LOADING OF AMPHIPATHIC WEAK ACIDS INTO LIPOSOMES IN RESPONSE TO TRANSMEMBRANE CALCIUM ACETATE GRADIENTS

We describe a novel procedure to load amphipathic weak acid molecules into preformed liposomes. Differences in calcium acetate concentration s across the liposomal membrane induce an increase of the internal pH. This pH imbalance serves as an efficient driving force to load and ac cumulate weak acids (5(6)-carboxyfluorescein and nalidixic acid) insid e the lipid vesicles. The mechanism of loading and the relevance of th e method in drug delivery systems are discussed.