Mechanisms of enhanced pulmonary vasoconstriction and calcium sensitization following chronic hypoxia

CH results in pressure dependent basal tone and enhanced depolarization- and endothelin-1 (ET-1)-induced vasoconstriction in the pulmonary circulation through Rho kinase (ROK)-dependent Ca2+ sensitization, responses that may contribute to the development of pulmonary hypertension (PH) in this setting. The free radical superoxide (O2-) has been implicated in these responses. Because NADPH oxidases (NOX) play a role in the development of PH, we hypothesized that membrane depolarization, increases in intraluminal pressure, and ET-1 signaling lead to pulmonary vascular smooth muscle (VSM) myofilament Ca 2+ sensitization and augmented vasoconstrictor reactivity following CH through NOX-derived O2- production. As epidermal growth factor receptor (EGFR) and Src kinases can mediate NOX activation, we further hypothesized that Src-induced EGFR activation mediates this response.;Vasoconstrictor responses to ET-1 and KCl were greater in Ca2+ permeabilized, endothelium-disrupted, pressurized, pulmonary arteries from CH (4 wk at 0.5 atm) rats compared to controls, and this effect of CH was abolished by NOX inhibition. NOX inhibition additionally prevented KCl-dependent O2- production in CH arteries. Furthermore, inhibition of EGFR and Src kinases also prevented augmented ET-1- and KCl-induced vasoconstriction and the development of basal tone. Rats treated chronically with an EGFR inhibitor (gefitinib) displayed reduced right ventricular pressure and diminished arterial remodeling associated with CH-dependent PH. We additionally determined that vascular smooth muscle membrane depolarization contributes to basal tone but not vasoconstriction to ET-1 in CH arteries by clamping membrane potential with valinomycin. Our studies support a novel role for a Src kinase/EGFR/NOX 2 signaling axis in the enhanced pulmonary vascular smooth muscle VSM Ca 2+ sensitization, vasoconstriction and PH following CH.