title: Compositional and structural characterization of monolayers and bilayers composed of native pulmonary surfactant from wild type mice.
abstract: This work comprises a structural and dynamical study of monolayers and bilayers composed of native pulmonary surfactant from mice. Spatially resolved information was obtained using fluorescence (confocal, wide field and two photon excitation) and atomic force microscopy methods. Lipid mass spectrometry experiments were also performed in order to obtain relevant information on the lipid composition of this material. Bilayers composed of mice pulmonary surfactant showed coexistence of distinct domains at room temperature, with morphologies and lateral packing resembling the coexistence of liquid ordered (lo)/liquid disordered (ld)-like phases reported previously in porcine lung surfactant. Interestingly, the molar ratio of saturated (mostly DPPC)/non-saturated phospholipid species and cholesterol measured in the innate material corresponds with that of a DOPC/DPPC/cholesterol mixture showing lo/ld phase coexistence at a similar temperature. This suggests that at quasi-equilibrium conditions, key lipid classes in this complex biological material are still able to produce the same scaffold observed in relevant but simpler model lipid mixtures. Also, robust structural and dynamical similarities between mono- and bi-layers composed of mice pulmonary surfactant were observed when the monolayers reach a surface pressure of 30mN/m. This value is in line with theoretically predicted and recently measured surface pressures, where the monolayer-bilayer equivalence occurs in samples composed of single phospholipids. Finally, squeezed out material attached to pulmonary surfactant monolayers was observed at surface pressures near the beginning of the monolayer reversible exclusion plateau (~40mN/m). Under these conditions this material adopts elongated tubular shapes and displays ordered lateral packing as indicated by spatially resolved LAURDAN GP measurements.
authors.affiliation: MEMPHYS, Center of Biomembrane Physics, University of Southern Denmark, Odense, Denmark; Membrane Biophysics and Biophotonics group, University of Southern Denmark, Odense, Denmark; Department of Biochemistry and Molecular Biology, University of Southern Denmark, Odense, Denmark.
authors.forename: Jorge
authors.initials: J
authors.lastname: Bernardino de la Serna
authors.forename: Soren
authors.initials: S
authors.lastname: Hansen
authors.forename: Zane
authors.initials: Z
authors.lastname: Berzina
authors.forename: Adam C
authors.initials: AC
authors.lastname: Simonsen
authors.forename: Hans K
authors.initials: HK
authors.lastname: Hannibal-Bach
authors.forename: Jens
authors.initials: J
authors.lastname: Knudsen
authors.forename: Christer S
authors.initials: CS
authors.lastname: Ejsing
authors.forename: Luis A
authors.initials: LA
authors.lastname: Bagatolli
mesh_terms: D000818:Animals; D001992:Bronchoalveolar Lavage Fluid; D008051:Lipid Bilayers / Q000737:chemistry*; D013058:Mass Spectrometry; D051379:Mice; D018625:Microscopy, Atomic Force; D008856:Microscopy, Fluorescence; D015394:Molecular Structure; D011663:Pulmonary Surfactants / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D011663:Pulmonary Surfactants
keywords: Fluorescence microscopy; LAURDAN GP function; Liquid immiscibility; Membrane domains; Native pulmonary surfactant membranes