Immunocytochemical localization of cytochrome P4501A1 in liver of rainbow trout (Oncorhynchus mykiss)
Multiple cytochrome P450 isozymes have been characterized in livers of trout (Oncorhynchus mykiss), scup (Stenotomus chrysops) and other fishes. Of these, trout P450 LM41, and scup P450c (or P4501A1) are probably homologous, representing the dominant and possibly only forms of P450 stimulated by inducers of the 3-MC (PAH) type such as β-naphthoflavone (BNF). Immunohistochemistry using scup P4501A1 monoclonal antibodies localized this isozyme within hepatocytes, and presumably sinusoidal endothelial and biliary epithelial cells of scup and trout. In this study ultrastructural localization determined intracellular loci of this isozyme. Juvenile trout (O. mykiss) were injected once i.p. with 50 μg/g BNF in cod liver oil. After 5 days, livers were processed for electron microscopy. Ultrathin sections were incubated with anti-P4501A1 and 10 nm colloidal gold. Membranes of granular endoplasmic reticulum (GER) were labeled in perinuclear regions of hepatocytes within specific domains and not dispersed along all membranes. Hepatocyte plasma membrane, particularly microvilli, at bile canaliculus was labeled, as was luminal plasma membrane of biliary epithelial cells surrounding passageways. Endothelial plasma membrane at sinusoid and immediately subjacent cytoplasm was labeled, perhaps providing for bioactivation of blood-borne xenobiotics. Localization within biliary epithelial cells could signify the potential to bioactivate PAH, explaining the common finding of biliary as well as hepatocytic tumors of trout liver. © 1992.
Lester, SM; Braunbeck, TA; Teh, SJ; Stegeman, JJ; Miller, MR; Hinton, DE
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