Increased ion permeability of planar lipid bilayer membranes after treatment with the C5b-9 cytolytic attack mechanism of complement.

Abstract

The ion permeability of planar lipid bilayers, as measured electrically, increased modestly upon treatment with purified [human] [complement [C] complex C5b,6 [b fragment of the 5th C component plus the 6th S component] and [guinea pig] C components C7 and C8. The subsequent addition of C9 greatly amplified this change. No permeability changes occurred when, components were added individually to the membrane, when they were used in paired combinations, or when C5b,6, C7, C8 and C9 were admixed prior to addition. There is a significant parallel between the permeability changes induced in the model membrane and damage produced in biological membranes by the C5b-9 attack sequence. The efficiency of membrane action by C5b-9 was critically dependent on the order in which components were added to the membrane. There were also differences in the electrical properties of membranes treated with C5b-8 and C5b-9, although in both cases the enhanced bilayer permeability is best attributed to the formation of trans-membrane channels. The mechanism of membrane action by C apparently involves the production of a stable channel across the lipid bilayer, resulting in cell death by colloid-osmotic lysis.