The aim of this study was to investigate the location of photodegradable nitric oxide (NO) store using a pharmacological approach in mouse gastric fundus. The ultraviolet light irradiation (UV, 360 nm, 60 s), electrical field stimulation (EFS; 4 Hz, 25 V, I ms, 15s-train), exogenous nitric oxide (NO; 10 mu M), nitroglycerin (100 mu M) and isoproterenol (5 nM) induced relaxation in mouse gastric fundus preparations in the absence or presence of an intact mucosa. The NO scavenger, haemoglobin (20 mu M), significantly inhibited the relaxation of intact and denuded mucosa stomach fundus to UV light irradiation, EFS and NO, but not to nitroglycerin and isoproterenol. The superoxide anion generator, pyrogallol (50 mu M), inhibited relaxation of intact and denuded mucosa stomach fundus induced by UV light irradiation, EFS, NO, but not to nitroglycerin and isoproterenol. The inhibition observed with pyrogallol was prevented by exogenous Cu/Zn superoxide dismutase (SOD; 100 U/ml), a membrane impermeable antioxidant. The Cu/Zn SOD inhibitor, diethyldithiocarbamic acid (DETCA; 8 mM), inhibited the relaxation of intact and denuded mucosa stomach fundus to UV light irradiation, EFS, NO and nitroglycerin but not those to isoproterenol. Exogenous SOD (100 U/ml) partially prevented the inhibitory effect of DETCA on relaxation to UV light irradiation, EFS, NO but not to nitroglycerin. DETCA-induced inhibition of the nitroglycerin-induced relaxation was partially prevented by the cell-permeable polyethylene-glycol-superoxide dismutase (100 U/ml). These results indicate that photodegradable NO store is, at least in part, unlikely to be within smooth muscle cells, and furthermore, that UV light-induced relaxation is not dependent on gastric mucosal layer. (c) 2006 Elsevier B.V. All rights reserved.