Depolarization of the mitochondrial inner membrane potential (DeltaPsi(m)) associated with oxidative stress is thought to be a critical factor in cardiac dysfunction and cell injury following
ischemia-reperfusion or exposure to
cardiotoxic agents. In isolated cardiomyocytes, mitochondrially-generated
reactive oxygen species (ROS) can readily trigger cell-wide collapse or oscillations of DeltaPsi(m) but it is not known whether these phenomena scale to the level of the whole heart. Here we utilize two-photon
laser scanning fluorescence microscopy to track DeltaPsi(m), ROS, and
reduced glutathione (GSH) levels in intact perfused guinea-pig hearts subjected to simulated
ischemia reperfusion or GSH depletion with the
thiol oxidizing agent diamide. Exposure to oxidative stress by either method provoked heterogeneous DeltaPsi(m) depolarization and occasional oscillation in clusters of myocytes in the epicardium in association with increased mitochondrial ROS production. Furthermore, the whole-heart oxidative stress dramatically increased the sensitivity of seemingly quiescent cells to DeltaPsi(m) depolarization induced by a localized
laser flash. These effects were directly correlated with depletion of the intracellular GSH pool. Unexpectedly, hearts perfused with nominally Ca2+-free
solution or those switched from 0.5 mM Ca2+ to nominally Ca2+-free
solution also displayed heterogeneous DeltaPsi(m) depolarization and oscillation, in parallel with net oxidation of the GSH pool. The findings demonstrate that metabolic heterogeneity initiated by mitochondrial ROS-induced ROS release is present in the intact heart, and that the redox state of the
glutathione pool is a key determinant of loss of DeltaPsi(m).