Use of Cyclodextrin for AFM Monitoring of Model Raft Formation

• Published in: Biophysical journal Vol. 86; no. 2; pp. 861 - 869
• Main Authors: Giocondi, Marie-Cécile, Milhiet, Pierre Emmanuel, Dosset, Patrice, Grimellec, Christian Le
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.02.2004; Biophysical Society
• Subjects: Cellular biology; Cholesterol; Cholesterol - chemistry; Cyclodextrins - chemistry; Lipid Bilayers - chemistry; Lipids; Macromolecular Substances; Membrane Fluidity; Membrane Microdomains - chemistry; Membrane Microdomains - diagnostic imaging; Membranes; Microscopy, Atomic Force - methods; Molecular Conformation; Permeability; Phase Transition; Phosphatidylcholines - chemistry; Sphingomyelins - chemistry; Ultrasonography
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(04)74161-2

The lipid rafts membrane microdomains, enriched in sphingolipids and cholesterol, are implicated in numerous functions of biological membranes. Using atomic force microscopy, we have examined the effects of cholesterol-loaded methyl- β-cyclodextrin (M βCD-Chl) addition to liquid disordered (l d)-gel phase separated dioleoylphosphatidylcholine (DOPC)/sphingomyelin (SM) and 1-palmitoyl-2-oleoyl phosphatidylcholine (POPC)/SM supported bilayers. We observed that incubation with M βCD-Chl led to the disappearance of domains with the formation of a homogeneously flat bilayer, most likely in the liquid-ordered (l o) state. However, intermediate stages differed with the passage through the coexistence of l o-l d phases for DOPC/SM samples and of l o-gel phases for POPC/SM bilayers. Thus, gel phase SM domains surrounded by a l o matrix rich in cholesterol and POPC could be observed just before reaching the uniform l o state. This suggests that raft formation in biological membranes could occur not only via liquid-liquid but also via gel-liquid immiscibility. The data also demonstrate that M βCD-Chl as well as the unloaded cyclodextrin M βCD make holes and preferentially extract SM in supported bilayers. This strongly suggests that interpretation of M βCD and M βCD-Chl effects on cell membranes only in terms of cholesterol movements have to be treated with caution.