Translocation of HA-TGN38 to the plasma membrane. RBL-Syt IX⁻ (Ai-iii) or RBL-Syt IX⁺ (Aiv-vi,B) were either left untreated (Ai,iv) or triggered with the calcium ionophore A23187 (1 μM) and the phorbol ester TPA (50 nM) for 30 minutes at 37°C (Aii,v), or incubated with monoclonal anti-HA antibodies (2 μg/mL) for 30 minutes at 4°C and subsequently allowed to internalize the surface bound antibodies at 37°C for 30 minutes without (Aiii,vi) or with Alexa Fluor 488-conjugated Tfn (50 μg/mL) (B) Cells were then labeled with monoclonal anti-HA antibodies, followed by Cy3-conjugated donkey anti–mouse IgG (Ai-ii,iv-v) or labeled with Cy3-conjugated donkey anti–mouse IgG (Aiii,vi,B). Bars represent 3 μm (A) and 4 μm (B).