15-hydroxy-11-alpha-9-alpha-(epoxymethano)prosta-5-13-dienoic-acid and diphenyleneiodonium

We tested whether mitochondria function as the O(2) sensor underlying hypoxic pulmonary vasoconstriction (HPV). In buffer-perfused rat lungs, rotenone, myxothiazol, and diphenyleneiodonium, which inhibit mitochondria in the proximal region of the electron transport chain (ETC), abolished HPV without attenuating the response to U46619. Cyanide and antimycin A inhibit electron transfer in the distal region of the ETC, but they did not abolish HPV. Cultured pulmonary artery (PA) myocytes contract in response to hypoxia or to U46619. The hypoxic response was abolished while the response to U46619 was maintained in mutant (rho(0)) PA myocytes lacking a mitochondrial ETC. To test whether reactive oxygen species (ROS) derived from mitochondria act as signaling agents in HPV, the antioxidants pyrrolidinedithiocarbamate and ebselen and the Cu,Zn superoxide dismutase inhibitor diethyldithiocarbamate were used. These abolished HPV without affecting contraction to U46619, suggesting that ROS act as second messengers. In cultured PA myocytes, oxidation of intracellular 2',7'-dichlorofluorescin diacetate (DCFH) dye increased under 2% O(2), indicating that myocytes increase their generation of H(2)O(2) during hypoxia. This was attenuated by myxothiazol, implicating mitochondria as the source of increased ROS during HPV. These results indicate that mitochondrial ATP is not required for HPV, that mitochondria function as O(2) sensors during hypoxia, and that ROS generated in the proximal region of the ETC act as second messengers in the response.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Animals; Antimycin A; Antioxidants; Cells, Cultured; Electron Transport; Enzyme Inhibitors; Hypoxia; In Vitro Techniques; Ion Channels; Lung; Methacrylates; Mitochondria; Models, Biological; Muscle, Smooth, Vascular; Onium Compounds; Oxygen; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Reactive Oxygen Species; Rotenone; Signal Transduction; Thiazoles; Uncoupling Agents; Vasoconstriction; Vasoconstrictor Agents

The present study was designed to point out similarities between the effects on pulmonary circulation caused by hypoxia and by a chemoreceptor stimulant (S1867, an almitrine analog). Isolated rat lungs were perfused at a constant flow with homologous blood and ventilated under normoxic, hypoxic or hyperoxic conditions. (1) At 0.25 microgram/ml, S1867 potentiated the hypoxic pressor response, while at 1 microgram/ml, it induced a significant increase in pulmonary artery pressure (PAP) at 21% O2. (2) Since the expression of an oxygen-binding protein (NADPH-oxidase like) has been demonstrated in the rat carotid bodies, we studied the effects of the NADPH-oxidase inhibitor diphenyleneiodonium (DPI) on HPV and on S1867-induced pulmonary vascular responses. Both responses were totally abolished by DPI (40 microM), whereas the vasoconstriction induced by a thromboxane A2 analog (U46619) remained unchanged. (3) Vascular responses to hypoxia and S1867 (1 microgram/ml) were both reversed by a bolus of the sulfhydryl oxidant diamide (3 mg). (4) The S1867-induced response was prevented and reversed by the supply of inhaled oxygen, which was without action on the vasoconstriction induced by U46619. These results suggest that the almitrine analog and hypoxia act at least partly through the same cellular mechanism, involving a DPI-sensitive protein.

Topics: 15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; Almitrine; Animals; Blood Pressure; Chemoreceptor Cells; Disease Models, Animal; Enzyme Inhibitors; Hypoxia; In Vitro Techniques; Male; NADPH Oxidases; Nitric Oxide Synthase; Onium Compounds; Perfusion; Prostaglandin Endoperoxides, Synthetic; Pulmonary Artery; Pulmonary Circulation; Rats; Rats, Sprague-Dawley; Respiratory System Agents; Thromboxane A2; Vasoconstriction