Ramakrishnan N, McClain D E, Catravas G N
Office of Chair of Science, Armed Forces Radiobiology Research Institute, Bethesda, MD 20889-5603.
Int J Radiat Biol. 1993 Jun;63(6):693-701. doi: 10.1080/09553009314552091.
The role of cellular membranes in thymocyte apoptosis has been examined. Trolox, a water soluble analogue of vitamin E and inhibitor of membrane damage, inhibits DNA fragmentation in thymocytes exposed to gamma-radiation. Trolox is most effective in inhibiting DNA fragmentation when added to cells within 30 min post-irradiation. Exposure to trolox only during irradiation did not prevent DNA fragmentation, suggesting that it does not work by scavenging free radicals generated during radiation exposure. Incubation of the irradiated cell suspension with trolox for 2 h post-irradiation was sufficient to prevent DNA fragmentation measured at 24 h in irradiated cells. This suggests that trolox irreversibly inhibits a cellular lesion required for apoptosis. The induction of DNA fragmentation appears to be related to a concurrent, pronounced flow of Ca2+ into the cell. At 3 h post-irradiation the amount of Ca2+ in irradiated thymocytes was more than twice that of unirradiated thymocytes. Membrane damage has been shown to affect the transport of Ca2+. Trolox treatment completely blocked the radiation-induced influx of Ca2+ into the thymocytes. These results suggest that membrane damage is a critical lesion that is involved in DNA fragmentation in thymocyte apoptosis.
细胞凋亡过程中细胞膜的作用已得到研究。生育酚（Trolox）是维生素E的水溶性类似物，也是膜损伤抑制剂，它能抑制受γ射线照射的胸腺细胞中的DNA片段化。在照射后30分钟内将生育酚添加到细胞中时，其抑制DNA片段化的效果最为显著。仅在照射期间暴露于生育酚并不能防止DNA片段化，这表明它并非通过清除辐射暴露期间产生的自由基来发挥作用。在照射后用生育酚孵育辐照后的细胞悬液2小时，足以防止在辐照后24小时测量到的DNA片段化。这表明生育酚不可逆地抑制了细胞凋亡所需的细胞损伤。DNA片段化的诱导似乎与同时发生的、明显的Ca2+流入细胞有关。在照射后3小时，辐照后胸腺细胞中的Ca2+含量是未辐照胸腺细胞的两倍多。膜损伤已被证明会影响Ca2+的转运。生育酚处理完全阻断了辐射诱导的Ca2+流入胸腺细胞。这些结果表明，膜损伤是胸腺细胞凋亡过程中参与DNA片段化的关键损伤。
