Fig. 2. Time-dependent mRNA expression of Mrp1 (A) and AFP (B) in cultured rat small hepatocytes. Cells were cultured for up to 9 weeks. Cells were harvested at day 1 and weeks 1, 3, 5 and 9 with Trizol. mRNA of Mrp1 and AFP was quantitatively measured by real-time PCR and normalized to 18S rRNA and mRNA expression of 1-week cultures [Ct value for Mrp1=27.61±0.46; Ct value for 18S=13.9±0.97; the quotient (Ct value for Mrp1 ÷ Ct value for 18S)=13.71±0.8 (n=4, mean±standard deviation); Ct value for AFP=35.41±0.6; the quotient (Ct value for AFP/Ct value for 18S=21.5±1.0) (n=4, mean±SD)]. 0.0023% AFP mRNA was detected in 1-day cultures relative to 1-week cultures.