Abstract
Cells emerging from a dental pulp explant were studied in order to elucidate the origin of precursor cells implicated in the formation of reparative dentin in vivo. Such cells observed at the very early stage of culture (days 5-10) were different from fibroblast-like cells obtained after one subculture. These early cells were round or elongated, with thin spinous processes, highly mobile, and contained numerous lipid vesicles. Incorporation of 1-[14C]palmitic acid did not show an increased incorporation of radiolabeled total lipids or triglycerides into these early cells compared to cells after four subcultures or control skin fibroblasts, suggesting that the lipids in vesicles were not synthesized by the cells. Since these cells also show a high level of fluid phase uptake via macropinocytosis, it is suggested that these lipids originate from macropinocytosis. Between days 10 and 20, these cells spontaneously start conversion into cells that have a fibroblast-like morphology, are less mobile, and lack lipid vesicles. Their morphology, movement, and macropinocytosis suggest that these cells, which migrate from the pulp explants, are mesenchymal cells related to mononuclear phagocytes/histiocytes.