Cholesterol movement between human skin fibroblasts and phosphatidylcholine vesicles

Cultured human lung fibroblasts, incubated with cholesterol/phosphatidylcholine vesicles (cholesterol: phosphatidylcholine molar ratio 1:1) incorporated vesicle [3H]-cholesterol linearly for at least 48 h by an exchange process without gaining sterol mass. The incorporation of [3H]cholesterol by the cells was markedly enhanced in the presence of purified bovine serum albumin. A fraction of the incorporated vesicle [3H]cholesterol was esterified by the cells.

Section: Resultsmentioning

confidence: 99%

mentioning

confidence: 99%

Serum albumin enhances the uptake of [3H]cholesterol from phosphatidylcholine vesicles by cultured human fibroblasts

Slotte¹,

Björkerud²

1984

“…The implication here may be that cholesterol movement within the cell may be as likely to be as a result of membrane or vesicle movement as it is the movement of monomeric cholesterol. The movement of cholesterol from cells to extracellular particles, however, is much faster (Poznansky & Czekanski, 1982;Lange et al, 1983). An explanation for this may lie in our observation that gangliosides increase the rate of cholesterol desorption from SUVs and may do so in spite of low curvatures (Thomas & Poznansky, 1988).…”

Section: Discussionmentioning

confidence: 99%

“…The movement of cholesterol from the plasma membrane (cell surfaces) to plasma lipoproteins or phospholipid vesicles is a relatively fast process, with a halftime (ti) in the range of 1-4 h (Lange et al, 1983;Poznansky & Czekanski, 1982), whereas the movement from the plasma membrane to the intracellular membranes is a much slower process (Poznansky & Czekanski, 1982; Slotte & Lundberg, 1983; Robertson & Poznansky, 1985;Lundberg & Suominen, 1985). Three factors likely to be responsible for the large difference in cholesterol efflux rates from the two sides of the plasma membrane are: (i) the asymmetric disposition of membrane proteins; (ii) asymmetric dispositions of lipids; and (iii) the curvature of the surface from which cholesterol is leaving.…”

Section: Introductionmentioning

confidence: 99%

Effect of surface curvature on the rate of cholesterol transfer between lipid vesicles

Thomas

Poznansky

1988

The effect of surface curvature on the spontaneous movement of cholesterol between membranes was investigated by measuring the rates of cholesterol transfer from donor vesicles of various sizes to a common acceptor vesicle. Donor vesicles of size in the range 40-240 nm were prepared by extruding multilamellar dispersions through polycarbonate filters of different pore sizes under pressure. The smallest donor vesicle and the acceptor vesicles were obtained by the normal sonication procedures. The rate of cholesterol transfer, as measured by the movement of [3H]cholesterol, decreases with increasing size of the donor vesicle in an almost linear fashion. The extrapolation of the results gave a half-time (t1/2) of 16-20 h of the desorption of cholesterol from a planar bilayer, and this can be considered as a reference value for most cellular membranes which are characterized by very low curvatures. Our earlier studies have shown that the t1/2 for cholesterol efflux is influenced by the presence of gangliosides and phosphatidylethanolamine, and the asymmetric distribution of these lipids in the plasma membrane could partially account for the large difference in the rates of cholesterol movement from the two sides of the plasma membrane. The small differences in rates arising from asymmetric distribution will be magnified by the longer t1/2 obtained here for membranes of low curvatures, so that the large difference in rates might be a coupled effect of lipid asymmetry and low curvature of the plasma membrane. This, in turn, may have a role in maintaining the large differences in cholesterol/phospholipid molar ratios observed between plasma membrane and intracellular membranes.

“…The aim of the present study was to examine whether there is a spontaneous movement of sterols from the plasma membrane to the endoplasmic reticulum of cultured cells. Previous attempts to address this question have included the measurement of the esterification of plasmamembrane-derived tracer-labelled cholesterol (Lange & Matthies, 1984;Poznansky & Czekanski, 1982). The results from such studies demonstrate that hardly any of the plasma-membrane-derived rH]cholesterol can be found in the esterified form, even during prolonged incubations.…”

Section: Discussionmentioning

confidence: 99%

Movement of plasma-membrane sterols to the endoplasmic reticulum in cultured cells

Slotte

Bierman

1987

The spontaneous turnover of plasma-membrane sterols, as measured by their transfer to the endoplasmic reticulum, was measured in quiescent cultured human skin fibroblasts and monkey arterial smooth-muscle cells. The plasma-membrane sterol pool was pulse-labelled with trace amounts of either [3H]desmosterol or [3H]cholesterol. We then measured the enzymic conversion of [3H]desmosterol into [3H]cholesterol and of [3H]cholesterol into [3H]cholesteryl esters in intact cells. Depending on the probe used, markedly different transfer or conversion rates were found in these cells. In quiescent human skin fibroblasts, incubated in a serum-free medium, about 1.1% of the plasma-membrane [3H]desmosterol was converted into [3H]cholesterol/h, whereas in monkey arterial smooth-muscle cells the corresponding rate was 0.4%. Under similar experimental conditions, these cells esterified less than 0.02% (fibroblasts) and 0.12% (smooth-muscle cells) of the plasma-membrane [3H]cholesterol/h. The movement of sterols from the plasma membrane to the endoplasmic reticulum, as measured by the conversion of [3H]desmosterol into [3H]cholesterol was not blocked by colchicine, but was markedly enhanced by 3% (w/v) dimethyl sulphoxide. In all, these results indicate that plasma-membrane sterols of cultured cells are continuously transferred to the interior of the cell at a rate substantially higher than previously appreciated. This turnover of plasma-membrane sterol molecules took place even when there was no mass transfer of sterols into the cells.