Characterization of a system of mineralized-tissue formation by rat dental pulp cells in culture.

Pulp tissue was obtained from maxillary incisors of young adult male Wistar rats, minced and digested with 0.5% trypsin and 0.02% EGTA at 37 degrees C for 30 min. Dissociated cells were cultured with or without 10 nM dexamethasone using Eagle's minimal essential medium supplemented with 10% fetal bovine serum and 50 micrograms/ml ascorbic acid. Confluent cells were subcultured at 7 days and the medium further supplemented with beta-glycerophosphate (beta-GP). Dexamethasone in primary culture and/or secondary culture enhanced the formation of mineralized tissue while > 5 mM beta-GP was necessary for mineralization to occur. Biochemical analysis of the radiolabelled medium revealed that these cells produced type I, type I trimer and type III collagens. Analysis of [32PO4]-labelled medium, using DEAE-Sephacel ion-exchange chromatography and sodium dodecylsulphate-polyacrylamide gel electrophoresis, showed that these cells produced phosphophoryn-like protein. These results indicate that some of the rat dental pulp cells in culture express an odontoblast-like phenotype.