scholarly journals Reverse cholesterol transport in the isolated perfused rat spleen

1990 ◽  
Vol 268 (2) ◽  
pp. 499-505 ◽  
Author(s):  
M A Mindham ◽  
P A Mayes ◽  
N E Miller
Keyword(s):  
Whole Blood ◽  
Chemical Potential ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Potential Gradient ◽  
Cholesterol Transport ◽  
Unesterified Cholesterol ◽  
Chemical Potential Gradient ◽  
High Specific Radioactivity

1. A method has been developed which enables the rat spleen to be loaded in vivo with [3H]cholesterol to a high specific radioactivity using cholesterol-labelled erythrocytes. The erythrocytes were shown to be rapidly degraded by the spleen and not released intact during subsequent perfusion. 2. When labelled spleens were perfused with whole blood or serum, lipoproteins in the high-density lipoprotein (HDL) range were shown to be the principal lipoprotein vehicles for the removal of cholesterol, the specific radioactivity of cholesterol being much greater in the HDL fractions than in other lipoproteins, particularly in the d 1.175-1.210 fraction. 3. The formation of [3H]cholesteryl ester was restricted to the major HDL fractions. 4. Experiments utilizing individual HDL fractions added to a basal perfusate indicated that HDL1 (d 1.050-1.085) was of less importance in the removal of cholesterol from the spleen than HDL subfractions of higher density. Also, a decrease in density of the lipoproteins was observed during perfusion, concurrent with uptake of cholesterol, especially in the d 1.085-1.125 subfraction. 5. When [3H]cholesterol-labelled spleens were perfused with whole blood, about half of the radioactivity released was detected in erythrocytes, indicating a rapid exchange or transport of cholesterol. Thus erythrocytes could play an important role in the transfer of unesterified cholesterol when the chemical potential gradient is favourable.

scholarly journals Reverse cholesterol transport in the rat. Studies using the isolated perfused spleen in conjunction with the perfused liver

1991 ◽  
Vol 279 (2) ◽  
pp. 503-508 ◽  
Author(s):  
M A Mindham ◽  
P A Mayes
Keyword(s):  
Reverse Cholesterol Transport ◽  
Liver Perfusion ◽  
Density Lipoprotein ◽  
Cholesterol Transport ◽  
Perfused Liver ◽  
Unesterified Cholesterol ◽  
Rapid Exchange ◽  
Net Release ◽  
Complete Process

1. A new method combining the use of an isolated perfused extrahepatic tissue with a perfused liver was developed as a model system for the study of reverse cholesterol transport. Rat spleens, initially labelled in vivo with [3H]cholesterol, were perfused for 3 h with whole blood. The spleen was then replaced with an isolated rat liver, whose uptake of cholesterol from the spleen-derived blood and excretion of cholesterol into bile constituents were determined. 2. During spleen perfusion, a net release of cholesterol mass and radioactivity to lipoproteins was observed. 3. During liver perfusion, there was also a rapid exchange or transport of unesterified cholesterol between high-density lipoprotein (HDL) and the liver, in particular with HDL2 (d = 1.085-1.125). 4. The liver showed an increased uptake of cholesteryl ester from serum that had previously been used in spleen perfusion. 5. Approximately half of the [3H]cholesterol released by the spleen was recovered in erythrocytes. During subsequent liver perfusion there was a substantial uptake of radioactivity from the erythrocytes, although less than that recorded from serum lipoproteins. 6. In all experiments there was significant excretion of [3H]cholesterol into bile; most (85%) was in bile acids. Thus the complete process of reverse cholesterol transport is observed in this dual-perfusion system.

scholarly journals An alternative procedure for incorporating radiolabelled cholesteryl ester into human plasma lipoproteins in vitro

1985 ◽  
Vol 226 (1) ◽  
pp. 319-322 ◽  
Author(s):  
D C K Roberts ◽  
N E Miller ◽  
S G L Price ◽  
D Crook ◽  
C Cortese ◽  
...  
Keyword(s):  
Cholesteryl Ester ◽  
Human Plasma ◽  
Specific Radioactivity ◽  
Density Lipoprotein ◽  
Plasma Lipoproteins ◽  
Cholesteryl Esters ◽  
Simple Method ◽  
High Specific Radioactivity

