Properties of a superoxide anion-generating microsomal NADH oxidoreductase, a potential pulmonary artery PO2 sensor

In this study, we describe properties of a microsomal NADH oxidoreductase that is a potential PO2-dependent source of vasoactive reactive O2 species in the calf pulmonary artery. Microsomes show an NADH-dependent production of superoxide anion (O2-.), as detected by lucigenin-elicited chemiluminescence, a superoxide dismutase inhibited reduction of nitro blue tetrazolium (NBT) and 2,6-dichlorophenol-indophenol, and O2 consumption. The microsomal production of O2-. was modulated by physiologically relevant levels of NADH and PO2, and O2-. production was reduced by inhibitors of NADH-dependent microsomal electron transport. Microsomes catalyzed an NADH-mediated reduction of several electron acceptor dyes, cytochrome c (rotenone insensitive) and methemoglobin. On reduction with dithionite, a cytochrome with an absorbance at approximately 558 nm was observed. Arterial O2-. levels (chemiluminescence) were also reduced by NBT and microsomal electron transport inhibitors. In pulmonary arteries, NBT selectively inhibited PO2 and lactate elicited changes in force generation, presumably by trapping O2-. and preventing H2O2 formation. Thus these studies are consistent with an involvement of O2-.-derived H2O2 generation via a microsomal NADH-cytochrome b558 electron transport system in calf pulmonary artery smooth muscle PO2 and lactate-elicited tone responses.