Caspase 3 activation in growth factor–deprived erythroblasts and the effect of zVAD-FMK on apoptosis.

(A) Caspase 3 activity in day 6 erythroblast lysates, made at the indicated times following growth factor withdrawal, was determined with a colorimetric assay. Means of 2 experiments are shown. (B) To determine the effect of caspase inhibition on apoptosis, erythroblasts on day 5 to 7 of culture were washed and then returned to medium with no growth factors, Epo 2 U/mL and SCF 20 ng/mL (ES), or no growth factors and the pan-caspase inhibitor zVAD-FMK (100 μM, n = 6). The mean percentage ± SEM of apoptotic cells after 8 hours, as determined by annexin V binding, is shown.