Autocrine/paracrine pattern of superoxide production through NAD(P)H oxidase in coronary arterial myocytes

Abstract

The present study tested the hypothesis that membrane-bound NAD(P)H oxidase in coronary arterial myocytes (CAMs) is capable of producing superoxide (O₂^•−) toward extracellular space to exert an autocrine- or paracrine-like action in these cells. Using a high-speed wavelength-switching fluorescent microscopic imaging technique, we simultaneously monitored the binding of dihydroethidium-oxidizing product to exogenous salmon testes DNA trapped outside CAMs and to nuclear DNA as indicators of extra- and intracellular O₂^•−production. It was found that a muscarinic agonist oxotremorine (OXO; 80 μM) increased O₂^•−levels more rapidly outside than inside CAMs. In the presence of superoxide dismutase (500 U/ml) plus catalase (400 U/ml) and NAD(P)H oxidase inhibitor diphenylene iodonium (50 μM) or apocynin (100 μM), these increases in extra- and intracellular O₂^•−levels were substantially abolished or attenuated. The O₂^•−increase outside CAMs was also confirmed by detecting oxidation of nitro blue tetrazolium and confocal microscopic localization of Matrigel-trapped OxyBURST H₂HFF Green BSA staining around these cells. By electron spin resonance spectrometry, the extracellular accumulation of O₂^•−was demonstrated as a superoxide dismutase-sensitive component outside CAMs. Furthermore, RNA interference of NAD(P)H oxidase subunits Nox1 or p47 markedly blocked OXO-induced increases in both extra- and intracellular O₂^•−levels, whereas small inhibitory RNA of Nox4 only attenuated intracellular O₂^•−accumulation. These results suggest that Nox1 represents a major NAD(P)H oxidase isoform responsible for extracellular O₂^•−production. This rapid extracellular production of O₂^•−seems to be unique to OXO-induced M₁-receptor activation, since ANG II-induced intra- and extracellular O₂^•−increases in parallel. It is concluded that the outward production of O₂^•−via NAD(P)H oxidase in CAMs may represent an important producing pattern for its autocrine or paracrine actions.