IP3, still on the move but now in the slow lane.

In this issue of Science Signaling, Dickinson et al show that the intracellular messenger inositol 1,4,5-trisphosphate (IP3 ), which triggers the release of calcium (Ca2+ ) from the endoplasmic reticulum, is a slowly diffusing local signal, rather than a rapidly diffusing global one. These findings have implications for the understanding of the mechanisms of Ca2+ wave propagation, especially long-range, cell-to-cell propagating Ca2+ waves.