De Weer P, Rakowski R F
Nature. 1984;309(5967):450-2. doi: 10.1038/309450a0.
The sodium pump of animal cells is electrogenic, that is, it normally exports more sodium ions than it imports potassium ions. In the squid giant axon, the resulting net outward electric current has a density of a few microA cm-2, and contributes 1-2 mV to the resting membrane potential. The pump is driven by the free energy of hydrolysis of ATP, and in some instances it has been possible to run the pump backwards and synthesize ATP by lowering the [ATP]/[ADP] X [Pi] ratio and steepening the transmembrane Na+ and K+ gradients. Here we have examined the question of whether a backward-running sodium pump conserves its Na+/K+ greater than 1 stoichiometry. We demonstrate reversal of the sodium pump of squid giant axon, and find that backward pumping indeed produces a net inward electric current. This current is voltage-sensitive. Our observations have mechanistic implications for models of the sodium pump.
动物细胞的钠泵是生电的，也就是说，它通常排出的钠离子比摄入的钾离子多。在枪乌贼巨大轴突中，由此产生的外向净电流密度为几微安每平方厘米，并对静息膜电位贡献1 - 2毫伏。该泵由ATP水解的自由能驱动，在某些情况下，可以通过降低[ATP]/[ADP]×[Pi]比值并加大跨膜Na⁺和K⁺梯度来使泵逆向运转并合成ATP。在这里，我们研究了逆向运转的钠泵是否保持其Na⁺/K⁺大于1的化学计量关系这一问题。我们证明了枪乌贼巨大轴突钠泵的逆向运转，并发现逆向泵送确实产生内向净电流。该电流对电压敏感。我们的观察结果对钠泵模型具有机制上的启示。
