Coexistence of immiscible phases of palmitoyl-sphingomyelin and palmitoyl-ceramide in monolayers

MARIA FERNANDA SUÁREZ, BRUNO MAGGIO AND MARÍA LAURA FANANI

Los Cocos, Córdoba

Congreso; XXXVIII Reunión Anual de la Sociedad Argentina de Biofísica: Biofisica de Sistemas Autoorganizados; 2009

Sociedad Argentina de Biofísica

Lipid monolayer systems have been applied to explore in detail the interaction and organization palmitoylsphingomyelin (pSM) and the related lipid palmitoylceramide (pCer). Langmuir balance measurements of the binary mixture reveal favourable interactions between the lipid molecules. Fluorescence microscopy data reflect the presence of pCer-enriched domains coexisting, at low Cer content (<30 mol% pCer), with a pSM-enriched phase. A thermodynamically stable point is observed near a compositional ratio of 2:1 (pSM:pCer) [1]. At higher Cer contents, the phase diagram no longer reveals the presence of the pSM-enriched (liquid-expanded) phase and a condensed behaviour is evidenced. Even though calorimetric data suggests the presence of several Cer-enriched phases in the pSM/pCer mixtures above 30mol% pCer [1], fluorescence studies no longer distinguish the presence of more than one condensed phase due to a low partition coefficient of the fluorescent probes in the liquid-condensed phases. The exploration of phase coexistence on probe-free Cer-enriched monolayers by Brewster Angle Microscopy reveals the presence of two immiscible condensed phases of different thickness and Cer composition. The study of the pattern organization and dynamics of condensed domains surrounded by a condensed continuous phase is a scarcely studied field largely because of the technical difficulties on the probe-free imaging of the monolayers.     [1]    J.V.Busto, M.L.Fanani, L.De Tullio, J.Sot, B.Maggio, F.M.Goni, and A.Alonso, Coexistence of immiscible mixtures of palmitoylsphingomyelin and palmitoylceramide in monolayers and bilayers, Biophys J (2009) In Press.