Comparison of the effect of verapamil on the cell-cycle status of KTLS cells isolated from BM of HU-treated mice. KTLS cells were isolated from BM of HU-treated mice (100 mg/kg/d for 3 days) and stained with Rh123 and Hoechst 33342 to determine the cell-cycle status of KTLS subsets. FACS plots of the purified HSCs show Hoechst 33342 staining v rhodamine staining (a) without and (b) with verapamil. Verapamil inhibited the efflux of Rh123. The boxes show populations that were purified for further analysis: (I) G0/G1 Rh123^lo and (II) S/G2/M Rh123^mid (these cells in S/G2/M have the ability to efflux Rh123 dye). G0/G1 Rh123^lo cells represent about 15% to 18% of KTLS cells, while S/G2/M Rh123^mid cells represent 4% to 8% of KTLS cells.