Alkaline phosphatase and calcification, correlated or not?

The effects of alkaline phosphatase inhibitors (levamisole, L-bromotetramisole) on the activity of the enzyme and on calcification in vitro were studied, to find out whether there is a relationship between alkaline phosphatase and calcification. Metatarsal bones of 15 1/4-day-old embryonic mice were dissected and cultured for 40 hours in the presence and absence of inhibitor. Levamisole and L-bromotetramisole fully inhibited calcification in vitro when present in concentrations which almost totally inhibited alkaline phosphatase activity, as measured biochemically or histochemically. However, incorporation of 3H-thymidine and 35S-sulphate was also inhibited. Furthermore, D-bromotetramisole, the dextroform of bromotetramisole which has no effect on alkaline phosphatase, inhibited calcification and 3H-thymidine and 35S-sulphate incorporation as well. The results of this study show that these inhibitors cannot be used to study the relationship between alkaline phosphatase and calcification. In addition, they suggest that although alkaline phosphatase may be important for the process of calcification, it is probably not a critical factor.