Once constrictor responses had

reached a stable plateau, relaxation was studied by constructing cumulative concentration–response curves to CPA or ACh in the continued presence of arsenite. These curves were generally completed within ∼60 min so that total cumulative exposure to arsenite was 90 min and 150 min in the two protocols. Preliminary experiments demonstrated that lower concentrations of Epigenetics Compound Library molecular weight arsenite (10 μM) did not affect relaxation under these experimental conditions. To evaluate the role of O2•− and H2O2, catalase (2000 units/ml, from bovine liver), manganese(III) tetrakis (1-methyl-4-pyridyl) porphyrin (MnTMPyP, 100 μM) or the NADPH oxidase inhibitor apocynin (1-(4-hydroxy-3-methoxyphenyl)ethanone, 100 μM) were co-administered with L-NAME and indomethacin. RAV leaflets, and endothelium-denuded rings of iliac artery and aorta were incubated with arsenite (100 μM), Crizotinib cost apocynin (100 μM) or both for 60 min in oxygenated Holman’s buffer containing L-NAME (300 μM) and indomethacin (10 μM) at 37 °C. To assess

the production of reactive oxygen species (ROS) dihydroethidium (DHE, 5 μM) was then added for a further 30 min, following which the preparations were washed and fixed in 4% paraformaldehyde and images collected with a Leica SP5 confocal microscope (excitation 514 nm, emission 560–630 nm). This protocol was designed to match the total exposure of rings preincubated

with 100 μM arsenite for 30 min in mechanical experiments in which it took a further ∼60 min to construct full concentration–relaxation curves. It should be noted that selleck kinase inhibitor oxidation of DHE can generate two products, ethidium and 2-hydroxyethidium, which possess overlapping emission spectra and whose fluorescence is enhanced by binding to DNA (Zielonka and Kalyanaraman, 2010). Although H2O2 does not oxidize DHE directly and the formation of 2-hydroxyethidium is specific for O2•−, H2O2 may promote the formation of ethidium in the presence of peroxidase activity or haem proteins so that increased fluorescence in DHE-loaded vascular smooth muscle/endothelial cells may reflect production of both O2•− and H2O2 (Fernandes et al., 2007 and Ray et al., 2011). The RAV was used to circumvent the complicating effects of signals transmitted from subjacent smooth muscle to the endothelium. All imaging data presented were acquired in the presence of L-NAME in order to avoid potentially confounding effects of NO which has been reported to promote the formation of ethidium in the presence of molecular oxygen (Zielonka and Kalyanaraman, 2010). The maximal percentage reversal of PE-induced tone (Rmax) by CPA or ACh and concentrations giving 50% reversal of this constrictor response (IC50 for CPA) or 50% of maximal relaxation (EC50 for ACh) were determined for each experiment.