Ojugo A S, McSheehy P M, Stubbs M, Alder G, Bashford C L, Maxwell R J, Leach M O, Judson I R, Griffiths J R
Division of Biochemistry, St George's Hospital Medical School, London, UK.
Br J Cancer. 1998 Mar;77(6):873-9. doi: 10.1038/bjc.1998.144.
To investigate the possible dependence of 5-fluorouracil (5FU) uptake in tumours on the intra- (pHi) and extracellular (pHe) pH, a pH gradient (deltapH) was imposed across the plasma membrane of ascites tumour cells in vitro, similar to that known to occur in some solid tumours in vivo, by incubation in media of PHe 5-8. A > or = 2:1 (intracellular/extracellular) accumulation of radiolabelled 5FU occurred after 5 min incubation of the cells with 0.5 mM 5FU at pHe of 5.0, 5.5 or 6.0. 5FU metabolism is slow under these conditions, and 5FU uptake was not affected by longer incubations up to 20 min, nor by the absence of a sodium gradient. pHi was estimated from the distribution of the weak acid, 5.5-dimethyl-2,4-oxazolidione ([14C]DMO) across the cell membrane. There was significant correlation between the intracellular/extracellular 5FU ratio and pHe (from pHe 6-8), deltapH and pHi (P < 0.02). Similar results were obtained with HT29 cells. Incubation with a drug that made plasma membranes permeable to H+ significantly decreased 5FU uptake in Lettre cells. The co-transport of 5FU may occur on a proton symport using the proton motive force of the deltapH.
为了研究肿瘤细胞对5-氟尿嘧啶（5FU）的摄取是否可能依赖于细胞内（pHi）和细胞外（pHe）pH值，通过在pH值为5-8的培养基中孵育，在体外腹水肿瘤细胞的质膜上施加了一个pH梯度（deltapH），类似于体内某些实体瘤中已知存在的情况。在pH值为5.0、5.5或6.0的条件下，将细胞与0.5 mM 5FU孵育5分钟后，放射性标记的5FU出现了≥2:1（细胞内/细胞外）的积累。在这些条件下，5FU代谢缓慢，长达20分钟的更长孵育时间以及不存在钠梯度均不影响5FU的摄取。通过弱酸5,5-二甲基-2,4-恶唑烷二酮（[14C]DMO）在细胞膜上的分布来估计pHi。细胞内/细胞外5FU比率与pHe（从pHe 6至8）、deltapH和pHi之间存在显著相关性（P < 0.02）。HT29细胞也获得了类似的结果。用一种使质膜对H+通透的药物孵育可显著降低Lettre细胞中5FU的摄取。5FU的共转运可能通过利用deltapH的质子动力在质子同向转运体上发生。
