Bernard P A, Cockrell R S
Biochim Biophys Acta. 1979 Nov 8;548(2):173-86. doi: 10.1016/0005-2728(79)90127-0.
The Na+ and K+ permeability properties of rat brain mitochondria were determined to explain the influences of these cations upon respiration. A new procedure for isolating exceptionally intact mitochondria with minimal contamination by synaptosomes was developed for this purpose. Respiration was uncoupled by Na+ and less so by K+. Uncoupling was maximal in the presence of EDTA plus Pi and was decreased by Mg2+. Maximal uncoupler-stimulated respiration rates were inhibited by Na+ but largely unaffected by K+. The inhibition by Na+ was relatively insensitive to Mg2+. Membrane Na+ and K+ conductances as well as neutral exchanges (Na+/H+ and K+/H+ antiport activities) were determined by swelling measurements and correlated with metabolic effects of the cations. Cation conductance, i.e. electrophoretic Na+ or K+ permeation, was increased by EDTA (Na+ greater than K+) and decreased by Mg2+. Magnesium preferentially suppressed Na+ conductance so as to reverse the cation selectivity (K+ greater than Na+). Neutral cation/H+ exchange rates (Na+ greater than K+) were not influenced by chelator or Mg2+. The extent of cation-dependent uncoupling of respiration correlated best with the inner membrane conductance of the ion according to an empirical relationship derived with the model K+ conductor valinomycin. The metabolic influences of Na+ and K+ can be explained in terms of coupled flow of these ions with protons and their effect upon the H+ electrochemical gradient although alternative possibilities are discussed. These in vitro studies are compared to previous observations in situ to assess their physiological significance.
测定了大鼠脑线粒体的钠钾通透性特性，以解释这些阳离子对呼吸作用的影响。为此开发了一种新的分离方法，可分离出异常完整且突触体污染最小的线粒体。钠可使呼吸解偶联，而钾的作用较小。在存在乙二胺四乙酸（EDTA）和无机磷酸盐（Pi）的情况下，解偶联作用最大，而镁离子（Mg2+）可使其降低。最大解偶联剂刺激的呼吸速率受到钠的抑制，但很大程度上不受钾的影响。钠的抑制作用对镁离子相对不敏感。通过肿胀测量确定了膜的钠钾电导率以及中性交换（钠氢和钾氢反向转运活性），并将其与阳离子的代谢效应相关联。阳离子电导率，即电泳性钠或钾的通透，因EDTA而增加（钠大于钾），因镁离子而降低。镁优先抑制钠电导率，从而逆转阳离子选择性（钾大于钠）。中性阳离子/氢交换速率（钠大于钾）不受螯合剂或镁离子的影响。根据用钾导体缬氨霉素推导的经验关系，呼吸作用中阳离子依赖性解偶联的程度与离子的内膜电导率最相关。尽管讨论了其他可能性，但钠和钾的代谢影响可以用这些离子与质子的耦合流动及其对氢电化学梯度的影响来解释。将这些体外研究与先前的原位观察结果进行比较，以评估它们的生理意义。
