Fig. (3).

Tentative mechanism of selective accumulation of giant mitochondria. Normal turnover of mitochondria is associated with their continuous removal by autophagy and fusion/fission, generating new mitochondria and preventing mitochondrial enlargement (a). Mitochondrial damage (e.g., by ROS) may lead to disturbed fission and enlargement of certain mitochondria (b). There is a reason to believe that autophagy of enlarged mitochondria is energy consuming and thus more complicated than that of normal mitochondria. Because of this, a further mitochondrial enlargement and a progressive amassing of giant dysfunctional mitochondria may take place within long-lived postmitotic cells, such as cardiac myocytes.