Two distinct dopamine D2 receptor genes in the European eel: molecular characterization, tissue-specific transcription, and regulation by sex steroids.

Two full-length cDNA encoding putative dopamine D2-like receptors were cloned from the brain of female European eel. The deduced protein sequences, termed D2A- and D2B-R, exhibit closer phylogenetic relationships to vertebrate D2 receptors compared with D3 and D4 or D1 receptors. The two protein sequences share 100% identity within the transmembrane domains containing the highly conserved amino acids involved in dopamine binding. Accordingly, an apparent single population of sites on eel brain membranes bound [3H]spiperone, a D2-R-specific antagonist, with a Kd of 0.2 ± 0.04 nm. However, D2A- and D2B-R significantly differ within the amino terminus and the third intracellular loop. As analyzed by quantitative PCR and in situ hybridization, both receptor transcripts were found, with different relative abundance, in the majority of brain areas and in the pituitary, whereas in the retina, olfactory epithelium, spinal cord, and adipose tissue, only D2A-R gene was expressed. Because sex steroid hormones recent...