Effect of Sodium Chloride on a Lipid Bilayer

• Published in: Biophysical journal Vol. 85; no. 3; pp. 1647 - 1655
• Main Authors: Böckmann, Rainer A., Hac, Agnieszka, Heimburg, Thomas, Grubmüller, Helmut
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01.09.2003; Biophysical Society
• Subjects: Biochemistry; Biophysical Phenomena; Biophysics; Calorimetry; Carbon - chemistry; Chlorine - chemistry; Computer Simulation; Diffusion; Dose-Response Relationship, Drug; Fatty Acids - chemistry; Fluorescence; Lipid Bilayers - chemistry; Lipids; Lipids - chemistry; Membranes; Models, Chemical; Models, Statistical; Molecular biology; Phosphatidylcholines - chemistry; Salt; Sodium Chloride - pharmacology; Spectrometry, Fluorescence; Static Electricity; Time Factors
• ISSN: 0006-3495; 1542-0086
• DOI: 10.1016/S0006-3495(03)74594-9

Electrostatic interactions govern structural and dynamical properties of membranes and can vary considerably with the composition of the aqueous buffer. We studied the influence of sodium chloride on a pure POPC lipid bilayer by fluorescence correlation spectroscopy experiments and molecular dynamics simulations. Increasing sodium chloride concentration was found to decrease the self-diffusion of POPC lipids within the bilayer. Self-diffusion coefficients calculated from the 100ns simulations agree with those measured on a millisecond timescale, suggesting that most of the relaxation processes relevant for lipid diffusion are faster than the simulation timescale. As the dominant effect, the molecular dynamics simulations revealed a tight binding of sodium ions to the carbonyl oxygens of on average three lipids leading to larger complexes with reduced mobility. Additionally, the bilayer thickens by ∼2Å, which increases the order parameter of the fatty acyl chains. Sodium binding alters the electrostatic potential, which is largely compensated by a changed polarization of the aqueous medium and a lipid dipole reorientation.