(190an) Diffusion in Nanodomains of Model Lipid Membranes Studied by PFG NMR with High Gradients

The plasma membrane of eukaryotic cells is a dynamic entity which cannot be described as completely homogeneous over a broad range of length scales ranging from less than 1 nanometer to several hundreds of nanometers. The study of domain (i.e. lipid raft) formation in biomembranes has become an attractive field of study due to implication that these domains play significant roles in signal transduction, the survival of cancer cells and the ability of viruses to penetrate the membrane. Model membranes composed of a ternary mixture of saturated and unsaturated lipids and cholesterol have been shown to be an appropriate model for the eukaryotic cell membrane. Until now, research has been focused on micron-sized domains due to spatial resolution limitations. Recently, nanodomains have been observed in model membranes on the order of 100 nm. This work presents additional information on such domain formation from the study of diffusion behavior of lipids as a function of diffusion time. The diffusion study was carried out in DOPC/DPPC/Chol model membranes by PFG NMR with high gradient strength (up to 35 T/m). The use of high gradient strengths allows for the use of sufficiently small diffusion times and as a result, PFG NMR studies of diffusion in lipid bilayers can be conducted over much smaller mean square displacements than previously reported. In this work, a change in behavior of lipids with increasing diffusion time is observed at temperatures below the main transition temperature. This change is believed to occur due to the exchange of lipid molecules between the domains and the surrounding environment.