Acute ROS in Cardiac Calcium Signaling

Abstract

Modulation of cardiac function usually involves changes in cellular Ca2+ signaling. Reactive oxygen species (ROS) have been implicated in effecting changes in cardiac Ca2+ signaling. It has been unclear, however, exactly what these changes are and if they are ultimately detrimental or beneficial. The work reported here investigates the effect of acute application of H2O2 in low concentrations on Ca2+ signaling in the heart cell. The driving hypothesis is that ROS in short bursts is a non - detrimental physiological signal that fine tunes Ca2+ signaling. To this end the effect of ROS is investigated in 3 modules. i. the effect of rapid application of 100 μM H2O2 on Ca2+ signaling in heart cells, ii. the effect of H2O2 on Ca2+ signaling during β-adrenergic activation in heart cells and finally to examine endogenously generated ROS, iii. Ca2+ signaling in a murine model of NOX2 overexpression (NOX2 is a ROS generating enzyme). Using a combination of confocal imaging of fluorescent Ca2+ dyes and electrophysiological techniques such as whole cell voltage clamp and current clamp; Ca2+ sparks, Ca2+ transients, ICa, Sarcoplasmic Reticulum (SR) Ca2+ load and Sarcoplasmic/Endoplasmic Reticulum Ca2+ ATPase (SERCA) function were measured in all three paradigms listed above. The work shows that low concentrations of H2O2 for a brief period deplete SR load without affecting other parameters of Ca2+ signaling, and this depletion of SR load is prevented by β-adrenergic activation. The results further our understanding of ROS modulation of Ca2+ signaling and lays some groundwork for further exploration into the pathways by which ROS may interact with other modifiers of the Ca2+ signaling machinery of the cardiac cell.