A dynamical model for phase transitions of lipids induced by calcium ions

Lipid membranes exist essentially in two different phases. A phase transition can be triggered off either by changing the temperature or, isothermally, by varying an external factor such as ionic concentration, pH, organic solvents, etc. Since the isothermal transition may be induced at physiological temperature, it may play an important regulatory role in diverse cellular functions. Based on the Landau-Ginsburg theory, the thermotropic transitions of lipids has been described by a number of models. In the present work a dynamical model for an isothermal phase transition of phospholipids induced by ionic binding is proposed. The properties of the model show that by ionic binding, phospholipids may form spatial heterogeneous distributions of lipids in fluid and crystalline phases. This heterogeneity possibly being the cause of membrane instabilities, which favour enhanced vesicle fusions observed in the presence of Ca2+.