A primordial dopamine D1‐like adenylyl cyclase‐linked receptor from Drosophila melanogaster displaying poor affinity for benzazepines

Abstract

We report here the isolation from Drosophila melanogaster of a 2.0 kb cDNA clone encoding a 385 amino acid protein (d DA1) displaying, within putative transmembrane domains, highest amino acid sequence homology (49–53%) to members of the vertebrate dopamine D1‐like receptor family. When expressed in either Sf9 or COS‐7 cells, d DA1 did not bind the specific D1‐like receptor antagonist [3 H]SCH‐23390 or numerous other dopaminergic, adrenergic or serotoninergic ligands with high affinity. However, like vertebrate dopamine D1‐like receptors, d DA1 stimulated the accumulation of cAMP in response to DA (EC 50 ∼300 nM) and 6,7‐ADTN (EC 50∼500 nM). The dopaminergic rank order of potency (DA > NE⪢5‐HT) and the lack of stimulation by other possible neurotransmitters (octopamine, tyramine, tryptamine) or DA metabolites (e.g. N‐acetyl dopamine) found in Drosophila suggests that this receptor functionally belongs to the dopamine D1‐like subfamily. Benzazepines, which characteristically bind to vertebrate dopamine D1‐like receptors with high affinity, were relatively poor in stimulating (SKF‐38393, SKF‐82526; EC 50 > 10 μ M) d DA1‐mediated accumulation of cAMP. Of the numerous compounds tested, a few dopaminergic antagonists inhibited DA‐stimulated production of cAMP in a concentration‐dependent manner, albeit with considerably reduced affinity, and with the rank order of potency: (+)‐butaclamol(K b∼125nM) > SCH‐23390(K b∼230nM) > α‐flupenthixol (K b ∼ 400 nM) > chlorpromazine ≥ spiperone (K b ∼ 680 nM) ≥ clozapine In situ hybridization revealed that d DA1 receptor mRNA is expressed as a maternal transcript, and at later blastoderm stages is restricted to apical regions of the cortical peripheral cytoplasm. The generation of inter‐species D1 receptor chimeras may help to identify those particular sequence‐specific motifs or amino acid residues confering high affinity benzazepine receptor interactions.