Murchison D, Griffith W H
Department of Medical Pharmacology and Toxicology, College of Medicine, Texas A&M University System Health Science Center, College Station 77843-1114, USA.
Brain Res. 2000 Jan 31;854(1-2):139-51. doi: 10.1016/s0006-8993(99)02297-0.
Mitochondria participate in intracellular Ca2+ buffering and signalling. They are also major mediators of cell death. Toxic Ca2+ accumulation in mitochondria is widely believed to initiate cell death in many cell types by opening the permeability transition pore (PTP). In non-neuronal cells, the PTP has been implicated as a Ca2+ release mechanism in physiological Ca2+ signalling. In neurons, Ca2+ release from mitochondria has been attributed primarily to mitochondrial Na+/Ca2+ exchange. Using fura-2 ratiometric microfluorimetry in acutely dissociated rat basal forebrain neurons, we show that mitochondria are able to buffer non-toxic Ca2+ loads arising from caffeine-sensitive internal stores or from extracellular influx through voltage gated channels. We also show that these non-toxic Ca2+ loads are reversibly released from mitochondria through the PTP and the Na+/Ca2+ exchanger. Evoked Ca2+ transients have characteristic peak and shoulder features mediated by mitochondrial buffering and release. Depolarizing mitochondria with carbonyl cyanide m-chlorophenylhydrazone (CCCP, 5 microM) causes release of mitochondrial Ca2+ and prevents Ca2+ uptake. In CCCP, the magnitudes of evoked Ca2+ transients are increased, and the peak and shoulder features are eliminated. The PTP antagonist, cyclosporin A, (CSA, 2 microM) and the Na+/Ca2+ exchange blocker, clonazepam, (CLO, 20 microM) reversibly inhibited both the shoulder features of evoked Ca2+ transients and Ca2+ transients associated with CCCP application. We suggest that central neuronal mitochondria buffer and release Ca2+ through the PTP and Na+/Ca2+ exchanger during physiological Ca2+ signalling. We also suggest that CLO blocks both the PTP and the mitochondrial Na+/Ca2+ exchanger.
线粒体参与细胞内钙离子的缓冲和信号传导。它们也是细胞死亡的主要介质。线粒体中有毒性的钙离子积累被广泛认为是通过打开通透性转换孔（PTP）在许多细胞类型中引发细胞死亡的原因。在非神经元细胞中，PTP被认为是生理钙离子信号传导中的一种钙离子释放机制。在神经元中，线粒体释放钙离子主要归因于线粒体钠/钙交换。通过在急性分离的大鼠基底前脑神经元中使用fura-2比率微荧光测定法，我们发现线粒体能够缓冲由咖啡因敏感的内部储存或通过电压门控通道的细胞外流入产生的无毒钙离子负荷。我们还表明，这些无毒的钙离子负荷通过PTP和钠/钙交换体从线粒体中可逆地释放出来。诱发的钙离子瞬变具有由线粒体缓冲和释放介导的特征性峰值和肩部特征。用羰基氰化物间氯苯腙（CCCP，5 microM）使线粒体去极化会导致线粒体钙离子释放并阻止钙离子摄取。在CCCP存在的情况下，诱发的钙离子瞬变幅度增加，并且峰值和肩部特征消失。PTP拮抗剂环孢素A（CSA，2 microM）和钠/钙交换阻滞剂氯硝西泮（CLO，20 microM）可逆地抑制了诱发的钙离子瞬变的肩部特征以及与应用CCCP相关的钙离子瞬变。我们认为，在生理钙离子信号传导过程中，中枢神经元线粒体通过PTP和钠/钙交换体缓冲和释放钙离子。我们还认为，CLO同时阻断了PTP和线粒体钠/钙交换体。