A simple method has been developed for labelling human plasma lipoproteins to high specific radioactivity with radioactive cholesteryl esters in vitro. After isolation by preparative ultracentrifugation, the selected lipoprotein was incubated for 30 min at 4 degrees C in human serum (d greater than 1.215) that had been prelabelled with [4-14C]cholesteryl oleate or [1,2-3H]cholesteryl linoleate, and was then re-isolated by ultracentrifugation. All major lipoprotein classes were labelled by the procedure. Specific radioactivities of up to 18 d.p.m. pmol-1 (46 d.p.m. ng-1) were achieved. When radiolabelled high-density lipoprotein was infused intravenously, the radioactive cholesteryl ester behaved in vivo indistinguishably from endogenous cholesteryl esters produced by the lecithin (phosphatidylcholine): cholesterol acyltransferase reaction.

Active sodium transport in toad bladder despite removal of serosal potassium

1965 ◽  
Vol 208 (2) ◽  
pp. 401-406 ◽  
Author(s):  
Alvin Essig
Keyword(s):  
Sodium Transport ◽  
Chemical Potential ◽  
Potential Gradient ◽  
Ringer Solution ◽  
Active Sodium ◽  
Chemical Potential Gradient ◽  
Control Value ◽  
Active Sodium Transport ◽  
Solution Bathing ◽  
Determining Factor

Previous studies have demonstrated that removal of potassium from sodium-Ringer solution bathing the serosal surface of the toad badder depressed net sodium transport to some 5% of control value, whereas with choline-Ringer solution as serosal medium removal of serosal potassium depressed net sodium transport only to some 55% of control value. Although transport is down a chemical potential gradient in the latter situation, it appears to be an active process, for it is depressed by anaerobiosis, and persists against an electrochemical potential gradient. The data suggest that the concentration of potassium at the serosal aspect of the sodium pump is not in itself the rate-determining factor for active sodium transport following removal of serosal potassium.

scholarly journals Exogenous cholesterol transport in rabbit plasma lipoproteins

1973 ◽  
Vol 134 (2) ◽  
pp. 531-537 ◽  
Author(s):  
L. L. Rudel ◽  
J. M. Felts ◽  
M. D. Morris
Keyword(s):  
Free Cholesterol ◽  
Specific Radioactivity ◽  
Plasma Lipoproteins ◽  
Cholesterol Transport ◽  
Low Density ◽  
Cholesteryl Esters ◽  
Exogenous Cholesterol ◽  
Rate Of Increase ◽  
Chylomicron Metabolism

1. The appearance of exogenous cholesterol in free cholesterol and ester cholesterol of plasma chylomicra, very-low-density (VLD), low-density (LD) and high-density (HD) lipoproteins was studied in unanaesthetized rabbits after ingestion of a meal containing 5% fat and 0.08% [3H]cholesterol. 2. The specific radioactivity of ester cholesterol of VLD lipoproteins reached the highest value of any lipoprotein fraction and for each lipoprotein it increased at a faster rate and reached a higher maximum than that of free cholesterol; the maximum in VLD lipoproteins occurred later than in chylomicra. 3. The pattern of appearance of exogenous cholesterol in chylomicra and VLD lipoproteins of plasma was similar to the pattern previously observed in lymph. The specific radioactivity of ester cholesterol in plasma VLD lipoproteins was higher than that in chylomicra in spite of a larger pool size and dilution of cholesteryl esters from VLD lipoproteins produced by the liver. These results support the concept that during absorption the major portion of exogenous cholesterol is transported in VLD lipoproteins as ester cholesterol. 4. The specific radioactivity of ester cholesterol of chylomicra and VLD lipoproteins increased at a faster rate than that of LD and HD lipoproteins. However, the rate of increase and the absolute values of the specific radioactivity in LD and HD lipoproteins were identical. Since cholesteryl esters are thought not to exchange between lipoproteins, this observation supports the hypothesis that a result of VLD lipoprotein and chylomicron metabolism is the formation of LD and HD lipoproteins. 5. Results in vivo showed that the free cholesterol of individual plasma lipoproteins does not equilibrate within a period of 24h.

