Ultraviolet radiation-induced decreases in tension and phosphorylase a formation in rat aorta

Helical strips of rat aorta contracted with norepinephrine (10 nM) respond to ultraviolet (UV) radiation (340-360 nm) with a transient decrease in tension. The UV radiation-dependent relaxation is completely reversible and endothelial cell-independent. Although decreased tension is associated with a rise in tissue cGMP content, the cAMP level is unchanged after UV radiation. A significant inhibition of phosphorylase a formation which occurs coincidently with the rise in cGMP and decline in tension is observed with UV radiation. The effects of UV radiation on cGMP, phosphorylase a formation and tension were blocked by methylene blue. Relaxation and inhibition of phosphorylase a formation in response to UV radiation were also partially reversed with higher concentrations of norepinephrine (100 nM). Our results suggest that cGMP may mediate UV radiation-dependent reactions by reducing cytoplasmic Ca2+.