Thrombin releases calcium from internal stores of ultraviolet C-treated V79 fibroblasts independent of phosphatidylinositol bisphosphate hydrolysis: Role of oxidative stress

V79 fibroblasts were treated with ultraviolet (UV) C radiation alone as wel l as in conjunction with chronic oxidative stress. The effects of these tre atments on calcium signaling were observed at 30 min post-irradiation. In t he absence of extracellular calcium, thrombin released calcium from interna l stores of UVC-irradiated V79 fibroblasts even after exposure to neomycin. In neomycin-treated control and chronic oxidative stress cells, no calcium release by thrombin was observed after chelation of external calcium. Calc ium release by thrombin from internal stores of UV-irradiated and neomycin- treated cells was completely abolished by pretreatment with N-acetyl cystei ne and dexamethasone. Cellular total soluble thiol content which is a good indicator of cellular reduced glutathione (GSH) level was significantly ele vated 30 min after ultraviolet radiation, indicating an adaptive response a fter oxidative stress. Chronic oxidative stress alone resulted in a much sm aller increase in GSH but chronic oxidative stress in conjunction with UVC produced a very prominent elevation in GSH levels. Our data suggest that th rombin can cause calcium release from internal stores of ultraviolet-irradi ated fibroblasts which is independent of phosphatidylinositol bisphosphate hydrolysis and is directly related to the level of oxidative stress. Involv ement of phopholipadse A(2) and a role for its products as possible mediato rs of calcium release from intracellular stores, is strongly indicated.