O2 sensing in the human ductus arteriosus:: redox-sensitive K+ channels are regulated by mitochondria-derived hydrogen peroxide

The ductus arteriosus (DA) is a fetal artery that allows blood ejected from the right ventricle to bypass the pulmonary circulation in utero. At birth, functional closure of the DA is initiated by an O-2-induced, vasoconstrictor mechanism which, though modulated by endothelialderived endothelin and prostaglandins, is intrinsic to the smooth muscle cell (DASMC) [Michelakis et al., Circ. Res. 91 (2002); pp. 478486]. As pO(2) increases, a mitochondrial O-2-sensor (electron transport chain complexes I or III) is activated, which generates a diffusible redox mediator (H2O2). H2O2 inhibits voltagegated K+ channels (Kv) in DASMC. The resulting membrane depolarization activates Ltype Ca2+ channels, thereby promoting vasoconstriction. Conversely, inhibiting mitochondrial ETC complexes I or III mimics hypoxia, depolarizing mitochondria, and decreasing H2O2 levels. The resulting increase in K+ current hyperpolarizes the DASMC and relaxes the DA. We have developed two models for study of the DAs O-2-sensor pathway, both characterized by decreased O-2-constriction and Kv expression: (i) preterm rabbit DA, (ii) ionicallyremodeled, human term DA. The O-2-sensitive channels Kv1.5 and Kv2.1 are important to DA O-2-constriction and overexpression of either channel enhances DA constriction in these models. Understanding this O-2-sensing pathway offers therapeutic targets to modulate the tone and patency of human DA in vivo, thereby addressing a common form of congenital heart disease in preterm infants.