The effects of hydrogen peroxide on intracellular calcium handling and contractility in the rat ventricular myocyte

Elevations in reactive oxygen species are implicated in many disease states and cause systolic and diastolic myocardial dysfunction. To understand the underlying cellular dysfunction, we characterised the effects of H2O2 on [Ca2+]i handling and contractility in the rat ventricular myocyte. This was achieved using patch clamping, [Ca2+]i measurement using Fluo-3, video edge detection and confocal microscopy. All experiments were performed at 37 °C. 200 μM H2O2 resulted in a 44% decrease in the [Ca2+]i transient amplitude, a 30% increase in diastolic [Ca2+]i and an 18% decrease in the rate of systolic Ca2+ removal. This was associated with a 61% reduction in systolic shortening, a contracture of 3 μm and a 42% increase in relaxation time respectively. The decrease in the [Ca2+]i transient amplitude could be explained by a 27% decrease in SR Ca2+ content. This, in turn results from a 22% decrease of SERCA activity. The decreased SR Ca2+ content also provides a mechanism for a reduction in [Ca2+]i spark frequency with no evidence for a Ca2+ independent modification of ryanodine receptor open probability. We conclude that decreased SERCA activity is the major factor responsible for the changes of the systolic [Ca2+]i transient.