Signal-transducing function of Na1-K1-ATPase is essential for ouabain’s effect on [Ca21]i in rat cardiac myocytes

transducing function of Na1-K1-ATPase is essential for ouabain’s effect on [Ca21]i in rat cardiac myocytes. Am J Physiol Heart Circ Physiol 281: H1899–H1907, 2001.—We showed before that Na1-K1-ATPase is also a signal trans-ducer in neonatal rat cardiac myocytes. Binding of ouabain to the enzyme activates multiple signal pathways that regulate cell growth. The aims of this work were to extend such studies to adult cardiac myocytes and to determine whether the signal-transducing function of Na1/K1-ATPase regulates the well-known effects of ouabain on intracellular Ca21 con-centration ([Ca21]i). In adult myocytes, ouabain activated protein tyrosine phosphorylation and p42/44 mitogen-acti-vated protein kinases (MAPKs), increased production of re-active oxygen species (ROS), and raised both systolic and diastolic [Ca21]i. Pretreatment of myocytes with several Src kinase inhibitors, or overexpression of a dominant negative Ras, antagonized ouabain-induced activation of MAPKs and increases in [Ca21]i. Treatment with PD-98059 (a MAPK kinase inhibitor) or overexpression of a dominant negative MAPK kinase 1 also ablated the effect of ouabain on MAPKs and [Ca21]i. N-acetyl-cysteine, which blocks the effect of ouabain on ROS, did not prevent the ouabain-induced rise in [Ca21]i. Clearly, the activation of the Ras/MAPK cascade, but not ROS generation, is necessary for ouabain-induced in-creases in [Ca21]i in rat cardiac myocytes. signal transduction Na1-K1-ATPASE is an energy-transducing ion pump in most mammalian cells (20, 29). It carries out the active transport of Na1 and K1 across the plasma membrane. This enzyme also serves as a functional receptor for digitalis compounds such as ouabain (6, 20, 27). At non-toxic concentrations, ouabain causes a partial inhibition of the ion-pumping function of cardiac Na1-K1-ATPase. This can lead to a small increase in intracellular Na1 concentration, which in turn raises intracellular Ca21 concentration ([Ca21]i) through the Na1/Ca21 exchange