Kinetics of ammonium and nitrate uptake by eucalypt roots and associated proton fluxes measured using ion selective microelectrodes

2003 ◽  
Vol 30 (11) ◽  
pp. 1165 ◽  
Author(s):  
Trevor P. Garnett ◽  
Sergey N. Shabala ◽  
Philip J. Smethurst ◽  
Ian A. Newman
Keyword(s):  
Nitrate Uptake ◽  
Gradual Increase ◽  
Eucalyptus Nitens ◽  
Proton Efflux ◽  
Initial Exposure ◽  
High Affinity ◽  
Proton Fluxes ◽  
Nitrogen Concentrations ◽  
Highly Correlated ◽  
Kinetics Of

Ion-selective microelectrodes were used non-invasively to measure the concentration dependence of NH4+ and NO3– fluxes around the roots of intact solution-cultured Eucalyptus nitens (Deane & Maiden) Maiden. In addition, NH4+ and H+ fluxes were measured simultaneously at a range of NH4+ concentrations, and NO3– and H+ fluxes were measured simultaneously at a range of NO3– concentrations. Nitrogen concentrations ranged from 10–250 μM, i.e. in the range corresponding to the high affinity transport system (HATS). Both NH4+ and NO3– fluxes exhibited saturating Michaelis–Menten-style kinetics. The Km was 16 μM for NH4+ and 18 μM for NO3–. Values of Vmax were 53 nmol m–2 s–1 for NH4+ and 37 nmol m–2 s–1 for NO3–. Proton fluxes were highly correlated with NH4+ and NO3– fluxes, but the relationships were different. Proton efflux increased with increasing NH4+ concentration and mirrored the changing NH4+ fluxes. The ratio between NH4+ and H+ fluxes was 1 : –1.6. Proton influx was evident with initial exposure to NO3–, with the flux stoichiometry for NO3– : H+ being 1 : 1.4. Subsequent increases in NO3– concentration caused a gradual increase in H+ efflux such that the flux stoichiometry for NO3– : H+ became 1 : –0.8. The presence of 100 μM NH4+ greatly reduced NO3– fluxes and caused a large and constant H+ efflux. These results are evidence that E. nitens has a preference for NH4+ as a source of N, and that the fluxes of NH4+ and NO3– are quantitatively linked to H+ flux.

The shoot is important for high-affinity nitrate uptake in Egeria densa, a submerged vascular plant

2012 ◽  
Vol 125 (5) ◽  
pp. 669-678 ◽  
Author(s):  
Shu Takayanagi ◽  
Yuma Takagi ◽  
Akifumi Shimizu ◽  
Hiroshi Hasegawa
Keyword(s):  
Nitrate Uptake ◽  
Vascular Plant ◽  
Egeria Densa ◽  
High Affinity

Systems analysis of digoxin kinetics and inotropic response in the rat heart: effects of calcium and KB-R7943

2004 ◽  
Vol 287 (4) ◽  
pp. H1857-H1867 ◽  
Author(s):  
Michael Weiss ◽  
Myoungki Baek ◽  
Wonku Kang
Keyword(s):  
Rat Heart ◽  
Site Response ◽  
High Capacity ◽  
Left Ventricular ◽  
Limiting Factor ◽  
Inotropic Response ◽  
Influx Rate ◽  
High Affinity ◽  
Reverse Mode ◽  
Kinetics Of

To gain more insight into the mechanistic processes controlling the kinetics of inotropic response of digoxin in the perfused whole heart, an integrated kinetic model was developed incorporating digoxin uptake, receptor binding (Na+-K+-ATPase inhibition), and cellular events linking receptor occupation and response. The model was applied to data obtained in the single-pass Langendorff-perfused rat heart for external [Ca2+] of 0.5 and 1.5 mM under control conditions and in the presence of the reverse-mode Na+/Ca2+ exchange inhibitor KB-R7943 (0.1 μM) in perfusate. Outflow concentration and left ventricular developed pressure data measured for three consecutive doses (15, 30, and 45 μg) in each heart were analyzed simultaneously. While disposition kinetics of digoxin was determined by interaction with a heterogeneous receptor population consisting of a high-affinity/low-capacity and a low-affinity/high- capacity binding site, response generation was >80% mediated by binding to the high-affinity receptor. Digoxin sensitivity increased at lower external [Ca2+] due to higher stimulus amplification. Coadministration of KB-R7943 significantly reduced the positive inotropic effect of digoxin at higher doses (30 and 45 μg) and led to a saturated and delayed receptor occupancy-response relationship in the cellular effectuation model. The results provide further evidence for the functional heterogeneity of the Na+-K+-ATPase and suggest that in the presence of KB-R7943 a reduction of the Ca2+ influx rate via the reverse mode Na+/Ca2+ exchanger might become the limiting factor in digoxin response generation.

