Phase state and surface topography of palmitoyl-ceramide monolayers

MARIA LAURA FANANI; BRUNO MAGGIO

CHEMISTRY AND PHYSICS OF LIPIDS

ELSEVIER IRELAND LTD

Año: 2010 vol. 163 p. 594 - 600

0009-3084

In cell biology (and in many biophysical) studies there is a natural tendency to consider ceramide as a highly condensed, solid-type lipid conferring rigidity and close packing to biomembranes. In the present work we advanced the understanding of the phase behavior of palmitoyl-ceramide restricted to a planar interface using Langmuir monolayers under strictly controlled and known surface packing conditions. Surface pressure-molecular area isotherms were complemented with molecular area-temperature isobars and with observations of the surface topography by Brewster Angle Microscopy. The results described herein indicate that palmitoyl-ceramide can exhibit expanded, as well as condensed phase states. Formation of three phases was found, depending on the surface pressure and temperature: a solid (1.80 nm thick), a liquid-condensed (1.73 nm thick, likely tilted) and a liquid-expanded (1.54 nm thick) phase over the temperature range 5-62?C. A large hysteretic behavior is observed for the S phase monolayer that may indicate high resistance to domain boundary deformation. A second (or higher) order S¨LC phase transition is observed at about room temperature while a first order LC¨LE transition occurs in a range of temperature encompassing the physiological one (observed above 30?C at low surface pressure). This phase behavior broadens the view of ceramide as a type of lipid not-always-rigid but able to exhibit polymorphic properties.