The cytolytic action of complement (C) is believed to be due to the formation of trans-membrane channels by insertion of peptides from C5b-9 into the lipid bilayer. We have previously reported that phospholipid (PL) is released from the liposomal bilayer by activated C, along with channel formation. Since channel formation and PL removal involve lipid-protein interactions, the chemical properties of the lipids in the membrane would be expected to influence these processes. In the present work, we have studied the C-mediated release of 86Rb+ from the aqueous compartment and 14C-phosphatidyl choline (PC) from the lipid bilayer of liposomes containing different amounts of cholesterol, and liposomes made from PL differing with respect to acyl chain length and unsaturation.
Effect of acyl chain length. Liposomes prepared from C(14:0)2, C(16:0)2 and C(18:0)2 lecithins, with a cholesterol/PL ratio of 0.75, were treated with antibody (Ab) and C.