Yuan X J, Tod M L, Rubin L J, Blaustein M P
Department of Medicine, University of Maryland School of Medicine, Baltimore 21201.
Am J Physiol. 1994 Jul;267(1 Pt 1):L52-63. doi: 10.1152/ajplung.1994.267.1.L52.
Hypoxia-induced pulmonary vasoconstriction (HPV) is triggered by a rise in cytosolic Ca2+ concentration ([Ca2+]i) that is partially controlled by voltage-gated Ca2+ channels. Hypoxia inhibits voltage-gated K+ (KV) channels in pulmonary artery (PA) myocytes. This depolarizes the cells, opens voltage-gated Ca2+ channels, thereby increases [Ca2+]i, and initiates HPV. In intact animals and isolated perfused lungs, metabolic inhibitors and reducing agents augment HPV. We compared the effects of hypoxia with the glycolysis inhibitor, 2-deoxy-D-glucose (2-DOG), and the reducing agent, reduced glutathione (GSH), on voltage-gated steady-state K+ currents (IK,ss) and membrane potential (Em) in cultured rat pulmonary and mesenteric arterial (MA) smooth muscle cells. Bath application of 10 mM 2-DOG (glucose-free) or 5-10 mM GSH reversibly reduced IK,ss by 25-35% in PA myocytes, with 5 mM ATP present in the pipette solution. Neither hypoxia nor 2-DOG significantly affected IK,ss in MA myocytes, but GSH did reduce IK,ss in these cells. Furthermore, hypoxia, 2-DOG, and GSH depolarized PA cells in the absence as well as in the presence of external Ca2+. Hypoxia, 2-DOG, and GSH also evoked action potentials on the top of the steady depolarization in 36-50% of PA myocytes but not in any MA myocytes; removal of external Ca2+ abolished the action potentials without affecting the steady depolarization. These effects were comparable to those produced by 4-aminopyridine (5-10 mM), a blocker of KV channels. This implies that the action potentials are attributable to Ca2+ influx through voltage-gated Ca2+ channels opened by the steady depolarization due to KV channel inhibition. In the presence of 2-DOG or GSH, hypoxia had no further effect on IK,ss or Em in PA cells; this implies that hypoxia, 2-DOG, and GSH all block the same K+ channels. The data suggest that 1) the hypoxia-induced decrease of IK,ss and the resultant depolarization in PA myocytes may be related to a local decrease of intracellular ATP level and/or a change in redox status of the membrane or cytosol and 2) extracellular Ca(2+)-dependent action potentials may be responsible for at least part of the increase in [Ca2+]i during HPV. Similarities between the effects of hypoxia, 2-DOG, and GSH on IK,ss and Em in PA myocytes, along with the dissimilar responses of PA and MA myocytes, suggest that a common mechanism may underlie the responses of PA cells to these treatments.
缺氧诱导的肺血管收缩（HPV）是由胞质Ca2+浓度（[Ca2+]i）升高触发的，而[Ca2+]i的升高部分受电压门控Ca2+通道控制。缺氧抑制肺动脉（PA）肌细胞中的电压门控K+（KV）通道。这使细胞去极化，打开电压门控Ca2+通道，从而增加[Ca2+]i，并引发HPV。在完整动物和离体灌注肺中，代谢抑制剂和还原剂会增强HPV。我们比较了缺氧与糖酵解抑制剂2-脱氧-D-葡萄糖（2-DOG）和还原剂还原型谷胱甘肽（GSH）对培养的大鼠肺动脉和肠系膜动脉（MA）平滑肌细胞中电压门控稳态K+电流（IK,ss）和膜电位（Em）的影响。在移液管溶液中存在5 mM ATP的情况下，浴槽中加入10 mM 2-DOG（无糖）或5 - 10 mM GSH可使PA肌细胞中的IK,ss可逆性降低25 - 35%。缺氧和2-DOG对MA肌细胞中的IK,ss均无显著影响，但GSH确实降低了这些细胞中的IK,ss。此外，在不存在和存在细胞外Ca2+的情况下，缺氧、2-DOG和GSH均使PA细胞去极化。缺氧、2-DOG和GSH还在36 - 50%的PA肌细胞中在稳定去极化的基础上诱发动作电位，但在任何MA肌细胞中均未诱发；去除细胞外Ca2+可消除动作电位而不影响稳定去极化。这些效应与由5 - 10 mM的KV通道阻滞剂4-氨基吡啶产生的效应相当。这意味着动作电位归因于Ca2+通过因KV通道抑制导致的稳定去极化而打开的电压门控Ca2+通道内流。在存在2-DOG或GSH的情况下，缺氧对PA细胞中的IK,ss或Em没有进一步影响；这意味着缺氧、2-DOG和GSH均阻断相同的K+通道。数据表明：1）缺氧诱导的PA肌细胞中IK,ss降低及由此产生的去极化可能与细胞内ATP水平的局部降低和/或膜或胞质氧化还原状态的变化有关；2）细胞外Ca(2+)依赖性动作电位可能至少部分负责HPV期间[Ca2+]i的增加。缺氧、2-DOG和GSH对PA肌细胞中IK,ss和Em的影响之间的相似性，以及PA和MA肌细胞的不同反应，表明PA细胞对这些处理的反应可能有共同机制。
