The peripheral actin cortex in cells is essential for secretory vesicle exocytosis, but also acts as a barrier for vesicle release. Wollman and Meyer report that antigen activation triggers cyclical waves of Ca2+ and PtdIns(4,5)P2 that promote N-WASP-mediated oscillations in F-actin polymerization. These permit secretion when F-actin levels are low, but impede exocytosis when F-actin levels are high.
