Redox-Mediated Reciprocal Regulation of SERCA and Na+/Ca2+-Exchanger Contributes to SR Ca2+-Depletion in Cardiac Myocytes

Myocardial failure is associated with increased oxidative stress and abnormal excitation-contraction coupling characterized by depletion of sarcoplasmic reticulum (SR) Ca 2+ -stores and a reduction in Ca 2+ -transient amplitude. Little is known about the mechanisms whereby oxidative stress affects Ca 2+ -handling and contractile function; however, reactive thiols may be involved. We used an in vitro cardiomyocyte system to test the hypothesis that short-term oxidative stress induces SR Ca 2+ -depletion via redox-mediated regulation of sarco-endoplasmic reticulum Ca 2+ -ATPase (SERCA) and the sodium-Ca 2+ -exchanger (NCX) and that this is associated with thiol oxidation. Adult rat ventricular myocytes paced at 5 Hz were superfused with H 2 O 2 (100 μM, 15 min). H 2 O 2 caused a progressive decrease in cell shortening followed by diastolic arrest, which was associated with decreases in SR Ca 2+ -content, systolic [Ca 2+ ] i and Ca 2+ -transient amplitude, but no change in diastolic [Ca 2+ ] i . H 2 O 2 caused reciprocal effects on the activities of SERCA (decreased) and NCX (increased). Pretreatment with the NCX inhibitor KB-R7943 prior to H 2 O 2 increased diastolic [Ca 2+ ] i , and mimicked the effect of SERCA inhibition with thapsigargin. These functional effects were associated with oxidative modification of thiols on both SERCA and NCX. In conclusion, redox-mediated SR Ca 2+ -depletion involves reciprocal regulation of SERCA and NCX, possibly via direct oxidative modification of both proteins.