Exposure of NIH 3T3 fibroblasts to 245 ㎚ short wave UV radiation resulted in the inhibition of phosphorylation of 80 Kd protein. This inhibition was correlated with the inhibition of protein kinase activity in cells by UV light. Intracellular levels of the second messenger molecules in UV damaged cells were measured. It was found that UV light decreased the levels of $IP_3$ and $Ca^{2+}$. $IP_3$ contents measured by the competitive binding assay using bovine adrenal binding protein, were reduced by 80 % in the fibroblasts treated with 15 J/$m^2$ of UV light. UV treatment also lowered the level of cytoplasmic free $Ca^{2+}$. The cells were loaded with 20μM quin 2/AM prior to the UV treatment and cytoplasmic free $Ca^{2+}$ contents were monitored by measuring fluorescence intensities of $Ca^{2+}$ contents were monitored by measuring fluorescence intensities of $Ca^{2+}$ bound quin 2, intracellular concentrations of $Ca^{2+}$ were immediately reduced by UV exposure. The results suggest that UV light causes an acute reduction of $IP_3$ and $Ca^{2+}$ contents in cells, followed by the inhibition of phosphorylation of 80 Kd protein, which interacts with the biochemical responses of mammalian cells to UV light.
