Involvement of organic cation transporter-3 and plasma membrane monoamine transporter in serotonin uptake in human brain vascular smooth muscle cells
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Serotonin, Organic cation transporter, Monoamine transporter, Vascular smooth muscle cells
The 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 SERT.
Frontiers in Pharmacology
Li, R.,Yang, C.,Kwan, Y.,Chan, S.,Lee, S.,& Leung, G. (2013). Involvement of organic cation transporter-3 and plasma membrane monoamine transporter in serotonin uptake in human brain vascular smooth muscle cells. Frontiers in Pharmacology, 4 (14). http://dx.doi.org/10.3389/fphar.2013.00014