title: Rapid transmembrane diffusion of ceramide and dihydroceramide spin-labelled analogues in the liquid ordered phase.
abstract: In order to study the basic physical phenomena underlying complex lipid transbilayer movement in biological membranes, we have measured the transmembrane diffusion of spin-labelled analogues of sphingolipids in phosphatidylcholine (PC) large unilamellar vesicles in the absence or presence of cholesterol, going from a fluid ( liquid disordered) l(d), phase to a more viscous, liquid ordered (l(o)), phase. We have found cholesterol to reduce the transverse diffusion of glucosylceramide (GlcCer) and galactosylceramide (GalCer) in a concentration-dependent manner. However, surprisingly, we could neither detect any influence of cholesterol on the rapid flip-flop of ceramide nor on the flip-flop of dihydroceramide, for which the tau(1/2) of flip-flop remains in the order of 1 minute at 20 degrees C in the presence of cholesterol. As a consequence of rapid flip-flop of ceramide in both the l(o) and the l(d) phase, ceramide is likely to distribute between the two monolayers of a membrane, and could in principle partition into segregated domains in each side of the plasma membrane of eukaryotic cells.
authors.affiliation: Institut de Biologie Physico-Chimique, UMR CNRS 7099, 13 rue Pierre et Marie Curie, Paris, France.
authors.forename: Antje
authors.initials: A
authors.lastname: Pohl
authors.forename: Iván
authors.initials: I
authors.lastname: López-Montero
authors.forename: Florent
authors.initials: F
authors.lastname: Rouvière
authors.forename: Fabrice
authors.initials: F
authors.lastname: Giusti
authors.forename: Philippe F
authors.initials: PF
authors.lastname: Devaux
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D002518:Ceramides / Q000378:metabolism*; D002784:Cholesterol; D004058:Diffusion; D008051:Lipid Bilayers / Q000378:metabolism*; D008954:Models, Biological; D044367:Phase Transition; D010713:Phosphatidylcholines; D013107:Sphingolipids; D013113:Spin Labels
chemical_list: D002518:Ceramides; D008051:Lipid Bilayers; D010713:Phosphatidylcholines; D013107:Sphingolipids; D013113:Spin Labels; C109343:dihydroceramide; D002784:Cholesterol