Fig. 5. Localization of syn1A at the apical and basolateral domains of polarized MDCK cells. MDCK cells cotransfected with syn1A and munc-18-1 were grown on permeable filters for 4 days. Before fixation the apical surface of cell monolayer was labeled using concanavalin A (CONA, A',B') as described in Materials and Methods. Cells expressing syn1A were detected using the anti-syn1 antibody followed by secondary antibody conjugated to rhodamine (SYN1, A,B). Consecutive horizontal optical sections through the cell monolayers were recorded by means of confocal fluorescence microscopy at 0.5 µm intervals. Sections are shown at the level of the apical surface (AP, A,A') and the nucleous (BL, B,B'). Note the presence of syn1A at both the apical and basolateral sides of the expressing cells. Bars, 10 µm.