Loss of ATP8B1 increases the apical diffusion rate of Cdc42. (A) Schematic representation of the experimental setup used to determine the apical membrane diffusion rate. (B) Still images from representative photoconversion videos based on which the dissociation traces in C were generated. (C) Mean normalized dissociation traces for control W4 cells expressing Dendra-Cdc42(HVR) WT (n = 11) or Dendra-Cdc42(HVR) D185 (n = 6) or ATP8B1-depleted cells expressing Dendra-Cdc42(HVR) WT (n = 17). (D) Residential half-lives determined from mean decay traces shown in C using curve fitting. Statistics were performed using half-lives from individual cell traces. Error bars represent SEM. *, P < 0.05; n.s., P > 0.05. (E) Mean normalized dissociation traces for control or ATP8B1-depleted W4 cells expressing Dendra-Cdc42(HVR) WT (n = 6), 1.5×PBR (shCTRL n = 7, shATP8B1 n = 9), or 2×PBR (shCTRL n = 12, shATP8B1 n = 8). (C and E) Light areas indicate SEM. (F) Apical membrane size in ATP8B1-depleted W4 cells expressing YFP, YFP-Cdc42(1.5×PBR), or YFP-Cdc42(2×PBR). *, P < 0.00002; n.s., P > 0.05. E.V., empty vector.