Abstract

Suspensions of thymocytes from young rats were incubated with 2,3,7,8- tetrachlorodibenzo- p -dioxin (TCDD), which resulted in a sustained increase in cytosolic free Ca 2+ concentration followed by DNA fragmentation and loss of cell viability. Both the Ca 2+ increase and DNA fragmentation were prevented in cells treated with the inhibitor of protein synthesis, cycloheximide, and DNA fragmentation and cell killing were not detected when cells were incubated in a "Ca 2+ -free" medium or pretreated with high concentrations of the calcium probe, quin-2 tetraacetoxymethyl ester. These results indicate that TCDD can kill immature thymocytes by initiating a suicide process similar to that previously described for glucocorticoid hormones.