ELSEVIER Marine Environmental Research zyxwvutsrqponmlkjihgfedcbaZY Vol. 42, No. l-4, pp. 283-286, 1996 Copyright 0 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0141-1136(95)00045-3 0141-1136/96/$15.00+0.00 CYPlAl-, CYP2B- and CYP3A-Like Proteins in Rainbow Trout (Oncorhynchus mykiss) Liver: CYPlAl-Specific Down-Regulation After Prolonged Exposure to PCB Malin Celander,ab John J. Stegeman’ & Lars Fiirlin”* “Department of Zoophysiology, University of Geteborg, Medicinaregatan 18, S-413 90 Giiteborg, Sweden ‘Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA ABSTRACT Induction of cytochrome P450 IA (CYPIA) has been widely employed as a bio- marker for exposure to halogenated aromatic hydrocarbons, such as co-planar PCB, in the aquatic environment. Recently, however, non-responsiveness to PCB has been reported in fish collected from heavily PCB-contaminated sites in North America and Europe. In a recent study, we investigated the CYPIAI system in juvenile rainbow trout (Oncorhynchus mykiss) after an initial intra peritoneal injection of either carrier vehicle, 3-methylcholanthrene (3-MC) or a PCB mixture (Clophen AN) in a 20-week laboratory experiment. Furthermore, we showed that prolonged exposure to PCB seems to impair the inducibility of the CYPlAl system in rainbow trout liver (Celander & Forlin, 199.5). In the present study, immunoblot analyses confirms that this apparent down-regulation was specific to CYPlAI, while levels of CYP2B- and CYP3A-like proteins remained mainly unchanged. Copyright 0 1996 Elsevier Science Ltd Induction of cytochrome P450 1A (CYPIA) has been widely employed as a biomarker for exposure to halogenated aromatic hydrocarbons such as co-planar PCB in the aquatic environment. Recently, fish from heavily PCB contaminated sites in North America and Europe have been found to have unexpectedly low levels of CYPl zyxwvutsrqponmlkjihgfe A and/or were non- inducible by additional PCB treatment (Monosson & Stegeman, 1991; Wirgin et al., 1992; Fijrlin & Celander, 1995; Eggens et al., 1995). This suggests that long-term and/or high- dose exposure to PCB alters responsiveness of the CYPlA system. In a recent study, we investigated the CYPlAl system in juvenile rainbow trout (Oncorhynchus mykiss) after an initial intra peritoneal injection of either 5 ml carrier *Author to whom correspondence should be addressed. 283