Lieberman E M, Pascarella J, Brunder D, Hargittai P T
Department of Physiology, School of Medicine, East Carolina University, Greenville, NC 27834-4354.
J Neurochem. 1990 Jul;55(1):155-64. doi: 10.1111/j.1471-4159.1990.tb08833.x.
Crayfish axons exposed to a high or low extracellular K+ concentration ([K+]o) maintain intracellular Na+ and K+ concentrations constant, for up to 3 h, by adjusting both the Na+/K+ transport "coupling ratio" and turnover rate in compensation for changes in ion fluxes due to altered electrochemical gradients. These findings give rise to the prediction that the steady-state consumption of high-energy phosphate (approximately P) [ATP and phospho-L-arginine (Arg-P)] is inversely proportional to the [K+]o, i.e., directly proportional to the product of membrane conductance and magnitude of the transmembrane electrochemical gradients for Na+ and K+. This investigation was designed to test this hypothesis. The [K+]o did not influence total approximately P consumption (Q approximately P) of the axon. For a [K+]o between 0.5 and 21.6 mM, Q approximately P averaged 52.8 +/- 4.7%/h (n = 44) of the initial [ATP] + [Arg-P]. Unlike total Q approximately P, the ouabain-sensitive portion of Q approximately P was markedly influenced by [K+]o. In 0.5 mM K+o, ouabain poisoning reduced Q approximately P to 8%/h, a result indicating that 85% of the total Q approximately P was ouabain sensitive. For 1.35 mM K+o, the ouabain-sensitive portion was 66%; at 5.4 mM K+o, 45%; and at 13.5 mM K+o, 41%. There was a small but significant increase in the ouabain-sensitive Q approximately P at 21.6 mM K+o, compared with Q approximately P at 5.4 mM K+o. The pattern of effect of [K+]o on Q approximately P was similar to its effect on the electrical power content of the Na+ and K+ electrochemical gradients. In contrast to the generally accepted Na+ flux (JNa)/approximately P stoichiometry of 3, an actual ratio of JNa/approximately P stoichiometry of approximately 33:1 was calculated for the experiments reported here, a result suggesting that cells in a zero-membrane current steady state utilize efficient energy conservation mechanisms that may not operate under non-steady-state conditions.
暴露于高或低细胞外钾离子浓度（[K⁺]ₒ）的小龙虾轴突，通过调整钠钾转运“偶联比率”和周转率，在长达3小时的时间内维持细胞内钠和钾浓度恒定，以补偿因电化学梯度改变而导致的离子通量变化。这些发现引发了这样的预测：高能磷酸盐（约P）[三磷酸腺苷（ATP）和磷酸-L-精氨酸（Arg-P）]的稳态消耗与[K⁺]ₒ成反比，即与膜电导以及钠和钾的跨膜电化学梯度大小的乘积成正比。本研究旨在验证这一假设。[K⁺]ₒ并未影响轴突的总约P消耗（Q约P）。对于0.5至21.6 mM之间的[K⁺]ₒ，Q约P平均为初始[ATP] + [Arg-P]的52.8±4.7%/小时（n = 44）。与总Q约P不同，Q约P中对哇巴因敏感的部分受[K⁺]ₒ的影响显著。在0.5 mM K⁺ₒ时，哇巴因中毒使Q约P降至8%/小时，这一结果表明总Q约P的85%对哇巴因敏感。对于1.35 mM K⁺ₒ，对哇巴因敏感的部分为66%；在5.4 mM K⁺ₒ时为45%；在13.5 mM K⁺ₒ时为41%。与5.4 mM K⁺ₒ时的Q约P相比，在21.6 mM K⁺ₒ时对哇巴因敏感的Q约P有小幅但显著的增加。[K⁺]ₒ对Q约P的影响模式与其对钠和钾电化学梯度的电功率含量的影响相似。与普遍接受的钠通量（JNa）/约P化学计量比3不同，对于此处报道的实验，计算得出的JNa/约P化学计量比实际约为33:1，这一结果表明处于零膜电流稳态的细胞利用了高效的能量守恒机制，而这些机制在非稳态条件下可能不起作用。
