The response of
ryanodine receptor (RyR) channels to cytoplasmic free
calcium concentration ([Ca(2+)]) is redox sensitive. Here, we report the effects of a mild oxidative stress on cardiac RyR (
RyR2) channels in Langendorff perfused rat hearts. Single
RyR2 channels from control ventricles displayed the same three responses to Ca(2+) reported in other mammalian tissues, characterized by low, moderate, or high maximal activation. A single episode of 5 min of global
ischemia, followed by 1 min of reperfusion, enhanced 2.3-fold the activity of NOX2 compared to controls and changed the frequency distribution of the different responses of
RyR2 channels to
calcium, favoring the more active ones: high activity response increased and low activity response decreased with respect to controls. This change was fully prevented by perfusion with
apocynin or
VAS 2870 before
ischemia and totally reversed by the extension of the reperfusion period to 15 min. In vitro activation of NOX2 in control SR vesicles mimicked the effect of the
ischemia/reperfusion episode on the frequencies of emergence of single
RyR2 channel responses to [Ca(2+)] and increased 2.2-fold the rate of
calcium release in Ca(2+)-loaded SR vesicles. In vitro changes were reversed at the single channel level by DTT and in isolated SR vesicles by
glutaredoxin. Our results indicate that in whole hearts a mild oxidative stress enhances the response of cardiac
RyR2 channels to
calcium via NOX2 activation, probably by S-glutathionylation of
RyR2 protein. This change is transitory and fully reversible, suggesting a possible role of redox modification in the physiological response of cardiac
RyR2 to cellular
calcium influx.