Cyclic tension force activates nitric oxide production in cultured human periodontal ligament cells

Background: Nitric oxide (NO) is involved in a number of physiological and pathophysiological processes. The aim of this study was to examine the abil ity of human periodontal ligament (PDL) cells to produce NO and whether mec hanical forces could induce NO production in the PDL cells. Methods: Human PDL cells were seeded onto flexible bottoms of a culture pla te and subjected to cyclic tension forces. NO production was evaluated by m easuring concentration of NO2- and NO3- (NO2-/NO3-), the oxidized products of NO, in the culture medium. We employed reverse transcription polymerase chain reaction (RT-PCR) methods to detect NO synthase mRNA in the PDL cells . NO synthase immunoreactivity was also evaluated in both stimulated and un stimulated PDL cells. Results: In unstimulated PDL cell culture, NO2-/NO3- increased to 140% of t he initial value in 12 hours. In contrast, NO2-/NO3- showed a 3-fold increa se when the cells had been subjected to cyclic tension forces for 12 hours. The increase in NO production was blocked by N-G-monomethyl-L-arginine (5 x 10(-4) M), an inhibitor of NO synthase. Endothelial NO synthase (ecNOS) m RNA was expressed in both stimulated and unstimulated PDL cells, whereas in ducible NO synthase (iNOS) mRNA was detected in neither culturing condition . We found strong ecNOS but not iNOS immunoreactivity in the stimulated PDL cells. Conclusions: These results suggest that human PDL cells produce NO by ecNOS and that the production is enhanced by stimulating the cells with cyclic t ension forces. Mechanically stimulated PDL cells may modulate the function of periodontium by the upregulated NO production.