A histochemical study of acid phosphatases in medullary bone matrix and osteoclasts in laying Japanese quail

Acid phosphatase activity in medullary bone matrix and osteoclasts of laying Japanese quail was examined histochemically. To avoid nonspecific staining, the reactivity of the enzyme was evaluated using both the azo dye method and the lead salt method and nonembedded thick sections and resin‐embedded thin sections. The pH of the incubation medium was also varied from the acid range (pH 5.0 and 6.5) to the alkaline range (pH 8.5). Medullary bone osteoclasts contain both tartrate‐resistant acid phosphatase (TRAP) activity and fluoride‐resistant acid phosphatase (FRAP) activity, and no significant difference in intensity was detected between active and inactive osteoclasts. The entire matrix of medullary bone was positive for tartrate‐resistant, fluoride‐sensitive acid phosphatase activity. No reaction product was observed in sections incubated in substrate‐free and pH 8.5 media. The results demonstrate the existence of FRAP in medullary bone osteoclasts and suggest that medullary bone matrix includes TRAP throughout the matrix.