Dextran enhances calcium-induced aggregation of phosphatidylserine liposomes: Possible implications for exocytosis

We have studied the calcium-induced aggregation of phosphatidylserine lipos omes in the presence of various concentration of a high-molecular water-sol uble polysaccharide dextran. It has been shown that threshold concentration s of calcium necessary to induce liposome aggregation in the presence of si milar to 1 mM concentration of dextran is about one order lower than in the absence of dextran. Soluble intracellular polymers may thus play an import ant role in the process of exocytosis.