(A, B) Role of phospholipase C in the initiation of CCR1 and CCR2 calcium signaling in human monocytes. Fura-2 AM loaded monocytes were left untreated or pretreated with 10 μM U73122 for 5 min. Calcium responses were elicited by 12.5 nM CCL3 (A, C, E) or 11.1 nM CCL2 (B, D, F). (C, D) Role of extracellular and intracellular calcium stores was determined by addition of 5mM EGTA to the cells 30s before agonist addition. Responses in the presence and absence of 5 mM EGTA were measured. (E, F) Role of the ER calcium stores was determined by 5 min. pretreatment with 50 μM of DBHQ prior to agonist addition. Cells with and without DBHQ were then stimulated by the chemokines. Representative data from one of three independent donors are presented.