Abstract
Low‐power laser therapy in medicine is widespread but the mechanisms are not fully understood. It has been suggested that low‐power laser irradiation (LPLI) could induce photochemical reaction and activate several intracellular signaling pathways. Reactive oxygen species (ROS) are considered to be the key secondary messengers produced by LPLI. Here, we studied the signaling pathway mediated by ROS upon the stimulation of LPLI. Src tyrosine kinases are well‐known targets of ROS and can be activated by oxidative events. Using a Src reporter based on fluorescence resonance energy transfer (FRET) and confocal laser scanning microscope, we visualized the dynamic Src activation in Hela cells immediately after LPLI. Moreover, Src activation by LPLI was in a dose‐dependent manner. The increase of Src phosphorylation at Tyr416 was detected by Western blotting. In the presence of vitamin C, catalase alone, or the combination of catalase and superoxide dismutase (SOD), the activation of Src by LPLI is significantly abolished. In contrast, Gö6983 loading, a PKC inhibitor, did not affect this response. Treatment of Hela cells with exogenous H~2~O~2~ also resulted in a concentration‐dependent activation of Src. These results demonstrated that it was ROS that mediated Src activation by LPLI. Cellular viability assay revealed that laser irradiation of low doses (≤25 J/cm^2^) promoted Hela cells viability while high doses impaired. Therefore, LPLI induces ROS‐mediated Src activation which may play an important role in biostimulatory effect of LPLI. J. Cell. Physiol. 217: 518–528, 2008. © 2008 Wiley‐Liss, Inc.