Alkaline Phosphatase Activity of Human Dental Pulpal Fibroblasts

Abstract

We cultured 200 strains of human pulpal fibroblasts (HPF), and found two types (HPF-1 and HPF-2), which showed a different response in alkaline phosphatase (ALPase) activity for 1,25(OH)₂D₃.
HPF and human gingival fibroblasts (Gin 1) were cultured for varying time periods in Dulbecco's modified Eagle medium supplemented with 10% fatal calf serum or a conditioned medium obtained from HPF, and the cell proliferation, protein content and alkaline phosphatase activity were measured. In addition, fibroblast chemotaxis induced by the conditioned medium was measured by the membrane filter method.
The daily dynamic course of HPF-1 proliferation was more active than that of HPF-2, and higher levels of spontaneous ALPase activity were observed. When cultured with 1,25(OH)₂D₃, ALPase activity was 5 times higher for HPF-1 and more than 10 times higher for HPF-2. However, there was no increase in activity when Gin 1 was cultured with 1,25(OH)₂D₃.
When cultured with the conditioned medium, HPF-1 proliferation increased markedly, followed by HPF-2 and Gin 1. However, there was no difference in total protein content among the three cell strains. ALPase activity in HPF-1 increased twofold with addition of the conditioned medium, while that of HPF-2 increased 3.5-5 fold that of the control. In addition, the conditioned medium induced the same levels of chemotactic migration for all three cell strains.
These data suggest that when cultured in 1,25(OH)₂D₃, the ALPase activity of human pulpal fibroblasts is more sensitive than that of human gingival fibroblasts. Furthermore, there are more than two types of fibroblasts in pulpal tissue, and they are different not only in their ALPase activity when cultured with 1,25(OH)₂D₃, but also in the ratio of cell proliferation and protein synthesis. These different and specific qualities may be significant in the defense of pulpal tissue against various foreign stimuli.