PH-DEPENDENT VESICLE-TO-MICELLE TRANSITION IN AN AQUEOUS MIXTURE OF DIPALMITOYLPHOSPHATIDYLCHOLINE AND A HYDROPHOBIC POLY-ELECTROLYTE

We and others have demonstrated several means of preparing synthetic bilayer membranes that respond to signals in an analogous fashion. Our approach exploits conformational transitions in membrane-associated polyelectrolyte chains to modulate bilayer structure and permeability. In particular, we have found that addition of the hydrophobic polyelectrolyte, poly(2-ethylacrylic acid), to aqueous dispersions of natural or synthetic phosphatidylcholines, renders the lipid membrane exceedingly sensitive to pH. pH sensitivity arises from the cooperative collapse of the polyelectrolyte chain from an expanded, hydrophilic state in basic solutions to a globular, hydrophobic coil upon acidification. Collapse of the chain is accompanied by rapid and quantitative release of vesicle contents, and the fact that release occurs near physiological pH makes this a process of some potential interest in biology and medicine. We present herein evidence that the release of vesicle contents is a result of membrane rupture caused by a reorganization of the surfactant aggregate from vesicular to mixed micellar form.