Heinz A, Jackson J W, Richey B E, Sachs G, Schafer J A
J Membr Biol. 1981;62(1-2):149-60. doi: 10.1007/BF01870207.
Uptake of alpha-aminoisobutyric acid (AIB) was examined in Ehrlich ascites tumor cells treated with the cation-exchange ionophore nigericin (20 microgram/ml). Membrane voltages were measured using the voltage-sensitive dye diethyloxadicarbocyanine (DOCC). In normal phosphate-buffered media, nigericin changed the distribution ratios of Na+ and K+ (the ratio of intra- to extracellular concentrations) nearly to unity, but AIB was still accumulated to a distribution ratio of approximately 9.0. When all but 40 mM Na+ in the medium was replaced by choline, nigericin resulted in K+ loss and Na+ gain and both cation distribution ratios approached 2.8-3.4, as would be expected if both ions were distributing near electrochemical equilibrium with a membrane voltage in the range of -28 to -33 mV. This conclusion was supported by the observation that the addition of 5 X 10(-7) M valinomycin to the nigericin-treated cell suspension produced no change in DOCC absorbance. In spite of the apparent zero electrochemical potential gradients for Na+ and K+, AIB was accumulated to a distribution ratio of 5.4 in the low-Na+ medium. Addition of 0.1 mM oubain or 50 microM vanadate did not alter the extent of AIB accumulation as would have been expected if a large component of the membrane voltage were due to electrogenic operation of the (Na+ + K+)-ATPase. Addition of lactate, pyruvate or glucose increased the AIB distribution ratios to 11.9, 9.4 and 15.3, respectively. The effect of glucose could be explained, at least in part, by an enhanced Na+ electrochemical potential gradient. However, neither lactate nor pyruvate produced any change either in membrane voltage or the intracellular Na+ concentration. Therefore, these results confirm the existence of a metabolic energy source which is coupled to AIB accumulation and operates in addition to the Na+ co-transport mechanism, and which is augmented by metabolic substrates such as lactate and pyruvate.
在用阳离子交换离子载体尼日利亚菌素（20微克/毫升）处理的艾氏腹水瘤细胞中检测了α-氨基异丁酸（AIB）的摄取。使用电压敏感染料二乙氧杂二羰花青（DOCC）测量膜电压。在正常的磷酸盐缓冲介质中，尼日利亚菌素将Na⁺和K⁺的分布比率（细胞内与细胞外浓度的比率）几乎改变为1，但AIB仍以约9.0的分布比率积累。当培养基中除40 mM Na⁺外的所有成分都被胆碱取代时，尼日利亚菌素导致K⁺流失和Na⁺增加，两种阳离子的分布比率接近2.8 - 3.4，正如如果两种离子在膜电压范围为 - 28至 - 33 mV时接近电化学平衡分布时所预期的那样。这一结论得到了以下观察结果的支持：向用尼日利亚菌素处理的细胞悬液中添加5×10⁻⁷ M缬氨霉素不会导致DOCC吸光度发生变化。尽管Na⁺和K⁺的电化学势梯度明显为零，但在低Na⁺培养基中AIB仍以5.4的分布比率积累。添加0.1 mM哇巴因或50 μM钒酸盐并没有改变AIB的积累程度，而如果膜电压的很大一部分是由于（Na⁺ + K⁺）-ATP酶的电生作用，那么预期会发生这种改变。添加乳酸、丙酮酸或葡萄糖分别将AIB的分布比率提高到11.9、9.4和15.3。葡萄糖的作用至少部分可以通过增强的Na⁺电化学势梯度来解释。然而，乳酸和丙酮酸都没有引起膜电压或细胞内Na⁺浓度的任何变化。因此，这些结果证实了存在一种与AIB积累相关联的代谢能量来源，它除了Na⁺共转运机制外还起作用，并且会被乳酸和丙酮酸等代谢底物增强。
