Ohno Yuta, Otsuka Yusuke, Nohara Masakatsu, Furihata Tomomi, Kuse Yoshiki, Itoh Yoshinori, Hara Hideaki, Anzai Naohiko
Department of Pharmacology, Chiba University Graduate School of Medicine.
Department of Pharmacy, Gifu University Hospital.
Biol Pharm Bull. 2017;40(12):2110-2116. doi: 10.1248/bpb.b17-00461.
While it is well known that L-carnitine [3-hydroxy-4-(trimethylazaniumyl)-butanoate] is an essential molecule for β-oxidation, it provides anti-oxidative effects as well. Since these effects have been observed in photoreceptor cells, the carnitine's intracellular concentration is considered to play a protective role against oxidative damage to those cells. However, even though its high hydrophilicity makes it likely that carnitine import is accomplished via a dedicated host transport system, the specific uptake process into those cells is currently unknown. Therefore, in this study, we sought to identify and characterize photoreceptor cell carnitine uptake transporter(s) utilizing 661W cells as a photoreceptor cell model. The results of our uptake assays showed that carnitine was transported into 661W cells in a saturable manner (K=5.5 mM), and that the activity was susceptible to extracellular pH and Na. While these data suggest the involvement of a transporter in 661W cell carnitine uptake, the observed transport profile did not correspond to any of the currently known carnitine transporters such as organic cation/carnitine transporter 1 (Octn1), Octn2, Octn3, B and Ct2. In fact, in our experiments, the mRNA expressions for such carnitine transporters in 661W cells were consistently very low and the carnitine transporter substrates did not inhibit the uptake activities. Taken as a whole, our results indicate that carnitine is transported into 661W cells in a carrier-mediated manner. However, since its transport modes cannot be fully explained by known carnitine transporters, it is highly likely that photoreceptor cells utilize a unique molecularly-based carnitine uptake system.
虽然众所周知左旋肉碱[3-羟基-4-(三甲基铵基)丁酸]是β-氧化的必需分子，但它也具有抗氧化作用。由于这些作用已在光感受器细胞中观察到，肉碱的细胞内浓度被认为对这些细胞的氧化损伤起保护作用。然而，尽管其高亲水性使得肉碱很可能通过专门的宿主转运系统进行转运，但目前尚不清楚其进入这些细胞的具体摄取过程。因此，在本研究中，我们试图利用661W细胞作为光感受器细胞模型来鉴定和表征光感受器细胞肉碱摄取转运体。我们摄取试验的结果表明，肉碱以可饱和的方式(K = 5.5 mM)转运到661W细胞中，并且该活性对细胞外pH值和Na敏感。虽然这些数据表明转运体参与了661W细胞肉碱的摄取，但观察到的转运特征并不对应于任何目前已知的肉碱转运体，如有机阳离子/肉碱转运体1(Octn1)、Octn2、Octn3、B和Ct2。事实上，在我们的实验中，661W细胞中这些肉碱转运体的mRNA表达一直非常低，并且肉碱转运体底物并未抑制摄取活性。总体而言，我们的结果表明肉碱以载体介导的方式转运到661W细胞中。然而，由于其转运模式无法用已知的肉碱转运体完全解释，光感受器细胞极有可能利用一种独特的基于分子的肉碱摄取系统。
