Quinlan D C, Hochstadt J
Proc Natl Acad Sci U S A. 1974 Dec;71(12):5000-3. doi: 10.1073/pnas.71.12.5000.
Balb/c 3T3 and simian virus-40-transformed Balb/c 3T3 (SV-3T3) cells were examined for their ability to transport nucleosides. Confluent (quiescent) 3T3 cells transported uridine at a rate 3-4 fold lower than did subconfluent cells. Adenosine uptake was independent of cell population density. Both adenosine and uridine were transported at the same rate by confluent and sub-confluent SV-3T3 cells. A membrane vesicle population (plasma membrane and endoplasmic reticulum) was isolated from 3T3 and SV-3T3 cells by nitrogen cavitation. With membrane vesicles derived from SV-3T3 cells it was determined that uptake occurred by a mediated process. Uptake of adenosine and uridine by membrane vesicles isolated from 3T3 and SV-3T3 cells demonstrated the same pattern as found in whole cells; that is, membrane vesicles from confluent 3T3 cells transported uridine at a rate 3-fold lower than did membrane vesicles from subconfluent 3T3 cells. Much of the adenosine taken up was converted to inosine, hypoxanthine, and ribose 1-phosphate, whereas uridine transport resulted only in the accumulation of uridine. Results obtained with membrane vesicles indicate that the lowered rate of uridine transport by confluent 3T3 cells seems due to an alteration in the membrane itself or a component(s) thereof, rather than to changes in subsequent cellular metabolic processes.
对Balb/c 3T3细胞和经猿猴病毒40转化的Balb/c 3T3（SV - 3T3）细胞进行了核苷转运能力检测。汇合（静止）的3T3细胞转运尿苷的速率比亚汇合细胞低3 - 4倍。腺苷摄取与细胞群体密度无关。汇合和亚汇合的SV - 3T3细胞转运腺苷和尿苷的速率相同。通过氮空化从3T3和SV - 3T3细胞中分离出膜泡群体（质膜和内质网）。对于源自SV - 3T3细胞的膜泡，确定摄取是通过介导过程发生的。从3T3和SV - 3T3细胞分离的膜泡对腺苷和尿苷的摄取表现出与全细胞相同的模式；也就是说，汇合的3T3细胞的膜泡转运尿苷的速率比亚汇合的3T3细胞的膜泡低3倍。摄取的大部分腺苷转化为肌苷、次黄嘌呤和磷酸核糖1 - 磷酸，而尿苷转运仅导致尿苷的积累。膜泡实验结果表明，汇合的3T3细胞尿苷转运速率降低似乎是由于膜本身或其某个成分的改变，而不是由于后续细胞代谢过程的变化。
