Fujimoto Seigo, Mori Mayumi, Tsushima Hiromi
Department of Cellular and Molecular Pharmacology, Nagoya City University Graduate School of Medical Sciences, Mizuho-cho, Mizuho-ku, 467-8601, Nagoya, Japan.
Eur J Pharmacol. 2003 Jan 10;459(1):65-73. doi: 10.1016/s0014-2999(02)02825-x.
The mechanisms underlying the hydrogen peroxide-induced relaxation of the norepinephrine-contraction were studied by measuring isometric force, myosin light chain (MLC(20)) phosphorylation and cyclic GMP in endothelium-denuded muscle from the guinea-pig aorta. Norepinephrine (5.2+/-1.3 microM) produced a phasic, followed by a tonic contraction. Hydrogen peroxide (10 and 100 microM), glyceryl trinitrate (30 and 300 nM) and 8-bromo cyclic GMP (30 and 100 microM) did not change the basal tone, but reduced the norepinephrine-induced contraction. Phosphorylation of MLC(20) (percentage of phosphorylated to total MLC(20)) was increased 1 min (5.9+/-1.0% vs. 35.9+/-4.9%) and, to a lesser extent, 20 min (3.7+/-1.7% vs. 13.9+/-1.6%) after the addition of norepinephrine. Hydrogen peroxide (100 microM) did not modify basal MLC(20) phosphorylation, but reduced the increase in MLC(20) phosphorylation induced by 1-min exposure to norepinephrine (20.9+/-4.1%). Its effect was abolished by catalase. When the tissue was incubated for 20 min with norepinephrine in the presence of hydrogen peroxide, norepinephrine-induced MLC(20) phosphorylation was not changed (13.6+/-1.5%), as compared to that in the absence of hydrogen peroxide. Hydrogen peroxide relaxed norepinephrine-stimulated aortas in a concentration-dependent fashion with EC(50) values of 5.9+/-0.2 microM. The relaxation was inhibited by soluble guanylate cyclase inhibitors and increased by an inhibitor of cyclic GMP-selective phosphodiesterase. In aorta precontracted with norepinephrine, hydrogen peroxide (100 microM) relaxed the tissue by 89+/-11% and almost doubled tissue concentrations of cyclic GMP, whereas sodium nitroprusside (1 microM) relaxed the tissue by 100% and increased cyclic GMP concentrations 30-fold. It is suggested that the inhibitory effects of hydrogen peroxide on the norepinephrine-induced phasic and sustained contractions are explained by a decrease in MLC(20) phosphorylation and by an alteration in MLC(20) phosphorylation-independent mechanisms, respectively. The effects of hydrogen peroxide were in part mediated by cyclic GMP.
通过测量豚鼠主动脉去内皮肌肉的等长力、肌球蛋白轻链（MLC(20)）磷酸化和环鸟苷酸，研究了过氧化氢诱导去甲肾上腺素收缩松弛的机制。去甲肾上腺素（5.2±1.3微摩尔）产生一个相性收缩，随后是一个强直收缩。过氧化氢（10和100微摩尔）、甘油三硝酸酯（30和300纳摩尔）和8-溴环鸟苷酸（30和100微摩尔）不改变基础张力，但降低去甲肾上腺素诱导的收缩。加入去甲肾上腺素后1分钟，MLC(20)磷酸化（磷酸化MLC(20)占总MLC(20)的百分比）增加（5.9±1.0%对35.9±4.9%），20分钟时增加程度较小（3.7±1.7%对13.9±1.6%）。过氧化氢（100微摩尔）不改变基础MLC(20)磷酸化，但降低1分钟暴露于去甲肾上腺素诱导的MLC(20)磷酸化增加（20.9±4.1%）。其作用被过氧化氢酶消除。当组织在过氧化氢存在下与去甲肾上腺素孵育20分钟时，与不存在过氧化氢时相比，去甲肾上腺素诱导的MLC(20)磷酸化没有变化（13.6±1.5%）。过氧化氢以浓度依赖方式松弛去甲肾上腺素刺激的主动脉，EC(50)值为5.9±0.2微摩尔。该松弛被可溶性鸟苷酸环化酶抑制剂抑制，并被环鸟苷酸选择性磷酸二酯酶抑制剂增强。在去甲肾上腺素预收缩的主动脉中，过氧化氢（100微摩尔）使组织松弛89±11%，并使组织中环鸟苷酸浓度几乎增加一倍，而硝普钠（1微摩尔）使组织松弛100%，并使环鸟苷酸浓度增加30倍。提示过氧化氢对去甲肾上腺素诱导的相性和持续性收缩的抑制作用分别由MLC(20)磷酸化减少和MLC(20)磷酸化非依赖机制改变来解释。过氧化氢的作用部分由环鸟苷酸介导。
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