ABSTRACT
One of the most fascinating but also controversial fields in cell biology concerns the organization of the cellular plasma membrane. In fact, the view of the cell membrane as a two-dimensional homogeneous structure has changed radically in recent years by demonstrations of lateral heterogeneities, patches and the existence of protein domains in the membrane. 13 The general consensus points to a direct relation between the lateral organization of proteins and lipids and their specific cellular function. 47 Similarly, a large body of evidence indicates that the size of many of these membrane domains is in the range of 30 to 800 nm. 68 However, other workers in the field have seriously questioned the existence of some membrane domains in living cells, in particular those known as membrane “rafts”. 9 Part of the controversy regarding the existence of membrane domains lays in their physical size, being smaller than the diffraction limit of light, and thus not resolvable by classical optical means. Moreover, there is increasing evidence that the assembly and disassembly of such complexes are rather dynamic and thus difficult to visualize using standard optical microscopy settings. 10 Finally, biochemical and biophysical approaches aimed at the study of protein domains have lead 186in many cases to contradictory results. 11 There is therefore a need for new high-resolution methodologies capable of directly imaging domains within the plasma membrane of intact cells.
