scholarly journals Stationary and Nonstationary Ion and Water Flux Interactions in Kidney Proximal Tubule: Mathematical Analysis of Isosmotic Transport by a Minimalistic Model

2019 ◽  
pp. 101-147 ◽  
Author(s):  
Erik Hviid Larsen ◽  
Jens Nørkær Sørensen
Keyword(s):  
Water Uptake ◽  
Time Course ◽  
Epithelial Transport ◽  
Water Flux ◽  
Experimental Studies ◽  
Physiological Parameter ◽  
Water Fluxes ◽  
Fluid Absorption ◽  
Knock Out ◽  
Osmotic Permeability

AbstractOur mathematical model of epithelial transport (Larsen et al. Acta Physiol. 195:171–186, 2009) is extended by equations for currents and conductance of apical SGLT2. With independent variables of the physiological parameter space, the model reproduces intracellular solute concentrations, ion and water fluxes, and electrophysiology of proximal convoluted tubule. The following were shown: Water flux is given by active Na+ flux into lateral spaces, while osmolarity of absorbed fluid depends on osmotic permeability of apical membranes. Following aquaporin “knock-out,” water uptake is not reduced but redirected to the paracellular pathway. Reported decrease in epithelial water uptake in aquaporin-1 knock-out mouse is caused by downregulation of active Na+ absorption. Luminal glucose stimulates Na+ uptake by instantaneous depolarization-induced pump activity (“cross-talk”) and delayed stimulation because of slow rise in intracellular [Na+]. Rate of fluid absorption and flux of active K+ absorption would have to be attuned at epithelial cell level for the [K+] of the absorbate being in the physiological range of interstitial [K+]. Following unilateral osmotic perturbation, time course of water fluxes between intraepithelial compartments provides physical explanation for the transepithelial osmotic permeability being orders of magnitude smaller than cell membranes’ osmotic permeability. Fluid absorption is always hyperosmotic to bath. Deviation from isosmotic absorption is increased in presence of glucose contrasting experimental studies showing isosmotic transport being independent of glucose uptake. For achieving isosmotic transport, the cost of Na+ recirculation is predicted to be but a few percent of the energy consumption of Na+/K+ pumps.

The Mechanism of Fluid Absorption at Ecdysis in the American Lobster Homarus Americanus

1980 ◽  
Vol 84 (1) ◽  
pp. 89-102 ◽  
Author(s):  
DONALD L. MYKLES
Keyword(s):  
Digestive Tract ◽  
Water Uptake ◽  
Principal Part ◽  
Sea Water ◽  
Homarus Americanus ◽  
Barium Sulphate ◽  
American Lobster ◽  
Water Fluxes ◽  
Fluid Absorption

1. The mechanism of fluid absorption at ecdysis was investigated in the stenohaline marine decapod, Homarus americanus. 2. Sea-water uptake began approximately 1 h before ecdysis, increased rapidly during ecdysis, and was completed 2 h after ecdysis. 3. Increased drinking rates were measured during and just after ecdysis. The quantity of water ingested was equal to the total amount of water absorbed during moult, indicating that fluid entered the haemolymph exclusively via the lining of the digestive tract. 4. It was estimated that 91 % of the ingested sea water appeared in the haemolymph by 2·5 h postecdysis. 5. The midgut appeared to be the principal part of the digestive tract involved in the absorption of fluid into the haemolymph. X-radiography of lobsters that ingested a suspension of barium sulphate during ecdysis demonstrated that accumulation and concentration of this compound occurred within the midgut during the 2·5 h of haemolymph expansion following ecdysis. Elevated net water fluxes across perfused midgut were observed in late proecdysis and 0·5 h after ecdysis.

scholarly journals Root water uptake and its pathways across the root: quantification at the cellular scale

2020 ◽  
Author(s):  
Mohsen Zarebanadkouki ◽  
Pavel Trtik ◽  
Faisal Hayat ◽  
Andrea Carminati ◽  
Anders Kaestner
Keyword(s):  
Water Flow ◽  
Water Uptake ◽  
Water Distribution ◽  
Water Flux ◽  
Root Water Uptake ◽  
Invasive Technique ◽  
Water Fluxes ◽  
Deuterated Water ◽  
Climate Conditions ◽  
Root Tissues

