Elustondo Pia A, Negoda Alexander, Kane Constance L, Kane Daniel A, Pavlov Evgeny V
Department of Physiology and Biophysics, Dalhousie University, Halifax, NS B3H 4R2, Canada.
Department of Human Kinetics, St. Francis Xavier University, Antigonish, NS B2G 2W5, Canada.
Biochim Biophys Acta. 2015 Feb;1847(2):231-240. doi: 10.1016/j.bbabio.2014.10.007. Epub 2014 Nov 1.
The permeability transition pore (PTP) is a large channel of the mitochondrial inner membrane, the opening of which is the central event in many types of stress-induced cell death. PTP opening is induced by elevated concentrations of mitochondrial calcium. It has been demonstrated that spermine and other polyamines can delay calcium-induced swelling of isolated mitochondria, suggesting their role as inhibitors of the mitochondrial PTP. Here we further investigated the mechanism by which spermine inhibits the calcium-induced, cyclosporine A (CSA) -sensitive PTP by using three indicators: 1) calcium release from the mitochondria detected with calcium green, 2) mitochondrial membrane depolarization using TMRM, and 3) mitochondrial swelling by measuring light absorbance. We found that despite calcium release and membrane depolarization, indicative of PTP activation, mitochondria underwent only partial swelling in the presence of spermine. This was in striking contrast to the high-amplitude swelling detected in control mitochondria and in mitochondria treated with the PTP inhibitor CSA. We conclude that spermine selectively prevents opening of the high-conductance state, while allowing activation of the lower conductance state of the PTP. We propose that the existence of lower conductance, stress-induced PTP might play an important physiological role, as it is expected to allow the release of toxic levels of calcium, while keeping important molecules (e.g., NAD) within the mitochondrial matrix.
通透性转换孔（PTP）是线粒体内膜上的一种大通道，其开放是多种应激诱导的细胞死亡中的核心事件。线粒体钙浓度升高会诱导PTP开放。已证明精胺和其他多胺可延迟钙诱导的分离线粒体肿胀，表明它们作为线粒体PTP抑制剂发挥作用。在此，我们通过使用三种指标进一步研究了精胺抑制钙诱导的、环孢素A（CSA）敏感的PTP的机制：1）用钙绿检测线粒体释放的钙；2）使用四甲基罗丹明甲酯（TMRM）检测线粒体膜去极化；3）通过测量吸光度检测线粒体肿胀。我们发现，尽管存在钙释放和膜去极化，这表明PTP被激活，但在精胺存在的情况下，线粒体仅发生部分肿胀。这与在对照线粒体和用PTP抑制剂CSA处理的线粒体中检测到的高幅度肿胀形成了鲜明对比。我们得出结论，精胺选择性地阻止高电导状态的开放，同时允许PTP较低电导状态的激活。我们提出，较低电导的、应激诱导的PTP的存在可能发挥重要的生理作用，因为预计它能使毒性水平的钙释放，同时将重要分子（如NAD）保留在线粒体基质内。
