion transport decreases natriuresis through activation of basolateral (NKA) and apical (NHE3) Na+ reabsorption. In contrast, activation of the more recently discovered NKA signaling function triggers cellular redistribution of RPT NKA and NHE3 and decreases Na+ reabsorption. We used gene targeting to test the respective contributions of NKA signaling and ion pumping to the overall regulation of RPT Na+ reabsorption. Knockdown of RPT NKA in cells and mice increased membrane NHE3 and Na+/HCO3− cotransporter (NBCe1A). Urine output and absolute Na+ excretion decreased by 65%, driven by increased RPT Na+ reabsorption (as indicated by decreased lithium clearance and unchanged glomerular filtration rate), and accompanied by elevated blood pressure. This hyper reabsorptive phenotype was rescued upon crossing with RPT NHE3−/− mice, confirming the importance of NKA/NHE3 coupling. Hence, NKA signaling exerts a tonic inhibition on Na+ reabsorption by regulating key apical and basolateral Na+ transporters. This action, lifted upon NKA genetic suppression, tonically counteracts NKA's ATP‐driven function of basolateral Na+ reabsorption. Strikingly, NKA signaling is not only physiologically relevant but it also appears to be functionally dominant over NKA ion pumping in the control of RPT reabsorption. [ABSTRACT FROM AUTHOR]

The thiazide sensitive Na+:Cl- cotransporter (NCC) is the principal via for salt reabsorption in the apical membrane of the distal convoluted tubule (DCT) in mammals and plays a fundamental role in managing blood pressure. The cotransporter is targeted by thiazide diuretics, a highly prescribed medication that is effective in treating arterial hypertension and edema. NCC was the first member of the electroneutral cation-coupled chloride cotransporter family to be identified at a molecular level. It was cloned from the urinary bladder of the Pseudopleuronectes americanus (winter flounder) 30 years ago. The structural topology, kinetic and pharmacology properties of NCC have been extensively studied, determining that the transmembrane domain (TM) coordinates ion and thiazide binding. Functional and mutational studies have discovered residues involved in the phosphorylation and glycosylation of NCC, particularly on the N-terminal domain, as well as the extracellular loop connected to TM7-8 (EL7-8). In the last decade, single-particle cryogenic electron microscopy (cryo-EM) has permitted the visualization of structures at high atomic resolution for six members of the SLC12 family (NCC, NKCC1, KCC1-KCC4). Cryo-EM insights of NCC confirm an inverted conformation of the TM1-5 and TM6-10 regions, a characteristic also found in the amino acid-polyamine-organocation (APC) superfamily, in which TM1 and TM6 clearly coordinate ion binding. The high-resolution structure also displays two glycosylation sites (N-406 and N-426) in EL7-8 that are essential for NCC expression and function. In this review, we briefly describe the studies related to the structure-function relationship of NCC, beginning with the first biochemical/functional studies up to the recent cryo-EM structure obtained, to acquire an overall view enriched with the structural and functional aspects of the cotransporter. [ABSTRACT FROM AUTHOR]

The thiazide sensitive Na+:Cl− cotransporter (NCC) is the principal via for salt reabsorption in the apical membrane of the distal convoluted tubule (DCT) in mammals and plays a fundamental role in managing blood pressure. The cotransporter is targeted by thiazide diuretics, a highly prescribed medication that is effective in treating arterial hypertension and edema. NCC was the first member of the electroneutral cation-coupled chloride cotransporter family to be identified at a molecular level. It was cloned from the urinary bladder of the Pseudopleuronectes americanus (winter flounder) 30 years ago. The structural topology, kinetic and pharmacology properties of NCC have been extensively studied, determining that the transmembrane domain (TM) coordinates ion and thiazide binding. Functional and mutational studies have discovered residues involved in the phosphorylation and glycosylation of NCC, particularly on the N-terminal domain, as well as the extracellular loop connected to TM7-8 (EL7-8). In the last decade, single-particle cryogenic electron microscopy (cryo-EM) has permitted the visualization of structures at high atomic resolution for six members of the SLC12 family (NCC, NKCC1, KCC1-KCC4). Cryo-EM insights of NCC confirm an inverted conformation of the TM1-5 and TM6-10 regions, a characteristic also found in the amino acid-polyamine-organocation (APC) superfamily, in which TM1 and TM6 clearly coordinate ion binding. The high-resolution structure also displays two glycosylation sites (N-406 and N-426) in EL7-8 that are essential for NCC expression and function. In this review, we briefly describe the studies related to the structure-function relationship of NCC, beginning with the first biochemical/functional studies up to the recent cryo-EM structure obtained, to acquire an overall view enriched with the structural and functional aspects of the cotransporter.

The salinization of irrigated land affects agricultural productivity. HIGH‐AFFINITY POTASSIUM (K+) TRANSPORTER 1;5 (OsHKT1;5)‐dependent sodium (Na+) transport is a key salt tolerance mechanism during rice growth and development. Using a previously generated high‐throughput activation tagging‐based T‐DNA insertion mutant pool, we isolated a mutant exhibiting salt stress‐sensitive phenotype, caused by a reduction in OsHKT1;5 transcripts. The salt stress‐sensitive phenotype of this mutant results from the loss of function of OsDNAJ15, which encodes plasma membrane‐localized heat shock protein 40 (Hsp40). osdnaj15 loss‐of‐function mutants show decreased plant height, increased leaf angle, and reduced grain number caused by shorter panicle length and fewer branches. On the other h'and, OsDNAJ15‐overexpression plants showed salt stress‐tolerant phenotypes. Intriguingly, salt stress facilitates the nuclear relocation of OsDNAJ15 so that it can interact with OsBAG4, and OsDNAJ15 and OsBAG4 synergistically facilitate the DNA‐binding activity of OsMYB106 to positively regulate the expression of OsHKT1;5. Overall, our results reveal a novel function of plasma membrane‐localized Hsp40 protein in modulating, alongside chaperon regulator OsBAG4, transcriptional regulation under salinity stress tolerance. [ABSTRACT FROM AUTHOR]

