Kone B C, Kikeri D, Zeidel M L, Gullans S R
Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston 02115.
Am J Physiol. 1989 Apr;256(4 Pt 1):C823-30. doi: 10.1152/ajpcell.1989.256.4.C823.
The dominant K+ transport pathways in rabbit inner medullary collecting duct (IMCD) cells were identified using an extracellular K+ electrode and fluorometric estimates of membrane potential. Ba2+ (5 mM) caused an initial rate of net K+ influx (61 +/- 6 nmol K+.min-1. mg protein-1) equivalent to the net K+ efflux (59 +/- 5 nmol K+. min-1.mg protein-1) induced by ouabain (0.1 mM). Addition of ouabain to Ba2+ -treated cells caused no net K+ flux. Membrane potential experiments demonstrated a K+ conductance that was inhibited by Ba2+. Thus K+ transport in the IMCD occurs principally via Ba2+ -sensitive K+ conductive pathway(s) and Na+-K+-ATPase. In studies that examine the metabolic determinants of K+ transport in the IMCD, glucose (but not 3-O-methylglucose) augmented oxygen consumption (QO2; + 12%) and cell K+ content (+12%), whereas iodoacetic acid, an inhibitor of glycolysis, promoted a release of cell K+. However, inhibition of mitochondrial oxidative phosphorylation with rotenone demonstrated that glycolysis alone could not maintain cell K+ content. Thus glucose metabolism plays an important role in K+ transport in the IMCD, but both glycolysis and oxidative phosphorylation are required to maintain optimal cellular K+ gradients.
利用细胞外钾离子电极和膜电位的荧光测定法，确定了兔肾内髓集合管（IMCD）细胞中主要的钾离子转运途径。钡离子（5 mM）引起的净钾离子内流初始速率（61±6 nmol K⁺·min⁻¹·mg蛋白⁻¹），相当于哇巴因（0.1 mM）诱导的净钾离子外流速率（59±5 nmol K⁺·min⁻¹·mg蛋白⁻¹）。在经钡离子处理的细胞中添加哇巴因，未引起净钾离子通量变化。膜电位实验证明存在一种受钡离子抑制的钾离子电导。因此，IMCD中的钾离子转运主要通过对钡离子敏感的钾离子传导途径和钠钾ATP酶进行。在研究IMCD中钾离子转运的代谢决定因素时，葡萄糖（而非3 - O - 甲基葡萄糖）增加了氧气消耗（QO₂；增加12%）和细胞钾离子含量（增加12%），而糖酵解抑制剂碘乙酸则促使细胞钾离子释放。然而，用鱼藤酮抑制线粒体氧化磷酸化表明，仅糖酵解无法维持细胞钾离子含量。因此，葡萄糖代谢在IMCD的钾离子转运中起重要作用，但糖酵解和氧化磷酸化都需要维持最佳的细胞钾离子梯度。
