Ishibashi Hitoshi, Hirao Kenzo, Yamaguchi Junya, Nabekura Junichi
Department of Developmental Physiology, National Institute for Physiological Sciences, Okazaki 444-8585, Japan.
Neurotoxicology. 2009 Jan;30(1):155-9. doi: 10.1016/j.neuro.2008.10.003. Epub 2008 Oct 22.
Gadolinium is a rare-earth lanthanide metal ion and is used as organic gadolinium complexes in magnetic resonance imaging (MRI). Although gadolinium-based MRI agents are thought to be safe in clinical use, the in vivo release of the toxic free inorganic gadolinium (Gd3+) has been reported in some patients with kidney disease. In central nervous system neurons, the inhibitory action of GABA is a consequence of relatively hyperpolarized Cl- equilibrium potential (ECl), which results from the activity of K+-Cl- co-transporter (KCC). The lanthanide ions are reported to affect GABAA receptors. However, little is known about the effect of Gd3+ on GABAA receptor function with intact intracellular Cl- concentration. In the present study, we investigated the effect of Gd3+ on GABAA receptor-mediated currents using gramicidin perforated patch recording method in cultured rat spinal cord neurons. The application of muscimol, a GABAA receptor agonist, caused outward current at a holding potential of -50 mV. Gd3+ inhibited the muscimol-induced outward current in a concentration-dependent and reversible manner. Gd3+ inhibited the maximum muscimol response but had no effect on the half-maximum concentration. The Gd3+ inhibition was accompanied by a depolarizing shift of the reversal potential. The Gd3+ action was blocked by furosemide, a blocker of both KCC and Na+-K+-Cl- co-transporter (NKCC), but not bumetanide, a specific blocker of NKCC. Gd3+ failed to inhibit the muscimol-induced outward currents recorded by conventional whole-cell patch-clamp method which cannot retain intact intracellular Cl- concentration. These results suggest that Gd3+ inhibits a KCC function and gives rise to increase in intracellular Cl- concentration. The reduction of outward chloride transport could be related to the neurotoxic effects of Gd3+.
钆是一种稀土镧系金属离子，在磁共振成像（MRI）中用作有机钆配合物。尽管基于钆的MRI造影剂在临床应用中被认为是安全的，但已有报道称，一些肾病患者体内会释放出有毒的游离无机钆（Gd3+）。在中枢神经系统神经元中，γ-氨基丁酸（GABA）的抑制作用是相对超极化的氯离子平衡电位（ECl）的结果，这是由钾-氯共转运体（KCC）的活性导致的。据报道，镧系离子会影响GABAA受体。然而，关于Gd3+对细胞内氯离子浓度完整时GABAA受体功能的影响知之甚少。在本研究中，我们使用短杆菌肽穿孔膜片钳记录法，研究了Gd3+对培养的大鼠脊髓神经元中GABAA受体介导电流的影响。应用GABAA受体激动剂蝇蕈醇，在-50 mV的钳制电位下引起外向电流。Gd3+以浓度依赖性和可逆的方式抑制蝇蕈醇诱导的外向电流。Gd3+抑制了蝇蕈醇的最大反应，但对半数最大浓度没有影响。Gd3+的抑制作用伴随着反转电位的去极化偏移。Gd3+的作用被呋塞米阻断，呋塞米是KCC和钠-钾-氯共转运体（NKCC）的阻断剂，但不被布美他尼阻断，布美他尼是NKCC的特异性阻断剂。Gd3+未能抑制用传统全细胞膜片钳方法记录的蝇蕈醇诱导的外向电流，该方法不能保持细胞内氯离子浓度完整。这些结果表明，Gd3+抑制KCC功能并导致细胞内氯离子浓度增加。外向氯离子转运的减少可能与Gd3+的神经毒性作用有关。
