Hirano M, Imaizumi Y, Muraki K, Yamada A, Watanabe M
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, Nagoya City University, Nagoya 467, Japan.
Pflugers Arch. 1998 Apr;435(5):645-53. doi: 10.1007/s004240050565.
Three major ionic currents, Ca2+-dependent K+ current (IK-Ca), delayed rectifier type K+ current (Ikd) and Ca2+ current (ICa), were activated by depolarization under whole-cell clamp in single smooth muscle cells isolated from guinea-pig urinary bladder. Externally applied ruthenium red (RuR) reduced the amplitude of IK-Ca and ICa at 0 mV (IC50 values were 4.2 and 5.6 muM, respectively), but did not affect IKd. Spontaneous transient outward currents (STOCs) and caffeine-induced outward currents (Icaf) at -30 mV were reduced by external 10 muM RuR. When 10 muM RuR was added to the pipette solution, IK-Ca during depolarization, STOCs and Icaf significantly decreased with time. RuR did not change the unitary current amplitude of the large-conductance Ca2+-dependent K+ (BK) channels, but reduced the open probability of the channel under excised patch-clamp recording mode. RuR reduced the channel activity more effectively from the cytosolic face than from the other. This inhibition decreased when the cytosolic Ca2+ concentration was increased. These results indicate that RuR blocks BK and Ca2+ channels in urinary bladder smooth muscle cells. The decrease in IK-Ca, STOCs and Icaf by RuR is attributable to the direct inhibition of BK channel activity, probably in addition to the inhibition of Ca2+ release from storage sites. The direct inhibition of BK channel activity by RuR may be related to the interaction of RuR with the Ca2+-binding sites of the channel protein.
在从豚鼠膀胱分离的单个平滑肌细胞中，通过全细胞膜片钳记录，去极化激活了三种主要的离子电流：钙依赖性钾电流（IK-Ca）、延迟整流型钾电流（Ikd）和钙电流（ICa）。细胞外应用钌红（RuR）可降低0 mV时IK-Ca和ICa的幅度（IC50值分别为4.2和5.6 μM），但不影响Ikd。细胞外10 μM RuR可降低-30 mV时的自发瞬时外向电流（STOCs）和咖啡因诱导的外向电流（Icaf）。当向微电极溶液中加入10 μM RuR时，去极化期间的IK-Ca、STOCs和Icaf随时间显著降低。RuR不改变大电导钙依赖性钾（BK）通道的单通道电流幅度，但在膜片钳记录模式下降低了通道的开放概率。RuR从胞质面比从其他面更有效地降低通道活性。当胞质钙浓度增加时，这种抑制作用减弱。这些结果表明，RuR阻断膀胱平滑肌细胞中的BK和钙通道。RuR导致IK-Ca、STOCs和Icaf降低归因于对BK通道活性的直接抑制，可能还包括对储存部位钙释放的抑制。RuR对BK通道活性的直接抑制可能与RuR与通道蛋白钙结合位点的相互作用有关。
