Among the many unsolved problems of calcium signalling the role of calcium elevations in apoptotic and necrotic cell death has been a focus of research in recent years. fluorescent high through put approaches which allowed dynamic measurements of both [Ca2+] in the intracellular compartments of interest and the downstream processes. Fluorescence single cell imaging has been the only possible approach to resolve the cell-to-cell heterogeneity and the complex subcellular spatiotemporal organization of the cytoplasmic and mitochondrial calcium signals and downstream events. We outline here fluorometric and fluorescence imaging protocols that we set up for the study of calcium in the context of apoptosis. release from the mitochondria can be assessed by monitoring the distribution of cytochrome release from Alisertib the mitochondria cyto is the classical example for these proteins. To monitor the effect of the Ca2+-induced PTP opening on cytochrome release time-lapse fluorescence imaging was performed in permeabilized HepG2 cells transfected with cyto release (Fig. 3C). Thus the combined effect of C2 and Ca2+ caused cytochrome release that was dependent on PTP opening. C2 + Ca2+-induced partial release of the native cytochrome has also been documented by biochemical analysis and by immunocytochemistry. 3.3 Real-time imaging of the calcium signal driven depolarization cyto c-GFP release and caspase activation in intact individual cells Isolated organelles and permeabilized cells provide a straightforward model for the study of the Ca2+ or Ca2+ mobilization-dependent mitochondrial membrane permeabilization. However initiation of a calcium signal by cell surface receptors and development of the complete apoptotic cascade requires intact cells. In addition to the calcium signal and mitochondrial permeabilization time-lapse imaging of caspase activation and visualization of PS exposure and Alisertib nuclear condensation/fragmentation is also feasible in intact cells. 3.3 Simultaneous measurement of [Ca2+]c and ΔΨm during RyR-mediated Ca2+ mobilization Time-lapse confocal imaging of [Ca2+]c and ΔΨm was performed in C2 pretreated intact H9c2 myotubes. Dock4 To rapidly mobilize the SR Ca2+ store caffeine was added together with Tg. RyR-mediated Ca2+ mobilization appeared as a Alisertib rapid and large initial increase in [Ca2+]c followed by a plateau phase and by a late increase (Fig. 4A lower left graph). During the Alisertib plateau phase the effect of Ca2+ entry on [Ca2+]c is usually balanced by continuous mitochondrial Ca2+ uptake. The image series in Fig. 4A shows that the late [Ca2+]c rise propagated as a wave throughout the C2-pretreated cells. Furthermore the late [Ca2+]c increase wave was closely coupled to a wave of mitochondrial depolarization (Fig. 4A). The late response was prevented by CsA. Thus the calcium signal brought about mitochondrial sequestration of Ca2+ and the ensuing [Ca2+]m rise brought on mitochondrial depolarization and Ca2+ release waves that exhibit comparable propagation properties to the waves recorded in permeabilized cells. Fig. 4 Real-time imaging of [Ca2+]c ΔΨm and cyto release in intact cells confocal imaging was used to visualize intracellular distribution of cytochrome in cyto from the mitochondria coupled to the rise of [Ca2+]m and PTP opening. 3.3 Simultaneous measurement of Ca2+ signal-induced ΔΨm loss and caspase activation in C2-pre treated intact H9c2 myotubes Release of cytochrome and other pro-apoptotic factors from mitochondria leads to the activation of effector caspases that execute the final phase of apoptosis. To monitor activation of caspases after [Ca2+]m rise we did simultaneous confocal imaging of ΔΨm and a cell-permeable fluorogenic caspase substrate (PhiPhiLux-G1D2). Images of FTMRE show that in response Alisertib to C2 + caffeine mitochondrial depolarization occurred in two myotubes (cells A and B) whereas ΔΨm was not changed in several small cells (e.g. cells C Alisertib and D) (Fig. 5A). After addition of the caspase substrate generation of the fluorescent cleavage product was observed in the myotubes displaying mitochondrial depolarization waves (shown in blue in the over lay image; time courses for cells A and B; Fig. 5A) but no change appeared in the non-depolarized cells (e.g. cells C and D; Fig. 5A). Next we studied whether collapse of ΔΨm elicited by uncoupler (protonophore) is sufficient to yield rapid cleavage of the caspase substrate (Fig. 5A second row). Uncoupler caused large decreases in FTMRE in every cell but the increase in PhiPhiLux fluorescence was almost undetectable. These data suggest that the mitochondrial changes associated with depolarization and Ca2+ release waves.