Expression of GSTP1 decreases As₂O₃ retention. Raji cells expressing GSTP1 (RG19 and RG20) and cells containing a vector not expressing GSTP1 (RV5 and RV7) were incubated in medium with 1 μM ⁷³AsIII for 24 hours. Cell-associated radioactivity was determined as described in “Materials and methods.” Each value represents the mean ± SD of triplicates. *Statistically significant (P < .05) differences in RG20 and RG19 cells, compared with those in RV5 and RV7 cell clones.