Calcium accumulation by chondrocyte mitochondria.

Chick epiphyseal plate mitochondria observed in vitro suggest that energy dependent Ca++ uptake was maximal in the presence of ATP and a respiratory substrate. However, nucleotides other than ATP had no effect on this type of cation uptake. The observation that Ca++ accumulation was sensitive to the presence of 2,4-DNP and a number of respiratory inhibitors suggested that the mechanism of cation accumulation was similar to that described in tissues that do not undergo biological mineralization. Non-energy supported Ca++ acumulation was studied in the presence of rotenone and antimycin A. Under these conditions, the amount of Ca++ bound by skeletal tissue mitochondria was greater than bound by mitochondria obtained from noncalcifying tissues. Following isopycnic centrifugation, the Ca++ loaded mitochondria banded at different sucrose densties but the Ca++ affinity of mitochondria at each density band was similar. Hence, no particular mitochondrial species seems to be responsible for cation transport.