Leibach J W, Cool D R, Del Monte M A, Ganapathy V, Leibach F H, Miyamoto Y
Department of Biochemistry and Molecular Biology, Medical College of Georgia, Augusta 30912.
Curr Eye Res. 1993 Jan;12(1):29-36. doi: 10.3109/02713689308999493.
The characteristics of taurine transport were studied in a human retinal pigment epithelial cell line (HRPE). Uptake of taurine into monolayer cultures of the HRPE cells was markedly stimulated by the presence of NaCl in the uptake medium whereas the uptake was negligible in its absence. This NaCl-dependent uptake was an active process as the cells were able to accumulate taurine against a concentration gradient. The uptake rate of taurine was found to be many-fold greater than that of gamma-aminobutyric acid (GABA). Unlabeled taurine and GABA competed with radiolabeled taurine for the uptake process, the former being more effective than the latter. However, uptake of radiolabeled GABA was not affected by unlabeled taurine and GABA. Substrate specificity studies revealed strong interaction of beta-amino acids with the transport system responsible for taurine uptake. alpha-Amino acids failed to inhibit taurine uptake. A specific anion requirement was observed for optimal activity of the taurine transport system and Cl- was the most supportive among several anions tested. Kinetic analyses showed that multiple Na+ and one Cl- were involved in transfer of one taurine molecule. The transport process consisted of a single saturable system with a Michaelis-Menten constant of 2.0 +/- 0.1 microM. These results show that the HRPE cell line expresses a high-affinity taurine transport system. This is the first demonstration of the presence of the taurine transporter in the human retinal pigment epithelium and the HRPE cell line may provide a useful model system for future studies involving taurine transport in the retinal pigment epithelium.
在人视网膜色素上皮细胞系（HRPE）中研究了牛磺酸转运的特性。在摄取培养基中存在氯化钠时，牛磺酸摄取到HRPE细胞单层培养物中的过程受到显著刺激，而在无氯化钠时摄取可忽略不计。这种依赖氯化钠的摄取是一个主动过程，因为细胞能够逆浓度梯度积累牛磺酸。发现牛磺酸的摄取速率比γ-氨基丁酸（GABA）的摄取速率高许多倍。未标记的牛磺酸和GABA与放射性标记的牛磺酸竞争摄取过程，前者比后者更有效。然而，放射性标记的GABA的摄取不受未标记的牛磺酸和GABA的影响。底物特异性研究揭示了β-氨基酸与负责牛磺酸摄取的转运系统之间有强烈相互作用。α-氨基酸不能抑制牛磺酸摄取。观察到牛磺酸转运系统的最佳活性需要特定阴离子，在所测试的几种阴离子中，Cl-最具支持性。动力学分析表明，一个牛磺酸分子的转运涉及多个Na+和一个Cl-。转运过程由一个单一的可饱和系统组成，米氏常数为2.0±0.1μM。这些结果表明，HRPE细胞系表达一种高亲和力的牛磺酸转运系统。这是首次证明人视网膜色素上皮中存在牛磺酸转运体，并且HRPE细胞系可能为未来涉及视网膜色素上皮中牛磺酸转运的研究提供一个有用的模型系统。
