The Journal of Bone and Joint Surgery, Vol 67, Issue 1 113-120, Copyright © 1985 by Journal of Bone and Joint Surgery, Inc
Calcium flux and endogenous calcium content in isolated mammalian growth-plate chondrocytes, hyaline-cartilage chondrocytes, and hepatocytes
JP Iannotti, CT Brighton, JL Stambough and BT Storey
The role of chondrocyte mitochondria in endochondral ossification has been
the subject of intensive investigation and controversy. The purpose of this
study was to quantitate the endogenous calcium content and the maximum
capacity for calcium accumulation and release in isolated mammalian
growth-plate chondrocytes and hyaline-cartilage chondrocytes. The results
indicated that the mitochondria of the isolated growth-plate and
hyaline-cartilage chondrocytes possess a greater endogenous calcium
content, a greater capacity for calcium accumulation, and a larger labile
Ca+2 pool than do the mitochondria of hepatocytes. Growth-plate and
hyaline-cartilage mitochondria had an endogenous calcium content of 908 and
142 nanomoles of Ca+2 per milligram of mitochondrial protein. The
growth-plate mitochondria had a maximum calcium capacity of 5249 nanomoles
of Ca+2 per milligram of mitochondrial protein. In comparison, the
mitochondria of hepatocytes had a much smaller endogenous-calcium content
and a smaller maximum Ca+2 capacity: twenty-one and 3262 nanomoles of Ca+2
per milligram of mitochondrial protein, respectively. The mitochondrial
labile-calcium pool in both growth-plate and hyaline-cartilage chondrocytes
was twofold greater than that in the mitochondria of hepatocytes.
Chondrocyte mitochondria released approximately 2400 nanomoles of Ca+2 per
milligram of mitochondrial protein, whereas hepatocyte mitochondria
released 1200 nanomoles of Ca+2 per milligram. These results suggest that
the chondrocyte mitochondria are specialized for calcium transport and are
important in the calcification of the extracellular matrix of the growth
plate.