Figure 5. Retinyl ester synthesis in the differentiated ARPE-19 cells. Cells cultured for 4 months on Transwell^® permeable membranes were incubated for 16 h with or without 4 μM all-trans retinol provided via the outside (basal) chamber. The cells were harvested, and the extracted retinoids were then analyzed with normal-phase high performance liquid chromatography (HPLC). A: Chromatogram overlay of retinoid extracts from ARPE-19 cells treated with (black) or without (red) all-trans retinol. The inset shows the absorbance spectrum from the peak observed in the treated ARPE-19 cells (black). B: Chromatogram of the authentic all-trans retinyl palmitate standard and its corresponding absorbance spectrum (inset).