Bratton D L
Department of Pediatrics, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
J Biol Chem. 1994 Sep 9;269(36):22517-23.
The resting plasma membrane of circulating blood cells demonstrates an asymmetric distribution of the phospholipid classes across the bilayer that is altered during cellular activation. To better understand the mechanisms governing transbilayer distribution of phospholipids, studies were conducted using the erythrocyte ghost, in which plasma membrane leaflet distribution of phospholipids can be readily probed. Preparation of ghosts by hypotonic lysis at increasingly high dilution markedly enhanced (up to 10-fold) calcium-induced (50-500 microM) transbilayer movement of phospholipids. The enhanced transbilayer movement was assessed by translocation of exogenously added sn-2-[6[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]caproyl]-labeled phosphatidylcholine and phosphatidylserine from the plasma membrane outer leaflet to the inner leaflet and vice versa, as well as transbilayer movement of endogenous phosphatidylserine to the outer leaflet. It was found that phospholipid movement was bidirectional and also nonspecific with regard to polar head group. It was further demonstrated that preparation of ghosts at increasing dilution resulted in depletion of cellular polyamines and that physiologic replenishment of spermine, and to a lesser extent spermidine, resulted in significant inhibition (50 and 25%, respectively) of transbilayer movement of phospholipids. Replenishment of other di- and polyamines demonstrated that inhibition was not simply dependent on total cationic charge but rather on charge density and suggestive of specific interaction of the polyamines, particularly spermine, with the plasma membrane. As most cells demonstrate both a high degree of regulation in maintenance of polyamine levels and the means for facile shifts within cellular polyamine pools, it is suggested that loss of membrane asymmetry during cellular activation may be mediated in part through enhanced transbilayer movement of phospholipids due to altered polyamine-membrane associations.
循环血细胞的静息质膜显示出磷脂类在双分子层中的不对称分布，这种分布在细胞激活过程中会发生改变。为了更好地理解磷脂跨双分子层分布的调控机制，研究人员使用了红细胞血影，其中磷脂的质膜小叶分布可以很容易地被探测到。在越来越高的稀释度下通过低渗裂解制备血影，显著增强了（高达10倍）钙诱导的（50 - 500微摩尔）磷脂跨双分子层运动。通过将外源添加的sn - 2 - [6[(7 - 硝基苯并 - 2 - 恶唑 - 1,3 - 二氮杂 - 4 - 基)氨基]己酰基]标记的磷脂酰胆碱和磷脂酰丝氨酸从质膜外小叶转运到内小叶以及反之亦然，以及内源性磷脂酰丝氨酸向外小叶的跨双分子层运动来评估增强的跨双分子层运动。结果发现磷脂运动是双向的，并且对于极性头部基团是非特异性的。进一步证明，在增加稀释度的情况下制备血影会导致细胞多胺的消耗，而精胺的生理补充，以及程度较小的亚精胺的补充，会导致磷脂跨双分子层运动的显著抑制（分别为50%和25%）。其他二胺和多胺的补充表明，抑制作用不仅仅取决于总阳离子电荷，而是取决于电荷密度，这表明多胺，特别是精胺，与质膜之间存在特异性相互作用。由于大多数细胞在维持多胺水平方面表现出高度的调节，并且在细胞内多胺库中具有容易发生变化的方式，因此有人提出，细胞激活过程中膜不对称性的丧失可能部分是由于多胺 - 膜结合的改变导致磷脂跨双分子层运动增强所介导的。