<p>The pathways of water across root tissues and their relative contribution to plant water uptake remain debated. This is mainly due to technical challenges in measuring water flux non-invasively at the cellular scale under realistic conditions.  We developed a new method to quantify water fluxes inside roots growing in soils. The method combines spatiotemporal quantification of deuterated water distribution imaged by rapid neutron tomography with an inverse simulation of water transport across root tissues. Using this non-invasive technique, we estimated for the first time the in-situ radial water fluxes [m s<sup>-1</sup>] in apoplastic and cell-to-cell pathways. The water flux in the apoplast of twelve days-old lupins (Lupinus albus L. cv. Feodora) was seventeen times faster than in the cell-to-cell pathway. Hence, the overall contribution of the apoplast in water flow [m<sup>3</sup> s<sup>-1</sup>] across the cortex is, despite its small volume of 5%, as large as 57±8 % (Mean ± SD for n=3) of the total water flow. This method is suitable to non-invasively measure the response of cellular scale root hydraulics and water fluxes to varying soil and climate conditions.</p>

scholarly journals Root water uptake and its pathways across the root: quantification at the cellular scale

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Mohsen Zarebanadkouki ◽  
Pavel Trtik ◽  
Faisal Hayat ◽  
Andrea Carminati ◽  
Anders Kaestner
Keyword(s):  
Water Flow ◽  
Water Uptake ◽  
Water Distribution ◽  
Water Flux ◽  
Root Water Uptake ◽  
Invasive Technique ◽  
Water Fluxes ◽  
Deuterated Water ◽  
Climate Conditions ◽  
Root Tissues

Abstract The pathways of water across root tissues and their relative contribution to plant water uptake remain debated. This is mainly due to technical challenges in measuring water flux non-invasively at the cellular scale under realistic conditions. We developed a new method to quantify water fluxes inside roots growing in soils. The method combines spatiotemporal quantification of deuterated water distribution imaged by rapid neutron tomography with an inverse simulation of water transport across root tissues. Using this non-invasive technique, we estimated for the first time the in-situ radial water fluxes [m s−1] in apoplastic and cell-to-cell pathways. The water flux in the apoplast of twelve days-old lupins (Lupinus albus L. cv. Feodora) was seventeen times faster than in the cell-to-cell pathway. Hence, the overall contribution of the apoplast in water flow [m3 s−1] across the cortex is, despite its small volume of 5%, as large as 57 ± 8% (Mean ± SD for n = 3) of the total water flow. This method is suitable to non-invasively measure the response of cellular scale root hydraulics and water fluxes to varying soil and climate conditions.

Monosaccharide Biosynthesis Pathways Database

Glycobiology ◽  
2021 ◽  
Author(s):  
Jaya Srivastava ◽  
P Sunthar ◽  
Petety V Balaji
Keyword(s):  
Expression Profiling ◽  
Experimental Studies ◽  
Structural Complexity ◽  
Evolutionary Relationships ◽  
Enzyme Assays ◽  
Biosynthesis Pathway ◽  
Knock Out ◽  
Set Up ◽  
Function Relationship ◽  
Natural Glycans

Abstract A distinctive feature of glycans vis-à-vis proteins and nucleic acids is its structural complexity which arises from the huge repertoire of monosaccharides, isomeric linkages and branching. A very large number of monosaccharides have so far been discovered in natural glycans. Experimentally, pathways for the biosynthesis have been characterized completely for 55 monosaccharides and partially for a few more. However, there is no single platform which provides information about monosaccharide biosynthesis pathways and associated enzymes We have gathered 572 experimentally characterized enzymes of 66 biosynthesis pathways from literature and set up a first of its kind database called the Monosaccharide Biosynthesis Pathways Database http://www.bio.iitb.ac.in/mbpd/). Annotations such as the reaction catalysed, substrate specificity, biosynthesis pathway and PubMed IDs are provided for all the enzymes in the database. Sequence homologs of the experimentally characterized enzymes found in nearly 13,000 completely sequenced genomes from Bacteria and Archaea have also been included in the database. This platform will help in the deduction of evolutionary relationships among enzymes such as aminotransferases, nucleotidyltransferases, acetyltransferases and SDR family enzymes. It can also facilitate experimental studies such as direct enzyme assays to validate putative annotations, establish structure–function relationship, expression profiling to determine the function, determine the phenotypic consequences of gene knock-out/knock-in and complementation studies.

