Evidence for monovalent phosphate transport in Ehrlich ascites tumor cells.
Evidence for monovalent phosphate transport in Ehrlich ascites tumor cells.
复制标题
艾利希腹水肿瘤细胞中单价磷酸盐转运的证据。
DOI：
10.1002/jcp.1041160204
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发表时间：
1983
影响因子：
5.6
通讯作者：
Levinson,C
中科院分区：
文献类型：
--
作者：
Bowen,JW;Levinson,C
为了确定艾利希腹水肿瘤细胞的 Na+ 依赖性 Pi 转运系统是否对 H2PO4− 或 HPO4−2 表现出特异性，通过测量 32PiPi 自交换来确定 Pfluxes。采用了三种实验方法。首先，研究了 0.5 和 5 mM 时 pH 对稳态 Pi 转运的影响。其次，确定了 pH 5.6 和 7.9 时 Pitransport 和微微浓缩 (0.25–9.2 mM) 之间的关系。第三，评估了 Pitransport 在 [HPO4−2] (0.5 mM) 恒定时对 [H2PO4−] (0.05–4.2 mM) 的依赖性，以及在 [H2PO4−] (0.5 mM) 恒定时相反的 [HPO4−2] (0.06–4.5 mM) 的依赖性。 Ks（表观半饱和常数）和 Jmax（最大传输速率）通过两种方法计算：加权线性回归（WLR）和非参数程序。 Pflux 对 pH 值的依赖性表明最佳转运发生在 pH 值 6.9 时。当细胞外 Pi 为 0.5 或 5 mM 时，Pi 转运随着 pH 值降低而降低。然而，在 pH 7.9 时，Pflux 仅在 0.5 mM Pi 中减少。在 pH 5.6 时，H2PO4− 占总 Pipresent 的 93%，计算得出的 Ksis 为 0.055 ± 0.026 mM (WLR)。这与根据通量初始阶段与 [H2PO4−] 关系 (0.056 ± 0.020 mM) 确定的 Ks 相同。然而，在 pH 7.9 时（其中 94% 的 Piis HPO4−2），测得的 Ksis 为 0.58 ± 0.11 mM (WLR)，比 pH 5.6 时高十倍。该值也比根据通量与 [HPO4−2] 曲线 (0.106 ± 0.16 mM) 计算出的 Ks 大五倍。非参数方法计算的动力学参数虽然有所不同，但给出了相似的相对结果。综上所述，这些结果支持两个结论：（1）H2PO4−是艾利希细胞 Na+ 依赖性 Pi 转运系统的底物，（2）H+ 可以抑制 Pi 转运。
In an effort to determine whether the Na+‐dependent Pitransport system of Ehrlich ascites tumor cells exhibits specificity for H2PO4−or HPO4−2, Pifluxes were determined by measuring32PiPiself‐exchange. Three experimental approaches were employed. First, the effect of pH on steady‐state Pitransport at 0.5 and 5 mM was studied. Second, the relationship between Pitransport and Piconcentration (0.25–9.2 mM) at pH 5.6 and 7.9 was determined. Third, the dependence of Pitransport on [H2PO4−] (0.05–4.2 mM) at constant [HPO4−2] (0.5 mM), and the converse, [HPO4−2] (0.06–4.5 mM) at constant [H2PO4−] (0.5 mM), was evaluated. Ks(apparent half‐saturation constant) and Jmax(maximal transport rate) were calculated by two methods: weighted linear regression (WLR) and a nonparametric procedure. The dependence of Piflux on pH indicates that optimum transport occurs at pH 6.9. Pitransport decreases as pH is reduced when extracellular Piis either 0.5 or 5 mM. However, at pH 7.9, Piflux is reduced only in 0.5 mM Pi. At pH 5.6, H2PO4−comprises 93% of the total Pipresent, and the calculated Ksis 0.055 ± 0.026 mM (WLR). This is the same as the Ksdetermined from the initial phase of the flux vs. [H2PO4−] relationship (0.056 ± 0.020 mM). However, at pH 7.9 (where 94% of Piis HPO4−2), the measured Ksis 0.58 ± 0.11 mM (WLR), which is ten times higher than at pH 5.6. This value is also five times greater than the Kscalculated from the flux vs. [HPO4−2] curve (0.106 ± 0.16 mM). Kinetic parameters calculated by the nonparametric method, though somewhat different, gave similar relative results. Taken together, these results support two conclusions: (1) H2PO4−is the substrate for the Na+‐dependent Pitransport system of the Ehrlich cell, and (2) H+can inhibit Pitransport.