Nucleobase transport in opossum kidney epithelial cells and Xenopus laevis oocytes:: the characterisation, structure-activity relationship of uracil analogues and oocyte expression studies of sodium-dependent and -independent hypoxanthine uptake

被引:22
作者
Shayeghi, M [1 ]
Akerman, R [1 ]
Jarvis, SM [1 ]
机构
[1] Univ Kent, Res Sch Biosci, Canterbury CT2 7NJ, Kent, England
来源
BIOCHIMICA ET BIOPHYSICA ACTA-BIOMEMBRANES | 1999年 / 1416卷 / 1-2期
基金
英国医学研究理事会;
关键词
nucleobase transport; kidney; uracil analog; expression cloning; hypoxanthine;
D O I
10.1016/S0005-2736(98)00213-2
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The characteristics of hypoxanthine transport were examined in opossum kidney (OK) epithelial cells and Xenopus laevis oocytes. In both cell types hypoxanthine influx was mediated by two distinct transport systems: a high-affinity Na+-dependent system and a Na+-independent transporter. Na+-dependent hypoxanthine transport in OK cells was saturable (K-m 0.78 +/- 0.29 mu M) and was inhibited by guanine, uracil, thymine and 5-fluorouracil (K-i values 0.5-7 mu M), whereas adenine had no effect. Substitutions at the 2- and 4-position had a marked effect on the ability of uracil to inhibit Na+/hypoxanthine influx by OK cells revealing that an oxo group at both the 2- and 4-positions of uracil is required for interacting with the transporter. The properties of Na+-dependent hypoxanthine influx in oocytes were similar to those observed in OK cells. In particular, xanthine and oxypurinol inhibited hypoxanthine influx, a characteristic not observed previously for the Na+/nucleobase carrier in pig LLC-PK1 renal cells. Na+-independent hypoxanthine influx in OK cells and oocytes was of a lower affinity (K-m 90-180 mu M). Adenine and guanine inhibited Na+-independent hypoxanthine flux in OK cells, but had no effect in oocytes. Injection of LLC-PK1 mRNA into oocytes resulted in a 1.5-fold stimulation of Na+/hypoxanthine flux over water-injected oocytes. These results reveal further heterogeneity in Na+/nucleobase cotransporters. (C) 1999 Elsevier Science B.V. All rights reserved.
引用
收藏
页码:109 / 118
页数:10
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