Membrane lipid domains and membrane lipid domain preparations : are they the same thing?

Early notions on membrane lipid domains were derived mainly from experimental models based on artificial membranes and from studies on membrane fractions prepared by density gradient centrifugation of a cell lysate obtained by treating cells with detergents under controlled conditions. These studies introduced the biological concept that Golgi apparatus is capable to sort proteins and to send them to the plasma membrane through “rafts”, membrane lipid domains highly enriched in glycosphingolipids, sphingomyelin, ceramide and cholesterol. This concept has evolved and has been expanded in the last 10 years, and now several experimental approaches with the potential for observing these domains in intact cells are available. Here we critically discuss the necessity of discriminate between what is present on a cell membrane and what we can prepare from cell membranes in a laboratory tube.