Xi Qi, Cheranov Sergei Y, Jaggar Jonathan H
Department of Physiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
Circ Res. 2005 Aug 19;97(4):354-62. doi: 10.1161/01.RES.0000177669.29525.78. Epub 2005 Jul 14.
Mitochondria regulate intracellular calcium (Ca2+) signals in smooth muscle cells, but mechanisms mediating these effects, and the functional relevance, are poorly understood. Similarly, antihypertensive ATP-sensitive potassium (KATP) channel openers (KCOs) activate plasma membrane KATP channels and depolarize mitochondria in several cell types, but the contribution of each of these mechanisms to vasodilation is unclear. Here, we show that cerebral artery smooth muscle cell mitochondria are most effectively depolarized by diazoxide (-15%, tetramethylrhodamine [TMRM]), less so by levcromakalim, and not depolarized by pinacidil. KCO-induced mitochondrial depolarization increased the generation of mitochondria-derived reactive oxygen species (ROS) that stimulated Ca2+ sparks and large-conductance Ca2+-activated potassium (KCa) channels, leading to transient KCa current activation. KCO-induced mitochondrial depolarization and transient KCa current activation were attenuated by 5-HD and glibenclamide, KATP channel blockers. MnTMPyP, an antioxidant, and Ca2+ spark and KCa channel blockers reduced diazoxide-induced vasodilations by >60%, but did not alter dilations induced by pinacidil, which did not elevate ROS. Data suggest diazoxide drives ROS generation by inducing a small mitochondrial depolarization, because nanomolar CCCP, a protonophore, similarly depolarized mitochondria, elevated ROS, and activated transient KCa currents. In contrast, micromolar CCCP, or rotenone, an electron transport chain blocker, induced a large mitochondrial depolarization (-84%, TMRM), reduced ROS, and inhibited transient KCa currents. In summary, data demonstrate that mitochondria-derived ROS dilate cerebral arteries by activating Ca2+ sparks, that some antihypertensive KCOs dilate by stimulating this pathway, and that small and large mitochondrial depolarizations lead to differential regulation of ROS and Ca2+ sparks.
线粒体调节平滑肌细胞内的钙（Ca2+）信号，但介导这些效应的机制及其功能相关性尚不清楚。同样，抗高血压的ATP敏感性钾（KATP）通道开放剂（KCOs）可激活多种细胞类型的质膜KATP通道并使线粒体去极化，但这些机制对血管舒张的贡献尚不清楚。在此，我们表明，二氮嗪（-15%，四甲基罗丹明[TMRM]）能最有效地使脑动脉平滑肌细胞线粒体去极化，利卡曲林的效果稍差，吡那地尔则不会使其去极化。KCO诱导的线粒体去极化增加了线粒体衍生的活性氧（ROS）的生成，后者刺激Ca2+火花和大电导Ca2+激活钾（KCa）通道，导致瞬时KCa电流激活。5-HD和格列本脲（KATP通道阻滞剂）可减弱KCO诱导的线粒体去极化和瞬时KCa电流激活。抗氧化剂MnTMPyP以及Ca2+火花和KCa通道阻滞剂使二氮嗪诱导的血管舒张减少>60%，但不改变吡那地尔诱导的舒张，因为吡那地尔不会升高ROS。数据表明，二氮嗪通过诱导线粒体小去极化来驱动ROS生成，因为纳摩尔浓度的质子载体羰基氰氯苯腙（CCCP）同样可使线粒体去极化、升高ROS并激活瞬时KCa电流。相比之下，微摩尔浓度的CCCP或电子传递链阻滞剂鱼藤酮可诱导线粒体大去极化（-84%，TMRM）、减少ROS并抑制瞬时KCa电流。总之，数据表明线粒体衍生的ROS通过激活Ca2+火花使脑动脉舒张，一些抗高血压KCOs通过刺激该途径舒张血管，并且线粒体小去极化和大去极化导致对ROS和Ca2+火花的不同调节。
