Steady-state analysis of tracer exchange across the C5b-9 complement lesion in a biological membrane.

Abstract

Resealed [human] erythrocyte ghosts were used to define the kinetics of tracer exchange across the membrane-bound terminal complex of the complement [C] cascade (C5b-9 [C components 5b through 9]). Under steady-state conditions and at net chemical equilibrium, C5b-9 ghosts showed no significant lysis above control levels as measured by Hb efflux. In 1 mM sucrose at 37.degree. C, [14C]sucrose isotopic exchange diffusion into C5b-9 ghosts occurred at 4.8 (.+-. 0.5, SEM) .times. 10-20 mol/sec per functional lesion, equivalent to an apparent permeability coefficient of 4.8 .times. 10-14 cm3/sec for the single C5b-9 lesion. No significant uptake of [14C]sucrose above control levels was observed in C5b67 ghosts. The apparent rate of tracer permeation through the C lesion is 1-2 orders of magnitude slower than predicted by a model of a transmembrane channel of dimensions permitting free diffusion of sucrose. Diffusion of small molecules across the complement lesion in biological membranes may be significantly restricted.