The actin-bundling activity of AnxA2 is involved in granule recruitment and fusion. Chromaffin cells were stimulated with a local application of 100 mM KCl for 10 s, and catecholamine secretion was monitored using carbon fiber amperometry. Control release was measured in nontransfected cells from the same culture dish. (A) Typical amperometric recordings obtained in nontransfected cells (NT), cells expressing AnxA2-K286A-GFP, and cells treated for 1 h with 5 µM WA. (B) The number of amperometric spikes per cell recorded in nontransfected cells (NT), cells transfected with AnxA2-WT-GFP (A2-WT) or AnxA2-K286A-GFP (A2-K286A), or WA-treated cells (NT+WA). Results represent the mean ± SD (error bars) from 25–55 cells. (C) Schema showing the different spike parameters of the amperometric response (means ± SEM) measured in D. *, P < 0.05; **, P < 0.01.