scholarly journals Dynamics of platelet-activating-factor release and uptake in a human neutrophil suspension

1991 ◽  
Vol 278 (2) ◽  
pp. 453-459 ◽  
Author(s):  
M Cluzel ◽  
C A Rohde ◽  
D W MacGlashan ◽  
B J Undem ◽  
F H Chilton
Keyword(s):  
Cellular Uptake ◽  
Rate Constant ◽  
Exponential Function ◽  
Human Neutrophil ◽  
Platelet Activating Factor ◽  
Mathematical Functions ◽  
Experimental Conditions ◽  
Zero Baseline ◽  
Factor Release

The present study has examined the dynamics of platelet-activating-factor (PAF) synthesis, release and uptake in order to understand better the trafficking of PAF between cells and medium. Initial experiments indicated that the amount of PAF found on the outside of the cell remained constant well after the synthesis from a precursor had apparently stopped, and in spite of a continued capacity of the cell to take up and catabolize PAF. These results suggested that PAF produced and stored within the cell is eventually released to the outside of the cell at a rate proportional to that of cellular uptake. In order to estimate the amount of PAF released from the cell, the processes of PAF release and uptake were modelled using simple mathematical functions. It was found that, under the experimental conditions used in this study, the uptake of PAF could be expressed as an exponential function tending to a non-zero baseline. Utilizing this rate constant for the uptake of PAF with the amount of PAF outside the cell, the amount of total PAF released from the cell was estimated. Data from the model suggested PAF was released in amounts 10-fold higher than could actually be measured over 30 min. In fact, the model predicted more PAF could be released from the cell than is synthesized, suggesting that a portion of the PAF which is released is taken up and then released again to the outside of the cell. The potential for PAF and/or its intermediates to be recycled was verified by demonstrating that a large proportion of exogenously provided 1-alkyl-2-lyso-sn-glycero-3-phosphocholine is taken up by the neutrophil, converted into PAF and then released again by the cell. These results suggest that PAF trafficking between the cell and medium is complex and involves many processes, which include synthesis, release, uptake, catabolism and recycling.

Effects of Antithrombotic Drugs in a Rat Model of Aspirin-Insensitive Arterial Thrombosis

1993 ◽  
Vol 69 (05) ◽  
pp. 509-514 ◽  
Author(s):  
W A Schumacher ◽  
T E Steinbacher ◽  
C L Heran ◽  
J R Megill ◽  
S K Durham
Keyword(s):  
Arterial Thrombosis ◽  
Light And Electron Microscopy ◽  
Platelet Activating Factor ◽  
Thrombin Inhibitor ◽  
Experimental Conditions ◽  
Once Daily ◽  
Thromboxane Receptor ◽  
Vessel Patency ◽  
Electrolytic Injury ◽  
Thromboxane Receptor Antagonist

SummaryThese studies describe experimental conditions where aspirin is less effective than other antiplatelet and anticoagulant drugs in inhibiting acute arterial thrombosis. External electrolytic injury of the rat carotid artery was used to induce occlusive thrombi in 97% of vehicle-treated rats. Thrombi were revealed by light and electron microscopy to be comprised primarily of platelets enmeshed in a fibrin network. The thrombin inhibitor D-phenylalanyl-L-prolyl-L-arginyl chloromethy ketone (PPACK; 6 mg/kg, i. v.) decreased thrombus weight by 90%. Aspirin alone (1, 10 and 30 mg/kg, i. v.), dipyridamole alone (5 mg/kg i. v.) and aspirin (1 and 10 mg/kg, i. v.) in combination with dipyridamole (5 mg/kg, i. v.) did not inhibit thrombosis. The platelet-activating factor (PAF) antagonist, WEB 2086, (1 mg/kg i. v.) was also ineffective. Other drugs had intermediate activity. Thrombi were decreased 56% by the thromboxane receptor antagonist, BMS 180,291, either alone (5.8 mg/kg i.v.) or in combination with aspirin (10 mg/kg, i.v.). Heparin (900 U/kg, i.v.), warfarin (0.25 mg/kg, p.o. once daily for 3 days) and ticlopidine (200 mg/ kg, p.o. once daily for 3 days) reduced thrombus weight by 63, 73 and 43% respectively. Reductions in thrombus weight were always associated with improvements in either average blood flow or vessel patency.

