title: Contributory role of endothelium and voltage-gated potassium channels in apocynin-induced vasorelaxations.
abstract: OBJECTIVE
  Although apocynin, the nicotinamide adenine dinucleotide phosphate oxidase inhibitor improves vascular function in hypertension, its specificity has been questioned. The present study examined whether apocynin-induced vasorelaxations involve endothelium and/or K channels in vascular cells.
  
  
  METHODS
  Aortas from Sprague-Dawley rats were suspended in organ baths for functional studies. Changes in intracellular calcium ([Ca]i) and nitric oxide ([NO]i) in rat endothelial cells were detected by fluorescence imaging. Whole-cell voltage-gated K (Kv) currents were recorded in vascular smooth muscle cells.
  
  
  RESULTS
  Apocynin-induced aortic relaxations were attenuated by the absence of endothelium, endothelial nitric oxide synthase inhibitor N-nitro-L-arginine methyl ester, or nitric oxide-dependent soluble guanylate cyclase inhibitor 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one. 4-Aminopyridine (4-AP, voltage-gated potassium channels blocker) attenuated apocynin-induced relaxations, its combined treatment with 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one (ODQ) did not cause further inhibition. Apocynin increased [Ca]i and [NO]i in endothelial cells, which were abolished by 4-AP, indicating the involvement of voltage-gated potassium channels in endothelial cells. In addition, apocynin-stimulated increase in endothelial nitric oxide synthase phosphorylation at Ser depended on the presence of extracellular Ca. Notably, 4-AP also reduced apocynin-induced relaxations in the absence of endothelium and apocynin increased 4-AP-sensitive voltage-gated potassium channel currents in vascular smooth muscle cells.
  
  
  CONCLUSIONS
  This study provides novel data showing that apocynin-induced relaxations of rat aortas are mediated by 4-AP-sensitive stimulation of [Ca]i and [NO]i increases in endothelium and by activation of voltage-gated potassium channels in vascular smooth muscle cells.
authors: State Key Laboratory of Medical Genomics, Department of Hypertension, Ruijin Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors: Wei-qing
authors: WQ
authors: Han
authors: Wing Tak
authors: WT
authors: Wong
authors: Xiao Yu
authors: XY
authors: Tian
authors: Yu
authors: Y
authors: Huang
authors: Ling-yun
authors: LY
authors: Wu
authors: Ding-liang
authors: DL
authors: Zhu
authors: Ping-jin
authors: PJ
authors: Gao
mesh_terms: D000098:Acetophenones / Q000494:pharmacology*; D000631:Aminopyridines / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001011:Aorta / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000378:metabolism; D002478:Cells, Cultured; D004730:Endothelium, Vascular / Q000166:cytology / Q000502:physiology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008297:Male; D023421:Models, Animal; D009569:Nitric Oxide / Q000378:metabolism; D018408:Patch-Clamp Techniques; D026902:Potassium Channel Blockers / Q000494:pharmacology; D024642:Potassium Channels, Voltage-Gated / Q000037:antagonists & inhibitors / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014664:Vasodilation / Q000187:drug effects* / Q000502:physiology*
chemical_list: D000098:Acetophenones; D000631:Aminopyridines; D000975:Antioxidants; D004791:Enzyme Inhibitors; D026902:Potassium Channel Blockers; D024642:Potassium Channels, Voltage-Gated; D009569:Nitric Oxide; C056165:acetovanillone; D002118:Calcium