Phase coexistence in films composed of DLPC and DPPC: a comparison between different model membrane systems

AGUSTÍN MANGIAROTTI; BENJAMÍN CARUSO; NATALIA WILKE

Carlos Paz

Congreso; XLII Reunion Anual de la Sociedad Argentina de Biofísica; 2013

Sociedad Argentina de Biofísica

For the biophysical studies of membranes, a variety of model systems are used to measure different parameters and to extract general principles of processes that occur in cellular membranes. However, there are very few reports in which the results obtained with the different models are compared. In this work, we quantitatively compared the phase coexistence in Langmuir monolayers, free standing bilayers and supported films composed of a lipid mixture of DLPC and DPPC. Two-phase segregation was observed in most of the systems for a wide range of lipid proportions using fluorescent microscopy. The lipid composition of the coexisting phaseswas determined and the distribution coefficient of the fluorescent probe in each phase was quantified, in order to explore their thermodynamic properties. The comparison between systems was carried out at 30 mN/m since it is accepted that at this or higher lateral pressures, the mean molecular area in bilayers is equivalent to that observed in monolayers. Our study showed that Langmuir monolayers and GUVs have a similar phase behavior. On the other hand, supported films showed a different composition of the phases and the distribution coefficient of the fluorescent probe was close to one. Our results suggest that in supported membranes, the presence of the rigid substrate could be leading to a stiffening of the liquid-expanded phase due to a loss in the degrees of freedom of the lipids when interact with the supporting material and this impacts on the properties of the coexisting phases.