Involvement of mitogen-activated protein kinases and reactive oxygen species in the inotropic action of ouabain on cardiac myocytes. A potential role for mitochondrial K

Binding of ouabain to Na/K-ATPase activated multiple signal transduction pathways including stimulation of Src, Ras, p42/ 44 MAPKs and production of reactive oxygen species (ROS) in rat cardiac myocytes. Inhibition of either Src or Ras ablated ouabain-induced increase in both [Ca] i and contractility. While PD98059 abolished the effects of ouabain on [Ca] i, it only caused a partial inhibition of ouabain-induced increases in contractility. On the other hand, pre-incubation of myocytes with N-acetyl cysteine (NAC) reduced the effects of ouabain on contractility, but not [Ca] i . Furthermore, 5-hydroxydecanoate (5HD) blocked ouabain-induced ROS production and partially inhibited ouabain-induced increases in contractility in cardiac myocytes. Pre-incubation of myocytes with both 5-HD and PD98059 completely blocked ouabain’s effect on contractility. Finally, we found that opening of mitochondrial K ATP channel by diazoxide increased intracellular ROS and significantly raised contractility in cardiac myocytes. These new findings indicate that ouabain regulates cardiac contractility via both [Ca] i and ROS. While activation of MAPKs leads to increases in [Ca] i , opening of mitochondrial K ATP channel relays the ouabain signal to increased ROS production in cardiac myocytes. (Mol Cell Biochem 242: 181–187, 2003)