Terasaki T, Kadowaki A, Higashida H, Nakayama K, Tamai I, Tsuji A
Department of Pharmaceutics, Faculty of Pharmaceutical Sciences, Kanazawa University, Japan.
Biol Pharm Bull. 1993 May;16(5):493-6. doi: 10.1248/bpb.16.493.
Xenopus laevis oocytes were used as an expression system to prove and characterize the carrier-mediated transport of uridine in the small intestine. Significant Na+ dependency was observed for the uptake of [3H]uridine by Xenopus laevis oocytes injected with poly(A)+RNA prepared from rabbit small intestinal mucosa. By contrast, the uptake of [3H]uridine was negligible in water-injected oocytes. There was no significant difference in the Na+ dependent uptake rates of [3H]uridine among oocytes expressed by using mRNA prepared by three different methods. The uptake of [3H]uridine by mRNA-injected oocytes was enhanced by increasing the culturing time after mRNA injection. Concentration dependency for uridine transport was observed with the Michaelis constant of 8.27 microM, which was comparable to that reported in the study using the brush-border membrane vesicles from rabbit small intestine (6.4 microM). Furthermore, the uptake of [3H]uridine was significantly inhibited by adenosine and thymidine, but not by adenine and uracil. Consequently, the transport system of uridine expressed in mRNA-injected oocytes is clarified to be similar to that functioning in the brush-border membrane of the small intestine.
非洲爪蟾卵母细胞被用作一种表达系统，以证实并表征小肠中尿苷的载体介导转运。在用从兔小肠黏膜制备的聚腺苷酸（poly(A)+）RNA注射的非洲爪蟾卵母细胞中，观察到[³H]尿苷摄取对钠离子有显著依赖性。相比之下，注射水的卵母细胞中[³H]尿苷的摄取可忽略不计。使用三种不同方法制备的mRNA表达的卵母细胞中，[³H]尿苷的钠离子依赖性摄取速率没有显著差异。mRNA注射后的卵母细胞对[³H]尿苷的摄取通过增加mRNA注射后的培养时间而增强。观察到尿苷转运的浓度依赖性，米氏常数为8.27微摩尔，这与使用兔小肠刷状缘膜囊泡的研究中报道的数值（6.4微摩尔）相当。此外，[³H]尿苷的摄取受到腺苷和胸腺嘧啶核苷的显著抑制，但不受腺嘌呤和尿嘧啶的抑制。因此，mRNA注射的卵母细胞中表达的尿苷转运系统被阐明与小肠刷状缘膜中起作用的转运系统相似。
