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

Abstract

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.

Contribution of Mitophagy to Cell‐Mediated Mineralization: Revisiting a 50‐Year‐Old Conundrum

“…This calcium buffering capability is responsible for optimal respiratory chain functioning and calcium signaling 14. In the presence of inorganic phosphate ions, calcium ions that are sequestered into the mitochondrial matrix are precipitated as CaP 13. In the present study, CaP granule‐containing mitochondria were sequestered by double‐membrane organelles (Figure 1F).…”

Viral pro-survival proteins block separate stages in Bax activation but changes in mitochondrial ultrastructure still occur

“…Changes in the mitochondrial ultrastructure of control cells undergoing apoptosis in response to FasL/CHX were clearly detectable ( Figure 6a) and were categorized according to the degree of matrix condensation and remodeling of cristae membranes (Figure 6b). We also noticed the appearance of electron dense granules in the matrix of mitochondria following treatment with FasL/CHX that have been reported previously as precipitates of calcium phosphate 28 and have been shown to be reversible in neuronal samples following periods of stimulation. 29 The presence of electron dense granules in the present study suggests there has been significant mitochondrial Ca 2 þ uptake.…”

Surviving Mass Extinctions through Biomineralized DNA

“…[35] On the other hand, mitochondria are able to capture high concentrations of calcium ions from cytosol by allowing the precipitation of HAp inside of them. [38,39] Such reservoirs of calcium and phosphate are mobilized when mitochondria are damaged or cells are necrosed [40] . Additionally, mitochondria are able to release polyphosphates, [41,42] archaic polymers present in all living species from Archae to Eukaryotes, to the cytosol, where they are then converted by hydrolysis to additional phosphates.…”