Ouabain decreases sarco(endo)plasmic reticulum calcium ATPase activity in rat hearts by a process involving protein...

Area of Science:

• Cardiology
• Molecular Biology
• Biochemistry

Background:

• Cardiac glycosides, such as ouabain, are known to enhance cardiac inotropy through alterations in calcium (Ca2+) cycling.
• The precise mechanisms underlying these effects, particularly the impact on sarcoplasmic reticulum Ca2+-ATPase (SERCA) function, remain incompletely understood.

Purpose of the Study:

• To investigate the effects of ouabain on sarcoplasmic reticulum Ca2+-ATPase (SERCA) function and Ca2+ handling in cardiac myocytes.
• To explore the role of oxidative and nitrosative stress in ouabain-induced cardiac dysfunction.

Main Methods:

• Primary rat cardiac myocytes and isolated perfused rat hearts were treated with ouabain.
• Calcium transients, intracellular reactive oxygen species (ROS), and SERCA protein modifications (oxidation, nitrotyrosine) were analyzed.
• Techniques included measurements of Ca2+ concentrations and time constants, exposure to ROS-inducing agents, and liquid chromatography-mass spectrometry.

Main Results:

• Ouabain (50 microM) significantly increased systolic and diastolic Ca2+ concentrations and prolonged the Ca2+ transient recovery time constant (tau(Ca2+)).
• Hydrogen peroxide (H2O2) mimicked ouabain's effect on tau(Ca2+), suggesting a role for reactive oxygen species.
• N-acetylcysteine and green tea extract prevented ouabain-induced changes in Ca2+ handling and cardiac function.
• Ouabain treatment led to increased oxidation and nitrotyrosine content in SERCA protein, indicative of oxidative and nitrosative stress.

Conclusions:

• Ouabain induces oxidative modifications to the sarcoplasmic reticulum Ca2+-ATPase (SERCA) protein.
• These structural and functional changes in SERCA likely contribute to altered Ca2+ cycling and cardiac dysfunction observed with ouabain treatment.
• Antioxidant interventions may mitigate ouabain's adverse cardiac effects.