Shimoda Larissa A, Suresh Karthik, Undem Clark, Jiang Haiyang, Yun Xin, Sylvester J T, Swenson Erik R
Division of Pulmonary and Critical Care Medicine, Johns Hopkins School of Medicine, Baltimore, MD, USA.
Division of Pulmonary and Critical Care Medicine, VA Puget Sound Health Care System and University of Washington School of Medicine, St. Louis, MO, USA.
Pulm Circ. 2021 Oct 5;11(4):20458940211049948. doi: 10.1177/20458940211049948. eCollection 2021 Oct-Dec.
Upon sensing a reduction in local oxygen partial pressure, pulmonary vessels constrict, a phenomenon known as hypoxic pulmonary vasoconstriction. Excessive hypoxic pulmonary vasoconstriction can occur with ascent to high altitude and is a contributing factor to the development of high-altitude pulmonary edema. The carbonic anhydrase inhibitor, acetazolamide, attenuates hypoxic pulmonary vasoconstriction through stimulation of alveolar ventilation via modulation of acid-base homeostasis and by direct effects on pulmonary vascular smooth muscle. In pulmonary arterial smooth muscle cells (PASMCs), acetazolamide prevents hypoxia-induced increases in intracellular calcium concentration ([Ca]), although the exact mechanism by which this occurs is unknown. In this study, we explored the effect of acetazolamide on various calcium-handling pathways in PASMCs. Using fluorescent microscopy, we tested whether acetazolamide directly inhibited store-operated calcium entry or calcium release from the sarcoplasmic reticulum, two well-documented sources of hypoxia-induced increases in [Ca] in PASMCs. Acetazolamide had no effect on calcium entry stimulated by store-depletion, nor on calcium release from the sarcoplasmic reticulum induced by either phenylephrine to activate inositol triphosphate receptors or caffeine to activate ryanodine receptors. In contrast, acetazolamide completely prevented Ca-release from the sarcoplasmic reticulum induced by hypoxia (4% O). Since these results suggest the acetazolamide interferes with a mechanism upstream of the inositol triphosphate and ryanodine receptors, we also determined whether acetazolamide might prevent hypoxia-induced changes in reactive oxygen species production. Using roGFP, a ratiometric reactive oxygen species-sensitive fluorescent probe, we found that hypoxia caused a significant increase in reactive oxygen species in PASMCs that was prevented by 100 μM acetazolamide. Together, these results suggest that acetazolamide prevents hypoxia-induced changes in [Ca] by attenuating reactive oxygen species production and subsequent activation of Ca-release from sarcoplasmic reticulum stores.
当察觉到局部氧分压降低时，肺血管会收缩，这一现象被称为低氧性肺血管收缩。过度的低氧性肺血管收缩会在登高到高海拔时发生，并且是高海拔肺水肿发展的一个促成因素。碳酸酐酶抑制剂乙酰唑胺通过调节酸碱平衡刺激肺泡通气以及对肺血管平滑肌的直接作用来减弱低氧性肺血管收缩。在肺动脉平滑肌细胞（PASMCs）中，乙酰唑胺可防止低氧诱导的细胞内钙浓度（[Ca]）升高，尽管其发生的确切机制尚不清楚。在本研究中，我们探讨了乙酰唑胺对PASMCs中各种钙处理途径的影响。使用荧光显微镜，我们测试了乙酰唑胺是否直接抑制钙库操纵性钙内流或肌浆网钙释放，这是PASMCs中低氧诱导的[Ca]升高的两个有充分记录的来源。乙酰唑胺对钙库耗竭刺激的钙内流以及去氧肾上腺素激活肌醇三磷酸受体或咖啡因激活兰尼碱受体诱导的肌浆网钙释放均无影响。相比之下，乙酰唑胺完全阻止了低氧（4% O）诱导的肌浆网钙释放。由于这些结果表明乙酰唑胺干扰了肌醇三磷酸和兰尼碱受体上游的机制，我们还确定了乙酰唑胺是否可能防止低氧诱导的活性氧生成变化。使用roGFP，一种对活性氧敏感的比率荧光探针，我们发现低氧导致PASMCs中活性氧显著增加，而100μM乙酰唑胺可阻止这种增加。总之，这些结果表明乙酰唑胺通过减弱活性氧生成以及随后激活肌浆网钙库的钙释放来防止低氧诱导的[Ca]变化。
