INVITRO INTERACTION OF L1210 CELLS WITH PHOSPHOLIPID VESICLES

Abstract

The in vitro uptake of phospholipid vesicles by mouse leukemia L1210 mouse leukemia cells was examined. Liposomes were generated by prolonged ultrasonic dispersion of aqueous dispersions of mixed lipids in the presence of radiolabeled inulin. Multilamellar vesicles were separated from unilamellar vesicles by column chromatography. Vesicle populations were examined by EM. Neutral vesicles were generated from egg yolk phosphatidylcholine and cholesterol, and surface charge was introduced via phosphatidylserine or octadecylamine. Uptake, measured as cell-associated radioactivity, was temperature dependent and strongly decreased by metabolic inhibitors. These results suggested that liposomes are taken up to a major extent by an energy-dependent mechansim. The uptake of liposomes by cells of a young culture was about 2-fold higher than uptake of liposomes by cells of a stationary culture. The uptake of positively charged liposomes by cells was about 20-fold higher than that of neutral or negatively charged vesicles. About 1/2 of the cell-associated radioactivity transferred by positively charged liposomes could be removed by cell surface treatment with trypsin or neuraminidase or a short exposure to 0.6 N NaCl.