Intact mitochondrial electron transport function is essential for signalling by hydrogen peroxide in cardiac myocytes

Oxidative stress has been proposed as a mediator of cardiac injury during i schemia and reperfusion. We examined the signalling events initiated by sho rt-term exposure of cardiac myocytes to oxidative stress elicited by hydrog en peroxide. A potent stimulation of tyrosine phosphorylation was observed within 1 to 2 min exposure to 1 mM hydrogen peroxide. Within 5 min, the ERK mitogen-activated protein kinases (ERK MAPKs) were activated. This activat ion of ERK MAPKs was blocked by N-acetylcysteine (NAC), implicating a role for free radicals in the signalling events. NAC failed to inhibit ERK MAPK activation by the hypertrophic agent, phenylephrine, or hyperosmotic shock. Myxothiazol, an inhibitor of complex III of the mitochondrial electron tra nsport chain, also inhibited ERK MAPK activation by hydrogen peroxide, but not by 12-O-tetradecanoylphorbol-13-acetate (TPA) or hyperosmotic shock. My xothiazol completely inhibited the increase in tyrosine phosphorylated prot eins observed with hydrogen peroxide treatment. A variety of inhibitors whi ch act at different levels of the mitochondrial electron transport chain (r otenone, theonyltrifluoroacetone, antimycin A, cyanide) also inhibited acti vation of the ERK MAPKs by hydrogen peroxide but not TPA or hyperosmotic sh ock. These studies suggest a novel mechanism of regulation of the ERK MAPK pathway and oxidative stress signalling by hydrogen peroxide. (C) 2000 Acad emic Press.