Intracellular reactive oxygen species mediate the linkage of Na+/K+-ATPase to hypertrophy and its marker genes in cardiac myocytes.
We showed before that in cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophy and transcriptional regulations of growth-related marker genes through multiple Ca2+-dependent signal pathways many of which involve Ras and p42/44 mitogen-activated protein kinases. The aim of this work was to explore the roles of intracellular reactive oxygen species (ROS) in these ouabain-initiated pathways. Ouabain caused a rapid generation of ROS within the myocytes that was prevented by preexposure of cells to N-acetylcysteine (NAC) or vitamin E. These antioxidants also blocked or attenuated the following actions of ouabain: inductions of the genes of skeletal alpha-actin and atrial natriuretic factor, repression of the gene of the alpha3-subunit of Na+/K+-ATPase, activation of mitogen-activated protein kinases, activation of Ras-dependent protein synthesis, and activation of transcription factor NF-kappaB. Induction of c-fos and activation of AP-1 by ouabain were not sensitive to NAC. Ouabain-induced inhibition of active Rb+ uptake through Na+/K+-ATPase and the resulting rise in intracellular Ca2+ were also not prevented by NAC. A phorbol ester that also causes myocyte hypertrophy did not increase ROS generation, and its effects on marker genes and protein synthesis were not affected by NAC. We conclude the following: (a) ROS are essential second messengers within some but not all signal pathways that are activated by the effect of ouabain on Na+/K+-ATPase; (b) the ROS-dependent pathways are involved in ouabain-induced hypertrophy; (c) increased ROS generation is not a common response of the myocyte to all hypertrophic stimuli; and (d) it may be possible to dissociate the positive inotropic effect of ouabain from its growth-related effects by alteration of the redox state of the cardiac myocyte.
Xie
Z
Z
Departments of Pharmacology and Medicine, Medical College of Ohio, Toledo, Ohio 43614, USA. ZXie@mco.edu
Kometiani
P
P
Liu
J
J
Li
J
J
Shapiro
J I
JI
Askari
A
A
D000111:Acetylcysteine / Q000494:pharmacology; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006332:Cardiomegaly / Q000235:genetics*; D002316:Cardiotonic Agents / Q000494:pharmacology; D002478:Cells, Cultured; D004789:Enzyme Activation; D005819:Genetic Markers; D006321:Heart / Q000187:drug effects; D009206:Myocardium / Q000201:enzymology*; D010042:Ouabain / Q000494:pharmacology; D016760:Proto-Oncogene Proteins c-fos / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D017382:Reactive Oxygen Species / Q000378:metabolism*; D012413:Rubidium / Q000493:pharmacokinetics; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014810:Vitamin E / Q000494:pharmacology
D000975:Antioxidants; D002316:Cardiotonic Agents; D005819:Genetic Markers; D016760:Proto-Oncogene Proteins c-fos; D017382:Reactive Oxygen Species; D018808:Transcription Factor AP-1; D014810:Vitamin E; D010042:Ouabain; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D000254:Sodium-Potassium-Exchanging ATPase; D012413:Rubidium; D002118:Calcium; D000111:Acetylcysteine