Pharmacological characteristics of high-affinity serotonin uptake systems established through gene transfer

Inactivation of a neurotransmitter, after its stimulated release, via high-affinity uptake mechanisms is an essential regulatory step of neurotransmission in both the central and peripheral nervous systems. To initiate explorations of the molecular mechanisms and the underlying biochemical architecture of high-affinity neurotransmitter uptake systems, we have used gene transfer technology to establish and identify novel cellular models that express these systems. Human genomic DNA was transfected into mouse L-M fibroblasts and two independently arising, clonal cell lines (L-S1 and L-S2) have been identified as expressing high-affinity serotonin (5-HT) uptake systems. The 5-HT uptake characteristics of L-S1 and L-S2 are essentially comparable (in terms of Na+ dependence, temperature sensitivity, imipramine antagonizability, kinetic saturability and high affinities) and those of L-S1 have been reported previously. Furthermore, competition studies utilizing catecholamine neurotransmitters and their amino acid precursors demonstrated that these systems are highly specific for 5-HT. Several known inhibitors of high-affinity 5-HT uptake systems (including amitriptyline, desipramine, fluoxetine, imipramine, nortriptyline, tryptamine, 5-methoxytryptamine and N-acetyl 5-methoxytryptamine) were assessed in terms of their respective potencies to inhibit 5-[3H]HT uptake by L-S1 and L-S2 cells. For L-S1 cells, the rank order of inhibitor potencies is imipramine greater than amitriptyline greater than fluoxetine greater than desipramine = nortriptyline greater than tryptamine greater than 5-methoxytryptamine greater than N-acetyl-5-methoxytryptamine. For L-S2, the rank order is similar to that of L-S1 except that fluoxetine is more potent than amitriptyline.(ABSTRACT TRUNCATED AT 250 WORDS)