Novel Double-Isotope Technique for Enzymatic Assay of Catecholamines, Permitting High Precision, Sensitivity and Plasma Sample Capacity

1981 ◽  
Vol 61 (5) ◽  
pp. 591-598 ◽  
Author(s):  
M. J. Brown ◽  
D. A. Jenner
Keyword(s):  
Plasma Sample ◽  
Specific Radioactivity ◽  
High Specific Radioactivity ◽  
Coefficients Of Variation ◽  
Isotope Technique ◽  
Noradrenaline And Adrenaline ◽  
Radioenzymatic Assays ◽  
Double Isotope ◽  
Catecholamine Concentration

1. A novel use of a double-isotope method is described which allows radioenzymatic assays to combine precision and sensitivity. 2. In the catechol O-methyltransferase assay separate portions of each plasma sample are incubated with either S-[3H]- or S-[14C]-adenosyl-l-methionine. Standards of noradrenaline and adrenaline are added to the latter portions and are thus converted into standards of [14C]metadrenalines. These are added to the 3H-labelled portions after the incubation, where they function as tracers. 3. The final recovery of 14C radioactivity corrects for (a) the efficiency of methylation in the plasma sample concerned and (b) the recovery of metadrenalines during the extraction procedures. 4. The 3H/14C ratio is constant in each assay for a given catecholamine concentration and is determined for samples to which standards of noradrenaline and adrenaline are added to the 3H- (as well as the I4C-) labelled portions before the initial incubation. 5. The sensitivity of the assay is increased by using high specific radioactivity S-[3H]adenosyl-l-methionine (60-85 Ci/mmol), and low backgrounds are maintained by catecholamine depletion in vivo in the rats used for enzyme preparation. 6. Both catecholamines (1.5 pg/ml; 10 pmol/l) may be detected; the coefficients of variation are 3.0 and 3.2% for noradrenaline and adrenaline respectively (intra-assay) and 4.6 and 5.0% (inter-assay).

scholarly journals Particle motion driven by solute gradients with application to autonomous motion: continuum and colloidal perspectives

2010 ◽  
Vol 667 ◽  
pp. 216-259 ◽  
Author(s):  
JOHN F. BRADY
Keyword(s):  
Chemical Potential ◽  
Particle Surface ◽  
Fluid Motion ◽  
Potential Gradient ◽  
Coarse Grained ◽  
Gradient Force ◽  
Total Force ◽  
Chemical Potential Gradient ◽  
Back Flow ◽  
Autonomous Motion

Diffusiophoresis, the motion of a particle in response to an externally imposed concentration gradient of a solute species, is analysed from both the traditional coarse-grained macroscopic (i.e. continuum) perspective and from a fine-grained micromechanical level in which the particle and the solute are treated on the same footing as Brownian particles dispersed in a solvent. It is shown that although the two approaches agree when the solute is much smaller in size than the phoretic particle and is present at very dilute concentrations, the micromechanical colloidal perspective relaxes these restrictions and applies to any size ratio and any concentration of solute. The different descriptions also provide different mechanical analyses of phoretic motion. At the continuum level the macroscopic hydrodynamic stress and interactive force with the solute sum to give zero total force, a condition for phoretic motion. At the colloidal level, the particle's motion is shown to have two contributions: (i) a ‘back-flow’ contribution composed of the motion of the particle due to the solute chemical potential gradient force acting on it and a compensating fluid motion driven by the long-range hydrodynamic velocity disturbance caused by the chemical potential gradient force acting on all the solute particles and (ii) an indirect contribution arising from the mutual interparticle and Brownian forces on the solute and phoretic particle, that contribution being non-zero because the distribution of solute about the phoretic particle is driven out of equilibrium by the chemical potential gradient of the solute. At the colloidal level the forces acting on the phoretic particle – both the statistical or ‘thermodynamic’ chemical potential gradient and Brownian forces and the interparticle force – are balanced by the Stokes drag of the solvent to give the net phoretic velocity.For a particle undergoing self-phoresis or autonomous motion, as can result from chemical reactions occurring asymmetrically on a particle surface, e.g. catalytic nanomotors, there is no imposed chemical potential gradient and the back-flow contribution is absent. Only the indirect Brownian and interparticle forces contribution is responsible for the motion. The velocity of the particle resulting from this contribution can be written in terms of a mobility times the integral of the local ‘solute pressure’ – the solute concentration times the thermal energy – over the surface of contact between the particle and the solute. This was the approach taken by Córdova-Figueroa & Brady (Phys. Rev. Lett., vol. 100, 2008, 158303) in their analysis of self-propulsion. It is shown that full hydrodynamic interactions can be incorporated into their analysis by a simple scale factor.

