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

Endovesiculation by large unilamellar vesicles (LUVs) induced by cationic amphiphiles is described in this work. A recent procedure to monitor phagocytosis of vesicles by macrophages by determining the amount of the simultaneously internalized water_soluble fluorescent dye HPTS with external quencher was adapted to LUVs (Daleke, D. L.; Hong, K.; Papahadjopoulos, D. Biochim. Biophys. Acta 1990, 1024, 352). Compared to dibucaine and safingol, the local anesthetic chlorpromazine (CPZ) was found to be the most efficient inducer of HPTS-internalization by LUVs. Control experiments using LUVs with entrapped HPTS indicated that the observed dye-internalization does not originate from transient lysis. A strong increase in activity above the critical micelle concentration of CPZ implies the importance of CPZ-micelles for endovesiculation. The significantly less efficient CPZ-induced HPTS-internalization by LUVs with 68 nm compared to 176 nm diameter further diminishes the likelihood of a micelle/bilayer fusion mechanism and supports the presence of 'zipper-type' endovesiculation by LUVs with diameters as small as 68 nm.