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Plasma membrane modifications have been widely recognized as crucial factors in cell injury and death. One of these modifications, surface blebbing, has been considered as an injury-marker associated with a series of biochemical and physiological modifications. Our study focused on the different effects of free radical-induced cell damage by quinone menadione (2-methyl-1,4-naphthoquinone) and by hyperthermic shock (45 degrees C) on the erythroleukemic cell line K562. Different techniques including immunofluorescence, freeze-fracturing, and electron paramagnetic resonance spectroscopy were employed. Menadione induced the formation of surface blebs, accompanied by a rearrangement of the microfilament system and changes in the distribution of plasma membrane proteins. In contrast, heat-shocked cells showed neither blebbing nor important cytoskeletal changes. Finally, the electron paramagnetic resonance results showed an increase in membrane order not specifically related to the type of free radical-induced stress. These cell death features appear to suggest the existence of two different types of pathways for necrotic cell death: both treatments induce cell injury and eventual death by modifying plasma membrane integrity and function. However, one involves cytoskeleton-dependent surface blebbing, whereas the other does not.

The exposure of the epidermoid cell line A431 to different concentrations of CsCl was assessed using different methodological approaches. Two different effects were detected depending upon the concentration of the agent: at low concentrations, cell modification was represented mainly by a very pronounced cell flattening and an alteration of the cell-to-cell contacts, interpreted as an increase in cell adhesion. At higher concentrations, a clear pathogenic effect was observed that allowed the formulation of the hypothesis that specific mechanisms of toxicity at the subcellular level involving mitochondrial and cytoskeletal function can exist. In addition, membrane order parameters, as detected by electron paramagnetic resonance (EPR) spectroscopy, displayed a dose-dependent increase in membrane rigidity. Results reported here seem to suggest that cesium ions can enter the cell, modify plasma membrane integrity and alter some specific cytoplasmic components, e.g. the cytoskeleton. Considering that environmental contamination by cesium as a result of radioactive fallout is of major importance and that few data are available thus far on this matter, this study provides evidence for the possible mechanisms of action of the non-radioactive form of this ion in cells.

The effects of the oxidizing agent t-butylhydroperoxide (t-BHP) were investigated on three human cell lines of different origin and growth features (A431 epithelial cells, ADF astrocytoma cells and U937 leukemic cells) using electron microscopy and electron paramagnetic resonance spectroscopy. The results indicate that important biophysical and ultrastructural modifications are induced in the plasma and mitochondrial membranes of these cells and that these changes can ultimately lead to cell death. In addition, the cell cytoskeleton also appears to be a target of hydroperoxide-mediated stress. In particular, all three cell types undergo cytoskeletal alterations leading to surface blebbing, a typical characteristic of cell damage. However, the timing and extent of this damage as well as that occurring at the mitochondrial and plasma membrane levels seems to be different: cells with weak (ADF) or absent (U937) cell-to-cell and cell-substrate contacts and a poorly developed cytoskeleton appear to be more susceptible than other cell types (e.g., A431) to t-BHP-mediated injury. These diverse cell susceptibilities to hydroperoxide-mediated oxidative stress could thus depend upon cell histotype-associated growth featurs.