We investigated the possibility of there being any photosensitive materials stoves yielding nitric oxide (NO), and combined for the first time electrical field stimulation (EFS)- and UV light-induced relaxations in mouse gastric fundus. The tissue responded with relaxation to long wave UV light (366 nm). Repeated exposure to light decreased the fundic photorelaxation in that the initial photorelaxation was 31.5 +/- 6.9% whereas the last (10th) photorelaxation was 2.3 +/- 0.3%. There were no significant differences between EFS (30 V, 0.5 ms, 1 Hz, 15s)-induced relaxations obtained before (39.7 +/- 7.7%) and after (33.4 +/- 9.1%) UV irradiation, which were completely blocked by 10(-4) M L-N-G-nitroarginine methyl ester. Treatment of the tissue with NaNO2, L-N-G-nitro-arginine, S-nitrosoglutathione, or sodium nitroprusside for 30 min followed by prolonged washout restored the photorelaxation, whereas glyceryl trinitrate or L-arginine did not produce any improvement. EFS (30 V, 0.5 ms, 3 Hz) applied for 60 min significantly recovered the reduction of the photorelaxation. L-N-(delta)iminoethyl-L-ornithine, which does not contain NO2 moiety, abolished electrically induced relaxation; however, it did not change photorelaxations. UV irradiation caused relaxation only when the adventitial surface of the preparation was oriented to the source of UV light. These results indicate that there could be a photosensitive relaxant materials store yielding NO in the smooth muscle layer of the gastric fundus from mouse. This putative store can be refilled by NaNO2, L-N-G-nitro-arginine, sodium nitroprusside, S-nitrosoglutathione, or long-term EFS but not glyceryl trinitrate or L-arginine. Possible candidates for NO-yielding substances might not be an organic nitrate but an intracellular nitrite, nitrosylated substances, and unknown nitro-containing compounds, which could be all sensitive to UV light.