In this study we tested the hypothesis that stimulation of univalent-cation fluxes which follow the addition of growth factors are required for cell transition through the G1-phase of the cell cycle. The effect of two drugs, amiloride and bumetanide, were tested on exit of BALB/c 3T3 cells from G0/G1-phase and entry into S-phase (DNA synthesis). Amiloride, an inhibitor of the Na+/H+ antiport, only partially inhibited DNA synthesis induced by serum. Bumetanide, an inhibitor of the Na+/K+ co-transport, only slightly suppressed DNA synthesis by itself, but when added together with amiloride completely blocked cell transition through G1 and entry into S-phase. Similar inhibitory effects of the two drugs were found on the induction of ornithine decarboxylase (ODC) (a marker of mid-G1-phase) in synchronized cells stimulated by either partially purified fibroblast growth factor (FGF) or serum. To test this hypothesis further, cells arrested in G0/G1 were stimulated by serum, insulin or FGF. All induced similar elevations of cellular K+ content during the early G1-phase of the cell cycle. However, serum and FGF, but not insulin, released the cells from the G0/G1 arrest, as measured by ODC enzyme induction. This result implies that the increase in cellular K+ content may be necessary but not sufficient for induction of early events during the G1-phase. The synergistic inhibitory effects of amiloride and bumetanide on the two activities stimulated by serum growth factors, namely ODC induction (mid-G1) and thymidine incorporation into DNA (S-phase), suggested that the amiloride-sensitive Na+/H+ antiport system together with the bumetanide-sensitive Na+/K+ transporter play a role in the mitogenic signal.
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机译:在这项研究中,我们测试了以下假设:通过细胞周期的G1期进行细胞过渡需要刺激添加生长因子的单价阳离子通量。测试了两种药物阿米洛利和布美他尼对从G0 / G1期退出BALB / c 3T3细胞并进入S期(DNA合成)的影响。 Na + / H +反向转运抑制剂Amiloride仅部分抑制血清诱导的DNA合成。 Na + / K +共转运抑制剂布美他尼本身仅略微抑制DNA合成,但与阿米洛利一起加入时,则完全阻止了细胞通过G1过渡并进入S期。在部分纯化的成纤维细胞生长因子(FGF)或血清刺激的同步化细胞中,发现两种药物对鸟氨酸脱羧酶(ODC)(G1期中期的标志物)的诱导具有相似的抑制作用。为了进一步检验该假设,血清,胰岛素或FGF刺激了G0 / G1细胞停滞。在细胞周期的早期G1阶段,所有诱导的细胞K +含量都有相似的升高。然而,如通过ODC酶诱导所测量的,血清和FGF而不是胰岛素从G0 / G1停滞释放细胞。该结果暗示,细胞G +含量的增加可能是必需的,但不足以诱导G1期早期事件的发生。阿米洛利和布美他尼对血清生长因子刺激的两种活性(ODC诱导(中G1)和胸苷掺入DNA(S期))的协同抑制作用表明,阿米洛利敏感的Na + / H +反向转运系统与布美他尼敏感的Na + / K +转运蛋白在促有丝分裂信号中起作用。
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