Chalmers Susan, McCarron John G
Strathclyde Institute of Pharmacy and Biomedical Sciences, University of Strathclyde, John Arbuthnott Building, 27 Taylor Street, Glasgow, G4 0NR, UK.
J Cell Sci. 2008 Jan 1;121(Pt 1):75-85. doi: 10.1242/jcs.014522. Epub 2007 Dec 11.
Ca2+ uptake by mitochondria might both modulate the cytosolic Ca2+ concentration ([Ca2+]c) and depolarize the mitochondrial membrane potential (delta Psi m) to limit ATP production. To investigate how physiological Ca2+ signaling might affect energy production, delta Psi m was examined during Ca2+ oscillations in smooth muscle cells. In single, voltage-clamped smooth muscle cells, inhibition of mitochondrial Ca2+ accumulation inhibited inositol (1,4,5)-trisphosphate [Ins(1,4,5)P3]-evoked Ca2+ release and prolonged the time required for restoration of [Ca2+]c following activation of plasmalemmal Ca2+ currents (ICa). Ca2+ could be released from mitochondria immediately (within 15 seconds) after a [Ca2+]c rise evoked by Ins(1,4,5)P3 or ICa. Despite this evidence of mitochondrial Ca2+ accumulation, no change in delta Psi m was observed during single or repetitive [Ca2+]c oscillations evoked by these conditions. Occasionally, spontaneous, repetitive, persistent Ca 2+ oscillations were observed. In these cases, mitochondria displayed stochastic delta Psi m depolarizations, which were independent both of events in neighboring mitochondria and of the timing of the [Ca 2+]c oscillations themselves. Such delta Psi m depolarizations could be mimicked by increased exposure to either fluorescence excitation light or the delta Psi m-sensitive dye tetramethylrhodamine ethyl ester (TMRE) and were inhibited by antioxidants (ascorbic acid, catalase, Trolox and TEMPO) or the mitochondrial permeability transition pore (mPTP)-inhibitor cyclosporin A (CsA). Individual mitochondria within smooth muscle cells might depolarize during repetitive Ca2+ oscillations or during oxidative stress but not during the course of single [Ca2+]c transients evoked by Ca2+ influx or store release.
线粒体对钙离子的摄取可能既调节胞质钙离子浓度（[Ca2+]c），又使线粒体膜电位（ΔΨm）去极化，从而限制ATP的产生。为了研究生理性钙离子信号如何影响能量产生，在平滑肌细胞的钙离子振荡过程中检测了ΔΨm。在单个电压钳制的平滑肌细胞中，抑制线粒体钙离子积累可抑制肌醇（1,4,5）-三磷酸[Ins(1,4,5)P3]诱发的钙离子释放，并延长质膜钙离子电流（ICa）激活后恢复[Ca2+]c所需的时间。在由Ins(1,4,5)P3或ICa诱发的[Ca2+]c升高后，钙离子可立即（15秒内）从线粒体释放。尽管有证据表明线粒体有钙离子积累，但在这些条件诱发的单次或重复性[Ca2+]c振荡过程中，未观察到ΔΨm的变化。偶尔会观察到自发、重复、持续的钙离子振荡。在这些情况下，线粒体显示出随机的ΔΨm去极化，这与相邻线粒体中的事件以及[Ca2+]c振荡本身的时间无关。这种ΔΨm去极化可通过增加对荧光激发光或ΔΨm敏感染料四甲基罗丹明乙酯（TMRE）的暴露来模拟，并被抗氧化剂（抗坏血酸、过氧化氢酶、托洛克斯和TEMPO）或线粒体通透性转换孔（mPTP）抑制剂环孢素A（CsA）抑制。平滑肌细胞内的单个线粒体可能在重复性钙离子振荡期间或氧化应激期间去极化，但在由钙离子内流或储存释放诱发的单次[Ca2+]c瞬变过程中不会去极化。
