P-gp^+ve cells are resistant to cell death induced by UV irradiation. A7⁺ and CCRF cells, 4 × 10⁴ cells in 3-mL media, were subjected to UV-irradiation (2 to 10 minutes), removed from the UV source, and incubated for 24 hours. Cell viability was determined by Trypan blue exclusion and confirmed by fluorescence analysis following staining with PI (data not shown). In some wells, cells were preincubated with MRK 16 (50 μg/mL), UIC2 (5 μg/mL), or verapamil (5 μmol/L) for 30 minutes. Data are calculated as the mean ± SE of quadruplicate samples and are representative of at least two different experiments.