Ganglioside GM1 (GM1), sphingomyelin (SM) and cholesterol (Chol) are dominant lipid components of rafts in plasma membranes. The morphology of GM1(x)/SM0.6 (x)/Chol(0.4) SPBs on SiO2 surfaces has been studied by atomic force microscopy and fluorescence microscopy at various ratios of GM1/SM (x = 0-0.25). The unique changes in morphology depending on the GM1 concentrations are qualitatively explained by hydrogen bonding and the hydrophobic interactions between SM and Chol, and by hydrogen bonding and the steric effects between bulky GM1 headgroups under Ca2+ existing conditions and the electrostatic repulsion between the negative charges of GM1 headgroups under Ca2+ nonexisting conditions. (C) 2008 Elsevier B.V. All rights reserved.