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FIGURE 2. Compartmentalized cellular Ca2+ signaling
A: a simplified three-compartment model of the cell indicates the principal organelles participating in cellular Ca2+ handling and their resting [Ca2+]. The endoplasmic reticulum (ER) represents the main intracellular Ca2+ store, having a basal Ca2+ level almost as high as in the extracellular space, roughly 104 times higher than the cytoplasm and mitochondria. Cell stimulation leads to the activation of at least two seminal pathways. First, the 2+ release from the ER, triggering a reciprocal [Ca2+] increase in the cytosol and [Ca2+] drop in the ER (as measured by formation of IP3 leads to Ca the luminescent recombinant aequorin Ca2+ probes; top and middle in B, respectively). Second, extracellular signals or ER Ca2+ depletion activate Ca2+ influx routes, refilling the ER partially through mitochondria (see also FIGURE 3A). Note the almost 100 times greater response in mitochondria (bottom in B) compared with the cytosol, partly explained by the close physical association between the organelles.
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, TOP, the y-axis label incorrectly ranged from 0 to 80; the label should range from 0 to 3. The corrected figure is printed below. 