The Flavonols Quercetin, Myricetin, Kaempferol, and Galangin Inhibit the Net Oxygen Consumption by Immune Complex- Stimulated Human and Rabbit Neutrophils

2014 ◽  
Vol 69 (7-8) ◽  
pp. 346-356 ◽  
Author(s):  
Andréa S. G. Figueiredo-Rinhel ◽  
Everton O. L. Santos ◽  
Luciana M. Kabeya ◽  
Ana Elisa C. S. Azzolini ◽  
Livia M. C. Simões-Ambrosio ◽  
...  
Keyword(s):  
Oxygen Consumption ◽  
Immune Complex ◽  
Respiratory Burst ◽  
Human Neutrophil ◽  
Inflammatory Diseases ◽  
Cell Types ◽  
Oxygen Electrode ◽  
Experimental Models ◽  
Human Neutrophils ◽  
Experimental Conditions

Stimulated human neutrophils exhibit increased net oxygen consumption (NOC) due to the conversion of O2 into the superoxide anion by the NADPH oxidase enzymatic complex during the respiratory burst. In several inflammatory diseases, overproduction of these oxidants causes tissue damage. The present study aims to: (a) optimize the experimental conditions used to measure the NOC in serum-opsonized zymosan (OZ)-and insoluble immune complex (i-IC)-stimulated human and rabbit neutrophils; and (b) compare the effect of four flavonols (quercetin, myricetin, kaempferol, and galangin) on this activity. We used a Clark-type oxygen electrode to measure the NOC of stimulated neutrophils. Eliciting the neutrophil respiratory burst with OZ and i-IC yielded similar maximum O2 uptake levels within the same species, but the human neutrophil NOC was almost four times higher than the rabbit neutrophil NOC. The optimal experimental conditions established for both cell types were 4·106 neutrophils mL-1, 2 mg mL-1 OZ, and 240 µg mL-1 i-IC. Upon stimulation with OZ or i-IC, the tested flavonols reduced the human and rabbit neutrophil NOC in the same order of potency - quercetin and galangin were the most and the least potent, respectively. These compounds were around four times more effective in inhibiting the rabbit as compared to the human neutrophil NOC, respectively. The four flavonols were not toxic to human or rabbit neutrophils. The experimental conditions used are suitable for both the determination of human and rabbit neutrophil NOC and for the assessment of the modulatory effects of natural compounds on these activities. The relationship between the level of NOC and the inhibitory potency of the flavonols suggests that rabbit neutrophils can be useful experimental models to predict the effect of drugs on immune complexstimulated human neutrophils.

Electron transfer between ferrocene and hexacyanoferrate(III) across the water/1,2-dichloroethane interface

1988 ◽  
Vol 53 (5) ◽  
pp. 903-911 ◽  
Author(s):  
Josef Hanzlík ◽  
Jan Hovorka ◽  
Zdeněk Samec ◽  
Štefan Toma
Keyword(s):  
Electron Transfer ◽  
Aqueous Phase ◽  
Rate Constant ◽  
Potential Range ◽  
Ion Transfer ◽  
Potential Sweep ◽  
Experimental Conditions ◽  
Chemical Decomposition ◽  
Kinetics Of

Kinetics of electron transfer between ferrocene or its derivative (1,1'-diethyl- or 1,1'-distearoylferrocene) in dichloroethane and hexacyanoferrate(III) in water was studied by means of convolution potential sweep voltammetry. Within the accessible range of experimental conditions no effect of either the potential or concentrations of reactants on the rate constant of electron transfer from the organic to the aqueous phase (ko→w = 1 . 10-7 m4 mol-1 s-1) was observed. Electron transfer was shown to occur far from the potential range, in which the ferricenium ion transfer can take place. However, the reaction was complicated by the chemical decomposition of ferricenium in dichloroethane (k = 0·346 s-1).

scholarly journals Mathematical Functions to Model the Depth Distribution of Soil Organic Carbon in a Range of Soils from New South Wales, Australia under Different Land Uses

Soil Systems ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 46 ◽  
Author(s):  
Brian W. Murphy ◽  
Brian R. Wilson ◽  
Terry Koen
Keyword(s):  
Organic Carbon ◽  
Soil Organic Carbon ◽  
Exponential Function ◽  
Depth Distribution ◽  
Soil Depth ◽  
New South ◽  
Exponential Functions ◽  
Two Phase ◽  
Mathematical Functions ◽  
South Wales

