Temperature dependence of the topology of supported dimirystoyl-distearoyl phosphatidylcholine bilayers

Topology of fluid and gel domains in the supported bilayer two-component system formed from equimolar mixtures of dimyristoylphosphatidylcholine (DMPC) and distearoylphosphatidylcholine (DSPC) was determined by AFM, at various temperatures corresponding to the gel and the gel + fluid region of the phase diagram. The data show that, in the disconnected fluid part of the DMPC/DSPC gel-liquid crystal-phase-separation region, the size of fluid domains markedly exceeds that predicted from spectroscopic experiments or from Monte Carlo simulations. They provide a direct evidence for the transition from the disconnected fluid to the disconnected gel region of the phase diagram, again with gel-phase domains much larger than expected. Finally, images of the gel phase at different temperatures suggest that structural rearrangements of the phospholipids can disrupt the continuity of the supported bilayer. (C) 2001 Elsevier Science B.V. All rights reserved.