Li PengYun, Zeng XiaoRong, Yang Yan, Cai Fang, Liu ZhiFei, Li MiaoLing, Pei Jie, Zhou Wen
Institute of Myocardial Electrophysiology, Luzhou Medical College, Luzhou 646000, China.
Sci China C Life Sci. 2007 Oct;50(5):660-8. doi: 10.1007/s11427-007-0064-7.
The purpose of the present study was to further study the characteristics and regulation of spontaneous transient outward currents (STOCs) in freshly isolated porcine coronary artery smooth muscle cells (ASMCs). STOCs were recorded using the perforated whole-cell patch-clamp configuration. STOCs were voltage-dependent and superimposed stochastically onto whole-cell Ca(2+)-activated-K(+) (BK(Ca)) currents. Charybdotoxin (ChTX, 200 nmol/L), a selective blocker of BK(Ca) channels, completely inhibited STOCs within 10 min. STOCs activity was greatly suppressed when extracellular Ca(2+) concentration decreased from 1.8 mmol/L to 200 nmol/L, further removal of Ca(2+) abolished STOCs activity. Ca(2+) ionophore A23187 (10 micromol/L) increased STOCs activity significantly. Verapamil (20 micromol/L) and CdCl(2) (200 micromol/L), two kinds of organic L-type voltage-dependent Ca(2+) channels (L-VDCCs) antagonists, had little effect on STOCs. In addition, the ryanodine receptors (RyRs) agonist caffeine (5 mmol/L) significantly activated STOCs. Application of ryanodine (50 micromol/L) to block RyRs abolished STOCs, subsequent washout of ryanodine or application of caffeine failed to reproduce STOCs activity. Inhibition of inositol 1,4,5-trisphosphate receptors (IP(3)Rs) by 2APB (40 micromol/L) greatly suppressed the activity of STOCs, application of caffeine (5 mmol/L) in the presence of 2APB caused a burst of outward currents followed by inhibition of STOCs. These results suggest that STOCs in porcine coronary ASMCs are mediated by BK(Ca) channels. Extracellular Ca(2+) is essential for STOCs activity, while Ca(2+) entry through L-VDCCs has little effect on STOCs. Intracellular Ca(2+) release induced by RyRs is responsible for the regulation of STOCs, whereas IP3Rs might also be involved.
本研究的目的是进一步研究新鲜分离的猪冠状动脉平滑肌细胞（ASMCs）中自发瞬时外向电流（STOCs）的特征和调节机制。采用穿孔全细胞膜片钳技术记录STOCs。STOCs具有电压依赖性，随机叠加在全细胞钙激活钾（BK（Ca））电流上。大电导钙激活钾通道（BK（Ca））的选择性阻断剂查卡毒素（ChTX，200 nmol/L）在10分钟内完全抑制了STOCs。当细胞外Ca（2+）浓度从1.8 mmol/L降至200 nmol/L时，STOCs活性受到极大抑制，进一步去除Ca（2+）则消除了STOCs活性。钙离子载体A23187（10 μmol/L）显著增加了STOCs活性。两种有机L型电压依赖性钙通道（L-VDCCs）拮抗剂维拉帕米（20 μmol/L）和氯化镉（200 μmol/L）对STOCs影响不大。此外，ryanodine受体（RyRs）激动剂咖啡因（5 mmol/L）显著激活了STOCs。应用ryanodine（50 μmol/L）阻断RyRs可消除STOCs，随后洗脱ryanodine或应用咖啡因均无法恢复STOCs活性。2-氨基乙氧基二苯硼酸（2APB，40 μmol/L）抑制肌醇1,4,5-三磷酸受体（IP（3）Rs）可极大地抑制STOCs活性，在存在2APB的情况下应用咖啡因（5 mmol/L）会引发一阵外向电流，随后抑制STOCs。这些结果表明，猪冠状动脉ASMCs中的STOCs由BK（Ca）通道介导。细胞外Ca（2+）对STOCs活性至关重要，而通过L-VDCCs进入的Ca（2+）对STOCs影响不大。RyRs诱导的细胞内Ca（2+）释放负责STOCs的调节，而IP3Rs可能也参与其中。
