A putative β₂‐adrenoceptor from the rainbow trout (Oncorhynuchus mykiss)

Abstract

Extensive molecular characterization of mammalian b-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 b 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 b 2 -adrenoceptor shares a high degree of amino-acid sequence conservation with other vertebrate b 2 -adrenoceptors. The conclusion that this sequence is a rainbow trout b 2 -adrenoceptor is further supported by phylogenetic analysis of vertebrate b-adrenoceptor sequences and competitive pharmacological binding data. RNase protection assays demonstrate that the rainbow trout b 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-proteinbinding domain of the rainbow trout b 2 -adrenoceptor sequence suggests that the in vivo control of trout b 2 -adrenoceptor signaling differs substantially from that of mammals.

Ecotoxicological aspects related to the presence of pharmaceuticals in the aquatic environment

“…Within the most commonly used �-blockers propranolol is a non-specific antagonist, blocking both �1 and �2-receptors while metoprolol and atenolol present �1-receptors specificity [99]. Fish, like other vertebrates, possess �-receptors in the heart, liver and reproductive system [170,171] so that pro-longed exposure to drugs belonging to this therapeutic class may cause deleterious effects. From a two weeks study, it was observed that exposure to 500 µg L −1 of propranolol reduced growth rates of Japanese medaka [172].…”

In vivo and in vitro assessment of cardiac β-adrenergic receptors in larval zebrafish (Danio rerio)

“…Xiao et al, 1999;Bernstein, 2002). This dual coupling of 2AR might help explain why this receptor is not involved to the same extent as 1AR in G s -mediated cAMPexpression of ARs in the fish heart, and that fish hearts are responsive to classic AR ligands (Nickerson et al, 2001;Kawasaki et al, 2008;Mendonça and Gamperl, 2009;Steele et al, 2009). Some studies on fish ARs have also shown that they can have unexpected affinity for (presumed) subtype-specific agonists.…”

Toxicity screening of Diclofenac, Propranolol, Sertraline and Simvastatin using Danio rerio and Paracentrotus lividus embryo bioassays

“…As β-adrenergic receptors are also present in heart, hepatocytes and reproductive tissues of fish and other vertebrates, it is possible that these organisms can also be affected by β-blockers action (Nickerson et al, 2001). …”