Fig. 6. Distribution of syn1A and syn3 in polarized Caco-2 cells. Caco-2 cells cotransfected with syn1A and munc-18-1 (A-C' or untransfected (D,D') were grown on permeable filters for 7 days. Transfected cells were double-immunolabeled for syn1A (SYN1, A-C), and untransfected cells were stained for syn3 (SYN3, D). In all cases the apical cell membrane was labeled using concanavalin A (CONA, A'-D'). Consecutive horizontal optical sections through the cell monolayers were recorded as described in Fig. 5. In C-D', confocal sections in the vertical plane are shown with the apical side of the cell monolayer at the top. Note the presence of syn1A at both the apical (AP) and basolateral (BL) membranes, whereas endogenous syn3 appears exclusively at the apical side. Bars, 10 µm.