Leister K J, Schenerman M A, Racker E
Section of Biochemistry, Molecular and Cell Biology, Cornell University, Ithaca, NY 14853.
Proc Natl Acad Sci U S A. 1989 Feb;86(3):783-6. doi: 10.1073/pnas.86.3.783.
Quiescent C3H-10T1/2 mouse fibroblasts that have not undergone any type of stress have a relatively low rate of 2-aminoisobutyrate (Aib) uptake by means of system A, which is primarily energized by the transmembrane Na+ chemical gradient potential. System A activity in these cells is not sensitive to ouabain or proton ionophores. In contrast, methylcholanthrene-transformed and confluent C3H-10T1/2 cells treated with 0.4 mM ouabain for 16-20 hr utilize the membrane potential generated by the Na+, K+-ATPase pump to drive Aib transport by means of system A as shown by the sensitivity of transport activity to ouabain and proton ionophores. Since glucose is present during the assay, the proton ionophores do not affect the availability of ATP, as indicated by the undiminished uptake of 86Rb+ by the Na+, K+-ATPase pump. As cells progress through the G1 phase of the cell cycle, they show an increased system A activity prior to entry into the S phase, which is also dependent on the electrogenicity of the Na+, K+-ATPase pump. There appears to be in all these cases a qualitative shift in the bioenergetic mechanism for the uptake of Aib as well as a marked quantitative increase in Aib uptake. The high activity after ouabain treatment was sustained in the transformed cells after removal of the ouabain, whereas in the confluent 10T1/2 cells the rate of uptake decayed rapidly, suggesting a difference in the mode of regulation. We conclude that transformed cells and normal cells in late G1 or under stress make use of the membrane potential generated by the Na+, K+-ATPase pump to drive amino acid uptake by means of system A.
未经历任何类型应激的静止C3H - 10T1/2小鼠成纤维细胞通过系统A摄取2 - 氨基异丁酸（Aib）的速率相对较低，该系统主要由跨膜Na⁺化学梯度电位提供能量。这些细胞中的系统A活性对哇巴因或质子离子载体不敏感。相比之下，用0.4 mM哇巴因处理16 - 20小时的甲基胆蒽转化的汇合C3H - 10T1/2细胞利用Na⁺，K⁺ - ATP酶泵产生的膜电位通过系统A驱动Aib转运，转运活性对哇巴因和质子离子载体的敏感性表明了这一点。由于测定过程中存在葡萄糖，质子离子载体不会影响ATP的可用性，Na⁺，K⁺ - ATP酶泵对⁸⁶Rb⁺的摄取未减少就表明了这一点。随着细胞在细胞周期的G1期进展，它们在进入S期之前显示出系统A活性增加，这也依赖于Na⁺，K⁺ - ATP酶泵的电生性。在所有这些情况下，似乎Aib摄取的生物能量机制发生了质的转变，同时Aib摄取也有显著的量的增加。哇巴因处理后的高活性在去除哇巴因后在转化细胞中得以维持，而在汇合的10T1/2细胞中摄取速率迅速下降，这表明调节方式存在差异。我们得出结论，转化细胞以及处于G1晚期或受到应激的正常细胞利用Na⁺，K⁺ - ATP酶泵产生的膜电位通过系统A驱动氨基酸摄取。
