Effect of sterol structure on the transfer of sterols and phospholipids from liposomes to erythrocytes in vitro.

Human erythrocytes were incubated for 24 h with liposomes containing [3H]phosphatidylcholine, [14C]cholesterol and one of several other sterols. Of the other sterols, 3-hydroxycholest-3-en-2-one did not appear to be taken up by the cells, sterophenol was taken up at about the same rate as cholesterol, and cholesta-4,6-dien-3-one and 7-oxocholesterol were taken up much more rapidly than cholesterol. Each component of the liposomes was incorporated into the cells independently of the others and the rate of incorporation of the test sterol had little, if any, effect on the rate of incorporation of phospholipid or cholesterol. The results support the proposal that sterol exchange is mediated via the pool of monomers present in the medium rather than by a collision mechanism.