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 mu M or less of L-cysteine had no effect on responses. 2 Relaxations produced by exogenous NO. (0.25-2.5 mu M) were markedly prolonged and relaxations produced by sodium nitroprusside (0.001-0.3 mu M) 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 mu M) 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 mu M), ATP (3-100 mu M) and the calcium ionophore A23187 (0.1 mu M) 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.