Your cells know two “dying” programs: apoptosis and necrosis. The latter results in swelling, ripping of the cell membrane, release of the cell content to the environment and therefore inflammation of the neighbour cells. In contrast, apoptosis is the self-induced and well-controlled suicide program of the cell which results in shrinking and fragmentation and doesn’t harm the neighbour cells. However, as always in life, the is not just black and white. Both processes have some similarities, especially in the beginning. Moreover, both can be triggered by similar toxic stimuli, and the “magnitude of the initial insult, rather than the type of the stimulus […] plays a critical role in the decision of the cell to undergo either apoptosis or necrosis.” The “decision” seems to be controlled by the intracellular ATP (energy) concentration, as apopotosis needs much more energy than necrosis. The hypothesis about the interplay between insult magnitude and intracellular ATP was tested by L. Formigli et al. (2000). They treted rat fibroblasts with different concentrations of Antimycin A, a toxin which blocks the mitochondrial respiratory chain and therefore leads to hypoxia (reduced oxygen content) and so to reduced ATP production. Indeed they were abel to show, that low Antimycin A concentrations, which result just in a small damage of the intracellular ATP storages, lead more to apoptosis, while high concentrations, which attack the ATP storages, lead to necrosis. Concentrations between resulted in mixed cell deaths: They showed apoptotic DNA fragmentation and degradation combined with necrotic cytoplasmatic swelling and membrane disruption. This mixed dying strategy L. Formigli et al. named “aponecrosis”. It seems like that cells which experience a toxic stimulus first try apoptosis, when there is still a certain amount of ATP left. However, if the ATP concentrations are depleted before the apoptosis process is finished, the cell switches to necrosis. So message of the day: (I) dying needs energy and (II) there are more than two ways to die. "Aponecrosis: morphological and biochemical exploration of a syncretic process of cell death sharing apoptosis and necrosis."
L. Formigli, et al. Journal of cellular physiology 182.1 (2000): 41-49.
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