Lee C W, Jarvis S M
Department of Physiology, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
Neurochem Int. 1988;12(4):483-92. doi: 10.1016/0197-0186(88)90032-0.
The transport of [(3)H]adenosine at 22 degrees C was investigated in guinea pig cerebral cortical synaptosomes using an inhibitor-stop filtration method. Under these conditions adenosine was not significantly metabolized during the incubation period used to determine the initial rates of adenosine transport. The dose response curves for the inhibition of adenosine transport by nitrobenzylthioinosine (NBMPR), dilazep and dipyridamole were biphasic-approx. 50-60% of the transport activity was inhibited with IC(50) values of 0.7, 1 and 9 nM respectively, but the remaining activity was insensitive to concentrations as high as 1 ? M. Adenosine influx by both components was saturable (K(m) values of 17 +/- 3 and 68 +/- 8 ? M; V(max) values of 2.8 +/- 0.3 and 6.1 +/- 0.4 pmol/mg protein per s for NBMPR-sensitive and -insensitive components, respectively), and inhibited by other nucleosides and benzodiazepines. The two transport components also differed in their sensitivity to inhibition by other nucleosides and benzodiazepines indicating that the NBMPR-sensitive component of nucleoside transport in guinea pig synaptosomes exhibits a higher affinity than the NBMPR-insensitive component. However, both components have a broad specificity. Inhibition of adenosine transport by NBMPR was associated with high affinity binding of NBMPR to the synaptosomes (K(d) 88 +/- 6 pM). Binding of NBMPR to these sites was blocked by dilazep and dipyridamole with K(1) values similar to those measured for inhibiting NBMPR-sensitive adenosine influx. These results, together with previous findings using NBMPR and dipyridamole as ligand probes, suggest that there are two components of nucleoside transport in mammalian cerebral cortical synaptosomes that differ in their sensitivity to inhibition by NBMPR and other transport inhibitors.
在22℃下，采用抑制剂-停止过滤法研究了豚鼠大脑皮质突触体中[（3）H]腺苷的转运。在用于确定腺苷转运初始速率的孵育期间，腺苷在此条件下没有显著代谢。硝基苄硫肌苷（NBMPR）、双嘧达莫和地拉齐普对腺苷转运抑制的剂量反应曲线呈双相——分别约50 - 60%的转运活性被抑制，IC（50）值分别为0.7、1和9 nM，但剩余活性对高达1 μM的浓度不敏感。两种成分的腺苷内流均具有饱和性（NBMPR敏感和不敏感成分的K（m）值分别为17±3和68±8 μM；V（max）值分别为2.8±0.3和6.1±0.4 pmol/mg蛋白质每秒），并且受到其他核苷和苯二氮䓬类药物的抑制。这两种转运成分对其他核苷和苯二氮䓬类药物抑制的敏感性也不同，表明豚鼠突触体中核苷转运的NBMPR敏感成分比NBMPR不敏感成分具有更高的亲和力。然而，两种成分都具有广泛的特异性。NBMPR对腺苷转运的抑制与NBMPR与突触体的高亲和力结合有关（K（d）88±6 pM）。地拉齐普和双嘧达莫以与抑制NBMPR敏感腺苷内流测量值相似的K（1）值阻断NBMPR与这些位点的结合。这些结果，连同以前使用NBMPR和双嘧达莫作为配体探针的研究结果，表明在哺乳动物大脑皮质突触体中存在两种核苷转运成分，它们对NBMPR和其他转运抑制剂抑制的敏感性不同。