The nature of depth distribution of soil organic carbon (SOC) was examined in 85 soils across New South Wales with the working hypothesis that the depth distribution of SOC is controlled by processes that vary with depth in the profile. Mathematical functions were fitted to 85 profiles of SOC with SOC values at depth intervals typically of 0–5, 5–10, 10–20, 20–30, 30–40, 40–50, 50–60, 60–70, 70–80, 80–90 and 90–100 cm. The functions fitted included exponential functions of the form SOC = A exp (Bz); SOC = A + B exp (Cz) as well as two phase exponential functions of the form SOC = A + B exp (Cz) + D exp (Ez). Other functions fitted included functions where the depth was a power exponent or an inverse term in a function. The universally best-fitting function was the exponential function SOC = A + B exp (Cz). When fitted, the most successful function was the two-phase exponential, but in several cases this function could not be fitted because of the large number of terms in the function. Semi-log plots of log values of the SOC against soil depth were also fitted to detect changes in the mathematical relationships between SOC and soil depth. These were hypothesized to represent changes in dominant soil processes at various depths. The success of the exponential function with an added constant, the two-phase exponential functions, and the demonstration of different phases within the semi-log plots confirmed our hypothesis that different processes were operating at different depths to control the depth distributions of SOC, there being a surface component, and deeper soil component. Several SOC profiles demonstrated specific features that are potentially important for the management of SOC profiles in soils. Woodland and to lesser extent pasture soils had a definite near surface zone within the SOC profile, indicating the addition of surface materials and high rates of fine root turnover. This zone was much less evident under cropping.

The Rate-Constant for the Recombination of Methyl Radicals

1986 ◽  
Vol 39 (8) ◽  
pp. 1257 ◽  
Author(s):  
NL Arthur ◽  
JC Biordi
Keyword(s):  
Experimental Data ◽  
High Pressure ◽  
Rate Constant ◽  
Rate Constants ◽  
The Other ◽  
Methyl Radicals ◽  
Experimental Conditions ◽  
Temperature Range ◽  
Best Value ◽  
Limiting Value

Rate constants for the recombination of CH3 radicals have been measured by means of the rotating sector technique in the temperature range 373- 463 K, and at a pressure of 30 Torr . CH3 radicals were produced by the photolysis of acetone, and the experimental data were fitted to sector curves generated from Shepp's theory. The results give kb = (2.81�0.22)×1013 cm3 mol-1 s-1, which, under the chosen experimental conditions, is close to its high-pressure limiting value. A comparison is made with the other values of the rate constant reported in the literature, and a best value is suggested.

scholarly journals Mathematical Modelling of Water Absorption Kinetics Using Empirical and Phenomenological Models for Millets

2019 ◽  
Vol 8 (6) ◽  
pp. 1016-1021 ◽  
Keyword(s):  
Activation Energy ◽  
Water Absorption ◽  
Pearl Millet ◽  
Rate Constant ◽  
Finger Millet ◽  
Effective Diffusivity ◽  
Process Time ◽  
Absorption Kinetics ◽  
Experimental Conditions ◽  
Sigmoidal Model

Steeping is one of the major pre-treatment which can reduce anti-nutritional factors without losing dietary fibre and polyphenols unlike in dehulling. In the current study water absorption characteristics of pearl millet and finger millet during steeping at temperature 10°C, 20°C, 30°C, 40°C and 50°C were calculated. Two empirical and one phenomenological model were used to simulate water absorption kinetics. Both the Peleg model and Omoto model were found adequately capable to predict water uptake of pearl millet and finger millet under the designed experimental conditions with regression coefficient more than 0.96. Due to comparatively high variation in grain volume during the hydration process and longer process time, sigmoidal model cannot be utilized for calculation of effective diffusivity and activation energy. Peleg’s rate constant shows an inverse relationship with steeping temperature. The activation energy was calculated by substituting effective diffusivity with reciprocal of Peleg’s rate constant in Arrhenius equation and was found 25.97 kJ/mol and 32.36 kJ/mol respectively for pearl millet and finger millet.

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