On the nature of a transport alteration determining resistance to amethopterin in the L1210 leukemia.
On the nature of a transport alteration determining resistance to amethopterin in the L1210 leukemia.
复制标题
关于 L1210 白血病中决定氨甲蝶呤耐药性的转运改变的性质。
作者：
F. Sirotnak;S. Kurita;D. Hutchison
L1210白血病细胞对氨甲喋呤的摄取可能是通过主动转运机制来实现的。摄取与浓度梯度相反，与温度有关，需要随时可用的能源，最适pH为7.6，符合Michaelis-Menten动力学。在平衡状态下，游离氨甲喋呤-3 H在细胞内的最大累积浓度是体外浓度的8倍。叶酸和H2-叶酸都与氨甲喋呤-3H竞争同一体系，但程度有限。在对氨蝶呤、6-巯基嘌呤和5-氟尿嘧啶耐药的亚系(XVI4)中，转运速度降低了4倍。动力学分析显示，在这些耐药细胞中，系统的米氏常数(Km)增加，这表明载体组分的结合性质发生了变化，这是损害的基础。第二个亚系(XVI4a)直接来自原始亚系XVI4，其特征是缺乏亚端粒染色体和升高的二氢叶酸还原酶。该染色体变异体的细胞转运速率是正常的，尽管该系统的Km与XVI4亚系的细胞一样增加。XVI4a亚系细胞内游离氨基蝶呤-3 H的最大蓄积量是细胞外浓度的11倍以上。
The uptake of amethopterin-3H by L1210 leukemia cells appears to be mediated, probably, via an active transport mechanism. Uptake occurred against a concentration gradient, was temperature dependent, required a readily available source of energy, exhibited a pH optimum of 7.6 and conformed to Michaelis-Menten kinetics. The maximum intracellular concentration of unbound amethopterin-3H accumulated at equilibrium was 8-fold the external concentration. Both folate and H2-folate compete with amethopterin-3H for the same system, but to a limited degree. The rate of transport was reduced 4-fold in cells of a subline (XVI4) resistant to amethopterin, 6-mercaptopurine and 5-fluorouracil. Kinetic analysis revealed an increase in the Michaelis constant ( Km ) for the system in these resistant cells, suggesting an alteration in the binding properties of a carrier component as the basis for the impairment. A second subline (XVI4a) was derived directly from the original subline XVI4 and was characterized by the absence of the subtelocentric chromosome and an elevated dihydrofolate reductase. The rate of transport in cells of this chromosomal variant was normal, although the Km for the system was increased as in cells of subline XVI4. Maximum intracellular accumulation of unbound amethopterin-3H by cells of subline XVI4a was greater than 11-fold the external concentration.