(C) Isolated nuclei of senescent cells are permeable to both 70- and 500-kD dextrans, indicating impairment of the barrier function of nuclear envelope. Dark nuclei exclude fluorescent dextran. Bars, 10 µm. (D) Quantitation of results from C. Mean ± SD, n = 4; P < 0.000001 for both 70- and 500-kD dextrans. 