Renal luminal sodium transport is essential for physiological blood pressure control, and abnormalities in this process are strongly implicated in the pathogenesis of essential hypertension. Renal G protein-coupled receptors (GPCRs) are critical for the regulation of the reabsorption of essential nutrients, ions, and water from the glomerular filtrate. Recently, we showed that GPCR 37L1 (GPR37L1) is expressed on the apical membrane of renal proximal tubules (RPT) and regulates luminal sodium transport and blood pressure by modulating the function of the sodium proton exchanger 3 (NHE3). However, little is known about GPR37L1 intracellular signaling. Here, we show that GPR37L1 is localized to the nuclear membrane, in addition to the plasma membrane in human RPT cells. Furthermore, GPR37L1 signals via the PI3K/AKT/mTOR pathway to decrease the expression of DNA (cytosine-5)-methyltransferase 1 (DNMT1) and enhance NHE3 transcription. Overall, we demonstrate the direct role of a nuclear membrane GPCR in the regulation of renal sodium through epigenetic gene regulation. [ABSTRACT FROM AUTHOR]

Salinity is a global environmental threat to agricultural production and food security around the world. To delineate salt-induced damage from adaption events we analysed a pair of sorghum genotypes which are contrasting in their response to salt stress with respect to physiological, cellular, metabolomic, and transcriptional responses. We find that the salt-tolerant genotype Della can delay the transfer of sodium from the root to the shoot, more swiftly deploy accumulation of proline and antioxidants in the leaves and transfer more sucrose to the root as compared to its susceptible counterpart Razinieh. Instead Razinieh shows metabolic indicators for a higher extent photorespiration under salt stress. Following sodium accumulation by a fluorescent dye in the different regions of the root, we find that Della can sequester sodium in the vacuoles of the distal elongation zone. The timing of the adaptive responses in Della leaves indicates a rapid systemic signal from the roots that is travelling faster than sodium itself. We arrive at a model where resistance and susceptibility are mainly a matter of temporal patterns in signalling. [ABSTRACT FROM AUTHOR]

Effects of mutation Agouti yellow (Aу) linked with melanocortin type of obesity in mice on mineralocorticoid regulation mechanism and non-genomic effect of aldosterone on sodium transport were studied. Measurements of blood plasma aldosterone concentration and of expressions of mineralocorticoid receptor and alpha 1 subunit of Na,K-ATPase in cortical collecting ducts (CCD) of mice C57BL/6j-Aу/a and C57BL/6j as congenic strain did not reveal any difference. Study of expression of epithelial sodium channel alfa-subunit (ENaC) that takes a part in sodium transport in principal cells of CCD have shown decreased mRNA contents of these protein in mice C57BL/6j-Aу/a. In C57BL/6j-Aу/a mice, there was no decrease in the permeability of the CCD cell plasma membrane for sodium ions under acute exposure to aldosterone (10 nM), in contrast to mice of the C57BL/6j congenic line. Based on the results of the entire study, one can suppose that the Aу mutation may affect the transport of sodium ions in CCD cells and possibly in other types of cells. These findings make actual studies of molecular mechanisms of the effects of Aу mutation on the regulation of renal function.

Salinity is a global environmental threat to agricultural production and food security around the world. To delineate salt-induced damage from adaption events we analysed a pair of sorghum genotypes which are contrasting in their response to salt stress with respect to physiological, cellular, metabolomic, and transcriptional responses. We find that the salt-tolerant genotype Della can delay the transfer of sodium from the root to the shoot, more swiftly deploy accumulation of proline and antioxidants in the leaves and transfer more sucrose to the root as compared to its susceptible counterpart Razinieh. Instead Razinieh shows metabolic indicators for a higher extent photorespiration under salt stress. Following sodium accumulation by a fluorescent dye in the different regions of the root, we find that Della can sequester sodium in the vacuoles of the distal elongation zone. The timing of the adaptive responses in Della leaves indicates a rapid systemic signal from the roots that is travelling faster than sodium itself. We arrive at a model where resistance and susceptibility are mainly a matter of temporal patterns in signalling.

The thiazide-sensitive Na+-Cl- cotransporter (NCC) is the major pathway for salt reabsorption in the mammalian distal convoluted tubule, and the inhibition of its function with thiazides is widely used for the treatment of arterial hypertension. In mammals and teleosts, NCC is present as one ortholog that is mainly expressed in the kidney. One exception, however, is the eel, which has two genes encoding NCC. The eNCCα is located in the kidney and eNCCβ, which is present in the apical membrane of the rectum. Interestingly, the European eNCCβ functions as a Na+-Cl- cotransporter that is nevertheless resistant to thiazides and is not activated by low-chloride hypotonic stress. However, in the Japanese eel rectal sac, a thiazide-sensitive NaCl transport mechanism has been described. The protein sequences between eNCCβ and jNCCβ are 98% identical. Here, by site-directed mutagenesis, we transformed eNCCβ into jNCCβ. Our data showed that jNCCβ, similar to eNCCβ, is resistant to thiazides. In addition, both NCCβ proteins have high transport capacity with respect to their renal NCC orthologs and, in contrast to known NCCs, exhibit electrogenic properties that are reduced when residue I172 is substituted by A, G, or M. This is considered a key residue for the chloride ion-binding sites of NKCC and KCC. We conclude that NCCβ proteins are not sensitive to thiazides and have electrogenic properties dependent on Cl-, and site I172 is important for the function of NCCβ. [ABSTRACT FROM AUTHOR]

At the Nikanotee Fen Watershed, a pioneering reclamation project in the Athabasca Oil Sands Region, elevated sodium (Na+) in the porewater of mine-waste materials has been shown to migrate to the fen through groundwater, likely influencing fen vegetation health. Given the potential of Na+ to steer the ecological development of the fen, the goal of this research is to quantify the spatial distribution of Na+ and to characterize the Na+ mass balance of the surface and shallow subsurface of the fen. For a given time, the highest Na+ concentrations were generally found in the wettest part of the fen in the southwestern corner, and the lowest in the relatively dry northeast corner near the drainage outlet. Na+ concentrations in ponded surface water were responsive to rainfall-induced dilution and evapoconcentration, whereas porewater salinity in shallow groundwater was insensitive to meteorological conditions. Surface discharge controlled the mass efflux of Na+ from the system at an estimated average rate of 4 kg∙day−1 between June and August. Given the relatively small proportion of salt being flushed annually, and the greater rate of mass inflow relative to export, elevated salinity will likely be sustained for several decades. Since elevated Na+ concentrations are impacting the rooting zone of vegetation and have exceeded the salinity stress-threshold of mosses, targeting salt-tolerant vegetation will be important to maintain carbon accumulation in constructed systems.

