4). None of these CH5424802 agents alone significantly affected pIC50 and Rmax values for relaxation in the absence of arsenite, whereas the enhancement of relaxation observed following exposure to 100 μM arsenite for 30 min was fully prevented in each case ( Table 3). Exposure to 100 μM arsenite for 90 min significantly enhanced endothelial nuclear fluorescence in RAV leaflets loaded with DHE in the presence of L-NAME/indomethacin, an effect that was fully prevented by preincubation with 100 μM apocynin (Fig. 5). Exposure to 100 μM arsenite for 90 min did not increase fluorescence in either the media or adventitia of endothelium-denuded

RIA and aortic rings loaded with DHE (Fig. 6). Exposure to 100 μM arsenite for 90 min caused a ∼30% reduction

in force development in RIA rings constricted by 1 μM PE from 33.9 ± 2.9 mN to 23.5 ± 2.6 mN (n = 26 and 20) in the presence of L-NAME/indomethacin and from 30.9 ± 5.4 mN to 22.4 ± 5.3 mN (n = 9 and 9) in control rings (pooled data from Fig. 7; P < 0.01 in each case). This large depressor effect affected the analysis of endothelium-dependent relaxation, because absolute tension ultimately converged to a similar plateau in the presence and absence of arsenite at the highest concentrations of ACh. Consequently, normalization to initial pre-relaxation tone led to an apparent decrease in Rmax on a % basis ( Fig. 7A and B), whereas pEC50 values derived from the learn more concentration–relaxation curves were unaffected by arsenite ( Table 4). Similar experiments demonstrated that exposure to 100 μM arsenite for 90 min also impaired smooth muscle relaxations to the exogenous

NO donor MAHMA NONOate in endothelium-intact RIA rings incubated with L-NAME/indomethacin. The use of an exogenous NO donor excludes any potential effect of arsenite on the NO synthase pathway. Again this incubation protocol did not statistically affect pEC50 values derived from concentration–relaxation curves, whereas Rmax was reduced ( Fig. 7C; Table 4). Experiments were also performed in which the relaxant effects of arsenite on pre-relaxation tone were mimicked by reducing the concentration of PE used to induce constriction Mannose-binding protein-associated serine protease to 0.1 μM (Fig. 7C). Rmax and pEC50 values for MAHMA NONOate were then larger than in experiments conducted in the presence of 1 μM PE or 1 μM PE plus 100 μM arsenite, as complete relaxation was obtained in the presence of the lower concentration of 0.1 μM PE ( Fig. 7; Table 4). The present study has provided new insights into the mechanisms through which short-term exposure to inorganic arsenic can modulate endothelial, and therefore vascular, function. Arsenite was shown to potentiate EDHF-type relaxations by stimulating endothelial NADPH oxidase activity and thereby promoting the formation of H2O2 from O2•−, whereas relaxations mediated by endothelium-derived NO were unaffected.