Fig. 4.

Inhibition of clathrin-mediated internalization of Kir2.1 does not prevent the stimulation of channel surface expression by AG53 overexpression. (A) Surface expression of Kir2.1 was determined by chemiluminescence assay as in Fig. 1. Expression of AP180C efficiently inhibits the internalization of Kir2.1 (comparing Kir2.1 to Kir2.1+AP180C); however, it does not influence the AGS3-dependent increase of surface Kir2.1 (≈40% in either case, comparing Kir2.1+AGS3 with Kir2.1+AGS3+AP180C). Equal amounts of Kir2.1 were used for transfection in each experiment. Because a smaller amount of AGS3 was used for each transfection, the effects of AGS3 on the surface level of Kir2.1 appeared to be less compared with that in Figs. 1 or 2. (B) Exogenous biotinylated transferrin receptors are internalized normally and concentrated at the perinuclear recycling endosomes (indicated by arrows) in COS7 cells overexpressing AGS3.