Subsarcolemmal mitochondrial flashes induced by hypochlorite stimulation in cardiac myocytes

Mitochondrial superoxide flash (mitoflash) reflects quantal and bursting superoxide production and concurrent membrane depolarization triggered by transient mitochondrial permeability transition in many types of cells, at the level of single mitochondria. Here we investigate reactive oxygen species (ROS)-mediated modulation of mitoflash activity in cardiac myocytes and report a surprising finding that hypochlorite ions potently and preferentially triggered mitoflashes in the subsarcolemmal mitochondria (SSM), whereas hydrogen peroxide (H2O2) elicited mitoflash activity uniformly among SSM and interfibrillar mitochondria (IFM). The striking SSM mitoflash response to hypochlorite stimulation remained intact in cardiac myocytes from NOX2-deficient mice, excluding local NOX2-mediated ROS as the major player. Furthermore, it occurred concomitantly with SSM Ca(2+) accumulation and local Ca(2+) and CaMKII signaling played an important modulatory role by altering frequency and unitary properties of SSM mitoflashes. These findings underscore the functional heterogeneity of SSM and IFM and the oxidant-specific responsiveness of mitochondria to ROS, and may bear important ramifications in devising therapeutic strategies for the treatment of oxidative stress-related heart diseases.