title: Regulation of the black bullhead hepatic beta-adrenoceptors.
abstract: Black bullhead catfish (Ameiurus melas) were exposed to air for 1 h to examine the effect of an acute stress on the distribution and function of the hepatic beta-adrenoceptors (beta-ARs). Air exposure significantly reduced both adrenaline (ADR)- and noradrenaline (NADR)-stimulated glucose production in isolated hepatocytes with no effect on either receptor affinity (K(d)) or number of binding sites (B(max)). A 24 h exposure of isolated hepatocytes to the beta-agonist isoproterenol also had no significant impact on either binding parameter. Competition studies using selective agonists and antagonists suggest that the hepatic beta-AR in this species is pharmacologically beta(2)-like. However in addition to the beta(2)-AR, molecular evidence provides support for the existence of hepatic beta-ARs that phylogenetically group with the beta(3)-ARs and the beta(1)-ARs. Despite the presence of several potential phosphorylation sites in the third intracellular loop and cytoplasmic tail of the bullhead beta(2)-AR, no significant changes were observed in the binding parameters. While physiological data supports the presence of only a single subtype, molecular data supports the existence of multiple beta-AR subtypes in this species. The mechanisms thought to regulate mammalian beta-ARs exist in the bullhead ARs reported here but these mechanisms are not as effective in this fish system as in mammals.
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada.
authors.forename: Stephen G
authors.initials: SG
authors.lastname: Dugan
authors.forename: Xi
authors.initials: X
authors.lastname: Chen
authors.forename: James G
authors.initials: JG
authors.lastname: Nickerson
authors.forename: Colin J
authors.initials: CJ
authors.lastname: Montpetit
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Moon
mesh_terms: D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000388:Air; D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007059:Ictaluridae / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D008969:Molecular Sequence Data; D010802:Phylogeny; D011485:Protein Binding; D011943:Receptors, Adrenergic, beta / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013312:Stress, Physiological / Q000235:genetics / Q000378:metabolism
chemical_list: D000318:Adrenergic beta-Agonists; D011943:Receptors, Adrenergic, beta