Depletion and restoration of the putative photosensitive materials store yielding nitric oxide in the isolated mouse gastric fundus

We investigated the possibility of there being any photosensitive materials stoves yielding nitric oxide (NO), and combined for the first time electri cal field stimulation (EFS)- and UV light-induced relaxations in mouse gast ric fundus. The tissue responded with relaxation to long wave UV light (366 nm). Repeated exposure to light decreased the fundic photorelaxation in th at the initial photorelaxation was 31.5 +/- 6.9% whereas the last (10th) ph otorelaxation was 2.3 +/- 0.3%. There were no significant differences betwe en 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 b locked by 10(-4) M L-N-G-nitroarginine methyl ester. Treatment of the tissu e with NaNO2, L-N-G-nitro-arginine, S-nitrosoglutathione, or sodium nitropr usside for 30 min followed by prolonged washout restored the photorelaxatio n, whereas glyceryl trinitrate or L-arginine did not produce any improvemen t. 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; how ever, it did not change photorelaxations. UV irradiation caused relaxation only when the adventitial surface of the preparation was oriented to the so urce of UV light. These results indicate that there could be a photosensiti ve relaxant materials store yielding NO in the smooth muscle layer of the g astric 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 ni trite, nitrosylated substances, and unknown nitro-containing compounds, whi ch could be all sensitive to UV light.