Response of periodontal ligament fibroblasts and gingival fibroblasts to pulsating fluid flow: nitric oxide and prostaglandin E-2 release and expression of tissue non-specific alkaline phosphatase activity

The capacity of the periodontal ligament to alter its structure and mass in response to mechanical loading has long been recognized. However, the mech anism by which periodontal cells can detect physical forces and respond to them is largely unknown. Besides transmission of forces via cell-matrix or cell-cell interactions, the strain-derived flow of interstitial fluid throu gh the periodontal ligament may mechanically activate the periodontal cells , as well as ensure transport of cell signaling molecules, nutrients and wa ste products. Mechanosensory cells, such as endothelial and bone cells, are reported to respond to a flow of fluid with stimulated prostaglandin E-2 ( PGE(2)) and nitric oxide production. Therefore, we examined the PGE(2) and nitric oxide response of human periodontal ligament and gingival fibroblast s to pulsating fluid flow and assessed the expression of tissue non-specifi c alkaline phosphatase activity. Periodontal ligament and gingival fibrobla sts were subjected to a pulsating fluid flow (0.7 +/- 0.02 Pa, 5 Hz) for 60 min. PGE(2) and nitric oxide concentrations were determined in the conditi oned medium after 5, 10, 30 and 60 min of flowing. After fluid flow the cel ls were cultured for another 60 min without mechanical stress. Periodontal ligament fibroblasts, but not gingival fibroblasts, responded to fluid flow with significantly elevated release of nitric oxide and decreased expressi on of tissue non-specific alkaline phosphatase activity. In both periodonta l ligament and gingival fibroblasts, PGE(2) production was significantly in creased after 60 min of flowing. Periodontal ligament fibroblasts, but not gingival fibroblasts, produced significantly higher levels of PGE(2) during the postflow culture period. We conclude that human periodontal ligament f ibroblasts are more responsive to pulsating fluid flow than gingival fibrob lasts. The similarity of the early nitric oxide and PGE(2) responses to flu id flow in periodontal fibroblasts with bone cells and endothelial cells su ggests that these three cell types possess a similar sensor system for flui d shear stress.