Transport of adsorbates in microporous solids: arbitrary isotherm

1994 ◽  
Vol 446 (1926) ◽  
pp. 15-37 ◽  
Keyword(s):  
Driving Force ◽  
Chemical Potential ◽  
Transport Model ◽  
Potential Gradient ◽  
Isosteric Heat ◽  
Chemical Potential Gradient ◽  
Equilibrium Data ◽  
Random Walk Theory ◽  
Microporous Solids ◽  
Good Agreement

The transport of adsorbates in microporous random networks is examined in the presence of an arbitrary nonlinear local isotherm. The transport model is developed by means of a correlated random walk theory, assuming pore mouth equilibrium at an intersection in the network and a local chemical potential gradient driving force. The results demonstrate more rapid increase of the transport coefficient with adsorbed concentration than straightforward use of the classical Darken equation. Application of the theory to experimental data for diffusion of carbon dioxide in carbolac, with various local isotherm choices, shows good agreement when the activation energy associated with the mobility based on a chemical potential gradient driving force is taken as the Henry’s law region isosteric heat of adsorption. Furthermore, a combination of transport and equilibrium data can discriminate better among competing isotherms than the latter data alone.

scholarly journals Evidence for reverse cholesterol transport in vivo from liver endothelial cells to parenchymal cells and bile by high-density lipoprotein

1990 ◽  
Vol 268 (3) ◽  
pp. 685-691 ◽  
Author(s):  
H F Bakkeren ◽  
F Kuipers ◽  
R J Vonk ◽  
T J C Van Berkel
Keyword(s):  
Endothelial Cells ◽  
High Density Lipoprotein ◽  
Kupffer Cells ◽  
Reverse Cholesterol Transport ◽  
Density Lipoprotein ◽  
Cholesterol Transport ◽  
Cholesterol Esters ◽  
Liver Endothelial Cells ◽  
Parenchymal Cells

Acetylated low-density lipoprotein (acetyl-LDL), biologically labelled in the cholesterol moiety of cholesteryl oleate, was injected into control and oestrogen-treated rats. The serum clearance, the distribution among the various lipoproteins, the hepatic localization and the biliary secretion of the [3H]cholesterol moiety were determined at various times after injection. In order to monitor the intrahepatic metabolism of the cholesterol esters of acetyl-LDL in vivo, the liver was subdivided into parenchymal, endothelial and Kupffer cells by a low-temperature cell-isolation procedure. In both control and oestrogen-treated rats, acetyl-LDL is rapidly cleared from the circulation, mainly by the liver endothelial cells. Subsequently, the cholesterol esters are hydrolysed, and within 1 h after injection, about 60% of the cell- associated cholesterol is released. The [3H]cholesterol is mainly recovered in the high-density lipoprotein (HDL) range of the serum of control rats, while low levels of radioactivity are detected in serum of oestrogen-treated rats. In control rats cholesterol is transported from endothelial cells to parenchymal cells (reverse cholesterol transport), where it is converted into bile acids and secreted into bile. The data thus provide evidence that HDL can serve as acceptors for cholesterol from endothelial cells in vivo, whereby efficient delivery to the parenchymal cells and bile is assured. In oestrogen-treated rats the radioactivity from the endothelial cells is released with similar kinetics as in control rats. However, only a small percentage of radioactivity is found in the HDL fraction and an increased uptake of radioactivity in Kupffer cells is observed. The secretion of radioactivity into bile is greatly delayed in oestrogen-treated rats. It is concluded that, in the absence of extracellular lipoproteins, endothelial cells can still release cholesterol, although for efficient transport to liver parenchymal cells and bile, HDL is indispensable.

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