Stress–response relationships related to ageing and death of orthodox seeds: a study comparing viability and RNA integrity in soya bean (Glycine max) cv. Williams 82

2020 ◽  
Vol 30 (2) ◽  
pp. 161-172
Author(s):  
Christina Walters ◽  
Margaret B. Fleming ◽  
Lisa M. Hill ◽  
Emma J. Dorr ◽  
Christopher M. Richards
Keyword(s):  
Degradation Kinetics ◽  
Rna Degradation ◽  
Soya Bean ◽  
Rna Integrity ◽  
Viability Loss ◽  
Rna Integrity Number ◽  
Oxidative Stresses ◽  
Degradation Rates ◽  
Highly Correlated ◽  
Kinetics Of

AbstractCharacterizing non-lethal damage within dry seeds may allow us to detect early signs of ageing and accurately predict longevity. We compared RNA degradation and viability loss in seeds exposed to stressful conditions to quantify relationships between degradation rates and stress intensity or duration. We subjected recently harvested (‘fresh’) ‘Williams 82’ soya bean seeds to moisture, temperature and oxidative stresses, and measured time to 50% viability (P50) and rate of RNA degradation, the former using standard germination assays and the latter using RNA Integrity Number (RIN). RIN values from fresh seeds were also compared with those from accessions of the same cultivar harvested in the 1980s and 1990s and stored in the refrigerator (5°C), freezer (−18°C) or in vapour above liquid nitrogen (−176°C). Rates of viability loss (P50−1) and RNA degradation (RIN⋅d−1) were highly correlated in soya bean seeds that were exposed to a broad range of temperatures [holding relative humidity (RH) constant at about 30%]. However, the correlation weakened when fresh seeds were maintained at high RH (holding temperature constant at 35°C) or exposed to oxidizing agents. Both P50−1 and RIN⋅d−1 parameters exhibited breaks in Arrhenius behaviour near 50°C, suggesting that constrained molecular mobility regulates degradation kinetics of dry systems. We conclude that the kinetics of ageing reactions at RH near 30% can be simulated by temperatures up to 50°C and that RNA degradation can indicate ageing prior to and independent of seed death.

scholarly journals The Arabidopsis CHL1 protein plays a major role in high-affinity nitrate uptake

1998 ◽  
Vol 95 (25) ◽  
pp. 15134-15139 ◽  
Author(s):  
R. Wang ◽  
D. Liu ◽  
N. M. Crawford
Keyword(s):  
Nitrate Uptake ◽  
High Affinity

Kinetics of serotonin uptake in isolated rabbit lungs

1989 ◽  
Vol 66 (5) ◽  
pp. 2328-2337 ◽  
Author(s):  
F. A. Peeters ◽  
T. A. Bronikowski ◽  
C. A. Dawson ◽  
J. H. Linehan ◽  
H. Bult ◽  
...  
Keyword(s):  
Endothelial Function ◽  
Bolus Injection ◽  
Rabbit Lung ◽  
Future Studies ◽  
High Affinity ◽  
Lung Physiology ◽  
Extraction Pattern ◽  
Uptake Data ◽  
5 Ht Uptake ◽  
Kinetics Of

The single-pass, bolus-injection method was used to study the effect of serotonin (5-HT) concentration on the extraction of 5-HT by isolated perfused rabbit lungs. The extraction pattern suggested that an uptake model, which includes multiple parallel uptake processes, provided a better representation of the data than the simple Michaelis-Menten equation, which has commonly been used to fit the saturable uptake data in previous studies. In particular, the rabbit lung data could be fit with two such parallel pathways. Since the 5-HT uptake could virtually be completely blocked by imipramine, both pathways can be considered to be carrier-mediated processes. The high-affinity pathway was saturable within the range of concentrations studied, with a Km and Vmax of approximately 0.84 microM and 0.21 nmol.s-1.g wet lung wt-1. The Km for the low-affinity pathway was larger than concentrations for which accurate uptake measurements are practical in the perfused organ. Thus, for the low-affinity pathway, only Vmax/Km was identifiable. Vmax/Km values for the high- and low-affinity pathways were approximately 2.87 and 0.35 ml/s, respectively. The results suggest that it will be worthwhile to investigate the behavior of these uptake parameters in response to changes in lung physiology and endothelial function in future studies.

