Fig. 4. Accelerated telomere attrition and appearance of long TRFs under chronic oxidative stress. (A,C) Southern blot hybridisation of a telomeric probe to genomic DNA from HUVEC of different replicative ages. A shows blots from cells were grown under normal conditions or chronically treated with 0.1 µM t-BHP during successive passages; C shows blots from cells treated with 10 µM BSO. Note in both cases the appearance of long TRF species (*) in the stressed cells at later passages. (B) The mean TRF lengths corresponding to the blots shown in A are plotted as a function of the replicative age.