Role of reactive oxygen species and NAD(P)H oxidase in α1-adrenoceptor signaling in adult rat cardiac myocytes

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Abstract
We recently reported that α1-adrenoceptor (α1-AR) stimulation induces hypertrophy via activation of the mitogen/extracellular signal-regulated kinase (MEK) 1/2-extracellular signal-regulated kinase (ERK) 1/2 pathway and generates reactive oxygen species (ROS) in adult rat ventricular myocytes (ARVM). Here we investigate the intracellular source of ROS in ARVM and the mechanism by which ROS activate hypertrophic signaling after α1-AR stimulation. Pretreatment of ARVM with the ROS scavenger Mn(III)terakis(1-methyl-4-pyridyl) porphyrin pentachloride (MnTMPyP) completely inhibited the α1-AR-stimulated activation of Ras-MEK1/2-ERK1/2. Direct addition of H2O2 or the superoxide generator menadione activated ERK1/2, which is also prevented by MnTMPyP pretreatment. We found that ARVM express gp91phox, p22phox, p67phox, and p47phox, four major components of NAD(P)H oxidase, and that α1-AR-stimulated ERK1/2 activation was blocked by four structurally unrelated inhibitors of NAD(P)H oxidase [diphenyleneiodonium, phenylarsine oxide, 4-(2-aminoethyl)benzenesulfonyl fluoride, and cadmium]. Conversely, inhibitors for other potential ROS-producing systems, including mitochondrial electron transport chain, nitric oxide synthase, xanthine oxidase, and cyclooxygenase, had no effect on α1-AR-stimulated ERK1/2 activation. Taken together, our results show that ventricular myocytes express components of an NAD(P)H oxidase that appear to be involved in α1-AR-stimulated hypertrophic signaling via ROS-mediated activation of Ras-MEK1/2-ERK1/2.