Changes of osmotic fragility of red blood cells due to repletion or depletion of cholesterol in human and rat red cells in vitro.

The relation of membrane lipids and osmotic fragility of red cells of human and rat were studied in vitro by repletion and depletion of cell cholesterol. A decrease in the red cell cholesterol corresponded to an increase in osmotic fragility. Conversely, a repletion of red cell cholesterol decreased the osmotic fragility, but the procedure did not significantly change the phospholipid contents of red cells. Accordingly, osmotic fragility of the red cells correlated highly with the cholesterol content of the cell membrane (r = -0.922, p < 0.001) and with the molar ratio of cholesterol to phospholipid in the red cells (r = -0.887, p < 0.001). Red cells incubated with plasma had decreased membrane cholesterol and increased osmotic fragility, but the change was prevented by the inactivation of lecithin cholesterol acyltransferase (LCAT) in the plasma. The above results confirm that membrane cholesterol stabilizes human and rat red cells in vitro as well as in vivo, and the content of red cell cholesterol is regulated by the exchange of plasma free cholesterol in vitro. LCAT activity in the plasma is an influential factor in controlling the cholesterol content of red cells.