POS phagosome degradation. (A) RPE cells isolated from WT or Klc1^−/− mice, showing bound and ingested WT POSs, labeled with RHO antibody, from a 15-min pulse/30-min chase experiment. (B and C) Bound (B) and ingested (C) POSs in WT and Klc1^−/− RPE cells after a 15-min pulse/30-min chase. Data aggregated from four separate experiments; in each experiment, four to six fields of view from two to three Transwell filters were analyzed for each condition and each time point. The number of POSs is indicated as a percentage of the POS counted at the pulse time point in WT RPE. No significant difference was detected in the binding (B; Student’s t test, two-tailed; P = 0.22) or ingestion (C; P = 0.69) of POS immediately after the pulse. However, after chase, although the number of bound POSs showed no significant difference between WT and Klc1^−/− RPE cells (B; P = 0.45), there were many more ingested POS remaining in Klc1^−/− than WT RPE (C; *, P = 0.01). (D) EM of Klc1^−/− RPE. Phagosomes (P) were identified by the presence of disk membranes. AP, apical processes; BI, basal infoldings. (E) Number of phagosomes per length (millimeter) of RPE in WT or Klc1^−/− mice 3 h after light onset (n = 5 animals per genotype; *, P = 0.009). Bars: (A) 10 µm; (D) 1 µm. Error bars are means ± SEM.