Induction of apoptosis in rat myocardium under anoxic conditions

The effect of anoxic incubation of small slices of isolated rat hearts on respiration, internucleosomal DNA fragmentation, and mitochondrial ultrastructure was investigated. Anoxic incubation for 72 h induced apoptosis accompanied by internucleosomal DNA fragmentation and changes in respiration and mitochondrial ultrastructure. The mitochondrial population was characterized by morphological heterogeneity. In a significant part of the mitochondrial population there were signs of mitochondrial swelling and appearance of electron-dense mitochondria. Anoxia also induced the appearance of an atypical (and previously unknown) population of small electron-dense mitochondria. They were characterized by unusual localization inside electron-light mitochondria. Under anoxic conditions the inner mitochondrial membrane formed electron-dense ordered structures. All changes described here reflect two opposing processes occurring in mitochondria: apoptotic destruction and compensatory processes responsible for maintenance of mitochondria.