ACUTE PULMONARY ARTERIAL RESPONSES TO HYPOXIA

在预收缩的近端肺内动脉中，严重缺氧引起 三相反应：（1）早期短暂收缩， 内皮依赖性和L-NAME减少;（2）舒张，这是 非内皮依赖性，格列本脲降低，并与 降低平滑肌能量状态和细胞内pH;和（3）晚期 持续收缩，这是内皮依赖性的，不受L- NAME或吲哚美辛，并与平滑肌能量恢复相关 在肺动脉肌细胞中，严重缺氧 引起去极化和减少外向钾电流，这是 抑制4-氨基吡啶，但不TEA或Charybdotoxin。 基于这些 结果表明，低氧对肺动脉的直接影响是 平滑肌是去极化，这是因为延迟整流 钾（Kdr）通道被抑制，可能继发于去饱和 一种肌膜血红素蛋白。 如果这种直接影响表现出来， 然而，血管紧张素的增加取决于许多因素，包括 基线膜电位，细胞内钙离子浓度 ({ca2+ i）、能量状态和平滑肌中的细胞内pH，以及 是否存在内皮影响。 相对于 近端肺内动脉，我们假设，首先，早期缺氧 收缩是由抑制基底内皮源性NO引起的 活动 虽然缺氧抑制平滑肌中的Kdr通道， 去极化，激活电压依赖性钙通道，和 钙内流，这些事件并不有助于早期缺氧收缩 因为去极化太小，{Ca 2 +}i的上升太慢， 在缺氧松弛开始之前触发收缩。 第二、 缺氧松弛是由抑制受体相关的 血管收缩转导通路和ATP依赖的 钾离子通道（KATP），两者都是由 能量状态恶化和细胞内酸中毒 降低氧化磷酸化。 第三，晚期缺氧收缩是 由内皮因子引起，其上调糖酵解， 平滑肌的能量状态，导致细胞内pH值正常化 通过增强的Na-H交换;改善受体连接的 血管收缩刺激，包括内皮源性收缩剂 和继发于KATP通道失活的去极化， 直接缺氧抑制Kdr通道。 为了验证这些假设，我们 将在近端肺内动脉和体动脉中进行实验 测量膜电位、离子电流、{Ca 2 +}i和 动脉肌细胞内pH;等长张力，31 P核 磁共振波谱，葡萄糖利用，乳酸盐产生， 以及动脉中肌醇磷酸和甘油二酯的浓度 环;和透壁压力-直径关系和生物测定 灌注动脉中的内皮因子。 通过阐明直接 缺氧对肺动脉平滑肌的影响，以及这些 内皮细胞会改变这种效应，我们希望提高对内皮细胞的了解 体内肺血管对缺氧的反应，这一直难以 在完整动物或离体肺中进行机械研究。 理解 这些反应是重要的，因为它们优化了氧气交换， 肺正常而引起肺动脉高压、肺心病，并加重 慢性肺病患者的死亡率。

In precontracted proximal intrapulmonary arteries, severe hypoxia caused a triphasic response: (1) early transient contraction, which was endothelium-dependent and reduced by L-NAME; (2) relaxation, which was endothelium-independent, reduced by glibenclamide, and associated with decreased smooth muscle energy state and intracellular pH; and (3) late sustained contraction, which was endothelium-dependent, unaffected by L- NAME or indomethacin, and associated with recovery of smooth muscle energy state and intracellular pH. In pulmonary arterial myocytes, severe hypoxia caused depolarization and decreased outward potassium currents, which were inhibited by 4-aminopyridine, but not TEA or charybdotoxin. Based on these results, we propose that the direct effect of hypoxia on pulmonary arterial smooth muscle is depolarization, which occurs because delayed rectifier potassium (Kdr) channels are inhibited, perhaps secondary to desaturation of a sarcolemmal heme protein. If and when this direct effect is expressed as increased vasomotor tone, however, depends on many factors, including baseline membrane potential, intracellullar calcium concentration ({ca2+}i), energy state, and intracellular pH in smooth muscle, as well as the presence or absence of endothelial influences. With respect to proximal intrapulmonary arteries, we hypothesize, first, that early hypoxic contraction is caused by inhibition of basal endothelium-derived NO activity. Although hypoxia inhibits Kdr channels in smooth muscle, leading to depolarization, activation of voltage-dependent calcium channels, and calcium influx, these events do not contribute to early hypoxic contraction because the depolarization is too small and the rise in {Ca2+}i too slow to trigger contraction before the onset of hypoxic relaxation. Second, hypoxic relaxation is caused by inhibition of receptor-linked vasoconstrictor transduction pathways and activation of ATP-dependent potassium (KATP) channels in smooth muscle, both of which result from energy state deterioration and intracellular acidosis secondary to decreased oxidative phosphorylation. Third, late hypoxic contraction is caused by endothelial factors which upregulate glycolysis and improve energy state in smooth muscle, leading to normalization of intracellular pH via enhanced Na-H exchange; improved transduction of receptor-linked vasoconstrictor stimuli, including an endothelium-derived contractile factor; and depolarization secondary to inactivation of KATP channels and direct hypoxic inhibition of Kdr channels. To test these hypotheses, we will perform experiments in proximal intrapulmonary and systemic arteries of the pig, measuring membrane potential, ion currents, {Ca2+}i, and intracellular pH in arterial myocytes; isometric tension, 31P nuclear magnetic resonance spectroscopy, glucose utilization, lactate production, and concentrations of inositol phosphates and diacylglycerol in arterial rings; and transmural pressure-diameter relations and bioassays of endothelial factors in perfused arteries. By elucidating the direct effects of hypoxia on pulmonary arterial smooth muscle, and how these effects are altered by endothelium, we hope to improve understanding of in vivo pulmonary vasomotor responses to hypoxia, which have been difficult to study mechanistically in intact animals or isolated lungs. Understanding these responses is important, because they optimize oxygen exchange in normal lungs and cause pulmonary hypertension, cor pulmonale, and increased mortality in patients with chronic lung disease.