Kilberg M S, Christensen H N
Membr Biochem. 1980;3(1-2):155-68. doi: 10.3109/09687688009063883.
Plasma membrane vesicles isolated from Ehrlich ascites tumor cells have been used to investigate the role of the transmembrane potential in the energetics of Systems A and L. As expected, Na+ -dependent System A was responsive to changes in membrane potential. System L activity, as measured by transport of 2-amino-norbornane-2-carboxylic acid (BCH), was shown to be Na+ -independent and was not altered by changes in the membrane potential. The combination of valinomycin and nigericin decreased accumulation of MeAIB but not that of BCH. The presence of nigericin alone caused a significant decrease in uptake by System A and a decrease in uptake by System L to a lesser degree. The inhibitory action of nigericin might reflect its ability to dissipate the Na+ gradient rather than an effect on K+ or H+ flows. The results indicate that modes of energization not produced through the transmembrane potential must account for any uphill operation of System L.
从艾氏腹水瘤细胞中分离出的质膜囊泡已被用于研究跨膜电位在系统A和L能量学中的作用。正如预期的那样，依赖钠离子的系统A对膜电位的变化有反应。通过2-氨基降冰片烷-2-羧酸（BCH）转运来测量的系统L活性显示为不依赖钠离子，并且不会因膜电位的变化而改变。缬氨霉素和尼日利亚菌素的组合降低了甲基氨基异丁酸（MeAIB）的积累，但没有降低BCH的积累。单独存在尼日利亚菌素会导致系统A的摄取显著减少，而系统L的摄取减少程度较小。尼日利亚菌素的抑制作用可能反映了其消散钠离子梯度的能力，而不是对钾离子或氢离子流动的影响。结果表明，不是通过跨膜电位产生的能量供应模式必须解释系统L的任何上坡运转。
