PURPOSE: Pulmonary vasoconstriction in response to hypoxia is unusual inasmuch as local exposure of non-pulmonary vasculature (e.g., coronary) vessels to hypoxia results in vasodilation whereas pulmonary artery smooth muscle constricts. It has been suggested that human pulmonary artery smooth muscle (HPASMC) may relax in response to intracellular generation of reactive oxygen species (ROS) and that the production of ROS decreases under hypoxia.
METHODS: Using dihydrodichlorofluorescein diacetate, dihydroethidium and Amplex® Red we estimated ROS generation by confluent HPASMC and human coronary smooth cells (HCASMC) under normoxia (20%) and hypoxia (5%).
RESULTS: All three systems showed that HPASMC production of ROS is decreased under hypoxia and to a much greater extent than ROS production by HCASMC. A substantially greater percentage of normoxic ROS production by HPASMC is mitochondrial (>60%) compared to HCASMC (<30%) as judged by decrements in ROS production by both cell types caused by addition of the mitochondrial uncoupler, carbonyl cyanide m-chlorophenylhydrazone (n = 6, p<0.01). In both cell types, the likely location of ROS generation is the complex III ubisemiquinone as judged by ROS suppression by complex I and II inhibitors (rotenone and thenoyltrifluoroacetone; ∼50% suppression under normoxia and ∼80-90% under hypoxia). These results agree with some earlier reports (Michelakis et al., Circ. Res. 90:1307, 2002) but not with others which claim that hypoxia causes increased ROS generation by PASMC (Wang et al., Free Radic. Biol. Med. 42:642, 2007). Whether these discrepancies are due to species of origin of the cells, conditions of culture or other factors remains unclear.
CONCLUSION: Having used three different detectors of ROS and being sure of the purity and identity of the HPASMC used in these experiments we are confident that under these conditions hypoxia preferentially causes a decrease in ROS generation by HPASMC which is substantially greater than that observed in HCASMC.
CLINICAL IMPLICATIONS: Our results may explain the preferential vasoconstriction of pulmonary smooth muscle in response to hypoxia.
DISCLOSURE: Jinesh Mehta, No Financial Disclosure Information; No Product/Research Disclosure Information