Use of ionic currents to identify and estimate parameters in models of channel blockade

1990 ◽  
Vol 259 (2) ◽  
pp. H626-H634
Author(s):  
C. F. Starmer ◽  
V. V. Nesterenko ◽  
F. R. Gilliam ◽  
A. O. Grant
Keyword(s):  
Time Course ◽  
Experimental Studies ◽  
Ionic Currents ◽  
Blocking Agent ◽  
Model Parameters ◽  
Protein Conformations ◽  
Channel Blockade ◽  
Channel Blocking ◽  
Individual Contributions ◽  
Modulated Receptor

Models of ion channel blockade are frequently validated with observations of ionic currents resulting from electrical or chemical stimulation. Model parameters for some models (modulated receptor hypothesis) cannot be uniquely determined from ionic currents. The time course of ionic currents reflects the activation (fraction of available channels that conduct in the presence of excitation) and availability of channels (the ability of the protein to make a transition to a conducting conformation and where this conformation is not complexed with a drug). In the presence of a channel blocking agent, the voltage dependence of availability appears modified and has been interpreted as evidence that drug-complexed channels exhibit modified transition rates between channel protein conformations. Because blockade and availability both modify ionic currents, their individual contributions to macroscopic conductance cannot be resolved from ionic currents except when constant affinity binding to a bindable site is assumed. Experimental studies of nimodipine block of calcium channels and lidocaine block of sodium channels illustrate these concepts.

Dependence of ion fluxes on fluid transport by rat proximal tubule

1986 ◽  
Vol 250 (4) ◽  
pp. F680-F689 ◽  
Author(s):  
K. Bomsztyk ◽  
F. S. Wright
Keyword(s):  
Proximal Tubule ◽  
Fluid Transport ◽  
Rat Kidney ◽  
Water Flux ◽  
Fluid Secretion ◽  
Proximal Convoluted Tubule ◽  
Ion Fluxes ◽  
Fluid Absorption ◽  
Fluid Flux ◽  
K Transport

The effects of changes in transepithelial water flux (Jv) on sodium, chloride, calcium, and potassium transport by the proximal convoluted tubule were examined by applying a microperfusion technique to surface segments in kidneys of anesthetized rats. Perfusion solutions were prepared with ion concentrations similar to those in fluid normally present in the later parts of the proximal tubule. Osmolality of the perfusate was adjusted with mannitol. With no mannitol in the perfusates, net fluid absorption was observed. Addition of increasing amounts of mannitol first reduced Jv to zero and then reversed net fluid flux. At the maximal rates of fluid absorption, net absorption of Na, Cl, Ca, and K was observed. When Jv was reduced to zero, Na, Cl, and Ca absorption were reduced and K entered the lumen. Na, Cl, and Ca secretion occurred in association with the highest rates of net fluid secretion. The lumen-positive transepithelial potential progressively increased as the net fluid flux was reduced to zero and then reversed. The results demonstrate that changes in net water flux can affect Na, Cl, Ca, and K transport by the proximal convoluted tubule of the rat kidney. These changes in net ion fluxes are not entirely accounted for by changes in bulk-phase transepithelial electrochemical gradients.

Linking soil water and solutes fluxes to soil properties and vegetation types: insights from a case-study in the high tropical Andes of Ecuador

2021 ◽  
Author(s):  
Sebastián Páez-Bimos ◽  
Veerle Vanacker ◽  
Marcos Villacis ◽  
Marlon Calispa ◽  
Oscar Morales ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Water Conservation ◽  
Water Flux ◽  
Water Fluxes ◽  
Vegetation Types ◽  
Tropical Andes ◽  
Conservation Area ◽  
Solute Fluxes ◽  
Doc Concentration ◽  
Water Conservation Area