Abstract Background Capture and storage of the energy carrier hydrogen as well as of the greenhouse gas carbon dioxide are two major problems that mankind faces currently. Chemical catalysts have been developed, but only recently a group of anaerobic bacteria that convert hydrogen and carbon dioxide to acetate, formate, or biofuels such as ethanol has come into focus, the acetogenic bacteria. These biocatalysts produce the liquid organic hydrogen carrier formic acid from H2 + CO2 or even carbon monoxide with highest rates ever reported. The autotrophic, hydrogen-oxidizing, and CO2-reducing acetogens have in common a specialized metabolism to catalyze CO2 reduction, the Wood–Ljungdahl pathway (WLP). The WLP does not yield net ATP, but is hooked up to a membrane-bound respiratory chain that enables ATP synthesis coupled to CO2 fixation. The nature of the respiratory enzyme has been an enigma since the discovery of these bacteria and has been unraveled in this study. Results We have produced a His-tagged variant of the ferredoxin:NAD oxidoreductase (Rnf complex) from the model acetogen Acetobacterium woodii, solubilized the enzyme from the cytoplasmic membrane, and purified it by Ni2+–NTA affinity chromatography. The enzyme was incorporated into artificial liposomes and catalyzed Na+ transport coupled to ferredoxin-dependent NAD reduction. Our results using the purified enzyme do not only verify that the Rnf complex from A. woodii is Na+-dependent, they also demonstrate for the first time that this membrane-embedded molecular engine creates a Na+ gradient across the membrane of A. woodii which can be used for ATP synthesis. Discussion We present a protocol for homologous production and purification for an Rnf complex. The enzyme catalyzed electron-transfer driven Na+ export and, thus, our studies provided the long-awaited biochemical proof that the Rnf complex is a respiratory enzyme.

Glycophytic plants are susceptible to salinity and their growth is hampered in more than 40 mM of salt. Salinity not only affects crop yield but also limits available land for farming by decreasing its fertility. Presence of distinct traits in response to environmental conditions might result in evolutionary adaptations. A better understanding of salinity tolerance through a comprehensive study of how Na+ is transported will help in the development of plants with improved salinity tolerance and might lead to increased yield of crops growing in strenuous environment. Ion transporters play pivotal role in salt homeostasis and maintain low cytotoxic effect in the cell. High-affinity potassium transporters are the critical class of integral membrane proteins found in plants. It mainly functions to remove excess Na+ from the transpiration stream to prevent sodium toxicity in the salt-sensitive shoot and leaf tissues. However, there are large number of HKT proteins expressed in plants, and it is possible that these members perform in a wide range of functions. Understanding their mechanism and functions will aid in further manipulation and genetic transformation of different crops. This review focuses on current knowledge of ion selectivity and molecular mechanisms controlling HKT gene expression. The current review highlights the mechanism of different HKT transporters from different plant sources and how this knowledge could prove as a valuable tool to improve crop productivity. [ABSTRACT FROM AUTHOR]

Normal pregnancy is characterized by massive increases in plasma volume and electrolyte retention. Given that the kidneys regulate homeostasis of electrolytes and volume, the organ undergoes major adaptations in morphology, hemodynamics, and transport to achieve the volume and electrolyte retention required in pregnancy. These adaptations are complex, sometimes counterintuitive, and not fully understood. In addition, the demands of the developing fetus and placenta change throughout pregnancy. For example, during late pregnancy, K+ retention and thus enhanced renal K+ reabsorption are required despite many kaliuretic factors. The goal of this study was to unravel how known adaptive changes along the nephrons contribute to the ability of the kidney to meet volume and electrolyte requirements in mid and late pregnancy. We developed computational models of solute and water transport in the superficial nephron of the kidney of a rat in mid and late pregnancy. The midpregnant and late-pregnant rat superficial nephron models predicted that morphological adaptations and increased activity of Naþ/Hþ exchanger 3 (NHE3) and epithelial Naþ channel are essential for the enhanced Naþ reabsorption observed during pregnancy. Model simulations showed that for sufficient K+ reabsorption, increased activity of H+-K+-ATPase and decreased K+ secretion along the distal segments is required in both mid and late pregnancy. The model results also suggested that certain known sex differences in renal transporter pattern (e.g., the higher NHE3 protein abundance but lower activity in the proximal tubules of virgin female rats compared with male rats) may serve to better prepare females for the increased transport demand in pregnancy. [ABSTRACT FROM AUTHOR]

The kidney plays an essential role in homeostasis, accomplished through the regulation of pH, electrolytes and fluids, by the building blocks of the kidney, the nephrons. One of the important markers of the proper functioning of a kidney is the glomerular filtration rate. Diabetes is characterized by an enlargement of the glomerular and tubular size of the kidney, affecting the afferent and efferent arteriole resistance and hemodynamics, ultimately leading to chronic kidney disease. We postulate that the diabetes-induced changes in kidney may exhibit significant sex differences as the distribution of renal transporters along the nephron may be markedly different between women and men, as recently shown in rodents. The goals of this study are to (i) analyze how kidney function is altered in male and female patients with diabetes, and (ii) assess the renal effects, in women and men, of an anti-hyperglycemic therapy that inhibits the sodium-glucose cotransporter 2 (SGLT2) in the proximal convoluted tubules. To accomplish these goals, we have developed computational models of kidney function, separate for male and female patients with diabetes. The simulation results indicate that diabetes enhances Na+ transport, especially along the proximal tubules and thick ascending limbs, to similar extents in male and female patients, which can be explained by the diabetes-induced increase in glomerular filtration rate. Additionally, we conducted simulations to study the effects of diabetes and SGLT2 inhibition on solute and water transport along the nephrons. Model simulations also suggest that SGLT2 inhibition raises luminal [Cl–] at the macula densa, twice as much in males as in females, and could indicate activation of the tubuloglomerular feedback signal. By inducing osmotic diuresis in the proximal tubules, SGLT2 inhibition reduces paracellular transport, eventually leading to diuresis and natriuresis. Those effects on urinary excretion are blunted in women, in part due to their higher distal transport capacity. [ABSTRACT FROM AUTHOR]

