Specific issues of mitochondrial fragmentation (Fission)

In 1983 we discovered a phenomenon of the total fragmentation (fission) of the entire mitochondrial population in a cell following the exposure to a mitochondrial inhibitor. Further experiments showed that a wide range of substances acting on mitochondria can cause the transformation of filamentous structures to small globular vesicles (the thread–grain transition). Fragmentation of mitochondria clearly begins with the formation of a septum formed by the inner mitochondrial membranes, leading to the division of mitochondria into a number of compartments, not necessarily of the same configuration. Visible signs of fragmentation of the mitochondrial reticulum appeared after an hour of the exposure to mitochondrial inhibitors; the process of mitochondrial fission was markedly accelerated and developed within seconds when the cells stained with fluorescent probes were exposed to excitation light and were affected photodynamically. The crucial role of reactive oxygen species in the initiation of the process of mitochondrial fission is proposed. Before the formation of septa, local enlightenment of mitochondrial matrix (local swelling) can be observed, which indicates the possibility of the existence of intramitochondrial skeleton that maintains the shape of the mitochondria. The septum formation and fragmentation gives rise to different populations of mitochondria. Apparently, this is a part of the mechanism of mitochondrial quality control and elimination of damaged mitochondria.