Figure 1. Existence of stem-like side population cells in the human retinoblastoma WERI-Rb1 cell line. The cells were stained with Hoechst 33,342 and sorted with flow cytometry. A: A small population of cells (0.075±0.017%) was identified. B: Addition of 50 μM verapamil markedly reduced the staining of the SP cells. (n=3; x-axis, Hoechst red fluorescence intensity; y-axis, Hoechst blue fluorescence intensity).