Figure 6. Effects of singlet oxygen on DNA ladder formation.

RBL cells were incubated with 2 mM MNPE for an initial 2 h, changed to fresh medium, and incubated an additional 15 h. For etoposide treatment, 0.4 mM etoposide (Etop) was present all the time. MNPE (2 mM) was included from 3 to 5 h after etoposide addition, and the cells were incubated further for an additional 13 h in fresh medium containing etoposide. (A) DNA was extracted from cells, separated on a 2% agarose gel and stained with ethidium bromide. Typical data of triplicate experiments are shown. (B) Viability of cells that had been treated under the same conditions as (A) was assessed by measuring LDH activity.