Cytochrome c oxidase activity in osteoclasts appeared in an early stage of parathyroid hormone treatment.

Osteoclasts which appeared in an early stage of parathyroid hormone (PTH) administration were examined using cytochrome c oxidase activity. In the period of 1-2 hr after intraperitoneal administration of PTH, two types of osteoclasts were observed. The first type had a well-developed ruffled border characterized by deeply infolded extracellular channels, and many endocytic vacuoles were observed, as seen in control osteoclasts. Many of the mitochondria contained in the first type were with the reaction products of the enzyme on the crystal membrane and within the intermembrane space (type 1 mitochondria), and the distribution of type 1 mitochondria was similar to that seen in control osteoclasts. The second type had a ruffled border characterized by unclear extracellular channels and cytoplasmic projections. The numerical percentage of type 1 mitochondria in the second type of osteoclasts (45.3%) was significantly smaller than that in the first type (79.9%). Mitochondria which had the reaction products of the enzyme only on the crystal membrane including those with no reaction product (type 2 mitochondria) were predominant in the second type of osteoclasts. These results include two possible ways in which a morphologically regressive change of the ruffled border can occur in osteoclasts during an early stage of PTH treatment, and cytochrome c oxidase activity is closely associated with the change in the ruffled border.