Acute respiratory distress syndrome is often associated with elevated levels of CO2 (hypercapnia) and impaired alveolar fluid clearance. Misfolding of the Na,K-ATPase (NKA), a key molecule involved in both alveolar epithelial barrier tightness and resolution of alveolar edema, in the endoplasmic reticulum (ER) may decrease plasma membrane abundance of the transporter. Here, we investigated how hypercapnia affects the NKA β-subunit (NKA-β) in the ER. Exposing murine precisioncut lung slices and human alveolar epithelial A549 cells to elevated CO2 levels led to a rapid decrease of NKA-β abundance in the ER and at the cell surface. Knockdown of ER mannosidase a class 1B member 1 and ER degradationenhancing a-mannosidase like protein 1 by siRNA or treatment with the mannosidase a class 1B member 1 inhibitor kifunensine rescued loss of NKA-β in the ER, suggesting ER-associated degradation (ERAD) of the enzyme. Furthermore, hypercapnia activated the unfolded protein response by promoting phosphorylation of inositol-requiring enzyme 1a (IRE1α), and treatment with an siRNA against IRE1a prevented the decrease of NKA-β in the ER. Of note, the hypercapniainduced phosphorylation of IRE1a was triggered by a Ca2+-dependent mechanism. In addition, inhibition of the inositol trisphosphate receptor decreased phosphorylation levels of IRE1a in precision-cut lung slices and A549 cells, suggesting that Ca2+ efflux from the ER might be responsible for IRE1a activation and ERAD of NKA-b. In conclusion, here we provide evidence that hypercapnia attenuates maturation of the regulatory subunit of NKA by activating IRE1α and promoting ERAD, which may contribute to impaired alveolar epithelial integrity in patients with acute respiratory distress syndrome and hypercapnia. [ABSTRACT FROM AUTHOR]

Fine tuning of Na+ reabsorption takes place along the aldosterone-sensitive distal nephron, which includes the collecting duct (CD), where it is mainly regulated by aldosterone. In the CD, Na+ reabsorption is mediated by the epithelial Na+ channel and Na+ pump (Na+-K+-ATPase). Paracellular ion permeability is mainly dependent on tight junction permeability. Claudin-8 is one of the main tight junction proteins expressed along the aldosterone-sensitive distal nephron. We have previously shown a coupling between transcellular Na+ reabsorption and paracellular Na+ barrier. We hypothesized that aldosterone controls the expression levels of both transcellular Na+ transporters and paracellular claudin-8 in a coordinated manner. Here, we show that aldosterone increased mRNA and protein levels as well as lateral membrane localization of claudin-8 in cultured CD principal cells. The increase in claudin-8 mRNA levels in response to aldosterone was prevented by preincubation with 17-hydroxyprogesterone, a mineralocorticoid receptor antagonist, and by inhibition of transcription with actinomycin D. We also showed that a low-salt diet, which stimulated aldosterone secretion, was associated with increased claudin-8 abundance in the mouse kidney. Reciprocally, mice subjected to a high-salt diet, which inhibits aldosterone secretion, or treated with spironolactone, a mineralocorticoid receptor antagonist, displayed decreased claudin-8 expression. Inhibition of glycogen synthase kinase-3, Lyn, and Abl signaling pathways prevented the effect of aldosterone on claudin-8 mRNA and protein abundance, suggesting that signaling of protein kinases plays a permissive role on the transcriptional activity of the mineralocorticoid receptor. This study shows that signaling via multiple protein kinases working in concert mediates aldosterone-induced claudin-8 expression in the CD. [ABSTRACT FROM AUTHOR]

Metabolic intermediates, such as succinate and citrate, regulate important processes ranging from energy metabolism to fatty acid synthesis. Cytosolic concentrations of these metabolites are controlled, in part, by members of the SLC13 gene family. The molecular mechanism underlying Na(+)-coupled di- and tricarboxylate transport by this family is understood poorly. The human Na(+)/dicarboxylate cotransporter NaDC3 (SLC13A3) is found in various tissues, including the kidney, liver, and brain. In addition to citric acid cycle intermediates such as α-ketoglutarate and succinate, NaDC3 transports other compounds into cells, including N-acetyl aspartate, mercaptosuccinate, and glutathione, in keeping with its dual roles in cell nutrition and detoxification. In this study, we construct a homology structural model of NaDC3 on the basis of the structure of the Vibrio cholerae homolog vcINDY. Our computations are followed by experimental testing of the predicted NaDC3 structure and mode of interaction with various substrates. The results of this study show that the substrate and cation binding domains of NaDC3 are composed of residues in the opposing hairpin loops and unwound portions of adjacent helices. Furthermore, these results provide a possible explanation for the differential substrate specificity among dicarboxylate transporters that underpin their diverse biological roles in metabolism and detoxification. The structural model of NaDC3 provides a framework for understanding substrate selectivity and the Na(+)-coupled anion transport mechanism by the human SLC13 family and other key solute carrier transporters.

Abstract Background HKT channels mediate sodium uniport or sodium and potassium symport in plants. Monocotyledons express a higher number of HKT proteins than dicotyledons, and it is only within this clade of HKT channels that cation symport mechanisms are found. The prevailing ion composition in the extracellular medium affects the transport abilities of various HKT channels by changing their selectivity or ion transport rates. How this mutual effect is achieved at the molecular level is still unknown. Here, we built a homology model of the monocotyledonous OsHKT2;2, which shows sodium and potassium symport activity. We performed molecular dynamics simulations in the presence of sodium and potassium ions to investigate the mutual effect of cation species. Results By analyzing ion-protein interactions, we identified a cation coordination site on the extracellular protein surface, which is formed by residues P71, D75, D501 and K504. Proline and the two aspartate residues coordinate cations, while K504 forms salt bridges with D75 and D501 and may be involved in the forwarding of cations towards the pore entrance. Functional validation via electrophysiological experiments confirmed the biological relevance of the predicted ion coordination site and identified K504 as a central key residue. Mutation of the cation coordinating residues affected the functionality of HKT only slightly. Additional in silico mutants and simulations of K504 supported experimental results. Conclusion We identified an extracellular cation coordination site, which is involved in ion coordination and influences the conduction of OsHKT2;2. This finding proposes a new viewpoint in the discussion of how the mutual effect of variable ion species may be achieved in HKT channels.

