Interaction of phospholipid vesicles with rat hepatocytes: further characterization of vesicle-cell surface interaction; use of serum as a physiological modulator.

We investigated the interaction of small unilamellar phospholipid vesicle, containing the water-soluble fluorescent dye carboxyfluorescein (CF), with rat hepatocytes in vitro. Fetal calf serum (FCS) was previously shown to interfere with hepatocyte-vesicle interaction using egg-lecithin as a liposomal marker [Hoekstra, D., Scherphof, G (1979): Biochim, biophys, Acta 551, pp. 109-121.] We now demonstrate that FCS affects the binding of intact vesicles to the cell surface, as well as the transfer of individual lipid molecules between vesicles and cells. By contrast, transfer of the entrapped fluorophore from the vesicles to the interior of the cell is unaffected. These observations lead us to suggest that the sites on the surface of the hepatocyte at which stable adsorption, the transfer of vesicle contents, and the transfer of individual phospholipid molecules take place are, at least kinetically, not identical. The potential importance of the inhibitory effect of serum on defined steps in the process of vesicle-cell interaction is emphasized.