Interactions between Adsorbed Hydrogenated Soy Phosphatidylcholine (HSPC) Vesicles at Physiologically High Pressures and Salt Concentrations

• Published in: Biophysical journal Vol. 100; no. 10; pp. 2403 - 2411
• Main Authors: Goldberg, Ronit, Schroeder, Avi, Barenholz, Yechezkel, Klein, Jacob
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 18.05.2011; Biophysical Society; The Biophysical Society
• Subjects: Adsorption - drug effects; Biomechanical Phenomena - drug effects; Biophysics; Cryoelectron Microscopy; electron microscopy; friction; Lipids; Membrane; Nitrates - pharmacology; phosphatidylcholines; Phosphatidylcholines - chemistry; Physiology; Pressure; Salt; salt concentration; Scanning electron microscopy; sodium nitrate; Stress, Mechanical; Surface Properties - drug effects; Unilamellar Liposomes - chemistry
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/j.bpj.2011.03.061

Using a surface force balance, we measured normal and shear interactions as a function of surface separation between layers of hydrogenated soy phosphatidylcholine (HSPC) small unilamellar vesicles (SUVs) adsorbed from dispersion at physiologically high salt concentrations (0.15 M NaNO3). Cryo-scanning electron microscopy shows that each surface is coated by a close-packed HSPC-SUV layer with an overlayer of liposomes on top. A clear attractive interaction between the liposome layers is seen upon approach and separation, followed by a steric repulsion upon further compression. The shear forces reveal low friction coefficients (μ = 0.008–0.0006) up to contact pressures of at least 6 MPa, comparable to those observed in the major joints. The spread in μ-values may be qualitatively accounted for by different local liposome structure at different contact points, suggesting that the intrinsic friction of the HSPC-SUV layers at this salt concentration is closer to the lower limit (μ = ∼0.0006). This low friction is attributed to the hydration lubrication mechanism arising from rubbing of the hydrated phosphocholine-headgroup layers exposed at the outer surface of each liposome, and provides support for the conjecture that phospholipids may play a significant role in biological lubrication.