Micromolar concentrations of Al3+ induce phase separation, aggregation and dye release in phosphatidylserine-containing lipid vesicles.

The interaction of Al3+, Cd2+ and Mn2+ with phosphatidylserine-containing lipid vesicles was studied. Phase separation of vesicles was investigated by monitoring fluorescence quenching of the phospholipid analogue 1-palmitoyl-2-(6-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)] aminocaproyl)phosphatidylcholine (C6-NBD-PC). Aggregation was determined by turbidimetry and leakage of vesicles content during fusion was monitored by the fluorescence of released 6-carboxyfluorescein. Al3+ demonstrated quenching at less than 30 mumol/l with a maximum effect at 100 mumol/l. Al3+-induced aggregation and dye release from the lipid vesicles were observed in the same concentration range. The effect of Cd2+ and Mn2+ on quenching was much less pronounced and could only be demonstrated in the 0.1-1 mmol/l range. Increasing amounts of phosphatidylcholine or phosphatidylethanolamine in the vesicles decreased both Al3+-induced quenching and aggregation, whereas cholesterol only slightly increased aggregation without affecting quenching.