MITOCHONDRIAL CALCIUM OF INTACT AND MECHANICALLY DAMAGED BONE AND CARTILAGE CELLS STUDIED WITH K-PYROANTIMONATE

Cellular cation was localized with K-pyroantimonate Os fixation in whole fetal mouse metatarsal bones and in deliberately mechanically damaged specimens. X-ray microprobe analysis of ultrathin sections showed a positive correlation between the concentration of Ca (and Sb) and the amount of electron-dense precipitate. In non-damaged osteoblasts and growth-plate chondrocytes dense precipitate accumulated along the plasmalemma and the mitochondrial membranes, whereas damaged cells showed the precipitate on round granules in the mitochondrial matrix but not on membranes. Intermediate stages between these 2 patterns were also found. In a non-calcifying tissue such as liver no membrane-bound precipitate was found in intact cells. However, damaged liver cells showed precipitate-containing mitochondrial granules similar to those in damaged bone cells, but only after incubation of the damaged tissue for 1 h in a Ca-containing balanced salt solution. Freezing of fresh whole bones in liquid N2 before fixation in K-pyroantimonate Os did not change the precipitate pattern in the damaged cells. In intact cells it produced a random distribution of precipitate unrelated to membranes. The results are compared with those obtained in other studies on the subcellular localization of Ca and in biochemical studies in membrane versus matrix loading in Ca-accumulating isolated mitochondria.