MOLECULAR-CLONING, FUNCTIONAL EXPRESSION, AND MESSENGER-RNA TISSUE DISTRIBUTION OF THE HUMAN 5-HYDROXYTRYPTAMINE(2B) RECEPTOR

Clones encoding a portion of the human 5-hydroxytryptamine (5-HT)(2B) receptor gene were isolated from a human placental genomic library. Ba sed on distribution studies of 5-HT2B receptor mRNA, human uterus cDNA libraries were constructed and screened, resulting in the isolation o f several full-length cDNA clones. These clones harbored a common sing le open reading frame encoding a protein of 481 amino acids. The deduc ed amino acid sequence of the human 5-HT2B receptor displayed 91.5% id entity within the transmembrane domains and 82% identity overall with the rat 5-HT2B receptor. The human 5-HT2B receptor stably expressed in AV12-664 cells demonstrated high affinity (K-d = 10.18 +/- 1.60 nM), saturable [H-3]serotonin binding, similar to that previously described for the rat 5-HT2B receptor. The pharmacological profile of the human 5-HT2B receptor was virtually identical to that of the rat 5-HT2B rec eptor, with the exceptions of the 5-HT2A receptor antagonists ketanser in and spiperone. Both compounds exhibited higher affinity at the huma n 5-HT2B receptor (ketanserin, K-i = 376 +/- 58 nM; spiperone, K-i = 6 97 +/- 54 nM) than at the rat 5-HT2B receptor (ketanserin, K-i = 3559 +/- 175 nM; spiperone, K-i = 3278 +/- 92 nM). Functional coupling of t he human 5-HT2B receptor was also demonstrated in AV12-664 cells, wher e 5-HT produced a dose-dependent increase in phosphatidylinositol hydr olysis (EC(50) = 27 +/- 12 nM) analogous to that seen with the rat 5-H T2B receptor. Reverse transcription-polymerase chain reaction studies revealed human 5-HT2B receptor mRNA to be expressed in many tissues, i ncluding the central nervous system. The presence of 5-HT2B, receptor mRNA in human brain and not in rat brain raises the possibility that t he 5-HT2B receptor may be of significance in higher brain function.