Growing evidence implicates a role for Noxs, particularly Nox1 and Nox4, in the pathogenesis of experimental and human PAH.12,27 In addition to the constitutive expression of Nox1 in a variety of tissues, Nox1 expression is increased after inflammation, growth factor stimulation, and hypoxia.28 Nox1 also plays a critical role in physiological turnover of PASMCs by regulation of intracellular potassium.29 This evidence concerns the gene NOX4 and pulmonary arterial hypertension.