[Formation of mitochondrial reticulum in the diaphragmatic muscle in rat ontogeny]

The development of a complex system of mitochondrial reticulum of the rat diaphragm muscle fibers proceeds in several steps during ontogenesis. At first (19 day-old embryo and early postnatal period) the mitochondria grow in the longitudinal (with respect to the muscle fiber) direction, being located in the intermyofibrillar spaces. On the 9-10th day after birth there appear mitochondrial processes perpendicular to the long axis of muscle fiber at the levels of isotropic myofibrillar discs. These processes are later replaced by the branched giant mitochondria lying as if in floors across the muscle fiber. All mitochondria are interconnected by means of special contacts in a single system of mitochondrial reticulum. The functional role of complex mitochondria in the cross-striated muscle is discussed.