The activity of the Epithelial Na+ Channel (ENaC) in renal principal cells (PC) fine-tunes sodium excretion and consequently, affects blood pressure. The Gs-adenylyl cyclase-cAMP signal transduction pathway is believed to play a central role in the normal control of ENaC activity in PCs. The current study quantifies the importance of this signaling pathway to the regulation of ENaC activity in vivo using a knock-in mouse that has conditional expression of Gs-DREADD (designer receptors exclusively activated by designer drugs; GsD) in renal PCs. The GsD mouse also contains a cAMP response element-luciferase reporter transgene for non-invasive bioluminescence monitoring of cAMP signaling. Clozapine N-oxide (CNO) was used to selectively and temporally stimulate GsD. Treatment with CNO significantly increased luciferase bioluminescence in the kidneys of PC-specific GsD but not control mice. CNO also significantly increased the activity of ENaC in principal cells in PC-specific GsD mice compared to untreated knock-in mice and CNO treated littermate controls. The cell permeable cAMP analog, 8-(4-chlorophenylthio)adenosine 3′,5′-cyclic monophosphate, significantly increased the activity and expression in the plasma membrane of recombinant ENaC expressed in CHO and COS-7 cells, respectively. Treatment of PC-specific GsD mice with CNO rapidly and significantly decreased urinary Na+ excretion compared to untreated PC-specific GsD mice and treated littermate controls. This decrease in Na+ excretion in response to CNO in PC-specific GsD mice was similar in magnitude and timing as that induced by the selective vasopressin receptor 2 agonist, desmopressin, in wild type mice. These findings demonstrate for the first time that targeted activation of Gs signaling exclusively in PCs is sufficient to increase ENaC activity and decrease dependent urinary Na+ excretion in live animals.

The activity of the Epithelial Na+ Channel (ENaC) in renal principal cells (PC) fine-tunes sodium excretion and consequently, affects blood pressure. The Gs-adenylyl cyclase-cAMP signal transduction pathway is believed to play a central role in the normal control of ENaC activity in PCs. The current study quantifies the importance of this signaling pathway to the regulation of ENaC activity in vivo using a knock-in mouse that has conditional expression of Gs-DREADD (designer receptors exclusively activated by designer drugs; GsD) in renal PCs. The GsD mouse also contains a cAMP response element-luciferase reporter transgene for non-invasive bioluminescence monitoring of cAMP signaling. Clozapine N-oxide (CNO) was used to selectively and temporally stimulate GsD. Treatment with CNO significantly increased luciferase bioluminescence in the kidneys of PC-specific GsD but not control mice. CNO also significantly increased the activity of ENaC in principal cells in PC-specific GsD mice compared to untreated knock-in mice and CNO treated littermate controls. The cell permeable cAMP analog, 8-(4-chlorophenylthio)adenosine 3′,5′-cyclic monophosphate, significantly increased the activity and expression in the plasma membrane of recombinant ENaC expressed in CHO and COS-7 cells, respectively. Treatment of PC-specific GsD mice with CNO rapidly and significantly decreased urinary Na+ excretion compared to untreated PC-specific GsD mice and treated littermate controls. This decrease in Na+ excretion in response to CNO in PC-specific GsD mice was similar in magnitude and timing as that induced by the selective vasopressin receptor 2 agonist, desmopressin, in wild type mice. These findings demonstrate for the first time that targeted activation of Gs signaling exclusively in PCs is sufficient to increase ENaC activity and decrease dependent urinary Na+ excretion in live animals. [ABSTRACT FROM AUTHOR]

Biotechnology requires efficient microbial cell factories. The budding yeast Saccharomyces cerevisiae is a vital cell factory, but more diverse cell factories are essential for the sustainable use of natural resources. Here, we benchmarked nonconventional yeasts Kluyveromyces marxianus and Rhodotorula toruloides against S. cerevisiae strains CEN.PK and W303 for their responses to potassium and sodium salt stress. We found an inverse relationship between the maximum growth rate and the median cell volume that was responsive to salt stress. The supplementation of K1 to CEN.PK cultures reduced Na1 toxicity and increased the specific growth rate 4-fold. The higher K1 and Na1 concentrations impaired ethanol and acetate metabolism in CEN.PK and acetate metabolism in W303. In R. toruloides cultures, these salt supplementations induced a trade-off between glucose utilization and cellular aggregate formation. Their combined use increased the beta-carotene yield by 60% compared with that of the reference. Neural network-based image analysis of exponential-phase cultures showed that the vacuole-to-cell volume ratio increased with increased cell volume for W303 and K. marxianus but not for CEN.PK and R. toruloides in response to salt stress. Our results provide insights into common salt stress responses in yeasts and will help design efficient bioprocesses. [ABSTRACT FROM AUTHOR]

Nephron loss initiates compensatory hemodynamic and cellular effects on the remaining nephrons. Increases in single nephron glomerular filtration rate and tubular flow rate exert higher fluid shear stress (FSS) on tubules. In principal cell (PC) culture models FSS induces ERK, and ERK is implicated in the regulation of transepithelial sodium (Na) transport, as well as, proliferation. Thus, we hypothesize that high tubular flow and FSS mediate ERK activation in the cortical collecting duct (CCD) of solitary kidney which regulates amiloride sensitive Na transport and affects CCD cell number. Immunoblotting of whole kidney protein lysate was performed to determine phospho-ERK (pERK) expression. Next, sham and unilateral nephrectomized mice were stained with anti-pERK antibodies, and dolichos biflorus agglutinin (DBA) to identify PCs with pERK. Murine PCs (mpkCCD) were grown on semi-permeable supports under static, FSS, and FSS with U0126 (a MEK1/2 inhibitor) conditions to measure the effects of FSS and ERK inhibition on amiloride sensitive Na short circuit current (Isc). pERK abundance was greater in kidney lysate of unilateral vs. sham nephrectomies. The total number of cells in CCD and pERK positive PCs increased in nephrectomized mice (9.3 ± 0.4 vs. 6.1 ± 0.2 and 5.1 ± 0.5 vs. 3.6 ± 0.3 cell per CCD nephrectomy vs. sham, respectively, n > 6 per group, p < 0.05). However, Ki67, a marker of proliferation, did not differ by immunoblot or immunohistochemistry in nephrectomy samples at 1 month compared to sham. Next, amiloride sensitive Isc in static mpkCCD cells was 25.3 ± 1.7 μA/cm2 (n = 21), but after exposure to 24 h of FSS the Isc increased to 41.4 ± 2.8 μA/cm2 (n = 22; p < 0.01) and returned to 19.1 ± 2.1 μA/cm2 (n = 18, p < 0.01) upon treatment with U0126. Though FSS did not alter α- or γ-ENaC expression in mpkCCD cells, γ-ENaC was reduced in U0126 treated cells. In conclusion, pERK increases in whole kidney and, specifically, CCD cells after nephrectomy, but pERK was not associated with active proliferation at 1-month post-nephrectomy. In vitro studies suggest high tubular flow induces ERK dependent ENaC Na absorption and may play a critical role in Na balance post-nephrectomy.

