Cheng Yu, Gulbins Erich, Siemen Detlef
Department of Neurology, Otto von Guericke University, Magdeburg, Germany.
Cell Physiol Biochem. 2011;27(3-4):191-200. doi: 10.1159/000327944. Epub 2011 Apr 1.
Mitochondria are crucially involved in the intrinsic pathway of apoptosis. Upon induction of apoptosis, proapoptotic proteins of the Bcl-2 family, in particular Bax and Bak, transfer the death signal to the organelle. The outcome is release of proapoptotic factors, such as cytochrome c, and mitochondrial changes, such as depolarization. Details of the mechanism by which Bax mediates mitochondrial alterations, however, are unknown. Using the single-channel patch-clamp method, we studied mitoplasts (vesicles of inner membrane) from rat astrocyte and liver mitochondria and intact murine glioma mitochondria to determine the action of proapoptotic Bax and antiapoptotic Bcl-xL on the mitochondrial Ca(2+)-activated channel (mtBK) and the permeability transition pore (mtPTP). Bax (1 nM) inhibited the open probability of the mtBK, whereas Bcl-xL or control proteins had no effect. Incubating mitochondria with iberiotoxin, an inhibitor of mtBK, induced the release of cytochrome c. Bcl-xL inhibited the effects of Bax on mtBK. Furthermore, in patch-clamp studies Bcl-xL inhibited the mtPTP itself, whereas Bax had no direct effect on the mtPTP. We conclude that Bax exerts its proapototic effect by inhibiting mitochondrial K(+) channels, whereas Bcl-xL exerts its antiapoptotic effect by inhibiting the effects of Bax on mitochondrial potassium channels and by direct inhibition of the mtPTP.
线粒体在细胞凋亡的内在途径中起着至关重要的作用。在诱导细胞凋亡时，Bcl-2家族的促凋亡蛋白，特别是Bax和Bak，将死亡信号传递给该细胞器。结果是促凋亡因子如细胞色素c的释放以及线粒体变化如去极化。然而，Bax介导线粒体改变的机制细节尚不清楚。我们使用单通道膜片钳方法，研究了来自大鼠星形胶质细胞和肝线粒体的线粒体膜（内膜囊泡）以及完整的小鼠胶质瘤线粒体，以确定促凋亡的Bax和抗凋亡的Bcl-xL对线粒体钙激活通道（mtBK）和通透性转换孔（mtPTP）的作用。Bax（1 nM）抑制mtBK的开放概率，而Bcl-xL或对照蛋白则无作用。用mtBK抑制剂iberiotoxin孵育线粒体可诱导细胞色素c的释放。Bcl-xL抑制Bax对mtBK的作用。此外，在膜片钳研究中，Bcl-xL抑制mtPTP本身，而Bax对mtPTP没有直接影响。我们得出结论，Bax通过抑制线粒体钾通道发挥其促凋亡作用，而Bcl-xL通过抑制Bax对线粒体钾通道的作用以及直接抑制mtPTP发挥其抗凋亡作用。
