Characterization of spontaneous transient outward potassium currents in vascular smooth muscle cells of porcine coronary artery
CAI Fang1, LI Peng-Yun1, YANG Yan1, LIU Zhi-Fei1, LI Miao-Ling1, ZHOU Wen1, PEI Jie1, CHENG Jun1, LAN Huan1, Joachim B. Grammer2, ZENG Xiao-Rong1
1Institute of Myocardial Electrophysiology, Luzhou Medical College, Luzhou 646000, China; 2Department of Cardiac and Vascular Surgery, German Heart Center Munich, 80636 Munich, Germany
Abstract: Spontaneous transient outward currents (STOCs) play an important role in the myogenic regulation of small artery tone, such as coronary artery. In the present study, we investigated the electrophysiological properties and the regulation of STOCs in vascular smooth muscle cells (VSMCs) of porcine coronary artery by perforated patch-clamp technique. Our data showed that STOCs were dependent on voltage and extracellular calcium and that they were highly variable in their amplitudes and frequencies; STOCs superimposed stochastically onto whole-cell K+ currents which induced by step and ramp protocols. Their activity was completely abolished by ChTX [inhibitor of large-conductance Ca2+-activated potassium (BKCa) channels], removal of extracellular Ca2+, or addition of ryanodine (50 μmol/L) respectively. In contrast, CdCl2 and verapamil, inhibitors of voltage-dependent L-type Ca2+ channels, had little effect on STOCs. Caffeine (5 mmol/L) transiently increased STOCs (hump), followed by a temporary inhibition. Ca2+ ionophore A23187 increased both amplitude and frequency of STOCs. Na+ ionophore monensin increased the frequency of STOCs. The activity of STOCs was strongly inhibited by KB-R7943, a selective inhibitor of the reverse mode of the Na+/Ca2+ exchanger. Based on these observations, we conclude that STOCs are mediated by BKCa channels. The generation and activation of STOCs depend upon Ca2+ influx through Na+/Ca2+ exchange and release of Ca2+ from sarcoplasmic reticulum (SR) via ryanodine receptors. This suggests that Na+/Ca2+ exchange determines calcium store refilling. Recycling of entering Ca2+ from superficial SR may locally elevate Ca2+ concentration at the plasma membrane, thereby activating BKCa channels and then initiating STOCs.
Key words: perforated patch-clamp technique; coronary artery smooth muscle cells; spontaneous transient outward currents; BKCa channels; Na+/Ca2+ exchange; ryanodine receptor
猪冠状动脉平滑肌细胞的自发瞬时外向电流的特性
蔡 芳1，李鹏云1，杨 艳1， 刘智飞1，李妙龄1，周 文1，裴 杰1 ，程 俊1，兰 欢1，Joachim B. Grammer2，曾晓荣1
1泸州医学院心肌电生理学研究室，泸州646000；2德国慕尼黑心脏中心心血管外科研究所，慕尼黑 80636
摘 要：自发瞬时外向电流(spontaneous transient outward currents, STOCs)在小动脉的肌源性调节中起着非常重要的作用。我们应用穿孔膜片钳技术记录了猪冠状动脉平滑肌细胞上的STOCs，研究了其基本特性以及调节。结果显示：STOCs有明显的电压依赖性和钙依赖性，其频率和幅度具有变异性。STOCs可以随机叠加在阶跃刺激方案和斜坡刺激方案引出的全细胞钾电流上。STOCs活性可被大电导钙激活钾 (large-conductance Ca2+-activated potassium channels, BKCa)通道的特异性阻断剂ChTX、螯合胞外钙离子和50 μmol/L ryanodine 完全抑制。钙离子载体A23187可以明显增加STOCs的幅度和频率；然而L型钙通道阻断剂维纳帕米和CdCl2对STOCs的影响很小。咖啡因使STOCs瞬时爆发性的增加，然后抑制。钠离子载体可明显增加STOCs的频率；钠钙交换体选择性抑制剂KB-R7943可明显抑制STOCs。我们认为，STOCs是大电导钙激活钾通道所携带的，STOCs的产生和激活依赖于经钠钙交换的钙内流和经肌浆网ryanodine受体介导的钙释放，钠钙交换可能决定钙库重载，而细胞膜下肌浆网的胞内钙释放即钙火花）所致的局部钙浓度瞬时增加激活与其相邻的BKCa通道，产生STOCs。
关键词：穿孔膜片钳技术；冠状动脉平滑肌细胞；自发瞬时外向电流；大电导钙激活钾通道；钠钙交换；ryanodine受体
中图分类号：Q463; R331.3+8; R541.7+5