(A) Pacs1+/+ and Pacs1−/− splenocytes were labeled with Indo-1 and stained for B220, CD21, and CD23 to identify FOB and MZB cells. Fluorescence was measured for 30 seconds to establish a baseline and then cells were stimulated with the indicated amounts of anti-IgM (black arrowhead). Cytosolic Ca2+ flux was monitored with FACS analysis by measuring the violet:blue fluorescence emission ratio of Indo-1. Kinetic traces are displayed from five independent Pacs1+/+ and Pacs1−/− pairs and were normalized to baseline (Pacs1+/+ gray traces, Pacs1−/− pink traces). The mean Ca2+ flux for each genotype is overlaid in bold (­Pacs1+/+ black, Pacs1−/− red). 