Disruption of erythrocyte membranal organization by superoxide.

Human erythrocyte ghosts were covalently labeled with 4-maleimide-2,2,6,6-tetramethylpiperidinooxyl. Electron paramagnetic resonance (EPR) spectrometry revealed two major binding environments representing strongly (S) and weakly (W) immobilized species. The disorder parameter, W/S, determined from the respective peak amplitudes, was shown to be irreversibly elevated following treatment of the labeled ghosts with superoxide, indicating an increase in membrane fluidity. Labeled ghosts reduced with ascorbate showed no nitroxide EPR signals. However, following exposure of these membranes to superoxide, the nitroxide spectrum returned with a W/S ratio of 25. In contrast, the disorder parameter for spin-labeled ghosts decreased following exposure to hydroxyl radicals suggesting decreased fluidity, as a result of lipid peroxidation. This effect could be prevented by the inclusion of mannitol. These changes in membrane fluidity and/or protein mobility observed by EPR are compared with previous results obtained by other methods and provide additional evidence for physiologic alterations initiated by superoxide.