Induction of apoptosis in BL41 and BL41/B95 cells. (A) Analysis of DNA fragmentation 48 hours after irradiation with 150 Gy by DNA gel electrophoresis. M, 123-bp DNA ladder (GIBCO). (B) Apoptotic morphology was examined with Hoechst 33258 DNA staining. (C) Viability of irradiated cells was analyzed by trypan blue exclusion.