Membrane junctions in the intermembrane space of mitochondria from mammalian tissues

Delayed Onset of Age-Dependent Changes in Ultrastructure of Myocardial Mitochondria as One of the Neotenic Features in Naked Mole Rats (Heterocephalus glaber)

In this study, the ultrastructure of mitochondria in cardiomyocytes of naked mole rats (Heterocephalus glaber) aged from 6 months to 11 years was examined. Mitochondria in cardiomyocytes of naked mole rats have a specific ultrastructure that is different from those in cardiomyocytes of other mammalian species studied to date. In contrast to mitochondria of other mammalian cardiomyocytes, where the internal space is completely filled by tightly packed parallel rows of cristae, mitochondria in cardiomyocytes of naked mole rats have a chaotic pattern of cristae organization with wave-like contours. Gradual formation of mitochondrial ultrastructure occurs in naked mole rats for many years. Two mitochondrial populations are developed to the age of 5 years. In addition to the main population, there are some large organelles which exceed normal sizes by two to three times. Most cristae in these mitochondria are assembled into small groups, which form the curved and ring-like structures. The appearance of some specific structural changes (i.e. bundles of parallel cristae) is observed in the mitochondrial population of naked mole rat after 11 years of age. However, these bundles are very rare and of sporadic nature. Morphometric analysis has shown that the superficial density of the inner mitochondrial membrane is similar in all examined age groups of naked mole rats: 21.1 at 6 months; 23.21 at 3 years; 23.55 at 5 years; and 20.8 at 11 years. This level is almost two times lower than in other animals studied (mice and rats). The data demonstrate that pathological changes in mitochondrial apparatus are not present in naked mole rats at least until the age of 11 years. The mitochondrial apparatus corresponds to the phenotype in young animals, thus being another neotenic feature in naked mole rats.

Mitochondrial reticulum for cellular energy distribution in muscle

Intracellular energy distribution has attracted much interest and has been proposed to occur in skeletal muscle via metabolite-facilitated diffusion; however, genetic evidence suggests that facilitated diffusion is not critical for normal function. We hypothesized that mitochondrial structure minimizes metabolite diffusion distances in skeletal muscle. Here we demonstrate a mitochondrial reticulum providing a conductive pathway for energy distribution, in the form of the proton-motive force, throughout the mouse skeletal muscle cell. Within this reticulum, we find proteins associated with mitochondrial proton-motive force production preferentially in the cell periphery and proteins that use the proton-motive force for ATP production in the cell interior near contractile and transport ATPases. Furthermore, we show a rapid, coordinated depolarization of the membrane potential component of the proton-motive force throughout the cell in response to spatially controlled uncoupling of the cell interior. We propose that membrane potential conduction via the mitochondrial reticulum is the dominant pathway for skeletal muscle energy distribution.

Dynamic organization of mitochondria in human heart and in myocardial disease

Heart mitochondria, which, depending on their location within cardiomyofibers, are classified as either subsarcolemmal or interfibrillar, are the major sources of the high energy compound, adenosine triphosphate. Physiological differences between these two populations are reflected by differences in the morphology of their cristae, with those of subsarcolemmal mitochondria being mostly lamelliform, and those of interfibrillar mitochondria being mostly tubular. What determines the configuration of cristae, not only in cardiac mitochondria but in mitochondria in general, is unclear. The morphology of cardiac mitochondria, as well as their physiology, is responsive to the exigencies posed by a large variety of pathological situations. Giant cardiac mitochondria make an appearance in certain types of cardiomyopathy and as a result of dietary, pharmacological, and toxicological manipulation; such megamitochondria probably arise by a combination of fusion and true growth. Some of these enlarged organelles occasionally contain a membrane-bound deposit of beta-glycogen. Those giant mitochondria induced by experimental treatment usually can be restored to normal dimensions simply by supplying the missing nutrient or by deleting the noxious substance. In some conditions, such as endurance training and ischemia, the mitochondrial matrices become pale. Dense rods or plates are present in the outer compartment of mitochondria under certain conditions. Biochemical alterations in cardiac mitochondria appear to be important in heart failure. In aging, only interfibrillar mitochondria exhibit such changes, with the subsarcolemmal mitochondria unaffected. In certain heart afflictions, biochemical defects are not accompanied by obvious morphological transformations. Mitochondria clearly play a cardinal role in homeostasis of the heart.

Mitochondrial channel activity studied by patch-clamping mitoplasts

Patch-clamping mitoplasts, we have observed a complex pattern of conductance transitions. This report discusses primarily the 45, 120-150, 350, and 1,000 pS transitions.

Intramitochondrial inclusions in maturing and senescent muscle cells of rat myocardium

Intramitochondrial myelin-like structures were found in ventricular myocardial cells of the rat heart. These inclusions were found in both the first 2 postnatal weeks and in senescent stages. The origin of such myelin-like structures could be related to an age-dependent metabolic change, specifically to an inability to oxidize long-chain fatty acids described in both periods.

Giant mitochondria in a pleomorphic adenoma of the submandibular gland

A benign pleomorphic adenoma of the submandibular gland was examined by electron microscopy. In some areas, the epithelial cells comprising the tumor formed ductlike structures surrounding a lumen filled with membrane vesicles. The cells actually abutting the lumens had giant mitochondria measuring up to 8 micrometers in diameter; such enlarged organelles were absent from immediately subjacent cells. The giant mitochondria exhibited a variety of cristal arrangements, the most common being a quasireticulate one. They often contained expanded cristae that enclosed a number of helical filaments. Bundles of 14-nm tubules with faintly discernible axial periodicity were frequently present in the matrix compartment, as were amorphous dense inclusions. The basis for the occurrence of giant mitochondria only in duct cells may reside in microenvironmental factors rather than in altered nuclear or mitochondrial genomes.

