Dynamic modulation of Ca2+ sparks by mitochondrial oscillations in isolated guinea pig cardiomyocytes under oxidative stress

Local control of Ca2+-induced Ca2+ release (CICR) depends on the spatial organization of L-type Ca2+ channels and ryanodine receptors (RyR) in the dyad. Analogously, Ca2+ uptake by mitochondria is facilitated by their close proximity to the Ca2+ release sites, a process required for stimulating oxidative phosphorylation during changes in work Mitochondrial feedback on CICR is less well understood. Since mitochondria are a primary source of reactive oxygen species (ROS), they could potentially influence the cytosolic redox state, in turn altering RyR open probability. We have shown that self-sustained oscillations in mitochondrial inner membrane potential (Delta Psi(m)), NADH, ROS, and reduced glutathione (GSH) can be triggered by a laser flash in cardiomyocytes. Here, we employ this method to directly examine how acute changes in energy state dynamically influence resting Ca2+ spark occurrence and properties. Two-photon laser scanning microscopy was used to monitor cytosolic Ca2+ (or ROS), Delta Psi(m), and NADH (or GSH) simultaneously in isolated guinea pig cardiomyocytes. Resting Ca2+ spark frequency increased with each Delta Psi(m) depolarization and decreased with Delta Psi(m) repolarization without affecting Ca2+ spark amplitude or time-to-peak Stabilization of mitochondrial energetics by pretreatment with the superoxide scavenger TMPyP, or by acute addition of 4'-chlorodiazepam, a mitochondrial benzodiazepine receptor antagonist that blocks the inner membrane anion channel, prevented or reversed, respectively, the increased spark frequency. Cyclosporine A did not block the Delta Psi(m) oscillations or prevent Ca2+ spark modulation by Delta Psi(m). The results support the hypothesis that mitochondria exert an influential role on the redox environment of the Ca2+ handling subsystem, with mechanistic implications for the pathophysiology of cardiac disease. (C) 2011 Elsevier Ltd. All rights reserved.