Visualization of detergent solubilization of membranes: Implications for the isolation of rafts

Although different detergents can give rise to detergent-resistant membranes of different composition, it is unclear whether this represents domain heterogeneity in the original membrane. We compared the mechanism of action of five detergents on supported lipid bilayers composed of equimolar sphingomyelin, cholesterol, and dioleoylphosphatidylcholine imaged by atomic force microscopy, and on raft and nonraft marker proteins in live cells imaged by confocal microscopy. There was a marked correlation between the detergent solubilization of the cell membrane and that of the supported lipid bilayers. In both systems Triton X-100 and CHAPS (3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate) distinguished between the nonraft liquid-disordered (I-d) and raft liquid ordered (I-o) lipid phases by selectively solubilizing the I-d phase. A higher concentration of Lubrol was required, and not all the I-d phase was solubilized. The solubilization by Brij 96 occurred by a two-stage mechanism that initially resulted in the solubilization of some I-d phase and then progressed to the solubilization of both I-d and I-o phases simultaneously. Octyl glucoside simultaneously solubilized both I-o and I-d phases. These data show that the mechanism of membrane solubilization is unique to an individual detergent. Our observations have significant implications for using different detergents to isolate membrane rafts from biological systems.