Reduced lateral mobility of a fluorescent lipid probe in cholesterol-depleted erythrocyte membrane

Abstract

The effect of cholesterol depletion of the human erythrocyte membrane on the lateral diffusion rate of a fluorescent lipid probe is reported. At low temperatures (-5 to 5[deg]C), the diffusion of the probe is 50% slower in the cholesterol-depleted membrane than in non-depleted membrane. At high temperatures (30 to 40[deg] C), probe mobility is not affected by cholesterol depletion. These results suggest that cholesterol suppresses aspects of phospholipid phase changes in animal cells in a manner consistent with its behavior in artificial bilayers and multilayers.Whole erythrocytes were depleted of 30-50% of their cholesterol by incubation with a sonicated dispersion of dipalmitoyl phosphatidylcholine. Cells were then labeled with 3,3'-dioctadecylindocarbocyanine (diI), a phospholipid-like fluorescent dye, and hemolyzed into spherical ghosts. The rate of lateral motion of diI was measured by observing the fluorescence recovery after local photobleaching with a focused laser spot.The diffusion rate of the lipid probe in both control and cholesterol-depleted erythrocyte membrane is substantially smaller than in any cell or model membrane previously measured.