5-Hydroxytryptamine (5-HT, also commonly known as serotonin) is synthesized in enterochromaffin cells in the intestine and in serotonergic nerve terminals. In the periphery, 5-HT mediates gastrointestinal motility, platelet aggregation, and contraction of blood vessels. Many functions of the central nervous system are influenced by 5-HT, including sleep, motor activity, sensory perception, arousal and appetite. A family of 12 GPCRs and one ion channel mediate the biological effects of 5-HT (Hoyer et al., 1994). 5-HT2B which couples to Gq/11 is expressed in embryonic and adult cardiovascular tissues, gut, and brain from the rat, mouse, and human species. 5-HT2B receptors are responsible for many cardiovascular and central nervous system functions, such as blood vessel contraction, platelet shape changes, neuronal sensitization to tactile stimuli, and mediation of the hallucinogenic effects of phenylisopropylamin hallucinogens. It has also been shown to be required for heart development. GenScript's cloned human 5-HT2B -expressing cell line is generated in the CHO-K1 host.