Interaction between Ca2+ and dipalmitoylphosphatidylcholine membranes: I. Transition anomalies of ultrasonic properties

Abstract The effect of Ca 2+ on a gel-to-liquid crystal transition as well as the mechanical properties of dipalmitoylphosphatidylcholine bilayers was studied by an ultrasonic technique. Transition temperature increased with increase in Ca 2+ concentration, whereas the variation of ultrasonic anomalies indicated that dipalmitoylphosphatidylcholine bilayers exhibited maximum pseudocritical fluctuation at a Ca 2+ concentration of about 10 mM. Hardening of dipalmitoylphosphatidylcholine membranes due to the Ca 2+ binding was observed above 10 mM CaCl 2 , suggesting the lateral compression of the lipid bilayer by bound Ca 2+ . Long-range attraction between bound Ca 2+ and the head groups of surrounding lipid molecules was proposed from these calcium effects.