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

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 μ M or less of L ‐cysteine had no effect on responses. Relaxations produced by exogenous NO • (0.25–2.5 μ M ) were markedly prolonged and relaxations produced by sodium nitroprusside (0.001–0.3 μ M ) were enhanced by 1 and 3 m M L ‐cysteine. The enhancements by L ‐cysteine of responses to NO • and sodium nitroprusside may be attributed to the formation of S‐nitrosocysteine. Relaxations mediated by the nitroxyl anion (0.3 μ 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 m M ). EDRF‐mediated relaxations produced by acetylcholine (0.01–10 μ M ), ATP (3–100 μ M ) and the calcium ionophore A23187 (0.1 μ M ) were significantly reduced by 3 m M L ‐cysteine. 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.British Journal of Pharmacology (2000) 129 , 315–322; doi: 10.1038/sj.bjp.0703058