NICKERSON, J.G.*; DUGAN, S.G.; DROUIN, G.; MOON, T.W.; Univ. of Ottawa; Univ. of Ottawa; Univ. of Ottawa; Univ. of Ottawa: The β-Adrenergic Receptor System of the Rainbow Trout – Function and Molecular Biology.
Our understanding of the β-adrenoceptor (β-AR) system in fish is based primarily on the use of mammalian-AR specific agonists and antagonists and is poorly understood compared with this system in mammals. The objective of this study was to characterize the β-AR system from the rainbow trout (Oncorhynchus mykiss) at the molecular level and relate this information to receptor pharmacology. Partial cDNA clones of trout β-ARs were amplified from total RNA using nested RT-PCR. The sequences of the trout β-AR clones were compared with sequences of β-ARs reported in GenBank. Complete coding regions of the trout β-ARs were obtained using 5′ and 3′ RACE with gene-specific primers. Standard radiolabeled binding and displacement assays (using the mixed antagonist 3H-CGP) were undertaken in isolated red blood cells and semi-purified liver membranes. The three trout β-AR genes identified were phylogenetically most similar to the mammalian β2-AR (RT β2-AR) and the β3-AR (RT β3a– and β3b-ARs); no homologous β1-AR was found. RNase protection assays showed specific tissue distributions for each trout β-AR type. Pharmacologically the RT β2-AR is similar to the mammalian β2-AR, but the RT β3b-AR is ‘non-typical’. These studies support a unique β-AR system in this early branching vertebrate, provide some understanding of the evolution and regulation of this gene family, and define a red blood cell specific β-AR that may contribute to the unique control of blood oxygen affinities in trout. This study was supported by grants from NSERC Canada to GD and TWM.