The occurrence of paracrystalline mitochondrial inclusions in normal human skeletal muscle

Two different types of paracrystalline mitochondrial inclusions identical with or very similar to those already described in the literature for a variety of muscle diseases were found in human skeletal muscle biopsies obtained under general anesthesia before ischemia and after various periods of anoxia up to 150 min. As these crystalloids could be observed in seven of 14 healthy subjects and occurred in five of these seven cases either before or only 10 min after onset of ischemia, it is suggested that such mitochondrial inclusions develop not only under the influence of variant noxious stimuli, but may also represent a normal constituent of human skeletal muscle mitochondria.

Focal laminate segments in cytoplasmic processes of mouse myocardial fibroblasts

In mouse ventricular myocardium, we have found unusual fibroblasts whose cellular processes in some regions are particularly flattened and which contain linearly-arranged, electron-opaque structures ('central laminae"). The morphology of these focal laminate segments of fibroblast processes suggests that the intracellular laminae are adhesive entities which hold the plasmalemmata above and below them in close parallel apposition for short distances.

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.

Transvascular endomyocardial biopsy in infants and small children. Myocardial findings in 10 cases of cardiomyopathy

Transvascular endomyocardial biopsy specimens from nine children with congestive cardiomyopathy and one with hypertrophic cardiomyopathy were studied by light microscopy using sections 1 mu thick cut from Epon embedded tissue and by electron microscopy. There was a disparity between the severity of the physiologic impairment and the morphologic abnormalities. Interstitial fibrosis was present only in the one case in which significant viral antibody titers were obtained. The sizes of the cardiac muscle cells varied abnormally in all specimens. Cardiac muscle cells in two patients contained abnormal mitochondria, and a leptomeric fibril was found in one patient. Virologic cultures of the tissues were negative and no viral particles were identified by electron microscopy. An attempt was made to correlate the clinical and pathologic findings.

Ultrastructural differences in mitochondria of skeletal muscle in the prerigor and rigor states

Loss of cristae and matrix occur in the mitochondria of skeletal muscles prior to any observable changes in myofibrillar proteins during the development of rigor mortis. Care must be observed because ultrastructural changes in mitochondria in some studies may be attributed to a specific trauma, whereas the changes may be due to the lower pH in postmortem muscle.

[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.

Septate junctions between digestive vacuoles in human malacoplakia

Typical septate junctions between digestive vacuoles in phagocytic cells of human malacoplakia are described in this paper. Evidence for a honeycomb pattern of hexagonal subunits is presented for their cleft material. Junctions were not observed between other organelles or in cells other than phagocytes. It is assumed that the septate junctions described here may reflect a pathological change in the organization of the membrane components of digestive organelles.

Formaldehyde-induced appearance of septate junctions between digestive vacuoles

Tissue biopsies from (1) some chronic inflammatory diseases, (2) a necrotic tumoral process, (3) normal human lymphatic ganglia, and (4) two congenital diseases of the adrenal cortex were selected for study. A block from each biopsy was fixed in glutaraldehyde-paraformaldehyde; a second block was fixed in 10% formaldehyde. In all cases septate junctions between digestive vacuoles did occur in phagocytic cells and some adrenal cortex cells fixed in formaldehyde. These junctions were similar to those reported recently for malakoplakia phagocytes. Consistently, they were not found to attach organelles other than lysosomes derivatives. Both phagocytes and adrenal cortex cells in the material fixed in glutaraldehyde-paraformaldehyde did not display adhesive specializations between digestive vacuoles. This suggests that the septate junctions described herein are artifactuous structures induced by formaldehyde. There is, however, a certain degree of specificity of cells having the capability of developing these septate junctions. It is assumed that the coating material of digestive organelles in phogocytes and some other cells would be responsible for both cell specificity and organelle specificity of the formaldehyde-induced septate junctions.

Site-specific membrane particle arrays in magnesium-depleted Escherichia coli

The ultrastructure and polypeptide composition of a novel membrane junction in magnesium-starved Escherichia coli are described in this report. Freeze-fracture replicas reveal the junction as a site-specific membrane particle array with four fracture faces. Each junction consists of a cell membrane, a midline zone and a coupled membrane. Membrane particles associated with the junction extend from the hydrophobic region of the cell membrane across the hydrophilic midline zone and into the hydrophobic region of the coupled membrane. After negative staining or after rotary shadowing of freeze-fractured specimens, these particles were seen to consist of two similar but slightly offset bracket-shaped subunits separated by a small space. Optical analysis confirms this structure. Since the apposing membranes are bracketed or linked by their component particles, the name "bracket junction" is proposed for the complex. Methods are described for isolating a membrane fraction enriched in these junctional complexes; the fraction contains a prominent glycoprotein (mol wt 90,000) as well as a number of other components. The bracket junction is compared with the vertebrate gap junction in terms of both structure and possible roles in facilitating the permeation of the cell by small molecules.

Mitochondrial abnormalities in human phaeochromocytoma

Mitochondrial abnormalities are reported in four cases of phaeochromocytoma. These abnormalities include swelling and scant cristae, intramitochondrial dense bodies, septate-like junctions, intercristal fusion plus spheroidal bodies, and intramitochondrial rodlets. These structural mitochondrial changes are associated with reduction in activity of the mitochondrial enzymes, monoamine oxidase and succinic dehydrogenase.

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.