Pharmacological characterization of the cloned human 5-hydroxytryptamine transporter

We performed an extensive pharmacological study of the 5-hydroxytryptamine (5-HT) transporter polypeptide cloned from human placenta. Transient expression of this 630 amino acid polypeptide in HeLa cells led to saturable 5-HT uptake activity (K-m = 858 nM). This 5-HT uptake was blocked by selective 5-HT inhibitors, such as citalopram, litoxetine, sertraline, and indalpine, with K-i values in the low nanomolar range, and it exhibited a pharmacological profile similar to that found in rat brain. [H-3]Citalopram binding to membrane preparations of the transfected cells occurred to a single class of high-affinity binding sites (K-d = 5.3 nM) and was potently inhibited by selective 5-HT uptake inhibitors. The pharmacological profile of [H-3]citalopram binding to these transfected cells showed a good correlation with that of [H-3]paroxetine binding to the rat cerebral cortical 5-HT transporter (r = 0.79). These data confirm that the full pharmacological characteristics of the 5-HT transport system are conferred by the expression of the 630 amino acid human placental 5-HT transporter polypeptide. [H-3]Citalopram should, therefore, provide a useful probe for more insights at a molecular level into this cloned 5-HT transport system.