RV11 (Propionyl Erythromycin Mercaptosuccinate) Pharmacokinetics in Bronchial Secretions

1986 ◽  
Vol 14 (3) ◽  
pp. 137-141 ◽  
Author(s):  
E Concia ◽  
P Marone ◽  
G C Moreo ◽  
C Sardi ◽  
R Braschi
Keyword(s):  
Oral Dose ◽  
Plasma Concentrations ◽  
Bronchial Secretion ◽  
Dose Equivalent ◽  
Bronchial Secretions ◽  
Definitive Evidence ◽  
High Affinity ◽  
Diagnostic Bronchoscopy ◽  
Erythromycin Base ◽  
Kinetics Of

The kinetics of RV11 (propionyl erythromycin mercaptosuccinate) in serum and bronchial secretions was investigated in heterogeneous bronchopneumopathic patients requiring diagnostic bronchoscopy. A single oral dose, equivalent to 500 mg of erythromycin base, was administered to all patients and the bronchial secretion and plasma concentrations were determined after 2, 3 and 4 hr. The bronchial secretion and plasma levels consistently exceeded those reported previously for erythromycin per os, suggesting that RV11 may have an unusually high affinity for bronchial secretions in humans. The results of this study also suggested that RV11 might have different kinetics in bronchial secretions and serum, though further studies are required to provide definitive evidence.

scholarly journals Kinetics of binding, endocytosis, and recycling of EGF receptor mutants

1992 ◽  
Vol 117 (1) ◽  
pp. 203-212 ◽  
Author(s):  
S Felder ◽  
J LaVin ◽  
A Ullrich ◽  
J Schlessinger
Keyword(s):  
Point Mutation ◽  
Phorbol Ester ◽  
Egf Receptor ◽  
Receptor Internalization ◽  
Affinity Binding ◽  
High Affinity Binding ◽  
High Affinity ◽  
Low Concentrations ◽  
Internalization Rate ◽  
Kinetics Of

This report describes analysis of factors which regulate the binding of EGF to EGF receptor, receptor internalization, and receptor recycling. Three different methods were used to inhibit high-affinity EGF binding as measured at equilibrium: treatment of cells with an active phorbol ester (PMA), binding of a mAb directed against the EGF receptor (mAb108), and truncation of most of the cytoplasmic domain of the receptor. These treatments reduced the rate at which low concentrations of EGF bound to cells, but did not affect the rate of EGF dissociation. We conclude that high-affinity EGF binding on living cells results from a difference in the apparent on rate of EGF binding. We then used these conditions and cell lines to test for the rate of EGF internalization at different concentrations of EGF. We demonstrate that internalization of the EGF receptor is stimulated roughly 50-fold at saturating concentrations of EGF, but is stimulated an additional two- to threefold at low concentrations (less than 1 nM). Four treatments reduce the rate of internalization of low concentrations of EGF to the rate seen at saturating EGF concentrations. Phorbol ester treatment and mAb108 binding to "wild type" receptor reduce this rate (and reduce high-affinity binding). Point mutation at Lys721 (kinase negative EGF receptor) and point mutation at Thr654 (removing a major site of protein kinase C phosphorylation) reduce the internalization rate, without affecting high-affinity binding. We suggest that while EGF stimulates endocytosis for all receptors, high-affinity receptors bind and are internalized more quickly than low-affinity receptors. Tyrosine kinase activity and the Thr654 region appear necessary for this response.

scholarly journals Hexokinase Regulates Kinetics of Glucose Transport and Expression of Genes Encoding Hexose Transporters inSaccharomyces cerevisiae

2000 ◽  
Vol 182 (23) ◽  
pp. 6815-6818 ◽  
Author(s):  
Thomas Petit ◽  
Jasper A. Diderich ◽  
Arthur L. Kruckeberg ◽  
Carlos Gancedo ◽  
Karel Van Dam
Keyword(s):  
Glucose Transport ◽  
Mrna Levels ◽  
High Affinity ◽  
Expression Of Genes ◽  
Hexose Transporters ◽  
Genes Encoding ◽  
High Concentrations ◽  
Kinetics Of ◽  
Very High ◽  
Null Strain

ABSTRACT Glucose transport kinetics and mRNA levels of different glucose transporters were determined in Saccharomyces cerevisiaestrains expressing different sugar kinases. During exponential growth on glucose, a hxk2 null strain exhibited high-affinity hexose transport associated with an elevated transcription of the genesHXT2 and HXT7, encoding high-affinity transporters, and a diminished expression of the HXT1 andHXT3 genes, encoding low-affinity transporters. Deletion ofHXT7 revealed that the high-affinity component is mostly due to HXT7; however, a previously unidentified very-high-affinity component (Km = 0.19 mM) appeared to be due to other factors. Expression of genes encoding hexokinases from Schizosaccharomyces pombe orYarrowia lipolytica in a hxk1 hxk2 glk1 strain prevented derepression of the high-affinity transport system at high concentrations of glucose.

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