Isolation and Analysis of Platelet Lipid Rafts

The cell membrane can no longer be viewed as a homogenous fluid bilayer; instead, it is now known to contain discrete lateral microdomains with characteristic subsets of lipids and proteins. One such microdomain, termed the “lipid raft,” has received much attention over the past few years. Several excellent reviews of lipid rafts (1 –3 ) and of related membrane structures called caveolae (4 ,5 ) have been published recently. Lipid rafts are enriched in cholesterol and sphingolipids, producing islands in the plasma membrane in which the lipids exist in the liquid-ordered state, discrete from the bulk of the lipids existing in the liquid-disordered state. As a consequence, lipid rafts can be isolated as a low-density, insoluble fraction after low-temperature nonionic detergent extraction (6 ). These properties give rise to their alternate names, detergent-resistant membranes (DRMs), detergent-insoluble glycolipid-rich domains (DIGs), Triton-insoluble floating fraction (TIFF), and glycolipid-enriched membranes (GEMs).