电场对（钠，钾）-ATP酶的电致铷离子转运的激活作用。

Activation of electrogenic Rb+ transport of (Na,K)-ATPase by an electric field.

作者信息

Serpersu E H, Tsong T Y

出版信息

J Biol Chem. 1984 Jun 10;259(11):7155-62.

Abstract

Previous study shows that human erythrocytes when exposed, in an isotonic suspension, to an electric field that generated 6-15 mV of transmembrane potential induced a Rb+ uptake that was sensitive to ouabain, a potent inhibitor of (Na,K)-ATPase ( Serpersu , E. H., and Tsong , T. Y. (1983) J. Membr . Biol. 74, 191-201). Here we present evidence that this uptake indeed involved the activity of (Na,K)-ATPase. Transport of Rb+, K+, and Na+ were carefully monitored during the voltage stimulation. It is shown that the electric field stimulated only the ouabain-sensitive influx of Rb+, and this uptake was against a chemical concentration gradient. The rate of the stimulated Rb+ uptake was measured under different intracellular Na+ and extracellular Rb+ concentrations. The Km for the stimulated Rb+ uptake was, respectively, 7 mM for the intracellular Na+ and 1.7 mM for the extracellular Rb+, consistent with the values for the red cell (Na,K)-ATPase. Yet, the voltage-sensitive Rb+ uptake did not depend on the intracellular ATP level. Neither did the voltage stimulation cause an elevation of ATP concentration in the red blood cells as was observed in mitochondrial and chloroplast ATP synthetase systems under higher electric field conditions. Since only Rb+ uptake was stimulated by the voltage, it follows then that the Na+ and the K+ pumping activities of the (Na,K)-ATPase could be decoupled, and the K+ pumping activity may derive from the electrogenic component of the enzyme action. In the present case, the applied electric field could polarize the membrane to provide membrane potential required for the electrogenic transport of Rb+. Data also show that vanadate at 180 microM completely inhibited the ATP-dependent Na+ and Rb+ pumping activities of the enzyme, but only reduced the voltage-stimulated Rb+ uptake to 50% level. This represents the first systematic study of the activation of a transport ATPase by an externally applied electric field.

摘要

先前的研究表明，当人类红细胞在等渗悬浮液中暴露于产生6 - 15 mV跨膜电位的电场时，会诱导对哇巴因敏感的Rb⁺摄取，哇巴因是(Na,K)-ATP酶的一种有效抑制剂（Serpersu, E. H., 和Tsong, T. Y. (1983) J. Membr. Biol. 74, 191 - 201）。在此，我们提供证据表明这种摄取确实涉及(Na,K)-ATP酶的活性。在电压刺激期间仔细监测了Rb⁺、K⁺和Na⁺的转运。结果表明，电场仅刺激了对哇巴因敏感的Rb⁺内流，并且这种摄取是逆着化学浓度梯度进行的。在不同的细胞内Na⁺和细胞外Rb⁺浓度下测量了刺激的Rb⁺摄取速率。刺激的Rb⁺摄取的Km值，细胞内Na⁺分别为7 mM，细胞外Rb⁺为1.7 mM，这与红细胞(Na,K)-ATP酶的值一致。然而，电压敏感的Rb⁺摄取并不依赖于细胞内ATP水平。电压刺激也没有像在更高电场条件下在线粒体和叶绿体ATP合成酶系统中观察到的那样导致红细胞中ATP浓度升高。由于只有Rb⁺摄取受到电压刺激，因此可以得出结论，(Na,K)-ATP酶的Na⁺和K⁺泵浦活性可能解偶联，并且K⁺泵浦活性可能源自该酶作用的电生成分。在当前情况下，施加的电场可以使膜极化以提供Rb⁺电生转运所需的膜电位。数据还表明，180 microM的钒酸盐完全抑制了该酶的ATP依赖性Na⁺和Rb⁺泵浦活性，但仅将电压刺激的Rb⁺摄取降低到50%水平。这代表了对外部施加电场激活转运ATP酶的首次系统研究。