Adenosine triphosphate hydrolysis in rat dental tissues. A histochemical study of ion dependencies

The effect of EDTA-decalcification, reactivating and activating procedures on the hydrolysis of ATP was studied histochemically in developing dental tissues in the rat. The incubation media contained lead citrate at alkaline pH and lead nitrate at neutral pH, and the results with ATP as substrate were compared with those obtained with beta-glycerophosphate. The ion dependency of ATP hydrolysis could only be ascertained in decalcified sections. As in earlier studies on the hydrolysis of beta-glycerophosphate in dental tissues, this hydrolysis could readily be reactivated through preincubation of the sections in a series of 0.1 M solutions of divalent cations; Zn2+ being the most efficient. This treatment was now found also to give rise to an ATP hydrolysis, which occurred without the need for activating ions in the incubation medium. This ATP hydrolysis should thus be described as nonspecific and, in terms of ion dependency, as due to a metalloenzyme, i.e. alkaline phosphatase. Activating ion dependent ATP hydrolysis in the dental tissues was found in the blood vessels and in the apical part of the secretory ameloblasts. The former was activated by Mg2+, Ca2+ and Mn2+, and the latter by Ca2+ and--almost specifically--by Sr2+. Preincubation with Zn2+ always inhibited the ion dependant ATP hydrolysis in the dental tissues.