Bychkov R, Gollasch M, Ried C, Luft F C, Haller H
Franz Volhard Clinic, Humboldt University of Berlin, Germany.
Circulation. 1997 Jan 21;95(2):503-10. doi: 10.1161/01.cir.95.2.503.
Spontaneous transient outward potassium currents (STOCs) induce myogenic relaxation in small cerebral vessels. We found STOCs in human coronary artery vascular smooth muscle cells (VSMCs) and studied their regulation.
K+ currents were recorded in human coronary VSMCs by current- and voltage-clamp techniques. STOCs were recorded in the presence of 200 mumol/L Cd2+ and 10 mumol/L verapamil, which block voltage-dependent Ca2+ channels. STOCs were inhibited by iberiotoxin (100 nmol/L), a selective blocker of Ca(2+)-activated potassium channels (BKCa), and disappeared in a Ca(2+)-free bath. Iberiotoxin depolarized the VSMCs within 20 minutes from -44 +/- 7 to -18 +/- 5 mV (n = 17). The Ca2+ ionophore A23187 increased intracellular Ca2+ and stimulated whole-cell BKCa current. Depletion of Ca2+ from the sarcoplasmic reticulum with caffeine (4 mmol/L) abolished STOCs for several minutes. Ryanodine (50 mumol/L) transiently stimulated STOCs but then completely inhibited STOCs within 10 minutes. The firing frequency of STOCs was directly correlated with intracellular Na+ concentrations from 0 to 24 mmol/L. Lowering intracellular Na+ to zero abolished STOCs. We next gave monensin (30 mumol/L) to increase intracellular Na+. This maneuver resulted in an increase in whole-cell current fluctuations and STOCs. Monensin-induced STOCs were abolished by either lowering extracellular Ca2+ to zero or chelating Ca2+ intracellularly with BAPTA-AM (30 mumol/L).
STOCs resulted from BKCa activity and were dependent on extracellular Ca2+ but not significantly on voltage-dependent Ca2+ channels. STOCs were dependent on intracellular Na+ and intracellular calcium store refilling state. We suggest that Ca2+ entry into the cell through reverse-mode Na+/Ca2+ exchange determines calcium store refilling, which in turn regulates STOC generation in human coronary VSMCs.
自发性瞬时外向钾电流（STOCs）可诱导脑小血管出现肌源性舒张。我们在人冠状动脉血管平滑肌细胞（VSMCs）中发现了STOCs并对其调控机制进行了研究。
采用电流钳和电压钳技术记录人冠状动脉VSMCs中的钾电流。在存在200μmol/L Cd2+和10μmol/L维拉帕米（可阻断电压依赖性钙通道）的情况下记录到了STOCs。STOCs受到iberiotoxin（100 nmol/L，一种钙激活钾通道（BKCa）的选择性阻断剂）的抑制，且在无钙浴中消失。Iberiotoxin在20分钟内使VSMCs去极化，从-44±7 mV变为-18±5 mV（n = 17）。钙离子载体A23187增加细胞内钙离子并刺激全细胞BKCa电流。用咖啡因（4 mmol/L）耗尽肌浆网中的钙离子会使STOCs消失数分钟。Ryanodine（50μmol/L）短暂刺激STOCs，但随后在10分钟内完全抑制STOCs。STOCs的发放频率与细胞内钠离子浓度在0至24 mmol/L范围内直接相关。将细胞内钠离子浓度降至零可使STOCs消失。接下来我们给予莫能菌素（30μmol/L）以增加细胞内钠离子浓度。此操作导致全细胞电流波动和STOCs增加。莫能菌素诱导的STOCs可通过将细胞外钙离子浓度降至零或用BAPTA-AM（30μmol/L）在细胞内螯合钙离子而被消除。
STOCs由BKCa活性产生，依赖于细胞外钙离子，但对电压依赖性钙通道的依赖性不显著。STOCs依赖于细胞内钠离子和细胞内钙库的再充盈状态。我们认为，钙离子通过反向模式的钠/钙交换进入细胞决定了钙库的再充盈，进而调节人冠状动脉VSMCs中STOCs的产生。