<p>The high tropical Andes ecosystem, known as páramo, provides important hydrological services to densely populated areas in the Andean region. In order to manage these services sustainably, it is crucial to understand the biotic and abiotic processes that control both water quality and fluxes. Recent research in the páramo highlights a knowledge gap regarding the role played by soil-vegetation interactions in controlling soil-water processes and resulting water and solute fluxes.</p><p>Here, we determine the hydrological and geochemical fluxes in four soil profiles in the páramo of the Antisana´s water conservation area in northern Ecuador. Water fluxes were measured biweekly with field fluxmeters in the hydrological year Apr/2019- Mar/2020 under two contrasting vegetation types: tussock-like grass (TU) and cushion-forming plants (CU). Soil solution was collected in parallel with wick samplers and suction caps for assessing the concentrations of dissolved cations, anions and organic carbon (DOC). In addition, soil moisture was measured continuously in the upper meter of the soil profile, i.e. first three horizons (A, 2A and 2BC), using water content reflectometers. The vertical water flux in the upper meter of each soil profile was simulated using the 1D HYDRUS model. We carried out a Sobol analysis to identify sensitive soil hydraulic parameters. We then derived water fluxes by inverse modeling, based on the measured soil moisture. We validated the calculated water fluxes using the fluxmeter data. Solute fluxes were estimated by combining the water fluxes and the soil solution compositions.</p><p>Our preliminary results suggest that water fluxes and DOC concentration vary under different vegetation types. The fluxmeter data from the 2A horizon indicates that the cumulative water flux under TU (2.8 - 5.7 l) was larger than under CU (0.8 – 1.1 l) during the dry season (Aug-Sep and Dec-Jan). However, the opposite trend was observed in the wet season for maximum water fluxes. Moreover, the DOC concentration in the uppermost horizon was higher under CU (47.3 ±2.2 mg l<sup>-1</sup>) than under TU (3.1 ±0.2 mg l<sup>-1</sup>) vegetation during the monitoring period. We associate the water and solute responses under different vegetation types to the contrasting soil hydro-physical and chemical properties (e.g., saturated hydraulic conductivity and organic carbon content) in the uppermost soil horizon. Our study illustrates the existence of a spatial association between vegetation types, water fluxes and solute concentrations in Antisana´s water conservation area. By modelling the hydrological balance of the upper meter of the soil mantle, the water and solute fluxes will be estimated for soils with different vegetation cover.</p><p> </p>

Net Fluxes of Water in the Isolated Gills of Anguilla Dieffenbachii

1974 ◽  
Vol 60 (3) ◽  
pp. 769-781
Author(s):  
T. J. SHUTTLEWORTH ◽  
R. F. H. FREEMAN
Keyword(s):  
Sea Water ◽  
Water Flux ◽  
Freshwater Teleost ◽  
Osmotic Permeability ◽  
Direct Measurements ◽  
Net Flux ◽  
Anguilla Dieffenbachii ◽  
Net Fluxes ◽  
Freshwater Eels ◽  
Net Water Flux

1. Measurements of net flux of water have been made on isolated gills removed from freshwater-adapted and seawater-adapted eels and incubated in various media of differing osmotic pressure. 2. From these measurements it has been possible to determine the osmotic permeability coefficient of the gill directly from the net water flux. The values obtained (0.50±0.14x10-5 cm.sec-1 for freshwater eels and 0.43±0.07x10-5 cm.sec-1 for seawater-adapted eels) indicate that there was no significant change in this parameter on adaptation of the eels to sea water. 3. The direct measurements made of the net water flux across the isolated gills appear to be compatible with the osmoregulatory pattern of eels as deduced by other workers using different techniques. In particular they illustrate and further emphasize the significance of drinking in the freshwater fish. 4. Calculations indicate that, for a freshwater teleost, the osmotic and ionic problems caused by drinking in fresh water have an insignificant energetic effect and hence, energetically, it matters little to the fish whether it drinks or not.

scholarly journals Plasma Hepcidin Correlates Positively With Interleukin-6 in Patients Undergoing Pulmonary Endarterectomy

2011 ◽  
pp. 493-502 ◽  
Author(s):  
P. MARUNA ◽  
M. VOKURKA ◽  
J. LINDNER
Keyword(s):  
Acute Phase ◽  
Iron Metabolism ◽  
Time Course ◽  
Acute Phase Proteins ◽  
Human Subjects ◽  
Circulatory Arrest ◽  
Experimental Studies ◽  
Acute Phase Reactant ◽  
Deep Hypothermic Circulatory Arrest ◽  
Pulmonary Endarterectomy

