Abstract
1. In the present study, we investigated the roles of Na +-K +-ATPase and extracellular Na + or Ca 2+ ions in ultraviolet (UV) light-induced photorelaxation of methacholine-contracted mouse isolated gastric fundus in the presence of NaNO 2 (50 μM). 2. Ouabain (1–500 μM), sodium vanadate (10 μM to 3 mM) and amiloride (1–100 μM) completely inhibited the photorelaxation in a concentration-dependent manner. 3. Metabolic inhibitors, sodium azide (10–100 μM), 2,4-dinitrophenol (100 μM to 1 mM) and sodium fluoride (100 μM to 1 mM) significantly reduced photorelaxation. 4. Substitution of sucrose, lithium or KCl with extracellular Na + completely abolished the photorelaxant responses. 5. Replacement of all extracellular CaCl 2 with BaCl 2 also completely inhibited UV-induced relaxation. 6. Verapamil (1–10 μM) decreased UV-induced relaxation significantly. 7. These results suggest that nitric oxide produced from NaNO 2 by UV-light in mouse gastric fundus probably stimulates Na +-K +-ATPase activity, and photorelaxation of gastric smooth muscle is dependent on extracellular Na + and Ca 2+ ions.
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