Cation-induced aggregation and fusion of N-acyl-N-methyl-phosphatidylethanolamine vesicles

Aggregation and fusion of unilamellar vesicles consisting of N-acyl-N-methylphosphatidylethanolamine were studied as a function of mono- and divalent cation concentrations. The aggregation reactions were irreversible processes, as demonstrated by changes in monovalent ion concentrations and by the addition of ethylenediaminetetraacetic acid (EDTA) to chelate divalent cations, suggesting the possibility of some cation-induced vesicle fusion. An increase in the NaCl ionic strength of the vesicle suspension solutions diminishes the threshold concentration for Li+ and K+ and increases that corresponding to Mn2+, Mg2+ and Ca2+. However NaCl concentrations above 300 mM yield smaller threshold values for the divalent cation-induced processes, probably due to the increased size of phospholipid vesicles as the ionic strength of the medium increases.