Transport of folate compounds by leukemic cells. Evidence for a single influx carrier for methotrexate, 5-methyltetrahydrofolate, and folate in CCRF-CEM human lymphoblasts.
Transport of folate compounds by leukemic cells. Evidence for a single influx carrier for methotrexate, 5-methyltetrahydrofolate, and folate in CCRF-CEM human lymphoblasts.
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白血病细胞转运叶酸化合物。
DOI：
10.1016/0006-2952(87)90216-4
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发表时间：
1987
影响因子：
5.8
通讯作者：
Kumar,HP
中科院分区：
文献类型：
--
作者：
Henderson,GB;Tsuji,JM;Kumar,HP
比较了CCRF-CEM人淋巴母细胞中甲氨蝶呤、5-甲基四氢叶酸和叶酸转运的内流动力学和抑制剂特异性。每种叶酸化合物的流入进行了大约相同的Vmax，波动在相同的方式与介质中的离子组成，并被封闭的阴离子缺乏的缓冲液和缓冲盐水介质中含有生理浓度的葡萄糖和碳酸氢盐的氨甲蝶呤的低浓度的anN-羟基琥珀酰亚胺酯。5-甲基四氢叶酸和叶酸对甲氨蝶呤的内流均有抑制作用，后者的抑制常数（Ki）与其半数最大内流的Ki值相当。叶酸内流同样受到甲氨蝶呤的抑制。甲氨蝶呤的Ki与其内流的Kt相当，邻苯二甲酸酯和磷酸盐均以相同程度的有效性抑制叶酸和甲氨蝶呤。各种可逆和不可逆抑制剂使每种叶酸底物的流入减少> 90%，并且在每种情况下抑制的进展指示单一摄取组分。当叶酸浓度接近内流的Kt（10-50 μM）或接近生理条件的浓度（5-20 nM）时，叶酸内流对甲氨蝶呤内流抑制剂表现出相同的高灵敏度。这些结果表明，CCRF-CEM细胞具有一个单一的共享转运系统的甲氨蝶呤，5-甲基四氢叶酸，叶酸和其他高或低亲和力的摄取过程中不存在这些细胞。
Influx kinetics and inhibitor specificity have been compared for the transport of methotrexate, 5-methyltetrahydrofolate, and folate in CCRF-CEM human lymphoblastoid cells. Influx of each folate compound proceeded with approximately the sameVmax, fluctuated in the same fashion with the ionic composition of the medium, and was blocked by low concentrations of anN-hydroxysuccinimide ester of methotrexate in both an anion-deficient buffer and in a buffered saline medium containing physiological concentrations of glucose and bicarbonate. Moreover, methotrexate influx was inhibited by 5-methyltetrahydrofolate and folate, and the inhibition constants (Ki) of the latter compounds were equivalent to theirKtvalues for half-maximal influx. Folate influx was likewise inhibited by methotrexate. TheKifor methotrexate was equivalent to itsKtfor influx, ando-phthalate and phosphate each inhibited folate and methotrexate with the same degree of effectiveness. Various reversible and irreversible inhibitors reduced the influx of each folate substrate by >90%, and the progression of inhibition in each case was indicative of a single uptake component. Folate influx exhibited the same high sensitivity to inhibitors of methotrexate influx when measurements were performed at folate concentrations near theKtfor influx (10–50 μM) or at concentrations approximating physiological conditions (5–20 nM). These results indicate that CCRF-CEM cells possess a single shared transport system for the uptake of methotrexate, 5-methyltetrahydrofolate, and folate and that other high- or low-affinity uptake processes are not present in these cells.