Watching Ca²⁺ waves break

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...