title: Ultrastructure and lipid composition of detergent-resistant membranes derived from mammalian sperm and two types of epithelial cells.
abstract: Lipid rafts are micro-domains of ordered lipids (Lo phase) in biological membranes. The Lo phase of cellular membranes can be isolated from disordered lipids (Ld phase) after treatment with 1 % Triton  X-100 at 4 °C in which the Lo phase forms the detergent-resistant membrane (DRM) fraction. The lipid composition of DRM derived from Madin-Darby canine kidney (MDCK) cells, McArdle cells and porcine sperm is compared with that of the whole cell. Remarkably, the unsaturation and chain length degree of aliphatic chains attached to phospholipids is virtually the same between DRM and whole cells. Cholesterol and sphingomyelin were enriched in DRMs but to a cell-specific molar ratio. Sulfatides (sphingolipids from MDCK cells) were enriched in the DRM while a seminolipid (an alkylacylglycerolipid from sperm) was depleted from the DRM. Treatment with <5 mM methyl-ß-cyclodextrin (MBCD) caused cholesterol removal from the DRM without affecting the composition and amount of the phospholipid while higher levels disrupted the DRM. The substantial amount of (poly)unsaturated phospholipids in DRMs as well as a low stoichiometric amount of cholesterol suggest that lipid rafts in biological membranes are more fluid and dynamic than previously anticipated. Using negative staining, ultrastructural features of DRM were monitored and in all three cell types the DRMs appeared as multi-lamellar vesicular structures with a similar morphology. The detergent resistance is a result of protein-cholesterol and sphingolipid interactions allowing a relatively passive attraction of phospholipids to maintain the Lo phase. For this special issue, the relevance of our findings is discussed in a sperm physiological context.
authors.affiliation: Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine Utrecht University, Yalelaan 2, 3584 CM, Utrecht, The Netherlands.
authors.forename: Renske A
authors.initials: RA
authors.lastname: van Gestel
authors.affiliation: Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine Utrecht University, Yalelaan 2, 3584 CM, Utrecht, The Netherlands.
authors.forename: Jos F
authors.initials: JF
authors.lastname: Brouwers
authors.affiliation: Department of Pathology, Faculty of Veterinary Medicine Utrecht University, Utrecht, The Netherlands.
authors.forename: Anton
authors.initials: A
authors.lastname: Ultee
authors.affiliation: Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine Utrecht University, Yalelaan 2, 3584 CM, Utrecht, The Netherlands.
authors.forename: J Bernd
authors.initials: JB
authors.lastname: Helms
authors.affiliation: Department of Biochemistry and Cell Biology, Faculty of Veterinary Medicine Utrecht University, Yalelaan 2, 3584 CM, Utrecht, The Netherlands. B.M.Gadella@uu.nl.|Department of Farm Animal Health, Faculty of Veterinary Medicine Utrecht University, Utrecht, The Netherlands. B.M.Gadella@uu.nl.
authors.forename: Bart M
authors.initials: BM
authors.lastname: Gadella
mesh_terms: D000818:Animals; D002784:Cholesterol / Q000032:analysis*; D003902:Detergents / Q000737:chemistry; D004285:Dogs; D004847:Epithelial Cells / Q000737:chemistry / Q000166:cytology* / Q000648:ultrastructure; D008297:Male; D021962:Membrane Microdomains / Q000737:chemistry* / Q000648:ultrastructure; D010743:Phospholipids / Q000032:analysis*; D013094:Spermatozoa / Q000737:chemistry / Q000166:cytology* / Q000648:ultrastructure; D013107:Sphingolipids / Q000032:analysis*; D013109:Sphingomyelins / Q000032:analysis*; D013552:Swine
chemical_list: D003902:Detergents; D010743:Phospholipids; D013107:Sphingolipids; D013109:Sphingomyelins; D002784:Cholesterol
keywords: Cholesterol; Detergent-resistant membranes; Epithelial cell; Glycolipids; Lipid rafts; Phospholipids; Sperm; Ultrastructure