1. Rat hepatocytes suspended in 0.25 M-sucrose were electropermeabilized. This completely disrupted their plasma-membrane permeability barrier. 2. The endoplasmic reticulum in electroporated hepatocytes appeared morphologically preserved and maintained its permeability barrier as evidenced by electron-microscopic examination and latency measurements on luminal reticular enzymes. 3. Upon aerobic incubation with an NADPH-generating system and iron/ADP, porated hepatocytes peroxidized their membrane lipids at rates similar to those of matched microsomal preparations. 4. When hepatocytes were incubated with iron/EDTA and azide, radical formation detectable with dimethyl sulphoxide (DMSO) was only 10-20% that shown by microsomes. Omitting azide abolished hepatocyte reactivity with DMSO completely. Effects of hydroxyl-radical (.OH) scavengers and of added catalase suggest that the radical detected by DMSO is .OH. 5. Cytosolic inhibitor(s) from hepatocytes seemed to be a major factor limiting .OH formation. These were macromolecular, but showed a degree of heat-stability. Dialysis largely abolished inhibition, but this could be restored again by adding GSH. 6. Since .OH formation in hepatocytes seems to be much more stringently prevented than lipid peroxidation, free-radical damage originating from intracellular redox systems seems more likely to take the form of lipid peroxidation.
