A histochemical study of tartrate-resistant acid phosphatase activity in rat osteoblasts

Tartrate-resistant acid phosphatase (TRAP) activity in the metaphyseal and diaphyseal osteoblasts of the tibiae of young growing rats was histochemically examined. To evaluate the histochemical reactivity of TRAP, both the azo-dye method and the lead-salt method were used. In metaphyseal bone trabeculae, both osteoblasts end osteoclasts existed on the bone surfaces, indicating active bone remodeling. The osteoblasts appeared round or columnar in shape with abundant cytoplasm. Most osteoblasts were TRAP-positive and the reaction product was distributed throughout the cytoplasm, producing a granular appearance. Osteoclasts had the most intense TRAP activity among bone cells. In the endosteum of diaphyses, the bone surfaces were commonly covered with osteoblasts, indicating predominant bone formation. The osteoblasts in these areas were TRAP negative. On some endosteal surfaces, where bone remodeling was taking place, the osteoblasts co-existed with osteoclasts. In these areas the osteoblasts were TRAP-positive. From these results, it was shown that TRAP-positive osteoblasts existed, and that the osteoblasts located at or near the regions where osteoclastic bone resorption was taking place, became TRAP positive.