Ye Jian-Shan, Tipoe George L, Fung Peter C W, Fung Man-Lung
Department of Medicine, Faculty of Medicine, University of Hong Kong, Sassoon Road, Pokfulam, Hong Kong.
Pflugers Arch. 2002 May;444(1-2):178-85. doi: 10.1007/s00424-002-0785-1. Epub 2002 Feb 27.
Acute hypoxia increases the endogenous release of nitric oxide (NO) in rat carotid body and the expression of nitric oxide synthases is modulated by chronic hypoxia. The aim of the study was to examine hypoxia-induced NO generation in rat carotid body adapted to chronic hypoxia with inspired oxygen at 10% for 4 weeks. The concentration of NO was measured electrochemically with a Pt/Nafion/Pd-IrOx/POAP modified electrode inserted into the isolated carotid body superfused with bicarbonate-buffer saline at 35 degrees C. Acute hypoxia increased the concentration of NO by 471.3+/-71.4 nM in the carotid body of chronically hypoxic (CH) rats. The amount of NO release induced by hypoxia was significantly augmented when compared with that of the normoxic control (87.6+/-15.9 nM). The hypoxia-induced NO generation was markedly attenuated by pretreatment with L- NG-nitroarginine methylester (L-NAME; 500 microM), a non-selective nitric oxide synthase (NOS) inhibitor and also by removal of extracellular calcium with the calcium chelator EGTA (5 mM). Additionally, NO generation during hypoxia was reduced by 30% in the CH carotid body treated with S-methylisothiourea (SMT; 50 microM), a specific blocker of inducible NOS (iNOS). Immunohistochemical study revealed that positive iNOS protein immunoreactivity was detected in clusters of glomus cells in the carotid bodies of CH rats, but not in the normoxic group. Thus, chronic hypoxia enhances hypoxia-induced NO generation mediated by calcium-dependent NOSs and iNOS in the carotid body. Extracellular recording of sinus nerve activity of CH carotid bodies showed that L-NAME treatment enhanced the afferent discharge in response to hypoxia, confirming that the generation of NO suppresses the activities of carotid chemoreceptors. Taken together, our results suggest that hypoxia-induced NO production increases in the rat carotid body adapted to chronic hypoxia and that constitutive and inducible NOSs are involved in the NO generation. The enhancement of NO generation may play a physiological role in blunting the hypoxic chemosensitivity during chronic hypoxia.
急性低氧会增加大鼠颈动脉体中一氧化氮（NO）的内源性释放，且一氧化氮合酶的表达会受到慢性低氧的调节。本研究的目的是检测在吸入10%氧气4周适应慢性低氧的大鼠颈动脉体中，低氧诱导的NO生成情况。使用插入到在35℃下用碳酸氢盐缓冲盐水灌流的离体颈动脉体中的铂/全氟磺酸/钯 - 氧化铱/聚邻氨基苯酚修饰电极，通过电化学方法测量NO的浓度。急性低氧使慢性低氧（CH）大鼠颈动脉体中的NO浓度增加了471.3±71.4 nM。与常氧对照组（87.6±15.9 nM）相比，低氧诱导的NO释放量显著增加。用L - 硝基精氨酸甲酯（L - NAME；500 μM）预处理，一种非选择性一氧化氮合酶（NOS）抑制剂，以及用钙螯合剂乙二醇双四乙酸（EGTA；5 mM）去除细胞外钙，均可显著减弱低氧诱导的NO生成。此外，用S - 甲基异硫脲（SMT；50 μM）处理CH颈动脉体，一种诱导型NOS（iNOS）的特异性阻滞剂，低氧期间的NO生成减少了30%。免疫组织化学研究显示，在CH大鼠颈动脉体的球细胞簇中检测到阳性iNOS蛋白免疫反应性，而在常氧组中未检测到。因此，慢性低氧增强了颈动脉体中由钙依赖性NOS和iNOS介导的低氧诱导的NO生成。CH颈动脉体窦神经活动的细胞外记录显示，L - NAME处理增强了对低氧的传入放电，证实NO的生成抑制了颈动脉化学感受器的活动。综上所述，我们的结果表明，在适应慢性低氧的大鼠颈动脉体中，低氧诱导的NO生成增加，且组成型和诱导型NOS均参与NO的生成。NO生成的增强可能在慢性低氧期间减弱低氧化学敏感性中发挥生理作用。