Hepcidin, a recently discovered antimicrobial peptide synthesized in the liver, was identified to be the key mediator of iron metabolism and distribution. Despite our knowledge of hepcidin increased in recent years, there are only limited data on hepcidin regulation during systemic inflammatory response in human subjects. In a prospective study, the time course of plasma hepcidin was analyzed in relations to six inflammatory parameters – plasma cytokines and acute-phase proteins in patients undergoing uncomplicated pulmonary endarterectomy. Twenty-four patients (males, aged 52.6±10.2 years, treated with pulmonary endarterectomy in a deep hypothermic circulatory arrest) were enrolled into study. Hepcidin, interleukin (IL)-6, IL-8, tumor necrosis factor-α, C-reactive protein, α1-antitrypsin and ceruloplasmin arterial concentrations were measured before surgery and repeatedly within 120 h post-operatively. Hemodynamic parameters, hematocrit and markers of iron metabolism were followed up. In a postoperative period, hepcidin increased from preoperative level 8.9 ng/ml (6.2-10.7) (median and interquartile range) to maximum 16.4 ng/ml (14.1-18.7) measured 72 h after the end of surgery. Maximum post-operative concentrations of hepcidin correlated positively with maximum IL-6 levels. Both hepcidin and IL-6 maximum concentrations correlated positively with extracorporeal circulation time. In conclusions, the study demonstrated that plasma hepcidin is a positive acute-phase reactant in relation to an uncomplicated large cardiac surgery. Hepcidin increase was related to IL-6 concentrations and to the duration of surgical procedure. Our clinical findings are in conformity with recent experimental studies defining hepcidin as a type II acute-phase protein.

scholarly journals Modelling short-term variability in carbon and water exchange in a temperate Scots pine forest

2015 ◽  
Vol 6 (2) ◽  
pp. 485-503 ◽  
Author(s):  
M. H. Vermeulen ◽  
B. J. Kruijt ◽  
T. Hickler ◽  
P. Kabat
Keyword(s):  
Water Uptake ◽  
Scots Pine ◽  
Water Exchange ◽  
Carbon Sink ◽  
Pine Forest ◽  
Temperature Threshold ◽  
Water Fluxes ◽  
Local Data ◽  
Deep Soil ◽  
Scots Pine Forest

Abstract. The vegetation–atmosphere carbon and water exchange at one particular site can strongly vary from year to year, and understanding this interannual variability in carbon and water exchange (IAVcw) is a critical factor in projecting future ecosystem changes. However, the mechanisms driving this IAVcw are not well understood. We used data on carbon and water fluxes from a multi-year eddy covariance study (1997–2009) in a Dutch Scots pine forest and forced a process-based ecosystem model (Lund–Potsdam–Jena General Ecosystem Simulator; LPJ-GUESS) with local data to, firstly, test whether the model can explain IAVcw and seasonal carbon and water exchange from direct environmental factors only. Initial model runs showed low correlations with estimated annual gross primary productivity (GPP) and annual actual evapotranspiration (AET), while monthly and daily fluxes showed high correlations. The model underestimated GPP and AET during winter and drought events. Secondly, we adapted the temperature inhibition function of photosynthesis to account for the observation that at this particular site, trees continue to assimilate at very low atmospheric temperatures (up to daily averages of −10 °C), resulting in a net carbon sink in winter. While we were able to improve daily and monthly simulations during winter by lowering the modelled minimum temperature threshold for photosynthesis, this did not increase explained IAVcw at the site. Thirdly, we implemented three alternative hypotheses concerning water uptake by plants in order to test which one best corresponds with the data. In particular, we analyse the effects during the 2003 heatwave. These simulations revealed a strong sensitivity of the modelled fluxes during dry and warm conditions, but no single formulation was consistently superior in reproducing the data for all timescales and the overall model–data match for IAVcw could not be improved. Most probably access to deep soil water leads to higher AET and GPP simulated during the heatwave of 2003. We conclude that photosynthesis at lower temperatures than assumed in most models can be important for winter carbon and water fluxes in pine forests. Furthermore, details of the model representations of water uptake, which are often overlooked, need further attention, and deep water access should be treated explicitly.

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