Goto Kenichi, Rummery Nicole M, Grayson T Hilton, Hill Caryl E
Division of Neuroscience, John Curtin School of Medical Research, Australian National University, Canberra, ACT, 0200, Australia.
J Physiol. 2004 Nov 15;561(Pt 1):215-31. doi: 10.1113/jphysiol.2004.070458. Epub 2004 Oct 1.
The present study was designed to elucidate whether the conduction of vasomotor responses mediated by endothelium-derived hyperpolarizing factor (EDHF) in rat mesenteric arteries is altered during hypertension. Iontophoresed acetylcholine (ACh; 500 ms) caused EDHF-mediated hyperpolarization and vasodilatation at the local site and these responses spread through the endothelium to remote sites in 12-week-old Wistar-Kyoto rats (WKY). Conducted responses were significantly attenuated in age-matched spontaneously hypertensive rats (SHR) although the rate of decay with distance did not change. Inhibition of inwardly rectifying potassium (Kir) channels (30 microM barium) eliminated the difference between WKY and SHR by attenuating conducted responses in WKY but not SHR. At the local site, barium (30 microM) significantly reduced the duration but not the amplitude of ACh-induced hyperpolarization in WKY only. Barium had no effect when the iontophoretic stimulus was reduced to 350 ms. After blockade of EDHF in SHR, ACh elicited a depolarization which our indirect data suggest spreads along the vessel in the endothelium. Messenger RNA expression of Kir2.0 genes did not differ between the strains nor did the amplitude of K(+)-induced hyperpolarization, which was abolished by disruption of the endothelium. Immunohistochemistry revealed a decrease in connexin (Cx)37 but not Cx40 or Cx43 protein in endothelial cells of SHR compared to WKY. Results suggest that conduction of EDHF-mediated responses in WKY, but not in SHR, is facilitated by activation of Kir channels at the site of ACh application and not by differences in endothelial connexin expression. Lack of Kir channel involvement in hypertension may result from reduction in the duration of the hyperpolarization due to the development of ACh-mediated depolarization, rather than to any difference in Kir subunit expression or function.
本研究旨在阐明高血压期间大鼠肠系膜动脉中由内皮衍生超极化因子（EDHF）介导的血管舒缩反应传导是否发生改变。在12周龄的Wistar-Kyoto大鼠（WKY）中，离子导入乙酰胆碱（ACh；500毫秒）在局部位点引起EDHF介导的超极化和血管舒张，这些反应通过内皮扩散到远处位点。在年龄匹配的自发性高血压大鼠（SHR）中，传导反应显著减弱，尽管随距离的衰减率没有变化。内向整流钾（Kir）通道的抑制（30微摩尔钡）通过减弱WKY而非SHR中的传导反应消除了WKY和SHR之间的差异。在局部位点，钡（30微摩尔）仅显著缩短了WKY中ACh诱导的超极化的持续时间，而不影响其幅度。当离子导入刺激减少到350毫秒时，钡没有作用。在SHR中阻断EDHF后，ACh引发去极化，我们的间接数据表明其在内皮中沿血管扩散。Kir2.0基因的信使核糖核酸表达在两种品系之间没有差异，K(+)诱导的超极化幅度也没有差异，后者在内皮破坏后消失。免疫组织化学显示，与WKY相比，SHR内皮细胞中连接蛋白（Cx）37蛋白减少，但Cx40或Cx43蛋白没有减少。结果表明，在WKY中，EDHF介导的反应传导是由ACh应用位点的Kir通道激活促进的，而不是由内皮连接蛋白表达的差异促进的，在SHR中则不然。高血压中缺乏Kir通道参与可能是由于ACh介导的去极化的发展导致超极化持续时间缩短，而不是由于Kir亚基表达或功能的任何差异。
