Ultraviolet irradiation (UVB) interrupts calcium cell signaling in lens epithelial cells

A preliminary study was undertaken to establish whether low-dose UV irradiation (UVB) affects calcium cell signaling in rabbit lens epithelia. In a suspension of lens epithelial cells (line NN1003A), changes in intracellular Ca2+ were measured by Fura-2 fluorescence in response to exogenously added ATP. The cellular response to ATP, referred to as the calcium signal, is characterized by a brief increase and subsequent decrease in cytosolic Ca2+ levels. Ultraviolet B irradiation (1.8-9 mJ/cm2) was found to reduce the magnitude of the Ca2+ signal in a dose-dependent manner. A 5 min UVB exposure (9 mJ/cm2) completely altered the biphasic nature of the calcium signal, causing only an immediate and steady rise in cytosol Ca2+ levels. Lower fluences of UVB irradiation (2 min exposure times or 3.6 mJ/cm2) induced a 50% reduction in the calcium signal. When irradiated cells were returned to culture for 3 h after irradiation, calcium signals induced by ATP were normal. In view of the photooxidative nature of UVB irradiation, the oxidative state of cells was assessed by measuring glutathione (GSH) levels. Ultraviolet B irradiation caused a rapid 20% decline in GSH levels that returned to near-control values after a 3 h postirradiation incubation. The results of this study indicate that fluences lower than previously found to be cataractogenic can perturb calcium cell signaling in cultured lens epithelial cells.