Effect of calcium ion on the mechanical properties of lipid bilayer membrane
Issue title: Proceedings of the Fourth International Congress of Biorheology. Jikei University School of Medicine, Tokyo, Japan, 27 July – 1 August 1981. Dedicated to Alex Silberberg
Affiliations: Department of Textiles and Polymer Science, Faculty of Technology, Tokyo University of Agriculture and Technology, Nakamachi, Koganei, Tokyo 184, Japan
Note: [] Accepted by: Editor E. Fukada
Abstract: Elastic properties of dipalmitoyl phosphatidylcholine bilayers were studied by an ultrasonic technique as a function of the concentration of calcium ion. The ultrasonic velocity showed a broad minimum at about 10 mM CaCl2, indicating that the bulk modulus of membrane is smallest at this calcium ion concentration. Since the amount of calcium ions adsorbed to the membrane monotonously increases, calcium ions have two kinds of effects on the phosphatidylcholine membrane, namely softening effect at lower concentration and hardening at higher concentration. It is suggested that the softening is due to some structural change of hydrated water and the hardening is due to chelation of lipid molecules by adsorbed calcium ions. The estimation of bulk modulus and Young’s modulus revealed that Young’s modulus and rigidity are much smaller than the bulk modulus even in the gel phase.
