Fig. 5. The N-terminal LXL-motif is important for the steady-state plasma membrane localisation. (A) Confocal images of MDCK cells transfected with 2xL-A-KCNQ1 and double-labelled for KCNQ1 and markers of the endoplasmic reticulum (PDI) and the trans-Golgi network (TGN38). As illustrated, 2xL-A-KCNQ1 immunoreactivity is observed in close proximity to, but does not co-localize with that of the endoplasmic reticulum nor that of the Golgi apparatus. Ap, apical membrane, Ba, basal membrane. Bar, 4 µm. (B) MDCK cells transfected with 2xL-A-KCNQ1 were biotinylated at the basolateral membrane and chased at 37°C for 0 hours (a-c) or 1 hour (d-f). They were subsequently fixed (a-c) or treated with MesNa and then fixed (d-f), prior to permabilisation and double-labelling with the KCNQ1 antibody (a,d) and Alexa Fluor 488-streptavidin (b,e). After 1 hour of chase some of the KCNQ1-positive structures had been populated with internalised biotinylated plasma membrane proteins (yellow in f). Horizontal confocal scans through the cell layer at the basal level are shown in a1-f1, whereas a2-f2 show vertical confocal scans of the same cells. (c,f) Illustrated overlays of images a,b and images d,e, respectively.