Fig. 4. Effects of ceramides on antigen-stimulated Ca²⁺ mobilization in RBL cells parallel their effects on lipid order. (A-D) Ca²⁺ response of RBL cells treated with 32 µM C₂-cer (A,D), 32 µM C₂-dhcer (B) or 8 µM C₁₆-cer (C) in the presence (A-C) or absence (D) of extracellular Ca²⁺. Data are representative of at least three experiments for each ceramide. Corresponding controls for all cases are shown in the same panel. IgE-sensitized and indo-1-loaded cells were triggered by the addition of 200 ng/ml DNP-BSA. (E) Percent inhibition of antigen-stimulated Ca²⁺ mobilization in RBL cells by various ceramides, in the presence or absence of extracellular Ca²⁺, were calculated according to Eqn 2, and averages for all experiments are plotted with the bars showing s.e.m. Filled bars, C₂-cer; open bars, C₂-dhcer; dot-filled bar, C₁₆-cer.