Effects of DMSO treatment on functional activities of drug-metabolizing enzymes in Huh7 cells. Growing (open circle) or DMSO-treated (closed circle) Huh7 cells were incubated with various probe drugs (). The media were sampled at the indicated time points and metabolic activities of CYP1A2, CYP2C9, CYP2D6, and CYP3A4 were determined by measuring concentrations of relative metabolites, i.e. paraxanthine or luciferin, 4-hydroxydiclofenac, dextrorphan, and 1-hydroxymidazolam, respectively. In paraxanthine (F) or dextrorphan (E) production, additional CYP enzymes other than CYP1A2 or CYP2D6 may be involved (see text for more detail). Activities of UGT1A4 and UGT2B7 were also determined by measuring concentrations of lamotrigine N2-glucuronide and morphine 6-glucuronide, respectively, in the media. Data presented show the amount of metabolite produced, expressed in pmol per 106 cells except for luciferin (G) which shows luminescence unit (the mean of triplicate experiment ± standard deviation).