Li, RachelYang, CuiKwan, Y. W.Chan, S. W.Lee, Simon Ming YuenLeung, George P. H.2018-11-292018-11-291663-9812http://hdl.handle.net/1885/153241The serotonin (5-HT) uptake system is supposed to play a crucial part in vascular functions by "fine-tuning" the local concentration of 5-HT in the vicinity of 5-HT2 receptors in vascular smooth muscle cells. In this study, the mechanism of 5-HT uptake in human brain vascular smooth muscle cells (HBVSMCs) was investigated. [3H]5-HT uptake in HBVSMCs was Na+-independent. Kinetic analyses of [3H]5-HT uptake in HBVSMCs revealed a Km of 50.36 ± 10.2 mM and a Vmax of 1033.61 ± 98.86 pmol/mg protein/min. The specific serotonin re-uptake transporter (SERT) inhibitor citalopram, the specific norepinephrine transporter (NET) inhibitor desipramine, and the dopamine transporter (DAT) inhibitor GBR12935 inhibited 5-HT uptake in HBVSMCs with IC50 values of 97.03 ± 40.10, 10.49 ± 5.98, and 2.80 ± 1.04 μM, respectively. These IC50 values were 100-fold higher than data reported by other authors, suggesting that those inhibitors were not blocking their corresponding transporters. Reverse transcription-polymerase chain reaction results demonstrated the presence of mRNA for organic cation transporter (OCT)-3 and plasma membrane monoamine transporter (PMAT), but the absence of OCT-1, OCT-2, SERT, NET, and DAT. siRNA knockdown of OCT-3 and PMAT specifically attenuated 5-HT uptake in HBVSMCs. It is concluded that 5-HT uptake in HBVSMCs was mediated predominantly by a low-affinity and Na+-independent mechanism. The most probable candidates are OCT-3 and PMAT, but not the SERTapplication/pdfKeywords: 1 [2 (benzhydryloxy)ethyl] 4 (3 phenylpropyl)piperazine; carrier protein; citalopram; DAT protein; desipramine; dopamine transporter; messenger RNA; NET protein; noradrenalin transporter; organic cation transporter 1; organic cation transporter 2; organic Monoamine transporter; Organic cation transporter; Serotonin; Vascular smooth muscle cells201310.3389/fphar.2013.000142018-11-29