Haber R S, Pressley T A, Loeb J N, Ismail-Beigi F
Am J Physiol. 1987 Jul;253(1 Pt 2):F26-33. doi: 10.1152/ajprenal.1987.253.1.F26.
The Na+ ionophore monensin was used to study the Na+- and K+-dependence of ouabain-inhibitable 86Rb+ uptake in ARL 15 cells, a rat liver cell line. Graded concentrations of monensin rapidly induced incremental elevations of cellular Na+ that were stable for up to 2 h. In experiments in which cellular Na+ was thus "clamped" at various levels, the activation curve for ouabain-inhibitable 86Rb+ uptake as a function of intracellular Na+ was found to be steepest near basal Na+ levels (Hill coefficient approximately equal to 2.4), indicating that these cells can respond to relatively large changes in passive Na+ entry by increasing the race of Na-K pump function with only minimal increases in cellular Na+. Exposure of cells to monensin also permitted examination of the extracellular-K+ dependence of ouabain-inhibitable 86Rb+ uptake in the presence of saturating intracellular Na+ and yielded a Hill coefficient of approximately 1.5. The rate of ATP hydrolysis calculated from measurements of the maximal rate of ouabain-inhibitable 86Rb+ uptake in intact cells was similar to the enzymatic Vmax of the Na+-K+-ATPase in cell lysates, suggesting that the Na+-K+-ATPase activity in these broken-cell preparations closely reflects the functional transport capacity of the Na-K pump.
钠离子载体莫能菌素被用于研究钠钾依赖性哇巴因抑制的86Rb+摄取在ARL 15细胞（一种大鼠肝细胞系）中的情况。不同浓度的莫能菌素能迅速诱导细胞内钠离子浓度逐步升高，并在长达2小时内保持稳定。在将细胞内钠离子“钳制”在不同水平的实验中，发现哇巴因抑制的86Rb+摄取的激活曲线作为细胞内钠离子的函数，在基础钠离子水平附近最陡峭（希尔系数约等于2.4），这表明这些细胞仅通过细胞内钠离子的最小增加就能通过增加钠钾泵功能的速率来响应被动钠离子进入的相对较大变化。将细胞暴露于莫能菌素还能在细胞内钠离子饱和的情况下检测哇巴因抑制的86Rb+摄取对细胞外钾离子的依赖性，得到的希尔系数约为1.5。根据完整细胞中哇巴因抑制的86Rb+摄取的最大速率测量计算出的ATP水解速率，与细胞裂解物中钠钾ATP酶的酶促Vmax相似，这表明这些破碎细胞制剂中的钠钾ATP酶活性密切反映了钠钾泵的功能转运能力。
