(662b) Direct Chemical Imaging of the Sphingolipid and Cholesterol Distribution in Cell Membranes

Domains of different protein composition are known to be present in the plasma membranes of mammalian cells.  Different lipid species and cholesterol also seem to be organized into compositionally and functionally distinct plasma membrane domains.  For example, membrane domains that are enriched with cholesterol and sphingolipids, which are often referred to as lipid rafts, are hypothesized to be present in the plasma membrane.  However, the existence of lipid rafts and their significance to cell biology is controversial.  In fact, even though the abundances of cholesterol and sphingolipids within the cell undoubtedly influence many biological processes, the distributions of cholesterol and sphingolipids within the plasma membrane have not been definitively established.  Here we report the direct chemical imaging of the sphingolipid and cholesterol distribution in the plasma membranes of intact cells.  We have used high resolution secondary ion mass spectrometry to map the isotope enrichment from metabolically incorporated ¹⁵N-sphingolipids and ¹⁸O-cholesterol on the entire dorsal surfaces of fibroblast cells. Statistical methods are used to definitively determine whether the sphingolipids and cholesterol were heterogeneously distributed and co-localized within the plasma membrane.  Our results demonstrate that lipids are spatially organized within the plasma membrane.