CICR occurs after uncaging calcium at apical (red) but not basal (blue) locations.

Most models of intracellular Ca2+ signaling invoke calcium-induced calcium release (CICR), a positive feedback mechanism that amplifies small elevations in cytoplasmic Ca2+ to produce complex signals. But what determines the pattern of signaling, and how does a cell avoid triggering Ca2+ release in the wrong place? Ashby et al., reporting on page 283, addressed these questions with a powerful new technique and arrived at some surprising conclusions.

Using spatially restricted uncaging of caged Ca2+, the authors were able to boost cytosolic Ca2+ concentrations in specific regions within pancreatic acinar cells. These cells ordinarily produce polarized Ca2+ waves after stimulation with an agonist. When caged Ca2+ uncaged in the apical region of the cells, a CICR wave spreads from the apical region toward the...

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