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

Abstract

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 microM or less of L-cysteine had no effect on responses. 2. Relaxations produced by exogenous NO(*) (0.25 - 2.5 microM) were markedly prolonged and relaxations produced by sodium nitroprusside (0.001 - 0.3 microM) 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 microM) 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 microM), ATP (3 - 100 microM) and the calcium ionophore A23187 (0.1 microM) were significantly reduced by 3 mM L-cysteine. 5. The similarity between the inhibitory effects of L-cystei on responses to EDRF and on those to nitroxyl suggests that a component of the response to EDRF may be mediated by nitroxyl anion.

Figure 1

The effects of L-cysteine on relaxations to (a) acetylcholine (ACh 0.01–10 μM) and (b) adenosine triphosphate (ATP 1–100 μM) in intact aortic rings, and (c) sodium nitroprusside (SNP 0.001–10 μM) in endothelium-denuded aortic rings contracted with phenylephrine (1 μM) and expressed as percentages of phenylephrine-induced tone. Symbols are means and T-bars indicate s.e.means (n=4–9). In some cases the size of the symbol was greater than the s.e.mean. ^*P<0.05 when compared to respective control curves (two-way ANOVA).

Figure 2

Trace comparing relaxations to NO^• (0.25–2.5 μM in the (a) absence and (b) presence of 3 mM L-cysteine in an endothelium-denuded aortic ring contracted with 1 μM phenylephrine.

Figure 3

Mean data of the effects of L-cysteine on the areas of relaxations to NO^• (0.25, 0.75, 2.5 μM in endothelium-denuded aortic rings contracted with phenylephrine (1 μM). Responses expressed as area of relaxation (mm²) with amplification and time base as in Figure 2. Symbols are means and T-bars indicate s.e.means (n=5). ^*P<0.05 when compared to controls area (two-way ANOVA).

Figure 4

Mean data for the effects of L-cysteine (1 and 3 mM) on relaxations to Angeli's salt (0.3 μM) in endothelium-denuded aortic rings. Responses are expressed as a percentage of phenylephrine-induced tone. Symbols are means and T-bars indicate s.e.means (n=4). ^*P<0.05 when compared to control responses (paired t-test).

Figure 5

Traces illustrating the effects carboxy-PTIO (100 and 300 μM) and ODQ (10 μM) on relaxations to NO^• (0.75 μM) and Angeli's salt (0.75 μM) in endothelium-denuded rat aorta.

Figure 6

Traces illustrating the effects of (a) L-cysteine hydrochloride (L-cys.HCl) and (b) the free base of L-cysteine (3 mM) during sustained relaxations induced by acetylcholine (ACh, 1 μM) in endothelium-intact aortic rings, and by (c) sodium nitroprusside (SNP, 0.1 μM) in endothelium-denuded aortic rings contracted with 1 μM phenylephrine (Phe).