Ouabain decreases sarco(endo)plasmic reticulum calcium ATPase activity in rat hearts by a process involving protein oxidation
The effect of cardiac glycosides to increase cardiac inotropy by altering Ca2+ cycling is well known but still poorly understood. The studies described in this report focus on defining the effects of ouabain signaling on sarcoplasmic reticulum Ca2+-ATPase function. Rat cardiac myocytes treated with 50 μM ouabain demonstrated substantial increases in systolic and diastolic Ca2+ concentrations. The recovery time constant for the Ca2+ transient, τ, was significantly prolonged by ouabain. Exposure to 10 μM H2O2, which causes an increase in intracellular reactive oxygen species similar to that of 50 μM ouabain, caused a similar increase in τ. Concurrent exposure to 10 mM N-acetylcysteine or an aqueous extract from green tea (50 mg/ml) both prevented the increases in τ as well as the changes in systolic or diastolic Ca2+ concentrations. We also observed that 50 μM ouabain induced increases in developed pressure in addition to diastolic dysfunction in the isolated perfused rat heart. Coadministration of ouabain with N-acetylcysteine prevented these increases. Analysis of sarcoplasmic reticulum Ca2+-ATPase protein revealed increases in both the oxidation and nitrotyrosine content in the ouabain-treated hearts. Liquid chromatography-mass spectrometric analysis confirmed that the sarcoplasmic reticulum Ca2+-ATPase protein from ouabain-treated hearts had modifications consistent with oxidative and nitrosative stress. These data suggest that ouabain induces oxidative changes of the sarcoplasmic reticulum Ca2+-ATPase structure and function that may, in turn, produce some of the associated changes in Ca2+ cycling and physiological function.
Kennedy DJ, Vetteth S, Xie M, Periyasamy SM, Xie Z, Han C, Basrur V, Mutgi K, Fedorov V, Malhotra D, and Shapiro JI (2006b) Ouabain decreases sarco(endo)-plasmic reticulum calcium ATPase activity in rat hearts by a process involving protein oxidation. Am J Physiol Heart Circ Physiol 291: H3003-H3011.