Interactions of synthetic polymers with cell membranes and model membrane systems, 9. Reversal of Mg^(2+) Induced Structural Changes in Dipalmitoylphosphatidylglycerol Bilayers by Adsorbed Polyethyleneimines

Abstract

One can imagine a number of different ways in which synthetic polymers might modify the structural and functional properties of bilayer membranes. Our own experiments on polymer-lipid mixtures have demonstrated several of these. Treatment of aqueous phosphatidylcholine suspensions with poly(2-ethylacrylic acid) was shown by Tirrell, Takigawa and Seki to provide a method of preparation of environmentally sensitive vesicles which release their contents in a controlled manner in response to small changes in local pH. The most likely mechanism by which the polymer may effect vesicle disruption is that shown in Scheme 1: a pH-dependent conformational transition in poly(2-ethylacrylic acid) produces a globular, hydrophobic form of the polymer which solubilizes the lipid in the form of mixed micelles. More recently, we have described the observation of an unusual interdigitated gel phase in phosphatidylglycerol bilayers treated with ionene-6, (Scheme 2). Interdigitation results in a near-doubling of the lateral area of the bilayer, as the bilayer thickness is reduced to little more than half its normal value. We are currently exploring the consequences of this structural change in terms of bilayer stability and permeability.