Role of mitochondrial reactive oxygen species in hypoxia-dependent increase in intracellular calcium in pulmonary artery myocytes.
Previous studies examining the role of mitochondria-derived reactive oxygen species (ROS) in hypoxic responses have been mainly conducted in isolated lungs and cultured pulmonary artery smooth muscle cells (PASMCs) using mitochondrial inhibitors, and yielded largely conflicting results. Here we report that in freshly isolated mouse PASMCs, which are devoid of the mixed responses from multi-types of cells in lungs and significant changes in gene expression in cultured cells, the mitochondrial electron transport chain (ETC) complex I, II, or III inhibitors blocked hypoxia-induced increases in intracellular ROS and Ca2+ concentration ([ROS]i and [Ca2+]i) without effects on their resting levels. Inhibition of the complex I plus II and/or III did not produce an additive effect. Glutathione peroxidase-1 (Gpx1) or catalase gene overexpression to enhance H2O2 removal remarkably reduced hypoxic increases in [ROS]i and [Ca2+]i, whereas Gpx1 gene deletion had the opposite effect. None of these genetic modifications changed the resting [ROS]i and [Ca2+]i. H2O2 at 51 microM caused a similar increase in DCF fluorescence ([ROS]i) as that by hypoxia, but only induced 33% of hypoxic increase in [Ca2+]i. Moreover, H2O2 (5.1 microM) reversed the inhibition of the hypoxia-induced increase in [Ca2+]i by rotenone. Collectively, our study using various mitochondrial inhibitors and genetic approaches demonstrates that in response to acute hypoxia, the mitochondrial ETC molecules prior to the complex III ubisemiquinone site act as a functional unit to increase the generation of ROS, particularly H2O2, which is important for, but may not fully cause, the hypoxic increase in [Ca2+]i in freshly isolated PASMCs.
Wang
Qing-Song
QS
Center for Cardiovascular Sciences, Albany Medical College, Albany, NY 12208, USA.
Zheng
Yun-Min
YM
Dong
Ling
L
Ho
Ye-Shih
YS
Guo
Zhongmao
Z
Wang
Yong-Xiao
YX
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002374:Catalase / Q000235:genetics / Q000378:metabolism; D015687:Cell Hypoxia / Q000187:drug effects; D002478:Cells, Cultured; D045222:Electron Transport Chain Complex Proteins / Q000037:antagonists & inhibitors; D005979:Glutathione Peroxidase / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D008931:Mitochondria, Muscle / Q000187:drug effects*; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D011651:Pulmonary Artery / Q000187:drug effects* / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000494:pharmacology*; D000094765:Glutathione Peroxidase GPX1
D045222:Electron Transport Chain Complex Proteins; D017382:Reactive Oxygen Species; D002374:Catalase; D005979:Glutathione Peroxidase; D002118:Calcium; D000094765:Glutathione Peroxidase GPX1; C000722068:Gpx1 protein, mouse