THE CLONING AND EXPRESSION OF AN OK CELL CDNA-ENCODING A 5-HYDROXYTRYPTAMINE(1B) RECEPTOR

Serotonin 5-hydroxytryptamine or 5-HT) is an important biogenic amine that functions as both a neurotransmitter and a hormone in the central nervous system (CNS) and the periphery. We report here the isolation of a cDNA from the OK cell that encodes a serotonin receptor (OKc1). W hen expressed in cultured cells, it displayed the pharmacological prof ile and negative coupling with adenylyl cyclase characteristic of a 5- HT1B receptor subtype. Similar to the cloned rodent 5-HT1B receptors, it had high affinity for the beta-adrenergic ligand [I-125]iodocyanopi ndolol, because of the presence of an asparagine instead of a threonin e residue in the seventh transmembrane region. The ligands used displa yed the following rank order of potencies: cyanopindolol > RU24969 > m ethiothepin > serotonin > sumatriptan > methysergide > 8-OH-DPAT > iso proterenol. This profile correlates well (r = 0.97) with the native OK cell 5-HT1B receptor. When OKc1 is compared to the rat, mouse, and hu man 5-HT1B receptors, it has an amino acid sequence identity of 82%, b ut it is only 54% identical to the human 5-HT1D receptor.