Department of Pharmacology, Faculty of Health Sciences, Aarhus University, Aarhus, Denmark.
Am J Physiol Lung Cell Mol Physiol. 2010 Apr;298(4):L531-42. doi: 10.1152/ajplung.00220.2009. Epub 2010 Jan 29.
This study investigated the mechanisms underlying epithelium-derived hyperpolarizing factor (EpDHF)-type relaxation in rat bronchioles. Immunohistochemistry was performed, and rat bronchioles and pulmonary arteries were mounted in microvascular myographs for functional studies. An opener of small (SK(Ca)) and intermediate (IK(Ca))-conductance calcium-activated potassium channels, NS309 (6,7-dichloro-1H-indole-2,3-dione 3-oxime) was used to induce EpDHF-type relaxation. IK(Ca) and SK(Ca)3 positive immunoreactions were observed mainly in the epithelium and endothelium of bronchioles and arteries, respectively. In 5-hydroxytryptamine (1 microM)-contracted bronchioles (828 +/- 20 microm, n = 84) and U46619 (0.03 microM)-contracted arteries (720 +/- 24 microm, n = 68), NS309 (0.001-10 microM) induced concentration-dependent relaxations that were reduced by epithelium/endothelium removal and by blocking IK(Ca) channels with charybdotoxin and in bronchioles also by blocking SK(Ca) channels with apamin. Inhibition of cyclooxygenase, nitric oxide synthase, and cytochrome 2C isoenzymes, or blockade of large (BK(Ca))-conductance calcium-activated potassium channels with iberiotoxin, failed to reduce NS309 relaxation. In contrast to the pulmonary arteries, relaxations to a beta(2)-adrenoceptor agonist, salbutamol, were reduced in bronchioles by removing the epithelium or blocking IK(Ca) and/or SK(Ca) channels. Extracellular K(+) (2-20 mM) induced relaxation in both bronchioles and arteries. An inhibitor of Na(+)-K(+)-ATPase, ouabain, abolished relaxations to NS309, salbutamol, and K(+). These results suggest that IK(Ca) and SK(Ca)3 channels are located in the epithelium of bronchioles and endothelium of pulmonary arteries. Analog to the endothelium-derived hyperpolarizing factor (EDHF)-type relaxation in pulmonary arteries, these channels may be involved in EpDHF-type relaxation of bronchioles caused by epithelial K(+) efflux followed by activation of Na(+)-K(+)-ATPase in the underlying smooth muscle layer.
本研究旨在探讨上皮衍生超极化因子（EpDHF）型松弛的作用机制。通过免疫组织化学方法，并在微血管张力计上对大鼠细支气管和肺动脉进行功能研究。使用 SK(Ca) 和 IK(Ca) 通道开放剂 NS309（6,7-二氯-1H-吲哚-2,3-二酮 3-肟）诱导 EpDHF 型松弛。观察到 IK(Ca) 和 SK(Ca)3 阳性免疫反应主要存在于细支气管和动脉的上皮和内皮中。在 5-羟色胺（1 microM）收缩的细支气管（828 +/- 20 µm，n = 84）和 U46619（0.03 microM）收缩的动脉（720 +/- 24 µm，n = 68）中，NS309（0.001-10 microM）诱导浓度依赖性松弛，上皮/内皮去除和使用霍乱毒素阻断 IK(Ca) 通道以及在细支气管中使用 apamin 阻断 SK(Ca) 通道均可减少这种松弛。抑制环氧化酶、一氧化氮合酶和细胞色素 2C 同工酶，或使用 Iberiotoxin 阻断大电导钙激活钾通道（BK(Ca)），均不能减少 NS309 的松弛作用。与肺动脉不同，β2-肾上腺素能受体激动剂沙丁胺醇引起的松弛作用在去除上皮或阻断 IK(Ca) 和/或 SK(Ca) 通道后，在细支气管中减弱。细胞外 K+（2-20 mM）在细支气管和动脉中均诱导松弛。Na+-K+-ATP 酶抑制剂哇巴因消除了 NS309、沙丁胺醇和 K+的松弛作用。这些结果表明，IK(Ca) 和 SK(Ca)3 通道位于细支气管的上皮和肺动脉的内皮中。类似于肺动脉中的内皮衍生超极化因子（EDHF）型松弛，这些通道可能参与上皮细胞 K+外流引起的 EpDHF 型细支气管松弛，随后在平滑肌层中激活 Na+-K+-ATP 酶。
