Alteration of membrane phospholipid bilayer organization in human erythrocytes during drug-induced endocytosis.

Abstract

A B S T R A C T Our plan was to evaluate the potentially important role of phospholipids in erythrocyte shape alterations by determining if their orientation was altered during endocytosis. Stomatocytosis and endocytosis were induced in normal intact human erythrocytes by incubation with three agents: primaquine, vinblastine, and chlorpromazine, each of which has its own requirements and time course for producing endocytosis. The organization of the phospholipid bilayer was assessed by measuring the extent of degradation of phophatidylcholine (PC), phophatidylethanolamine (PE), phosphatidylserine (PS), and sphingomyelin (SM) produced by exposure of erythrocytes to a nonpenetrating protease-free phospholipase A2 alone or in combination with a purified sphingomyelinase as well. The induction of stomatocytosis did not change this orientation. However, correlating with the onset of endocytosis but not its extent, there was an increase ip PE degradation, which could be detected regularly only by use of phospholipase A2 alone. Use of the combination of phospholipase A2 and sphingomyelinase showed that the extent and course of endocytosis was paralleled by an apparent movement of PC and SM from the outer to the inner half of the lipid bilayer. Since no further PE was hydrolyzed and because no PS was ever degraded, this inward movement of PC and SM did not represent the establishment of complete symmetry in the membrane. By adjusting the experimental design it was possible to implicate the A preliminary report of this work was presented at the

The Aging Process of Human Neonatal Erythrocytes

“…The differences in the phospholipid degradation patterns between adult and neonatal red cells may arise in part from receptor-mediated endocytosis in neonatal red cells. Such differences bear some similarity to the differences between normal and primaquine-treated normal cells noted after drug-induced endocytosis (23). Differences in lipid-protein interactions are also suggested, although not defined by these experiments.…”

“…The organization of the phospholipid within the bilayer was examined by digesting the phospholipids in the outer portion of the membrane utilizing phospholipase A2 and sphingomyelinase C (12,23,24).…”

“…Because prior studies have shown that endocytosis is accompanied by lipid changes (23,25) but not by protein changes (Schrier SL, unpublished observations) we examined neonatal red cell membrane lipids in considerable detail. Our data agree with earlier reports that the neonatal red cell has a slightly higher cholesterol to phospholipid ratio and a higher sphingomyelin to PC ratio than the adult red cell (10,11,26).…”

“…The concept that membrane lipids are organized in domains has been gaining acceptance in the last few years (23,(30)(31)(32). The differences in the phospholipid degradation patterns between adult and neonatal red cells may arise in part from receptor-mediated endocytosis in neonatal red cells.…”

Phospholipids in animal eukaryotic membranes: transverse asymmetry and movement

“…Surprisingly, this shape change depends on the hydrolysis of cytoplasmic ATP (Schrier et al, 1986), at least when moderate amounts of amphipathic species were used. In fact, the insertion of such molecules into the membrane induced, by an unknown mechanism, the scrambling of a small fraction (10-20 %) of the membrane lipids (Schrier et al, 1983(Schrier et al, , 1992a. When ATP is available, the aminophospholipid translocase will remove phosphatidylserine and phosphatidylethanolamine from the outer leaflet and relocate them in the inner one.…”