Taguchi H, Heistad D D, Chu Y, Rios C D, Ooboshi H, Faraci F M
Department of Internal Medicine, University of Iowa College of Medicine, Iowa City, USA.
J Pharmacol Exp Ther. 1996 Dec;279(3):1514-9.
We tested the hypothesis that expression of inducible nitric oxide synthase (NO-synthase) in response to endotoxin (lipopolysaccharide) produces activation of potassium channels. Contraction of the rat thoracic aorta in response to phenylephrine was measured in vitro after treatment in vivo for 15 hr with vehicle (control) or lipopolysaccharide (10 mg/kg i.p.). Impaired contraction in response to phenylephrine was used as an index of inducible NO-synthase expression, and activation of potassium channels was examined with specific inhibitors. Contraction in response to 10(-5) M phenylephrine (expressed as a percentage of contraction in response to 85 mM KCI) was markedly impaired in lipopolysaccharide-treated rats, compared with control (15 +/- 5% vs. 131 +/- 10%, P < .05, mean +/- S.E.). Expression of inducible NO-synthase mRNA in the vessel wall in lipopolysaccharide-treated rats was confirmed using reverse transcription-polymerase chain reaction. Contraction of the aorta in lipopolysaccharide-treated rats was restored to normal by 0.3 mM aminoguanidine (an inhibitor of inducible NO-synthase). Contraction of the aorta in response to phenylephrine, which was inhibited by lipopolysaccharide, was not affected by glibenclamide (an inhibitor of ATP-sensitive potassium channels) but was increased 2-fold (P < .05) by iberiotoxin (50 nM), an inhibitor of Ca(+2)-dependent potassium channels. Relaxation of the aorta in response to sodium nitroprusside, an exogenous donor of nitric oxide, and 8-bromo-cyclic GMP was also inhibited by iberiotoxin. These findings suggest that nitric oxide produced by vascular expression of inducible NO-synthase activates calcium-dependent potassium channels and that this mechanism may contribute to impaired vasoconstrictor responses during sepsis.
诱导型一氧化氮合酶（NO合酶）在内毒素（脂多糖）刺激下的表达会导致钾通道激活。在用赋形剂（对照）或脂多糖（10mg/kg腹腔注射）体内处理15小时后，体外测量大鼠胸主动脉对去氧肾上腺素的收缩反应。对去氧肾上腺素反应性收缩减弱被用作诱导型NO合酶表达的指标，并用特异性抑制剂检测钾通道的激活情况。与对照组相比，脂多糖处理的大鼠对10⁻⁵M去氧肾上腺素的收缩反应（以对85mM氯化钾收缩反应的百分比表示）明显减弱（15±5%对131±10%，P<.05，平均值±标准误）。使用逆转录-聚合酶链反应证实了脂多糖处理大鼠血管壁中诱导型NO合酶mRNA的表达。0.3mM氨基胍（诱导型NO合酶抑制剂）可使脂多糖处理大鼠的主动脉收缩恢复正常。脂多糖抑制的对去氧肾上腺素的主动脉收缩不受格列本脲（ATP敏感性钾通道抑制剂）影响，但可被iberiotoxin（50nM，Ca²⁺依赖性钾通道抑制剂）增加2倍（P<.05）。iberiotoxin也抑制了主动脉对一氧化氮的外源性供体硝普钠和8-溴环鸟苷酸的舒张反应。这些发现表明，血管中诱导型NO合酶表达产生的一氧化氮激活了钙依赖性钾通道，并且该机制可能导致脓毒症期间血管收缩反应受损。
