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