Tupper J T
Biochim Biophys Acta. 1975 Jul 18;394(4):586-96. doi: 10.1016/0005-2736(75)90144-3.
In a previous study, evidence was presented for an external Na+-dependent, ouabain-insensitive component of Na+ efflux and an external K+-dependent component of K+ efflux in the Ehrlich ascites tumor cell. Evidence is now presented that these components are inhibited by the diuretic furosemide and that under conditions of normal extracellular Na+ and K+ they represent Na+-for-Na+ and K-+for-K+ exchange mechanisms. Using 86Rb to monitor K+ movements, furosemide is shown to inhibit an ouabain-insensitive component of Rb+ influx and a component of Rb+ efflux, both representing approx. 30 percent of the total flux. Inhibition of Rb+ efflux is greatly reduced by removal of extracellular K+. Furosemide does not alter steady-state levels of intracellular K+ and it does not prevent cells depleted of K+ by incubation in the cold from regaining K+ upon warming. Using 22Na to monitor Na+ movements, furosemide is shown to inhibit an ouabain-insensitive component of unidirectional Na+ efflux which represents approx. 22 percent of total Na+ efflux. Furosemide does not alter steady-state levels of intracellular Na+ and does not prevent removal of intracellular Na+ upon warming from cells loaded with Na+ by preincubation in the cold. The ability of furosemide to affect unidirectional Na+ and K+ fluxes but not net fluxes is consistent with the conclusion that these components of cation movement across the cell membrane represent one-for-one exchange mechanisms. Data are also presented which demonstrate that the uptake of alpha-aminoisobutyrate is not affected by furosemide. This indicates that these components of cation flux are not directly involved in the Na+-dependent amino acid transport system A.
在先前的一项研究中，已提出证据表明艾氏腹水肿瘤细胞中存在一种依赖细胞外钠离子、对哇巴因不敏感的钠离子外流成分，以及一种依赖细胞外钾离子的钾离子外流成分。现在有证据表明，这些成分会受到利尿剂速尿的抑制，并且在正常细胞外钠离子和钾离子条件下，它们代表钠离子与钠离子、钾离子与钾离子的交换机制。利用⁸⁶Rb监测钾离子运动，结果显示速尿会抑制Rb⁺内流中对哇巴因不敏感的成分以及Rb⁺外流的一个成分，这两个成分均约占总通量的30%。去除细胞外钾离子可大大降低对Rb⁺外流的抑制作用。速尿不会改变细胞内钾离子的稳态水平，也不会阻止在低温下孵育而耗尽钾离子的细胞在升温后重新获得钾离子。利用²²Na监测钠离子运动，结果显示速尿会抑制单向钠离子外流中对哇巴因不敏感的成分，该成分约占总钠离子外流的22%。速尿不会改变细胞内钠离子的稳态水平，也不会阻止通过在低温下预孵育而加载了钠离子的细胞在升温后去除细胞内的钠离子。速尿影响单向钠离子和钾离子通量但不影响净通量的能力与以下结论一致，即这些跨细胞膜的阳离子运动成分代表一对一的交换机制。还提供了数据表明α-氨基异丁酸的摄取不受速尿影响。这表明这些阳离子通量成分不直接参与依赖钠离子的氨基酸转运系统A。
