Le Hir M, Dubach U C
Pflugers Arch. 1984 May;401(1):58-63. doi: 10.1007/BF00581533.
The uptake of adenosine in brush border vesicles of the proximal tubule of the rat kidney has been studied with a filtration technique. The initial rate of uptake was almost 6 times greater in the presence of NaCl than in the presence of KCl. The stimulatory effect of Na+ was strictly dependent on a gradient of Na+ (out greater than in). The time course of uptake showed an overshoot with a maximum at 20 s with a gradient of NaCl, but not with KCl. Inosine and 5'-AMP were produced from adenosine within the vesicles. In the presence of an inhibitor or adenosine deaminase adenosine was not significantly metabolized during the first 20 s of uptake. Thus, kinetic parameters of transport could be studied in the absence of interferences with metabolism. A Km of 1.1 microM and a Vmax of 232 pmol X min-1 X mg protein-1 were calculated for the Na+ gradient-dependent transport. The dependency on a Na+ gradient, the capacity for uphill transport and the high affinity for adenosine situate this transport system apart from the mechanisms of transport of nucleosides described so far. It may be relevant in regard to the role of adenosine in the regulation of glomerular filtration.
采用过滤技术研究了大鼠肾近端小管刷状缘小泡对腺苷的摄取。在存在氯化钠的情况下，摄取的初始速率几乎比存在氯化钾时高6倍。钠离子的刺激作用严格依赖于钠离子梯度（外向内）。摄取的时间进程显示，在氯化钠梯度下，20秒时出现超调最大值，而氯化钾梯度下则没有。腺苷在小泡内生成肌苷和5'-AMP。在存在腺苷脱氨酶抑制剂的情况下，腺苷在摄取的前20秒内没有显著代谢。因此，可以在不干扰代谢的情况下研究转运的动力学参数。计算出钠离子梯度依赖性转运的Km为1.1微摩尔，Vmax为232皮摩尔×分钟-1×毫克蛋白-1。对钠离子梯度的依赖性、上坡转运能力和对腺苷的高亲和力使这个转运系统与迄今为止描述的核苷转运机制不同。这可能与腺苷在肾小球滤过调节中的作用有关。
