Oxidative Stress by Hydrogen Peroxide Reduces Cardiac Contractile Protein Performance and Enhances Cardiomyocyte Calcium Release

Cardiac oxidative stress correlates with diminished left ventricular function and has emerged as a public health concern. Hydrogen peroxide (H2O2) is considered the most relevant reactive oxygen species in vivo. Cardiac zinc status appears to protect against the detrimental effects of H2O2, although the mechanisms are not known. We examined the role of H2O2 in modulating the performance of cardiomyocytes in 36 rats divided into three diet groups: zinc deficient, normal and abundant. Cardiomyocytes were isolated and exposed to 50 μM H2O2. within 5 min intracellular zinc ion (Zn2+) rose as observed by FluoZin-3. Confocal microscopy demonstrated that Zn2+ diffused away from I-band of the intact cardiomyocyte after H2O2. Zinc normal and abundant groups showed significant intracellular Zn2+ release (2.4±0.4 nM and 1.9±0.4 nM, respectively) compared to zinc deficient group (0.7±0.2 nM). There were H2O2-dependent changes in sarcomere and calcium dynamics in all three zinc diet groups, although no differences in response to H2O2 among the groups. Sarcomere peak shortening was significantly increased (p<0.001) and diastolic sarcomere length was reduced after H2O2 exposure compared to control. Peak systolic calcium was elevated (p<0.05) by H2O2. We then explored the H2O2 effects on cardiac contractile proteins. Skinned rat myocardium displayed shorter myosin crossbridge time-on and reduced tension after 100 μM H2O2 exposure compared to control condition. In sliding filament experiments actin velocity was decreased from 0.74±0.17 μm/s to 0.30±0.1 μm/s after 100 μM H2O2 pretreatment of purified rabbit cardiac beta-myosin for 30 min. These data collectively suggest that oxidative stress due to H2O2 enhances calcium availability at the cellular level while reducing contractile protein performance at the molecular level and that cardiac zinc status does not protect against changes in cardiopmyocyte performance after H2O2 exposure.