Ionic environment, thickness and line tension as determinants of phase separation in whole Purified Myelin Membranes monolayers

PUSTERLA, JULIO; HERNANDEZ, JUAN MARTIN; WILKE, NATALIA; SCHNECK, EMANUEL; OLIVEIRA, RAFAEL G.

COLLOIDS AND SURFACES B-BIOINTERFACES

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2021 vol. 207 p. 112027 - 112027

0927-7765

Purified myelin membranes (PMM) were spread as monomolecular films at the air/aqueous solution interface,and visualized by Brewster Angle Microscopy (BAM) at different lateral pressures ( π ) on three specific aqueoussolutions: absence of salts, physiological conditions and presence of calcium. Coexistence of Liquid-Expanded(LE) and Liquid Ordered (LO) phases persisted up to collapse in the presence of salts, whereas monolayersbecame homogeneous at π ≥ 35− 40 mN/m when salts are absent. This PMM phase-mixing behavior in mono­layers is similar to the previously reported behavior of PMM multilamellar vesicles. Reflectivities (R p ) of p-polarized light from both phases were assessed throughout the whole π -range, and film thicknesses (t) werecalculated from the R p values and measured film refractive indices (n). The LO phase was found to be morereflective and thicker than the LE phase at π ≤ 15 mN/m, but less reflective and thinner at higher π .We also determined the line tension (λ) of PMM monolayers at the domain boundaries from the rate of domainshape relaxation, which turned out to be of the order of picoNewtons (pN) and decreased as π increased. Acorrelation between λ and thickness differences (Δt) was found, suggesting that Δt is a molecular determinant forλ in PMM monolayers.Both λ and Δt were found to increase markedly when calcium was present in the subphase. This result cor­roborates the concept of divalent cations as a stabilizing factor for phase separation, in line with earlier studieson this mixture forming multilamellar membrane arrangements.