FcγR-mediated Syk activation as well as LTB₄ amplification are Ca²⁺ regulated. (A) Rat alveolar macrophages were pretreated with EGTA (10 mM), BAPTA-am (50 μM), or both for 30 minutes prior to addition of LTB₄ (10 nM). Two minutes after LTB₄ treatment, the cells were challenged with IgG-SRBCs (1:33 ratio) and then incubated for 7 minutes at 37°C. *P < .05 compared with IgG-SRBC group and ^#P < .05 compared with IgG-SRBC plus LTB₄ group (ANOVA followed by Bonferroni t test). (B) Rat alveolar macrophages were pretreated with EGTA (10 mM), BAPTA-am (50 μM), or both for 30 minutes prior to IgG-SRBC challenge. Incubations were terminated by addition of lysis buffer, and lysates were subjected to immunoprecipitation and immunoblotting as described in “Materials and methods.” Data are given as mean ± SEM. *P < .05 compared with IgG-SRBC group (ANOVA followed by Bonferroni t test). Results are representative of 3 separate experiments.