Paracrystalline arrays in mitochondria following ageing of mitochondria in situ

Intermembrane inclusions induced by anoxia in heart and skeletal muscle mitochondria

Heart and skeletal muscle from rats of different ages were incubated in vitro in an oxygen-free medium supplied with substrates in order to investigate the effect of anoxia on muscle fine structure, particulary on the mitochondria. In skeletal muscle fibers anoxia has been found to induce changes similar to those previously described in ischemic muscles in vivo namely giant mitochondria, apparently derived by mitochondrial fusion, and intermembrane inclusions with a paracrystalline structure. The plate-like inclusions are mostly located in the intracristal spaces and are closely associated to cristal membranes even in markedly swollen mitochondria. Identical inclusions have been observed in cardiac muscle cells following anoxic injury, whereas they are never found in non-muscle cells such as endothelia, fibroblasts and nerve fibers. Cardiac and skeletal muscle fibers from newborn rats maintained in an oxygen-free medium show mitochondrial swelling but no intermembrane inclusions. The different response of mitochondria from developing vs adult striated muscle to anoxia may be due to changes during postnatal development in the quality or quantity of the protein component(s) involved in paracrystal formation.

[Intracristal linear inclusions in mitochondria of human rhabdomyoma cells (author's transl)]

Electron microscopic study of a rhabdomyoma of the soft palate of a 50-year-old woman revealed linear structures within the intracristal spaces of mitochondria. In the center of most cristae, an electron-dense line was found located in parallel arrangement to the limiting cristal membrane. The linear inclusion was separated from the cristal membrane by a narrow space of lower electron-density. Thus, when sectioned longitudinally, the abnormal cristae exhibited a pentalaminar appearance. Additionally, they were characterized by a greater diameter than that of normal cristae and a "rigid" configuration. Higher magnification showed that the intracristal line consisted of a row of periodically arranged, electron-dense dots. Sometimes, these seemed to be connected with the wall of the intracristal space by fine, electron-dense cross-striations. In some mitochondria of rhabdomyoma cells, crystals with a linear substructure were observed in both intra- and extracristal spaces. The crystalline bodies located within cristae had probably been formed by accumulation of linear inclusions. The extracristal bodies seemed to have arisen from fusion of pentalaminar cristae. It is supposed that the intracristal linear inclusions in mitochondria of rhabdomyoma cells represent crystallized proteins of mitochondrial enzymes.

Mitochondrial framework (reticulum mitochondriale) in rat diaphragm muscle

Reconstitution of rat diaphragm mitochondria has been carried out with the use of the serial section technique. It is shown that mitochondrial material is organized as networks transpiercing the I band regions of the muscle near the Z-discs. Each network forms tubules, oriented perpendicular to its plane, and branches, connecting the network with mitochondrial clusters in the fiber periphery. Such a system, defined as mitochondrial reticulum, is found to be characteristic of the diaphragm of adult animals. It is absent in the diaphragm of rat embryos and newborn rats. The junctions of the branches of mitochondrial reticulum are described. In the junction site, the outer membranes of two mitochondrial branches are in contact, and spaces between outer and inner membranes are filled with an osmiophilic substance. No junctions were found in the embryos and in newborn animals whose diaphragm contains single, elliptical or worm-like mitochondria. The hypothesis is put forward that the mitochondrial reticulum serves as a system for transport of energy, oxygen and fatty acid residues along mitochondrial membranes over distances commensurable with the muscle fiber diameter.

Incidence of intermembrane alterations in human heart mitochondria: a preliminary ultrastructural study

An alteration consisting of widening of the inner membrane space (approximately 240 A) of the human heart mitochondria was studied and compared in surgical and autopsy material. The presence of these changes in well-preserved surgical material suggests that it may be a morphologic manifestation of an unknown biochemical alteration.

Membrane junctions in the intermembrane space of mitochondria from mammalian tissues

There have been several reports describing paracrystalline arrays in the intermembrane space of mitochondria. On closer inspection these structures appear to be junctions of two adjoining membranes. There are two types. They can be formed between the outer and inner mitochondrial membranes (designated outer-inner membrane junctions) or between two cristal membranes (intercristal membrane junctions). In rat heart, adjoining membranes appeared associated via a central dense midline approximately 30 A wide. In rat kidney, the junction had a ladder-like appearance with electron-dense "bridges" approximately 80 A wide, spaced 130 A apart, connecting the adjoining membranes. We have investigated the conditions which favor the visualization of such structures in mitochondria. Heart mitochondria isolated rapidly from fresh tissue (within 30 min of death) contain membrane junctions in approximately 10-15% of the cross sections. This would indicate that the percentage of membrane junctions in the entire mitochondrion is far greater. Mitochondria isolated from heart tissue which was stored for 1 h at 0 degrees -4 degrees C showed an increased number of membrane junctions, so that 80% of the mitochondrial cross sections show membrane junctions. No membrane junctions are observed in mitochondria in rapidly fixed fresh tissue or in mitochondria isolated from tissue disrupted in fixative. Thus, the visualization of junctions in the intermembrane space of mitochondria appears to be dependent upon the storage of tissue after death. Membrane junctions can also be observed in mitochondria from other stored tissues such as skeletal muscle, kidney, and interstitial cells from large and small intestine. In each case, no such junctions are observed in these tissues when they are fixed immediately after removal from the animal. It would appear that most studies in the literature in which isolated mitochondria from tissues such as heart or kidney were used were carried out on mitochondria which contained membrane junctions. The presence of such structures does not significantly affect normal mitochondrial function in terms of respiratory control and oxidative phosphorylation.