Ligand-dependent resistance to radiation-induced apoptosis. (A) 32D cells expressing TRKA, TRKB, and 32D wild-type cells. Cells were starved for 3 hours and exposed to 5 Gy irradiation. Cells that were annexin-V and propidium iodide (PI) negative were counted as viable cells. Viability was calculated as the percentage of these cells over the total cell population. (B) BDNF prevented apoptosis of 32D cells expressing TRKB almost as efficiently as IL-3. Cells were analyzed by flow cytometry 26 hours after irradiation. Combined annexin-V and PI staining was used to distinguish early apoptotic (annexin-V⁺/PI⁻) and later apoptotic cells (annexin-V⁺/PI⁺). (C) K252a dramatically inhibited antiapoptotic effects of BDNF-mediated activation of TRKB, whereas only slight inhibition was observed if cells were cultured in the presence of IL-3 alone. Results presented are the mean plus or minus SD of at least 2 independent experiments. NGF/BDNF concentration was 100 ng/mL, murine IL-3 2 ng/mL.