Spectroscopic detection of endovesiculation by large unilamellar phosphatidylcholine vesicles: Effects of chlorpromazine, dibucaine, and safingol

Endovesiculation by large unilamellar vesicles (LUVs) induced by cationic a mphiphiles is described in this work. A recent procedure to monitor phagocy tosis of vesicles by macrophages by determining the amount of the simultane ously internalized water-soluble fluorescent dye HPTS with external quenche r was adapted to LUVs (Daleke, D. L.; Hong, K.; Papahadjopoulos, D. Biochim . Biophys. Acta 1990, 1024, 352). Compared to dibucaine and safingol, the l ocal anesthetic chlorpromazine (CPZ) was found to be the most efficient ind ucer of HPTS-internalization by LUVs. Control experiments using LUVs with e ntrapped HPTS indicated that the observed dye-internalization does not orig inate from transient lysis. A strong increase in activity above the critica l micelle concentration of CPZ implies the importance of CPZ-micelles for e ndovesiculation. The significantly less efficient CPZ-induced HPTS-internal ization by LUVs with 68 nm compared to 176 nm diameter further diminishes t he likelihood of a micelle/bilayer fusion mechanism and supports the presen ce of 'zipper-type' endovesiculation by LUVs with diameters as small as 68 nm. (C) 1999 Elsevier Science Ltd. All rights reserved.