Cholesterol is enriched in the sphingolipid patches on the substrate near nonpolarized MDCK cells, but not in the sphingolipid domains in their plasma membranes.

Information about the distributions of cholesterol and sphingolipids within the plasma membranes of mammalian cells provides insight into the roles of these molecules in membrane function. In this report, high-resolution secondary ion mass spectrometry was used to image the distributions of metabolically incorporated rare isotope-labeled sphingolipids and cholesterol on the surfaces of nonpolarized epithelial cells. Sphingolipid domains that were not enriched with cholesterol were detected in the plasma membranes of subconfluent Madin-Darby canine kidney cells. Surprisingly, cholesterol-enriched sphingolipid patches were observed on the substrate adjacent to these cells. Based on the shapes of these cholesterol-enriched sphingolipid patches on the substrate and their proximity to cellular projections, we hypothesize that they are deposits of membranous particles released by the cell.