Nephron loss initiates compensatory hemodynamic and cellular effects on the remaining nephrons. Increases in single nephron glomerular filtration rate and tubular flow rate exert higher fluid shear stress (FSS) on tubules. In principal cell (PC) culture models FSS induces ERK, and ERK is implicated in the regulation of transepithelial sodium (Na) transport, as well as, proliferation. Thus, we hypothesize that high tubular flow and FSS mediate ERK activation in the cortical collecting duct (CCD) of solitary kidney which regulates amiloride sensitive Na transport and affects CCD cell number. Immunoblotting of whole kidney protein lysate was performed to determine phospho-ERK (pERK) expression. Next, sham and unilateral nephrectomized mice were stained with anti-pERK antibodies, and dolichos biflorus agglutinin (DBA) to identify PCs with pERK. Murine PCs (mpkCCD) were grown on semi-permeable supports under static, FSS, and FSS with U0126 (a MEK1/2 inhibitor) conditions to measure the effects of FSS and ERK inhibition on amiloride sensitive Na short circuit current (Isc). pERK abundance was greater in kidney lysate of unilateral vs. sham nephrectomies. The total number of cells in CCD and pERK positive PCs increased in nephrectomized mice (9.3 ± 0.4 vs. 6.1 ± 0.2 and 5.1 ± 0.5 vs. 3.6 ± 0.3 cell per CCD nephrectomy vs. sham, respectively, n > 6 per group, p < 0.05). However, Ki67, a marker of proliferation, did not differ by immunoblot or immunohistochemistry in nephrectomy samples at 1 month compared to sham. Next, amiloride sensitive Isc in static mpkCCD cells was 25.3 ± 1.7 μA/cm2 (n = 21), but after exposure to 24 h of FSS the Isc increased to 41.4 ± 2.8 μA/cm2 (n = 22; p < 0.01) and returned to 19.1 ± 2.1 μA/cm2 (n = 18, p < 0.01) upon treatment with U0126. Though FSS did not alter α- or γ-ENaC expression in mpkCCD cells, γ-ENaC was reduced in U0126 treated cells. In conclusion, pERK increases in whole kidney and, specifically, CCD cells after nephrectomy, but pERK was not associated with active proliferation at 1-month post-nephrectomy. In vitro studies suggest high tubular flow induces ERK dependent ENaC Na absorption and may play a critical role in Na balance post-nephrectomy. [ABSTRACT FROM AUTHOR]

The Cooloola sedgefrog (Litoria cooloolensis) is one of a number of frog species endemic to the coastal sandy lowlands of east Australia exhibiting remarkable tolerance to dilute waters of low pH (< pH 3.5). To investigate the physiological and morphological underpinnings of acid tolerance in L. cooloolensis larvae, we compared Na+ balance, uptake and efflux rates, and gill and skin morphology in larvae reared in circum-neutral (pH 6.5) and pH 3.5 water. We hypothesised that L. cooloolensis larvae would be more resistant to ionregulatory disturbance and epithelial damage at low pH relative to acid-sensitive species. Net Na+ flux rates were not significantly different from zero in L. cooloolensis larvae reared at pH 3.5 and in acid-naïve animals maintained in pH 6.5 water. Animals reared at pH 6.5 and acutely exposed to pH 3.5, however, exhibited a net loss of Na+ due to inhibition of Na+ uptake. In contrast, L. cooloolensis larvae reared at pH 3.5 maintained Na+ balance at pH 3.5 and did not exhibit inhibition of Na+ uptake at this pH. Investigation of Na+ transport kinetics and the morphology of the gills and integument suggests tolerance of L. cooloolensis larvae to low pH may be attributed to a high capacity for branchial Na+ uptake, increased tight junction length and elevated mucus production at the gills and integument. These factors confer resistance to acid damage and disruption of ionic homeostasis which would otherwise result in the death of amphibian larvae exposed to waters of pH 4.0 and less. [ABSTRACT FROM AUTHOR]

Background: Capture and storage of the energy carrier hydrogen as well as of the greenhouse gas carbon dioxide are two major problems that mankind faces currently. Chemical catalysts have been developed, but only recently a group of anaerobic bacteria that convert hydrogen and carbon dioxide to acetate, formate, or biofuels such as ethanol has come into focus, the acetogenic bacteria. These biocatalysts produce the liquid organic hydrogen carrier formic acid from H2 + CO2 or even carbon monoxide with highest rates ever reported. The autotrophic, hydrogen-oxidizing, and CO2-reducing acetogens have in common a specialized metabolism to catalyze CO2 reduction, the Wood–Ljungdahl pathway (WLP). The WLP does not yield net ATP, but is hooked up to a membrane-bound respiratory chain that enables ATP synthesis coupled to CO2 fixation. The nature of the respiratory enzyme has been an enigma since the discovery of these bacteria and has been unraveled in this study. Results: We have produced a His-tagged variant of the ferredoxin:NAD oxidoreductase (Rnf complex) from the model acetogen Acetobacterium woodii, solubilized the enzyme from the cytoplasmic membrane, and purified it by Ni2+–NTA affinity chromatography. The enzyme was incorporated into artificial liposomes and catalyzed Na+ transport coupled to ferredoxin-dependent NAD reduction. Our results using the purified enzyme do not only verify that the Rnf complex from A. woodii is Na+-dependent, they also demonstrate for the first time that this membrane-embedded molecular engine creates a Na+ gradient across the membrane of A. woodii which can be used for ATP synthesis. Discussion: We present a protocol for homologous production and purification for an Rnf complex. The enzyme catalyzed electron-transfer driven Na+ export and, thus, our studies provided the long-awaited biochemical proof that the Rnf complex is a respiratory enzyme. [ABSTRACT FROM AUTHOR]

