Dubouskaya Tatsiana G, Hrynevich Sviatlana V, Waseem Tatsiana V, Fedorovich Sergei V
Laboratory of Biophysics and Engineering of Cell, Institute of Biophysics and Cell Engineering, Minsk, Belarus.
Department of Pharmacology, University of Oxford, Oxford, UK.
Acta Neurobiol Exp (Wars). 2018;78(4):343-351.
In the brain, pH can be lowered in both healthy and disease states. Previously, we showed that moderate extracellular acidification (down to pHo 7.0), but not intracellular acidification, leads to mitochondrial depolarization in synaptosomes. This indicates that the plasma membranes of neuronal presynaptic endings have proton receptors that can induce mitochondrial dysfunction when activated. In the present paper we attempt to identify this hypothetical receptor. First, we have demonstrated that lowering pHo to 7.0 does not induce sodium influx as monitored by the fluorescent dye Sodium Green. This fact, in conjunction with the absence of calcium influx in the same conditions - demonstrated previously, excludes ion channels as possible receptors. However, we showed that acidification-induced mitochondrial depolarization is sensitive to thapsigargin - an inhibitor of calcium release from intracellular stores, U73122 - an inhibitor of phospholipase C, as well as Cu2+ and Zn2+, which can block the metabotropic proton receptor ovarian cancer G protein-coupled receptor 1 (OGR1). Furthermore, using fluorescent dye Fluo-3 we have demonstrated that moderate extracellular acidification induces a cytosolic calcium increase. Excess calcium was scavenged by mitochondria (monitored by fluorescent dye Rhod-2). Our results suggest that the metabotropic OGR1 is a hypothetical presynaptic receptor for low pH. Its activation leads to phospholipase C activation and calcium release from the endoplasmic reticulum followed by accumulation in mitochondria, which likely causes a decrease in mitochondrial membrane potential.
在大脑中，无论是健康状态还是疾病状态，pH值都可能降低。此前，我们发现适度的细胞外酸化（降至细胞外pH值7.0），而非细胞内酸化，会导致突触体中的线粒体去极化。这表明神经元突触前末梢的质膜具有质子受体，激活后可诱导线粒体功能障碍。在本文中，我们试图鉴定这种假设的受体。首先，我们已证明，如用荧光染料Sodium Green监测，将细胞外pH值降至7.0不会诱导钠内流。这一事实，结合此前证明的在相同条件下不存在钙内流，排除了离子通道作为可能的受体。然而，我们发现酸化诱导的线粒体去极化对毒胡萝卜素（一种细胞内钙库释放钙的抑制剂）、U73122（一种磷脂酶C抑制剂）以及Cu2+和Zn2+敏感，Cu2+和Zn2+可阻断代谢型质子受体卵巢癌G蛋白偶联受体1（OGR1）。此外，使用荧光染料Fluo-3，我们证明适度的细胞外酸化会导致胞质钙增加。过量的钙被线粒体清除（用荧光染料Rhod-2监测）。我们的结果表明，代谢型OGR1是低pH值假设的突触前受体。其激活导致磷脂酶C激活和内质网释放钙，随后钙在线粒体中积累，这可能导致线粒体膜电位降低。
