Lee N-Y, Choi H-M, Kang Y-S
College of Pharmacy, Sookmyung Women's University, Seoul, Republic of Korea.
Placenta. 2009 Apr;30(4):368-74. doi: 10.1016/j.placenta.2009.01.011. Epub 2009 Feb 26.
Choline is an essential nutrient for phospholipids and acetylcholine biosynthesis in normal development of fetus. In the present study, we investigated the functional characteristics of choline transport system and inhibitory effect of cationic drugs on choline transport in rat conditionally immortalized syncytiotrophoblast cell line (TR-TBT). Choline transport was weakly Na(+) dependent and significantly influenced by extracellular pH and by membrane depolarization. The transport process of choline is saturable with Michaelis-Menten constants (K(m)) of 68microM and 130microM in TR-TBT 18d-1 and TR-TBT 18d-2 respectively. Choline uptake in the cells was inhibited by unlabeled choline and hemicholinium-3 as well as various organic cations including guanidine, amiloride and acetylcholine. However, the prototypical organic cation tetraethylammonium and cimetidine showed very little inhibitory effect of choline uptake in TR-TBT cells. RT-PCR revealed that choline transporter-like protein 1 (CTL1) and organic cation transporter 2 (OCT2) are expressed in TR-TBT cells. The transport properties of choline in TR-TBT cells were similar or identical to that of CTL1 but not OCT2. CTL1 was also detected in human placenta. In addition, several cationic drugs such as diphenhydramine and verapamil competitively inhibited choline uptake in TR-TBT 18d-1 with K(i) of 115microM and 55microM, respectively. Our results suggest that choline transport system, which has intermediate affinity and weakly Na(+) dependent, in TR-TBT seems to occur through a CTL1 and this system may have relevance with the uptake of pharmacologically important organic cation drugs.
胆碱是胎儿正常发育过程中磷脂和乙酰胆碱生物合成所必需的营养素。在本研究中，我们研究了大鼠条件永生化合体滋养层细胞系（TR-TBT）中胆碱转运系统的功能特性以及阳离子药物对胆碱转运的抑制作用。胆碱转运对Na(+)的依赖性较弱，且受细胞外pH值和膜去极化的显著影响。在TR-TBT 18d-1和TR-TBT 18d-2中，胆碱的转运过程具有饱和性，米氏常数（K(m)）分别为68μM和130μM。细胞对胆碱的摄取受到未标记胆碱、半胱氨酸-3以及包括胍、氨氯吡脒和乙酰胆碱在内的各种有机阳离子的抑制。然而，典型的有机阳离子四乙铵和西咪替丁对TR-TBT细胞中胆碱摄取的抑制作用非常小。RT-PCR显示胆碱转运样蛋白1（CTL1）和有机阳离子转运体2（OCT2）在TR-TBT细胞中表达。TR-TBT细胞中胆碱的转运特性与CTL1相似或相同，而与OCT2不同。在人胎盘中也检测到了CTL1。此外，几种阳离子药物如苯海拉明和维拉帕米竞争性抑制TR-TBT 18d-1中胆碱的摄取，其抑制常数（K(i)）分别为115μM和55μM。我们的结果表明，TR-TBT中具有中等亲和力且对Na(+)依赖性较弱的胆碱转运系统似乎是通过CTL1发生的，并且该系统可能与药理学上重要的有机阳离子药物的摄取有关。
