Differential actions of L-cysteine on responses to nitric oxide, nitroxyl anions and EDRF in the rat aorta

1. The effects of L-cysteine were tested in rat aortic rings on responses to nitric oxide free radical (NO(*)), nitroxyl (NO^-) derived from Angeli's salt and endothelium-derived relaxing factor (EDRF) activated by acetylcholine, ATP and the calcium ionophore A23187. Concentrations of 300 mM or less of L-cysteine had no effect on responses. 2. Relaxations produced by exogenous NO(*) (0.25-2.5 mM) were markedly prolonged and relaxations produced by sodium nitroprusside (0.001-0.3 mM) were enhanced by 1 and 3 mM L-cysteine. The enhancements by L-cysteine of responses to NO(*) and sodium nitroprusside may be attributed to the formation of S-nitrosocysteine. 3. Relaxations mediated by the nitroxyl anion (0.3 mM) donated from Angeli's salt were more prolonged than those produced by NO(*), and nitroxyl-induced relaxations were reduced by L-cysteine (1 and 3 mM). 4. EDRF-mediated relaxations produced by acetylcholine (0.01 -10 mM), ATP (3 - 100 mM) and the calcium ionophore A23187 (0.1 mM) were significantly reduced by 3 mM L-cysteine. 5. The similarity between the inhibitory effects of L-cysteine on responses to EDRF and on those to nitroxyl suggests that a component of the response to EDRF may be mediated by nitroxyl anion.