Molecular cloning, functional expression, and mRNA tissue distribution of the human 5-hydroxytryptamine2B receptor

Clones encoding a portion of the human 5-hydroxytryptamine (5-HT)2B receptor gene were isolated from a human placental genomic library. Based on distribution studies of 5-HT2B receptor mRNA, human uterus cDNA libraries were constructed and screened, resulting in the isolation of several full-length cDNA clones. These clones harbored a common single open reading frame encoding a protein of 481 amino acids. The deduced amino acid sequence of the human 5-HT2B receptor displayed 91.5% identity 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 (Kd = 10.18 +/- 1.60 nM), saturable [3H]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 receptor, with the exceptions of the 5-HT2A receptor antagonists ketanserin and spiperone. Both compounds exhibited higher affinity at the human 5-HT2B receptor (ketanserin, Ki = 376 +/- 58 nM; spiperone, Ki = 697 +/- 54 nM) than at the rat 5-HT2B receptor (ketanserin, Ki = 3559 +/- 175 nM; spiperone, Ki = 3278 +/- 92 nM). Functional coupling of the human 5-HT2B receptor was also demonstrated in AV12-664 cells, where 5-HT produced a dose-dependent increase in phosphatidylinositol hydrolysis (EC50 = 27 +/- 12 nM) analogous to that seen with the rat 5-HT2B receptor. Reverse transcription-polymerase chain reaction studies revealed human 5-HT2B receptor mRNA to be expressed in many tissues, including the central nervous system. The presence of 5-HT2B receptor mRNA in human brain and not in rat brain raises the possibility that the 5-HT2B receptor may be of significance in higher brain function.