Time-dependent expression patterns of AhRα (A), AhRβ (B), AhRR (C), ARNT (D), CYP1A1 (E) and UDPGT (F) mRNA in primary culture of salmon hepatocytes exposed to 5 μM NP and 1 μM PCB-77, both singly and in combination. Hepatocytes were sampled at 12, 24, 48 and 72 hours post-exposure. Expression of mRNA levels was quantified using quantitative (real-time) PCR with gene specific primer pairs. The data are given as % of the solvent control ± standard error of the mean (n = 3). Different letters denote exposure group means that are significantly different, for the respective mRNA expression using ANOVA followed by Tukey's multiple comparison test (p < 0.05).