Subsarcolemmal mitochondrial flashes induced by hypochlorite stimulation in cardiac myocytes

Abstract

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.

Mitochondrial Flash: Integrative Reactive Oxygen Species and pH Signals in Cell and Organelle Biology

“…Finally, mPTP opening is regulated by a number of signals, such as ROS and Ca 2+ . The roles of oxidants and antioxidants on mitochondrial flash regulation are consistent with mPTP as a trigger, and mitochondrial Ca 2+ uptake indeed enhances mitochondrial flash activity ( 26 , 32 , 41 , 86 ). In plant cells, atractyloside and H 2 O 2 induce mitochondrial flashes.…”

“…Indeed, ischemia drastically suppressed and anoxia abolished, while reperfusion caused a transient increase in flash frequency in intact cardiomyocytes ( 37 , 76 ). Superoxide/ROS signal in flash events detected using mt-cpFYP was confirmed by several groups using various cell types, oxidants, and antioxidants ( 32 , 35 , 37 , 60 , 65 , 86 ). Finally, other superoxide/ROS indicators, including MitoSOX, 2′,7′-dichlorodihydrofluorescein diacetate (DCF) and redox green fluorescent protein (roGFP), have been used to detect increases in superoxide during single mitochondrial flash events ( Table 1 ) ( 5 , 11 , 60 , 79 , 87 ).…”

Synchronism in mitochondrial ROS flashes, membrane depolarization and calcium sparks in human carcinoma cells

“…using cpYFP) generated ROS. [56,63,64,67,68]. Recently, Wang et al [56,63,64] and others showed the existence of superoxide flashes in individual mitochondria, using the mitochondrial matrix-targeted superoxide indicator, a circularly permuted yellow fluorescent protein (cpYFP).…”

Mitochondrial flashes regulate ATP homeostasis in the heart

“…Cells displaying healthy contractility were chosen for mitoflash measurement and those near the anode, where electrolysis can produce reactive oxygen species locally (Jackson et al, 1986), were avoided. These cautious measures were necessary because we have recently shown that ROS generated by electrolysis of Tyrode’s solution at the anode can cause significant increase in mitoflash as well as mitochondrial Ca 2+ (Zhang et al, 2014). To minimize interference from cell shortening, image acquisition in contracting cells was at 1 s/frame and synchronized with the electrical pacing, such that it was phase-locked with cell contraction.…”