A putative beta sub(2)-adrenoceptor from the rainbow trout (Oncorhynchus mykiss): molecular characterization and pharmacology

Extensive molecular characterization of mammalian beta -adrenoceptors has revealed complex modes of regulation and interaction. Relatively little attention, however, has focused on adrenoceptors from early branching vertebrates such as fish. Using an RT-PCR approach we have cloned a rainbow trout beta sub(2)-adrenoceptor gene that codes for a 409-amino-acid protein with the same seven transmembrane domain structure as its mammalian counterparts. This rainbow trout beta sub(2)-adrenoceptor shares a high degree of amino-acid sequence conservation with other vertebrate beta sub(2)-adrenoceptors. The conclusion that this sequence is a rainbow trout beta sub(2)-adrenoceptor is further supported by phylogenetic analysis of vertebrate beta -adrenoceptor sequences and competitive pharmacological binding data. RNase protection assays demonstrate that the rainbow trout beta sub(2)-adrenoceptor gene is highly expressed in the liver and red and white muscle, with lower levels of expression in the gills, heart, kidney and spleen of the rainbow trout. The lack of regulatory phosphorylation sites within the G-protein-binding domain of the rainbow trout beta sub(2)-adrenoceptor sequence suggests that the in vivo control of trout beta sub(2)-adrenoceptor signaling differs substantially from that of mammals.