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1 Pediatrics, Duke University Medical Center, Durham, NC, USA
2 Medicine, Duke University Medical Center, Durham, NC, USA
* To whom correspondence should be addressed. E-mail: grayc001{at}mc.duke.edu.
Pulmonary vasoconstriction is influenced by inactivation of nitric oxide (NO) with extracellular superoxide (.O2-). Because short-lived .O2- anion cannot diffuse across plasma membranes, its release from vascular cells requires specialized mechanisms that have not been well delineated in the pulmonary circulation. We have shown that the bicarbonate (HCO3-)-chloride anion exchange protein (AE2) expressed in the lung also exchanges .O2- for HCO3-. Thus, we determined whether .O2- release involved in pulmonary vascular tone depends on extracellular HCO3-. We assessed endothelium-dependent vascular reactivity and .O2- release in the presence or absence of HCO3- in pulmonary artery (PA) rings isolated from normal rats and those exposed to hypoxia for 3 days. Lack of extracellular HCO3- in normal PA rings significantly attenuated endothelial .O2- release, opposed hypoxic vasoconstriction and enhanced acetylcholinemediated vasodilation. Release of .O2- was also inhibited by AE2 inhibitor (SITS) and abolished in normoxia by NO synthase inhibitor (L-NAME). In contrast, hypoxia increased PA AE2 protein expression and .O2- release; the latter was not affected by LNAME or other inhibitors of enzymatic .O2- generation. Enhanced .O2- release by uncoupling NOS with geldanamycin was attenuated by hypoxia or by HCO3- elimination. These results indicate that .O2- produced by eNOS in normoxia and unidentified sources in hypoxia regulate pulmonary vascular tone via AE2.
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