DISTRIBUTION OF PROTEIN-KINASE CA AND ACCUMULATION OF EXTRACELLULAR CA2+ DURING EARLY DENTIN AND ENAMEL FORMATION

Activation of the protein kinase C (PKC)-related signal transduction s ystem has been associated with phenotypic expression in a wide variety of cell types. In in vitro studies, it has often been activated by re latively small increases in the Ca2+ concentration ([Ca2+]) in the med ium. The studies reported here explored the hypothesis that localized increases in the extracellular [Ca2+] and activation of the PKC-relate d pathway may be involved in early dentin and enamel formation, Whole- head, freeze-dried sections through the developing molars of 5-day-old rats were evaluated by methods that localized non-crystalline Ca2+. I mmunohistochemical methods were adapted for use with the freeze-dried sections, and two monoclonal antibodies were used to localize PKC alph a in the formative cells of the developing teeth. Low concentrations o f extracellular Ca2+ were observed in the early, unmineralized dentin in the area of ameloblast differentiation. Increased concentrations oc curred at the point of initial dentin mineralization, immediately befo re the beginning of enamel matrix deposition. PKC alpha was localized in the differentiating odontoblasts, at the beginning of dentin matrix deposition. It was intensely localized in the distal borders of the p re-ameloblasts, and appeared to redistribute in the cells during amelo blast differentiation. These observations suggest that local increases in the extracellular [Ca2+] and the PKC signal transduction pathway m ay be involved in key inductions in the early stages of dentin and ena mel formation.