Abstract 1619: Endothelin-1 Regulates Cardiac Contractility via a Mitochondrial ATP-Sensitive K+ Channel-Dependent Activation of Extracellular Signal-Regulated Kinase
Increased production of reactive oxygen species (ROS) has been linked to the pathogenesis of several cardiovascular diseases. However, it is largely unknown if ROS can regulate physiological cellular processes in the myocardium. The objective of the present study was to characterize the involvement of ROS in the positive inotropic effect of endothelin-1 (ET-1), the potential cellular sources of ROS, and the candidate downstream effectors of ROS. In the isolated perfused, paced rat heart preparation, intracoronary infusion of ET-1 (1 nmol/L) for 10 min increased developed tension by 45±6% (n=8, P<0.001). N-acetylcysteine (NAC, 500 μmol/L), a ROS scavenger, and MnTMPyP (10 μmol/L), a superoxide dismutase mimetic, decreased the ET-1-induced intropic effect by 33% (n=5, P<0.001) and 35% (n=5, P<0.05), respectively. Apocynin (100 μmol/L), an NAD(P)H oxidase inhibitor, attenuated the inotropic response to ET-1 by 36% (n=7, P<0.001). Moreover, 5-HD (200 μmol/L), a specific blocker of mitochondrial ATP-dependent K+ (mitoKATP) channels, decreased the inotropic effect of ET-1 by 43% (n=5, P<0.001). Western Blot analysis revealed that ET-1 significantly increased the levels of phosphorylated extracellular signal-regulated kinase (ERK) (P<0.001). The MEK1/2 inhibitor U0126 (1.5 μmol/L) significantly reduced the levels of phospho-ERK and attenuated the inotropic response to ET-1 by 49% (n=4, P<0.05). Moreover, ET-1-induced increase in ERK phosphorylation was attenuated by NAC (P<0.01), MnTMPyP (P<0.001), and 5-HD (P<0.05). In summary, our results indicate that the inotropic response to ET-1 is, at least in part, mediated by ROS in the adult intact rat heart. Our data suggest that NAD(P)H oxidase-induced ROS production stimulates the opening of mitoKATP channels, and mitochondria-derived ROS may activate ERK and enhance cardiac contractility.