Electron Microscopic Observations on the Accumulation of Divalent Cations in Intramitochondrial Granules

356

126

Rat liver mitochondria allowed to accumulate maximal amounts of Ca ++ and HPO4 = ions from the suspending medium in vitro during respiration have a considerably higher specific gravity than normal mitochondria and may be easily separated from the latter by isopycnic centrifugation in density gradients of sucrose or cesium chloride. When the mitochondria are allowed to accumulate less than maximal amounts of Ca++ and HPO4= from the medium, they have intermediate specific gravities which are roughly proportional to their content of calcium phosphate. Maximally "loaded" mitochondria are relatively homogeneous with respect to specific gravity. Correlated biochemical and electron microscopic studies show that Ca++-loaded mitochondria contain numerous dense granules, of which some 85 per cent are over 500 A in diameter. These granules are electron-opaque not only following fixation and staining with heavy metal reagents, but also following fixation with formaldehyde, demonstrating that the characteristic granules in Ca++-loaded mitochondria have intrinsic electron-opacity. The dense granules are almost always located within the inner compartment of the mitochondria and not in the space between the inner and outer membranes. They are frequently located at or near the cristae and they often show electrontransparent "cores." Such granules appear to be made up of clusters of smaller dense particles, but preliminary x-ray diffraction analysis and electron diffraction studies have revealed no evidence of crystallinity in the deposits. The electron-opaque granules decrease in number when the Ca++-loaded mitochondria are incubated with 2,4-dinitrophenol; simultaneously there is discharge of Ca ++ and phosphate from the mitochondria into the medium.

Section: Fmnae 15 Loaded Mitochondria Containing (Lense Granules (Dg)mentioning

confidence: 99%

Effect of Active Accumulation of Calcium and Phosphate Ions on the Structure of Rat Liver Mitochondria

Greenawalt

Rossi

Lehninger

1964

356

126

“…Inorganic phosphate accumulates concurrently, under these conditions, in a metabolic process which requires either adenosine triphosphate (ATP) or an electron transport-linked translocation of inorganic phosphate from the medium to the mitochondrial matrix (2,6). The continued uptake of calcium and phosphate by mitochondria results in the appearance of electron-opaque masses within the mitochondrial matrix (2,7).…”

mentioning

confidence: 99%

Liver Parenchymal Cell Injury

Reynolds

1965

Accumulation of calcium in the mitochondria of rat liver parenchymal cells at 16 and 24 hours after poisoning with carbon tetrachloride is associated with an increase in amount of liver inorganic phosphate, the persistence of mitochondrial adenosine triphosphatase activity, and the formation of electron-opaque intramitochondrial masses in cells with increased calcium contents. These masses, which form within the mitochondrial matrix adjacent to internal mitochondrial membranes, resemble those observed in isolated mitochondria which accumulate calcium and inorganic phosphate; are present in a locus similar to that of electron opacities which result from electron-histochemical determination of mitochondrial ATPase activity; and differ in both appearance and position from matrix granules of normal mitochondria. After poisoning, normal matrix granules disappear from mitochondria prior to their accumulation of calcium. As calcium-associated electron-opaque intramitochondrial masses increase in size, mitochondria degenerate in appearance. At the same time, cytoplasmic membrane systems of mid-zonal and centrilobular cells are disrupted by degranulation of the rough endoplasmic reticulum and the formation of labyrinthine tubular aggregates. The increase in amount of inorganic phosphate in rat liver following poisoning is balanced by a decreased amount of phosphoprorein. These chemical events do not appear to be related, however, as the inorganic phosphate accumulated is derived from serum inorganic phosphate.

“…Because these intramitochondrial granules become rarer during maturation of the egg, one may suppose that in certain developmental phases of the central cell and also of the subsequent egg cell, the metabolism in the cell or in the mitochondria alters, and that this becomes apparent in the appearance and disappearance of intramitochondrial granules. According to the investigations of Peachey (1964), the intramitochondrial granules become increasingly prominent when the cells of toad urinary bladder or the isolated mitochondria of rat kidney are kept in a medium with divalent cations, barium, strontium, or calcium. Small electron-transparent regions occasionally occur in the matrix of mitochondria and of plasrids during all developmental stages.…”

Section: Discussionmentioning

confidence: 99%

“…This opinion is in strong contrast with the hypotheses of Meyer (1883) and Schimper (1885), that plastids possess a continuity from one plant generation to another. Investigations of Renner (1934) and of Schwemmle and coworkers (1938) strongly indicate plastid inheritance, which must mean plastid continuity, at least a genetical one. Based on their own work on plastid inheritance, SchStz (1962), Stubbe (1962), and Haustein (1962) have already emphasized this fact.…”

Section: Introductionmentioning

confidence: 99%

On the Plastids, Mitochondria, and Other Cell Constituents During Oögenesis of a Plant

Diers

1966

In the liverwort Sphaerocarpus donnellii Aust., the behavior of the cell constituents, especially of mitochondria and plastids, was studied by electron microscopy during the development of the egg and its preceding ceils. A degeneration and elimination of mitochondria and plastids was not found in any of the developmental stages. In all growth phases of the archegonium, the plastids may deposit starch which becomes especially frequent in the maturing egg cell. No indications have been observed that new mitochondria or plastids generate from the nuclear evaginations, which often penetrate deeply into the cytoplasm of the maturing and fully developed eggs. A quantitative investigation based on general micrographs elucidates the numerical aspects of the cell constituents during o6genesis. With the increase of cell volume, the numbers of dictyosomes, mitochondria, plastids, and lipid bodies increase. From the stages of the mother cell of the axial row up to that of the mature egg, the cell volume enlarges about 8 times and the nucleus volume about 15 times. Simultaneously, the numbers of mitochondria and plastids increase up to 8 to 15 times. On the basis of these findings, mitochondria and plastids with three-dimensional narrow constrictions are interpreted as divisional stages.