NADPH-induced contractions of mouse aorta do not involve NADPH oxidase: a role for P2X receptors.
Reactive oxygen species elicit vascular effects ranging from acute dilatation because of hydrogen peroxide-mediated opening of K(+) channels to contraction arising from superoxide-dependent inactivation of endothelium-derived nitric oxide. Given that NADPH oxidases are major sources of superoxide in the vascular wall, this study examined the effects of exogenous NADPH, a substrate of these enzymes, on superoxide generation and isometric tone in mouse isolated aortic rings. NADPH caused concentration-dependent increases in superoxide generation (measured by lucigenin-enhanced chemiluminescence) and vascular tone (isometric tension recordings). However, surprisingly, whereas oxidized NADP(+) was unable to support superoxide production, it was equally as effective as reduced NADPH at stimulating vasocontraction. In addition, an NADPH oxidase inhibitor, diphenyleneiodonium, markedly attenuated NADPH-induced superoxide production, yet had no effect on vasocontractions to NADPH. In contrast, a broad specificity P2X receptor antagonist, pyridoxalphosphate-6-azophenyl-2',4'-disulfonic acid, as well as the P2X1 selective antagonist, NF023, markedly attenuated both endothelium-dependent and -independent vasocontractions to NADPH, as did the P2X-desensitizing agent alpha,beta-methylene-ATP. Importantly, alpha,beta-methylene-ATP had no effect on superoxide production induced by NADPH. In conclusion, these findings suggest little role for NADPH oxidase-derived superoxide in the contractile effects of NADPH in the mouse aorta. Rather, NADPH seems to act as an agonist at two distinct P2X receptor populations; one located on the endothelium and the other on smooth muscle layer, both of which ultimately lead to contraction.
Judkins
Courtney P
CP
Department of Pharmacology, Monash University, Clayton, Victoria 3800, Australia.
Sobey
Christopher G
CG
Dang
Thuy T
TT
Miller
Alyson A
AA
Dusting
Gregory J
GJ
Drummond
Grant R
GR
D000818:Animals; D001011:Aorta / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009249:NADP / Q000494:pharmacology*; D019255:NADPH Oxidases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D052250:Nitric Oxide Synthase Type III / Q000037:antagonists & inhibitors / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000378:metabolism; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D058469:Receptors, Purinergic P2X; D013482:Superoxide Dismutase / Q000378:metabolism; D014661:Vasoconstriction / Q000187:drug effects*
D004791:Enzyme Inhibitors; D017382:Reactive Oxygen Species; D018048:Receptors, Purinergic P2; D058469:Receptors, Purinergic P2X; D009249:NADP; D052250:Nitric Oxide Synthase Type III; D013482:Superoxide Dismutase; D019255:NADPH Oxidases