Redox control of oxygen sensing in the rabbit ductus arteriosus

1. How the ductus arteriosus (DA) closes at birth remains unclear. Inhibition of O-2-sensitive K+ channels may initiate the closure but the sensor mechanism is unknown. We hypothesized that changes in endogenous H2O2 could act as this sensor. 2. Using chemiluminescene measurements with luminol (50 muM) or Iucigenin (5 muM) we showed significantly higher levels of reactive O-2 species in normoxic, compared to hypoxic DA. This increase in chemiluminescence was completely reversed by catalase (1200 U ml(-1)). 3. Prolonged normoxia caused a significant decrease in K+ current density and depolarization of membrane potential in single fetal DA smooth mascle cells. Removal of endogenous H2O2 with intracellular catalase (200 U ml(-1)) increased normoxic whole-cell K+ currents (I-K) and hyperpolarized membrane potential while intracellular H2O2 (100 nM)and extracellular t-butyl H2O2 (100 muM) decreased I-K and depolarized membrane potential. More rapid metabolism of O-2(-). with superoxide dismutase (100 U ml(-1)) had no significant effect on normoxic K+ currents. 4. N-Mercaptopropionyglycine (NMPG), duroquinone and dithiothreitol all dilated normoxic-constricted DA rings, while the oxidizing agent 5,5'-dithiobis-(2-nitrobenzoic acid) constricted hypoxia-dilated rings. NMPG also increased I-K. We conclude that increased H2O2 levels, associated with a cytosolic redox shift at birth, signal K+ channel inhibition and DA constriction.