Tanaka Yoshio, Tang Guanghua, Takizawa Kei, Otsuka Kazuoki, Eghbali Mansoureh, Song Min, Nishimaru Kazuhide, Shigenobu Koki, Koike Katsuo, Stefani Enrico, Toro Ligia
Department of Chemical Pharmacology, Toho University School of Pharmaceutical Sciences, Funabashi-City, Chiba, Japan.
J Pharmacol Exp Ther. 2006 Apr;317(1):341-54. doi: 10.1124/jpet.105.096115. Epub 2006 Jan 4.
The role of K(+) channels in nitric oxide (NO)-induced vasorelaxation has been largely investigated in resistance vessels where iberiotoxin-sensitive MaxiK channels play a predominant role. However, the nature of the K(+) channel(s) involved in the relaxation triggered by NO-releasing compounds [nitroglycerin, NTG; NOR 3 [(+/-)-(E)-4-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexenamide]] or atrial natriuretic peptide (ANP) in the conduit vessel aorta has remained elusive. We now demonstrate that, in rat aorta, the relaxation due to these vasorelaxants is not affected by the MaxiK channel blocker iberiotoxin (10(-7)-10(-6) M) as was the control vascular bed used (mesenteric artery). The inability of iberiotoxin to prevent NO/ANP-induced aortic relaxations was not due to lower expression of MaxiK in aorta or due to the predominance of iberiotoxin-resistant channels in this conduit vessel. Aortic relaxations were strongly diminished by 4-aminopyridine (4-AP) (> or =5 x 10(-3) M) or by tetraethylammonium (>2 x 10(-3) M) at concentrations known to inhibit voltage-dependent K(+) (K(v)) 2-type channels but not by other K(+) channel inhibitors, glibenclamide, apamin, charybdotoxin, tertiapin, or E-4031 N-[4-[[1-[2-(6-methyl-2-pyridinyl)ethyl]-4-piperidinyl-]carbonyl]phenyl]methanesulfonamide dihydrochloride). Consistent with a role of K(v)2-type channels, K(v) currents in A7r5 aortic myocytes were stimulated by NTG and inhibited by > or =5 x 10(-3) M 4-AP. Furthermore, immunocytochemistry, immunoblot, and real-time polymerase chain reaction analyses confirmed the presence of K(v)2.1 channels in aorta. K(v)2.1 transcripts were approximately 100-fold more abundant than K(v)2.2. Our results support low-affinity 4-AP-sensitive K(v) channels, assembled at least partially by K(v)2.1 subunit, as downstream effectors of NO/ANP-signaling cascade regulating aortic vasorelaxation and further demonstrate vessel-specific K(+) channel involvement in NO/ANP-induced relaxation.
钾通道在一氧化氮（NO）诱导的血管舒张中的作用已在阻力血管中得到广泛研究，在这些血管中，对iberiotoxin敏感的大电导钙激活钾通道（MaxiK通道）起主要作用。然而，在大血管主动脉中，由释放NO的化合物[硝酸甘油，NTG；NOR 3 [（±）-（E）-4-乙基-2- [（E）-羟基亚氨基]-5-硝基-3-己烯酰胺]]或心房利钠肽（ANP）触发的舒张所涉及的钾通道的性质仍然不清楚。我们现在证明，在大鼠主动脉中，这些血管舒张剂引起的舒张不受MaxiK通道阻滞剂iberiotoxin（10^-7 - 10^-6 M）的影响，而所用的对照血管床（肠系膜动脉）则受其影响。iberiotoxin不能阻止NO/ANP诱导的主动脉舒张，这并非由于主动脉中MaxiK表达较低，也不是由于该大血管中存在对iberiotoxin耐药的通道占主导地位。在已知抑制电压依赖性钾通道（Kv）2型通道的浓度下，4-氨基吡啶（4-AP）（≥5×10^-3 M）或四乙铵（>2×10^-3 M）可显著减弱主动脉舒张，但其他钾通道抑制剂，如格列本脲、蜂毒明肽、蝎毒素、特律平或E-4031 N-[4-[[1-[2-（6-甲基-2-吡啶基）乙基]-4-哌啶基-]羰基]苯基]甲磺酰胺二盐酸盐则无此作用。与Kv2型通道的作用一致，NTG可刺激A7r5主动脉肌细胞中的Kv电流，而≥5×10^-3 M的4-AP可抑制该电流。此外，免疫细胞化学、免疫印迹和实时聚合酶链反应分析证实主动脉中存在Kv2.1通道。Kv2.1转录本的丰度比Kv2.2高约100倍。我们的结果支持低亲和力的对4-AP敏感的钾通道，至少部分由Kv2.1亚基组装而成，作为调节主动脉血管舒张的NO/ANP信号级联的下游效应器，并进一步证明血管特异性钾通道参与NO/ANP诱导的舒张。