The phosphorylation state of two serine residues within the C‐terminal domain of AtPIP2;1 (S280, S283) regulates its plasma membrane localization in response to salt and osmotic stress. Here, we investigated whether the phosphorylation state of S280 and S283 also influence AtPIP2;1 facilitated water and cation transport. A series of single and double S280 and S283 phosphomimic and phosphonull AtPIP2;1 mutants were tested in heterologous systems. In Xenopus laevis oocytes, phosphomimic mutants AtPIP2;1 S280D, S283D, and S280D/S283D had significantly greater ion conductance for Na+ and K+, whereas the S280A single phosphonull mutant had greater water permeability. We observed a phosphorylation‐dependent inverse relationship between AtPIP2;1 water and ion transport with a 10‐fold change in both. The results revealed that phosphorylation of S280 and S283 influences the preferential facilitation of ion or water transport by AtPIP2;1. The results also hint that other regulatory sites play roles that are yet to be elucidated. Expression of the AtPIP2;1 phosphorylation mutants in Saccharomyces cerevisiae confirmed that phosphorylation influences plasma membrane localization, and revealed higher Na+ accumulation for S280A and S283D mutants. Collectively, the results show that phosphorylation in the C‐terminal domain of AtPIP2;1 influences its subcellular localization and cation transport capacity. Salt‐stress associated changes in the phosphorylation state of Arabidopsis dual water‐ion permeable aquaporin AtPIP2;1 influence its channel function. Testing in a heterologous system revealed a phosphorylation‐mimic dependent inverse relationship between AtPIP2;1 water and ion channel function. [ABSTRACT FROM AUTHOR]

We characterized mouse blood pressure and ion transport in the setting of commonly used rodent diets that drive K+ intake to the extremes of deficiency and excess. Male 129S2/Sv mice were fed either K+-deficient, control, high-K+ basic, or high-KCl diets for 10 days. Mice maintained on a K+-deficient diet exhibited no change in blood pressure, whereas K+-loaded mice developed an ~10-mmHg blood pressure increase. Following challenge with NaCl, K+-deficient mice developed a salt-sensitive 8 mmHg increase in blood pressure, whereas blood pressure was unchanged in mice fed high-K+ diets. Notably, 10 days of K+ depletion induced diabetes insipidus and upregulation of phosphorylated NaCl cotransporter, proximal Na+ transporters, and pendrin, likely contributing to the K+-deficient NaCl sensitivity. While the anionic content with high-K+ diets had distinct effects on transporter expression along the nephron, both K+ basic and KCl diets had a similar increase in blood pressure. The blood pressure elevation on high-K+ diets correlated with increased Na+-K+-2Cl- cotransporter and γ-epithelial Na+ channel expression and increased urinary response to furosemide and amiloride. We conclude that the dietary K+ maneuvers used here did not recapitulate the inverse effects of K+ on blood pressure observed in human epidemiological studies. This may be due to the extreme degree of K+ stress, the low-Na+-to-K+ ratio, the duration of treatment, and the development of other coinciding events, such as diabetes insipidus. These factors must be taken into consideration when studying the physiological effects of dietary K+ loading and depletion. [ABSTRACT FROM AUTHOR]

Angiotensin II (ANG II) stimulates proximal nephron transport via activation of classical protein kinase C (PKC) isoforms. Acute fructose treatment stimulates PKC and dietary fructose enhances ANG II's ability to stimulate Na+ transport, but the mechanisms are unclear. We hypothesized that dietary fructose enhances ANG II's ability to stimulate renal proximal tubule Na+ reabsorption by augmenting PKC-α activation and increases in intracellular Ca2+. We measured total and isoform-specific PKC activity, basal and ANG II-stimulated oxygen consumption, a surrogate of Na+ reabsorption, and intracellular Ca2+ in proximal tubules from rats given either 20% fructose in their drinking water (fructose group) or tap water (control group). Total PKC activity was measured by ELISA. PKC-α, PKC-β, and PKC-γ activities were assessed by measuring particulate-to-soluble ratios. Intracelluar Ca2+ was measured using fura 2. ANG II stimulated total PKC activity by 53 ± 15% in the fructose group but not in the control group (-15 ± 11%, P < 0.002). ANG II stimulated PKC-α by 0.134 ± 0.026 but not in the control group (-0.002 ± 0.020, P < 0.002). ANG II increased PKC-γ activity by 0.008 ± 0.003 in the fructose group but not in the control group (P < 0.046). ANG II did not stimulate PKC-β in either group. ANG II increased Na+ transport by 454 ± 87 nmol·min-1·mg protein-1 in fructose group, and the PKC-α/β inhibitor Gö6976 blocked this increase (-96 ± 205 nmol·min-1·mg protein-1, P < 0.045). ANG II increased intracellular Ca2+ by 148 ± 53 nM in the fructose group but only by 43 ± 10 nM in the control group (P < 0.035). The intracellular Ca2+ chelator BAPTA blocked the ANG II-induced increase in Na+ transport in the fructose group. We concluded that dietary fructose enhances ANG II's ability to stimulate renal proximal tubule Na+ reabsorption by augmenting PKC-α activation via elevated increases in intacellular Ca2+. [ABSTRACT FROM AUTHOR]

Aim: Sexual dimorphisms are evident along the nephron: Females (F) exhibit higher ratios of renal distal to proximal Na+ transporters' abundance, greater lithium clearance (CLi) more rapid natriuresis in response to saline infusion and lower plasma [K+] vs. males (M). During angiotensin II infusion hypertension (AngII‐HTN) M exhibit distal Na+ transporter activation, lower proximal and medullary loop transporters, blunted natriuresis in response to saline load, and reduced plasma [K+]. This study aimed to determine whether responses of F to AngII‐HTN mimicked those in M or were impacted by sexual dimorphisms evident at baseline. Methods: Sprague Dawley rats and C57BL/6 mice were AngII infused via osmotic minipumps 2 and 3 weeks, respectively, and assessed by metabolic cage collections, tail‐cuff sphygmomanometer, semi‐quantitative immunoblotting of kidney and patch‐clamp electrophysiology. Results: In F rats, AngII‐infusion increased BP to 190 mm Hg, increased phosphorylation of cortical NKCC2, NCC and cleavage of ENaC two to threefold, increased ENaC channel activity threefold and aldosterone 10‐fold. K+ excretion increased and plasma [K+] decreased. Evidence of natriuresis in F included increased urine Na+ excretion and CLi, and decreased medullary NHE3, NKCC2 and Na,K‐ATPase abundance. In C57BL/6 mice, AngII‐HTN increased abundance of distal Na+ transporters, suppressed proximal‐medullary transporters and reduced plasma [K+] in both F and M. Conclusion: Despite baseline sexual dimorphisms, AngII‐HTN provokes similar increases in BP, aldosterone, distal transporters, ENaC channel activation and K+ loss accompanied by similar suppression of proximal and loop Na+ transporters, natriuresis and diuresis in females and males. [ABSTRACT FROM AUTHOR]

