Pharmacological actions of the coenzymes NAD(H) and NADP(H) on the rat anococcygeus muscle

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.

Evidence for two distinct P2-purinoceptors subserving contraction of the rat anococcygeus smooth muscle

1. The effects of the P2-purinoceptor agonists, adenosine 5'-triphosphate (ATP), alpha, beta-methylene ATP (alpha, beta-MeATP), beta, gamma-methylene ATP (beta, gamma-MeATP), L-beta, gamma-methylene ATP (L-beta, gamma-MeATP), adenosine-5'-O-(2-thiodiphosphate) (ADP beta S), and 2-methylthio ATP (2-MeSATP) were investigated on the isometric tension of the rat anococcygeus muscle. 2. Non-cumulative additions of ATP (100-1500 microM), alpha, beta-MeATP (1-300 microM), beta, gamma-MeATP (10-300 microM), L-beta, gamma-MeATP (3-100 microM) and ADP beta S (1-100 microM) produced concentration-dependent contractions, whereas 2-MeSATP (1-100 microM) had no effect. The rank order of potency was alpha, beta-MeATP > L-beta, gamma-MeATP > or = ADP beta S > beta, gamma-MeATP > > ATP > 2-MeSATP. 3. Contractions to cumulative additions of ATP, alpha, beta-MeATP, beta, gamma-MeATP and L-beta, gamma-MeATP were subject to desensitization whilst those to ADP beta S were unaffected. 4. Contractions to ATP, alpha, beta-MeATP, beta, gamma-MeATP and ADP beta S were abolished by the non-selective P2X/. P2Y-purinoceptor antagonist, suramin (100 microM). In contrast, contractions to ATP, alpha, beta-MeATP and beta, gamma-MeATP were not affected by the non-selective P1-purinoceptor antagonist 8-(p-sulphophenyl)-theophylline (8SPT, 30 microM). Blockade of P2X-purinoceptors with the selective P2X-purinoceptor antagonist pyridoxal-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS, 10 microM) or desensitization with L-beta, gamma-MeATP (10 microM) abolished contractions to alpha, beta-MeATP, but enhanced those to ADP beta S. The P2Y-purinoceptor antagonist, reactive blue 2 (RB2, 100 microM) enhanced contractions to ATP and alpha, beta-MeATP but abolished those to ADP beta S. 5. Simultaneous addition of alpha, beta-MeATP and ADP beta S produced an additive contraction. 6. The findings suggest that in the rat anococcygeus, smooth muscle cells are endowed with two distinct P2-purinoceptors which subserve contractions: a P2X-purinoceptor activated by ATP and its analogues, and another type of P2-purinoceptor activated by ADP beta S.