Oxidative Stress‐Induced Changes in Ca2+ Sensitivity of Cardiomyocytes Do Not Recover

Abstract

Ca2+ sensitivity plays a critical role in regulating cardiac contraction, and pathophysiological changes in Ca2+ sensitivity of cardiac contraction may significantly impact cardiac function. For example, oxidative stress causes myocardial dysfunction, which is due in part to a decrease in Ca2+ sensitivity. Oxidative stress (e.g., elevated H2O2) underlies, at least in part, various conditions of cardiac dysfunction including ischemia‐reperfusion injury, heart failure, hypertension, and atherosclerosis. In cardiac muscle, Ca2+ sensitivity can be dynamically assessed using a phase loop plot of concurrently measured cytosolic Ca2+ concentration ([Ca2+]cyt) and sarcomere length shortening (Spurgeon et al J Physiol 447:83–102, 1992; Han et al Am J Physiol 298:890–897, 2010; Schaible et al Am J Physiol 310:1533–40, 2016). We hypothesized that oxidative stress reversibly reduces Ca2+ sensitivity of cardiomyocytes within minutes. Cardiomyocytes were isolated from adult rat hearts (Sprague Dawley) using a modified Langendorff system. Cardiomyocytes were loaded with Fura‐2 AM (Ca2+ fluorescent indicator; 1 mM) and electrically stimulated every 2 s. [Ca2+]cyt and sarcomere shortening responses to stimulation were simultaneously measured using an IonOptix System. After stabilization for 30 min at 35°C, cardiomyocytes were exposed to PSS for 10 min, then to H2O2 (200 μM) for 10 min and finally to either PSS washout or DTT (1 mM)‐induced reduction for 10 min. H2O2‐induced oxidative stress increased basal [Ca2+]cyt and the amplitude of the evoked [Ca2+]cyt response. H2O2‐induced oxidative stress also reduced the extent of sarcomere shortening and slowed the kinetics of shortening/relaxation. As a result, H2O2‐induced oxidative stress reduced Ca2+ sensitivity reflected by a rightward shift in the phase loop plots. Interestingly, with both PSS washout and DTT‐induced reduction Ca2+ sensitivity was further reduced. These results support the hypothesis that H2O2‐induced oxidative stress reduces Ca2+ sensitivity of cardiomyocytes, but this effect was not immediately reversed, but indeed worsened by PSS washout or by DTT‐induced reduction. Together, these results provide insight into the dynamic effects of oxidative stress on Ca2+ sensitivity of cardiomyocytes that may be reflected under pathological conditions.This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.