title: Membrane fluidity change in erythrocytes induced by complement system.
abstract: The structural change in erythrocyte membranes induced by antibody and complement was studied using phospholipid spin-labels. Sheep erythrocytes were labeled with phosphatidylcholine spin-label and various intermediate cells (erythrocyte-antibody complex (EA), EA bound with complement components from C1 to C7 (EAC1-7), EAC1-8, and EAC1-9) were prepared. Electron spin resonance spectra of EA, EAC1-7, and EAC1-8 were very similar to that of the erythrocytes, while that of EAC1-9 was markedly different. The overall splitting value for the lysed EAC1-9 (53 G) was much smaller than that for the erythrocytes (57 G), indicating a marked fluidization around the phosphatidylcholine label. The unlysed EAC1-9 membranes contained a limited fraction of the fluidized area. When EA was reacted with complement in the presence of 36% bovine serum albumin, the membranes were fluidized similarly to the lysed EAC1-9, although the hemolysis was largely blocked. The membranes of unlysed EAC1-9 prepared in isotonic (ethylenedinitrilo)tetraacetic acid were also fluidized, but to somewhat smaller extent. The role of C9 in the modification of erythrocyte membranes was also demonstrated using Mg2+ ghosts, which were prepared by hypotonic hemolysis in the presence of Mg2+. The membranes of Mg2+ ghost of EAC1-7 were markedly fluidized when bound with C8 and C9, but not affected by binding of C8 only. The component C8 was found to give a latent effect on the membranes that caused irreversible fluidization upon osmotic shock. The terminal component thus creates a fluidized area in the erythrocyte membranes through which small ions and molecules may diffuse more easily and the resulting osmotic unbalance may finally cause hemolysis.
mesh_terms: D000818:Animals; D003186:Complement C9 / Q000494:pharmacology; D004578:Electron Spin Resonance Spectroscopy; D004910:Erythrocyte Membrane / Q000648:ultrastructure*; D004912:Erythrocytes / Q000276:immunology / Q000648:ultrastructure*; D006801:Humans; D008081:Liposomes; D008274:Magnesium / Q000494:pharmacology; D009996:Osmotic Fragility / Q000187:drug effects; D010713:Phosphatidylcholines / Q000097:blood; D010714:Phosphatidylethanolamines / Q000097:blood; D011817:Rabbits / Q000276:immunology; D012756:Sheep; D013113:Spin Labels
chemical_list: D003186:Complement C9; D008081:Liposomes; D010713:Phosphatidylcholines; D010714:Phosphatidylethanolamines; D013113:Spin Labels; D008274:Magnesium