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Keywords:

  • amphioxus;
  • cyclic AMP;
  • dopamine D1-like receptor;
  • expression in Chinese hamster ovary cells;
  • expression in Xenopus oocytes;
  • G protein-coupled receptor

Abstract

Dopamine receptors function to control many aspects of motor control and other forms of behaviour in both vertebrates and invertebrates. They can be divided into two main groups (D1 and D2) based on sequence similarity, ligand affinity and effector coupling. However, little is known about the pharmacology and functionality of dopamine receptors in the deuterostomian invertebrates, such as the cephalochordate amphioxus (Branchiostoma floridae) which has recently been placed as the most basal of all the chordates. A bioinformatic study shows that amphioxus has at least three dopamine D1-like receptor sequences. One of these receptors, AmphiD1/β, was found to have high levels of sequence similarity to both vertebrate D1 receptors and to β-adrenergic receptors. Here, we report on the cloning of AmphiD1/β from an adult amphioxus cDNA library, and its pharmacological characterization subsequent to its expression in both mammalian cell lines and Xenopus oocytes. It was found that AmphiD1/β has a similar pharmacology to vertebrate D1 receptors, including responding to benzodiazepine ligands. The pharmacology of the receptor exhibits ‘agonist-specific coupling’ depending upon the second messenger pathway to which it is linked. Moreover, no pharmacological characteristics were observed to suggest that AmphiD1/β may be an amphioxus orthologue of vertebrate β-adrenergic receptors.