Sphingolipid composition of lipid rafts and soluble domains in cultured skin fibroblasts. Lipid rafts were isolated from cultured skin fibroblasts (6 mg of total cell protein) and the lipids present in each of the 12 fractions were extracted and analysed by mass spectrometry as described previously . Individual species of ceramide (Cer, closed squares), glucosylceramide (GC, open diamonds), lactosylceramide (LC, closed triangles) and trihexosylceramide (THC, crosses) were summed and shown. Results are expressed as pmol lipid per mg of total protein. Lipid rafts are localised to fractions 3 and 4.