Reactive Oxygen Species in HaCaT Keratinocytes After UVB Irradiation Are Triggered by Intracellular Ca2+ Levels

It is recognized that reactive oxygen species (ROS) are responsible for skin damage due to UVB-radiation (UVB-R). However, the triggering substance(s) for ROS generation after UVB-R is uncertain with respect to the activation of NADPH oxidase (Nox), xanthine oxidase (XOD), and respiratory chain-chain reactions in mitochondria. As a first step in identifying the trigger(s) for UVB-induced ROS generation, we examined the relationship between Ca2+ levels and ROS generation in HaCaT keratinocytes. UVB-R exposure of HaCaT keratinocytes resulted in an immediate elevation of ROS that recurred 7hours later. This was accompanied by immediately elevated intracellular Ca2+. A Ca2+ chelating agent, BAPTA, abolished the elevation of ROS after UVB-R completely. In addition, exogenous H2O2 did not increase intracellular Ca2+ levels. This suggests that intracellular Ca2+ is the first trigger for UVB-induced ROS generation.