Zhang Yongde, Tazzeo Tracy, Chu Victor, Janssen Luke J
Department of Medicine, McMaster University, 50 Charlton Avenue East, Hamilton, Ontario, Canada L8N 4A6.
Cardiovasc Res. 2006 Jul 15;71(2):383-92. doi: 10.1016/j.cardiores.2006.04.002. Epub 2006 Apr 21.
The human radial artery has demonstrated superior long-term results as a graft in coronary bypass surgery, but undesirable post-surgical spasm limits its clinical application. Few have examined its excitatory properties, especially the underlying ion channel mechanisms. In this study, we investigated the kinetic and pharmacological properties of the smooth muscle membrane potassium currents of this important artery.
Using whole cell patch-clamp techniques, we found the K(+) current to be voltage-dependent and outwardly rectifying. Voltage-dependent inactivation was observed, being half-maximal at +28.0 mV but incomplete even at +40 mV. The K(+) currents were predominantly sensitive to the K(Ca) blocker tetraethylammonium (TEA; 63.9+/-12.1% inhibition, p<0.05), less sensitive to the Kv blocker 4-aminopyridine (4-AP; 32.8+/-4.4% inhibition, p<0.05), and the K(ATP) blocker glibenclamide (28.7+/-8.5% inhibition), at -20 mV testing potential. Resting membrane potential was -52.0+/-6.8 mV (n=5), and suppression of K(+) currents by TEA and iberiotoxin (IbTx) caused membrane depolarization. Western blot analysis with channel-specific antibodies confirmed the presence of K(Ca) and Kv channel proteins. TEA evoked 20.7+/-9.9% of the contractile response to 60 mM KCl, whereas IbTx caused about 10% of the above response at 10(-7) M. The nitric oxide donor SNAP augmented membrane K(+) currents in a concentration-dependent fashion; the augmentation was completely suppressed by TEA, but was relatively insensitive to the guanylate cyclase inhibitor ODQ.
The radial artery manifests mainly Ca(2+)-dependent K(+) currents at rest; this current is augmented by nitric oxide through a cGMP- and protein kinase G-independent action. The relatively depolarized membrane potential, as well as its muscular structure, predisposes the radial artery to spasm. Agents that activate the Ca(2+)-dependent K(+) current could be of therapeutic value in preventing post-surgical vasospasm.
人体桡动脉作为冠状动脉搭桥手术的移植物已显示出优异的长期效果，但术后不良的痉挛限制了其临床应用。很少有人研究其兴奋性特性，尤其是潜在的离子通道机制。在本研究中，我们调查了这条重要动脉平滑肌膜钾电流的动力学和药理学特性。
使用全细胞膜片钳技术，我们发现钾电流是电压依赖性且外向整流的。观察到电压依赖性失活，在+28.0 mV时达到半数最大失活，但即使在+40 mV时也不完全。在-20 mV测试电位下，钾电流主要对钙激活钾通道阻滞剂四乙铵（TEA；抑制率63.9±12.1%，p<0.05）敏感，对电压门控钾通道阻滞剂4-氨基吡啶（4-AP；抑制率32.8±4.4%，p<0.05）较不敏感，对ATP敏感性钾通道阻滞剂格列本脲（抑制率28.7±8.5%）敏感。静息膜电位为-52.0±6.8 mV（n = 5），TEA和埃博毒素（IbTx）对钾电流的抑制导致膜去极化。用通道特异性抗体进行的蛋白质印迹分析证实了钙激活钾通道和电压门控钾通道蛋白的存在。TEA诱发的收缩反应为60 mM氯化钾诱发反应的20.7±9.9%，而IbTx在10⁻⁷ M时引起上述反应的约10%。一氧化氮供体硝普钠（SNAP）以浓度依赖性方式增加膜钾电流；这种增加被TEA完全抑制，但对鸟苷酸环化酶抑制剂ODQ相对不敏感。
桡动脉在静息时主要表现为钙依赖性钾电流；一氧化氮通过一种不依赖环磷酸鸟苷（cGMP）和蛋白激酶G的作用增强该电流。相对去极化的膜电位及其肌肉结构使桡动脉易于发生痉挛。激活钙依赖性钾电流的药物在预防术后血管痉挛方面可能具有治疗价值。
