Wiedmer T, Sims P J
J Biol Chem. 1985 Jul 5;260(13):8014-9.
The carbocyanine dye 3,3'-dipropylthiodicarbocyanine iodide has been used to investigate changes in membrane potential (Em) which occur upon binding of complement proteins C5b-9 to the plasma membrane of blood platelets. Gel-filtered platelets exposed to C5b6 and C7 in serum-free medium show no change in Em from that of controls, as indicated by either 3,3,'-dipropylthiodicarbocyanine iodide fluorescence or by the distribution of [14C]tetraphenylphosphonium bromide. Addition of complement proteins C8 and C9 to the C5b67 platelets results in partial depolarization of Em, which spontaneously repolarizes to basal levels within 15-20 min at 37 degrees C. Under these conditions, C5b-9-treated platelets show no increase in lysis over complement-free controls. Isotonic replacement of external sodium by either potassium or choline alters both the rate and extent of membrane depolarization and inhibits the platelets' capacity to repolarize after C5b-9 assembly. Repolarization of Em to basal levels is also completely blocked by addition of ouabain, confirming that this recovery is mediated by the plasma membrane Na+/K+ pump. These results demonstrate that membrane binding of the C5b-9 proteins can induce a transient change in Em when bound to the plasma membrane at a sublytic concentration, providing a mechanism for target cell activation by these potentially cytolytic proteins.
羰花青染料3,3'-二丙基硫代二羰花青碘化物已被用于研究补体蛋白C5b-9与血小板质膜结合时发生的膜电位（Em）变化。在无血清培养基中暴露于C5b6和C7的凝胶过滤血小板，通过3,3'-二丙基硫代二羰花青碘化物荧光或[14C]溴化四苯基鏻的分布表明，其Em与对照相比没有变化。向C5b67血小板中添加补体蛋白C8和C9会导致Em部分去极化，在37℃下15 - 20分钟内会自发复极化至基础水平。在这些条件下，C5b - 9处理的血小板与无补体对照相比，裂解没有增加。用钾或胆碱等渗替代外部钠会改变膜去极化的速率和程度，并抑制血小板在C5b - 9组装后复极化的能力。添加哇巴因也完全阻断了Em复极化至基础水平，证实这种恢复是由质膜Na+/K+泵介导的。这些结果表明，当C5b - 9蛋白以亚溶细胞浓度与质膜结合时，其膜结合可诱导Em的瞬时变化，为这些潜在的溶细胞蛋白激活靶细胞提供了一种机制。