Kidney water conservation requires a hypertonic medullary interstitium, NaCl in the outer medulla and NaCl and urea in the inner medulla, plus a vascular configuration that protects against washout. In this work, a multisolute model of the rat kidney is revisited to examine its capacity to simulate antidiuresis. The first step was to streamline model computation by parallelizing its Jacobian calculation, thus allowing finer medullary spatial resolution and more extensive examination of model parameters. It is found that outer medullary NaCl is modestly increased when transporter density in ascending Henle limbs from juxtamedullary nephrons is scaled to match the greater juxtamedullary solute flow. However, higher NaCl transport produces greater CO2 generation and, by virtue of countercurrent vascular flows, establishment of high medullary PCO2. This CO2 gradient can be mitigated by assuming that a fraction of medullary transport is powered anaerobically. Reducing vascular flows or increasing vessel permeabilities does little to further increase outer medullary solute gradients. In contrast to medullary models of others, vessels in this model have solute reflection coefficients close to zero; increasing these coefficients provides little enhancement of solute profiles but does generate high interstitial pressures, which distort tubule architecture. Increasing medullary urea delivery via entering vasa recta increases inner medullary urea, although not nearly to levels found in rats. In summary, 1) medullary Na+ and urea gradients are not captured by the model and 2) the countercurrent architecture that provides antidiuresis also produces exaggerated PCO2 profiles and is an unappreciated constraint on models of medullary function. [ABSTRACT FROM AUTHOR]

Changes in cellular ion levels can modulate distinct signaling networks aimed at correcting major disruptions in ion balances that might otherwise threaten cell growth and development. Salt-inducible kinase 1 (SIK1) and salt overly sensitive 2 (SOS2) are key protein kinases within such networks in mammalian and plant cells, respectively. In animals, SIK1 expression and activity are regulated in response to the salt content of the diet, and in plants SOS2 activity is controlled by the salinity of the soil. The specific ionic stress (elevated intracellular sodium) is followed by changes in intracellular calcium; the calcium signals are sensed by calcium-binding proteins and lead to activation of SIK1 or SOS2. These kinases target major plasma membrane transporters such as the Na+,K+-ATPase in mammalian cells, and Na+/H+ exchangers in the plasma membrane and membranes of intracellular vacuoles of plant cells. Activation of these networks prevents abnormal increases in intracellular sodium concentration.

The prevalence of fungal infections and their resistance patterns in fungal isolates from large number of patients with impaired immunity still remains poorly monitored. In spite of significant advances being made in the improvement of antifungal drugs, only a limited number of antifungal drugs are currently available. The present study aimed to gain further mechanistic insights into the previously described anticandidal activity of natural monoterpenoid, perillyl alcohol (PA). We found that cellular transport across cell membrane was abrogated in presence of PA. This was demonstrated by dose and time dependent enhanced cellular leakage accompanied by inhibited sodium and potassium cellular transport. In addition, we found disrupted pH homeostasis which was depicted by enhanced extracellular pH. We further observed that mitochondrial energy status is highly integrated with the antifungal activity of PA. This was evident from inhibited propidium iodide (PI) uptake in presence of sodium azide and di-nitro phenol (DNP) which showed no fluorescence when treated with PA. Moreover, we observed that PA leads to disrupted mitochondrial membrane potential. Additional cell death hallmarks in response to PA such as nuclear fragmentation was also observed with 4',6-diamidino-2-phenylindole (DAPI) staining. Taken together, PA is a novel candidate that deserves further attention to be exploited as effective antifungal agent of pharmacological interest.

An understanding of physiological mechanisms of salt tolerance is necessary for breeding programs, in order to select the desired trait in different wheat genotypes. Three bread wheat genotype differing in salt tolerance were employed to assess ion distribution and growth responses under saline conditions. To evaluate ion distribution in plant, sodium and potassium concentrations as well as K+/Na+ ratios in different tissues including root, leaf 3 blade, flag leaf sheath and flag leaf blade were assessed in a pot experiment in the glasshouse using a factorial experiment based on a randomized complete block design with three replications . Four levels of NaCl (0, 50, 100 and 150 mM NaCl) were imposed as the salinity treatments when the leaf 4 was fully expanded. Salinity had a similar effect on shoot biomass of all genotypes at 150 mM NaCl. Root biomass decreased in all genotypes with increasing salinity and this decrease was more in sensitive one (Tajan) at 150 mM NaCl. The genotypes did not differ significantly in root uptake of sodium. Sodium contents reduced from root to shoot and Salt tolerance in wheat genotypes was related to lower sodium accumulation in leaves. The major differences of salt tolerant genotypes (Arg and Mahdavi) and sensitive one in sodium transport to the younger leaf were due to the rate of transfer from the root to the shoot, which was much lower in Arg and the capacity of the leaf sheath to extract and sequester sodium as it entered the flag leaf blade in Mahdavi. Salt tolerant genotypes maintained higher K+/Na+ ratios in flag leaf blade than in salt sensitive one. Its likely that reduction in sodium transfer from the root to the shoot and leaf sheath sequestration specially in flag leaf are the traits that interact to control leaf blade sodium and would appear to be the most important mechanisms contributing to the improved salt tolerance in tolerant genotypes.

Cystic Fibrosis (CF) is a monogenic disease caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, resulting in defective CFTR-mediated chloride and bicarbonate transport, with dysregulation of epithelial sodium channels (ENaC). These changes alter fluid and electrolyte homeostasis and result in an exaggerated proinflammatory response driven, in part, by infection. We tested the hypothesis that NLRP3 inflammasome activation and ENaC upregulation drives exaggerated innate-immune responses in this multisystem disease. We identify an enhanced proinflammatory signature, as evidenced by increased levels of IL-18, IL-1β, caspase-1 activity and ASC-speck release in monocytes, epithelia and serum with CF-associated mutations; these differences were reversed by pretreatment with NLRP3 inflammasome inhibitors and notably, inhibition of amiloride-sensitive sodium (Na+) channels. Overexpression of β-ENaC, in the absence of CFTR dysfunction, increased NLRP3-mediated inflammation, indicating that dysregulated, ENaC-dependent signalling may drive exaggerated inflammatory responses in CF. These data support a role for sodium in modulating NLRP3 inflammasome activation.