Binding kinetics and sequencing of hepatic α1-adrenergic receptors in two marine teleosts, mackerel (Scomber scombrus) and anchovy (Engraulis encrasicolus)

Liver alpha1-adrenoceptors (ARs) are demonstrated, or at least hypothesized, in fresh- and brackish-water teleosts while no data are available for marine teleosts. This study evaluates the presence of alpha1-ARs in the liver of two marine teleosts, the anchovy Engraulis encrasicolus and the mackerel Scomber scombrus, and examines on a broad scale the possibility that habitats posing different challenges also influence phenotypic trait selection. Binding assays were performed also on liver membranes from the carp Cyprinus carpio as a direct comparison with a freshwater species. Alpha1-ARs of the two marine teleosts showed higher [3H]prazosin affinity compared with those of the fresh/brackish water fish studied thus far, while the number of liver binding sites did not differ significantly from that of the carp, eel or trout. A preliminary phylogeny based upon amino acid sequence analysis indicated the presence of at least an alpha1-AR in mackerel and an alpha1D-AR in both anchovy and mackerel. This is the first indication of alkpha1-AR subtypes in any marine species but further studies are needed to ascertain the physiological role of these alpha1-ARs in these two marine species.