sodium-nitrite and 6-anilino-5-8-quinolinedione

1. Single skeletal muscle fibres from a mouse foot muscle were used to investigate the effects of nitric oxide on contractile function. 2. We measured force production and myoplasmic free Ca2+ concentration ([Ca2+]i) in single fibres exposed to the nitric oxide donors S-nitroso-N-acetylcysteine (SNAC) and nitroprusside. 3. The nitric oxide donors reduced myofibrillar Ca2+ sensitivity, whereas [Ca2+]i transients were increased during submaximal tetani. Force was largely unchanged. SNAC did not change maximum shortening velocity, the rate of force redevelopment, or force production at saturating [Ca2+]i. 4. The guanylyl cyclase inhibitor LY83583 increased tetanic [Ca2+]i but had no effect on Ca2+ sensitivity. LY83583 did not prevent the decrease in myofibrillar Ca2+ sensitivity in response to SNAC. The oxidizer sodium nitrite increased tetanic [Ca2+]i and decreased myofibrillar Ca2+ sensitivity. 5. We conclude that under our experimental conditions nitric oxide impairs Ca2+ activation of the actin filaments which results in decreased myofibrillar Ca2+ sensitivity.

Topics: Acetylcysteine; Aminoquinolines; Animals; Calcium; Enzyme Inhibitors; Guanylate Cyclase; In Vitro Techniques; Kinetics; Male; Mice; Mice, Inbred Strains; Muscle Contraction; Muscle Fibers, Skeletal; Muscle, Skeletal; Myofibrils; Nitric Oxide; Nitroprusside; Sodium Nitrite

Relaxations induced by electrical field stimulation and acetylcholine were compared with those induced by acidified sodium nitrite, sodium nitroprusside, S-nitrosoglutathione and S-nitroso-N-acetyl-D,L-penicillamine in the mouse corpus cavernosum precontracted with phenylephrine. NG-nitro-L-arginine inhibited electrical field stimulation- or acetylcholine-induced relaxation, but was ineffective on relaxations caused by the other stimuli. Hydroquinone and pyrogallol had no inhibitory action on the relaxations caused by any stimulus except acidified sodium nitrite. Incubation of the tissue with diethyldithiocarbamic acid significantly inhibited the relaxations induced by all stimuli except papaverine. In the tissues pre-treated with diethyldithiocarbamic acid, superoxide dismutase, hydroquinone and pyrogallol failed to yield restore or further inhibit the relaxations in response to electrical field stimulation or acetylcholine. LY 83583 (6-anilino-5,8-quinolinedione) and hydroxocobalamin clearly inhibited the relaxant responses to electrical field stimulation, acetylcholine, S-nitrosoglutathione and acidified sodium nitrite whereas there was significant enhancement of the relaxation produced by S-nitroso-N-acetyl-D,L-penicillamine. These findings suggest that the relaxant factor released from non-adrenergic non-cholinergic nerves or endothelial cells in mouse cavernosal tissue may be a superoxide anion-resistant nitric oxide-containing molecule and that S-nitrosoglutathione rather than S-nitroso-N-acetyl-D,L-penicillamine could be a suitable candidate for this.

Topics: Acetylcholine; Aminoquinolines; Animals; Chelating Agents; Ditiocarb; Electric Stimulation; Enzyme Inhibitors; Hematinics; Hydrogen-Ion Concentration; Hydroquinones; Hydroxocobalamin; In Vitro Techniques; Male; Mercaptoethanol; Mice; Muscle Relaxation; Muscle, Smooth; Mutagens; Nitric Oxide; Nitroarginine; Nitroprusside; Nitroso Compounds; Penis; Pyrogallol; S-Nitrosothiols; Sodium Nitrite; Vasodilator Agents

The biochemical mechanism subserving smooth muscle relaxant effects of sodium nitroprusside was examined on U46619, 9,11-dideoxy-9 alpha,11 alpha-methanoepoxy PGF2 alpha, precontracted guinea-pig lung strips and hilar bronchial rings. Lung strips were resistant to the relaxant action of sodium nitroprusside or sodium nitrite (NaNO2), whereas they markedly relaxed to 8-bromo-cyclic GMP (8-Br-cGMP), a membrane permeable analogue of cGMP. Precontracted bronchial rings completely relaxed to sodium nitroprusside, NaNO2, or 8-Br-cGMP in a concentration-dependent manner. Sodium nitroprusside (10 microM) substantially raised tissue cGMP level in lung strips. Conversely, sodium nitroprusside had no detectable effect on cGMP levels in bronchial rings. In the presence of 10 microM dipyridamole, an agent which preferentially inhibits cGMP-specific phosphodiesterase, cGMP levels in lung strips treated with sodium nitroprusside was significantly enhanced, but sodium nitroprusside demonstrated no relaxant effect on the preparations. However, dipyridamole potentiated sodium nitroprusside-induced precontracted bronchial ring relaxation without affecting the bronchial tissue cGMP level. In the presence of 10 microM LY83583 (6-anilino-5,8-quinoline-dione), a specific cGMP concentration-lowering agent, sodium nitroprusside-mediated elevation of cGMP level in lung strips was significantly reduced with no effect on the functional response. LY83583 demonstrated no inhibitory effect on either relaxation or cGMP level in bronchial rings treated with sodium nitroprusside. Our results suggest that precontracted smooth muscle in lung strips and in hilar bronchi respond distinctly to sodium nitroprusside. Furthermore, sodium nitroprusside mediates bronchial smooth muscle relaxation by mechanisms unrelated to cGMP.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Aminoquinolines; Analysis of Variance; Animals; Bronchi; Cyclic GMP; Dose-Response Relationship, Drug; Guanylate Cyclase; Guinea Pigs; Lung; Male; Muscle Relaxation; Muscle, Smooth; Nitroprusside; Prostaglandin Endoperoxides, Synthetic; Sodium Nitrite; Thromboxane A2; Vasoconstrictor Agents; Vasodilator Agents