Atomic force microscopy has been used to study the effect of cholesterol (Chol) on the structure of equimolar sphingomyelin (SM)/1,2-dioleoy-sn-glycero-3-phosphocholine (DOPC) binary bilayers and ceramide on the structure of SM/DOPC/cholesterol ternary bilayers. We found that the formation of microdomain structure in the binary lipid system was attributed to the interaction between cholesterol and SM with saturated lipid chain. As the contents of cholesterol increasing, the microdomain structure gradually expanded and formed a stable lamellar structure. When adding ceramide to equimolar SM/DOPC/Chol ternary system, as the proportion of ceramide increasing, a close aggregate structure appeared at first, and then developed to a retwork structure with particular microdomain. The results showed that the formations of microdomains were mainly due to the interaction of different functional groups, which belonged to individual molecule. These microdomains may play important roles in cellular signaling.

Key words: lipid raft, LB technique, atomic force microscopy (AFM)