Li Rachel W S, Tse Chung-Ming, Man Ricky Y K, Vanhoutte Paul M, Leung George P H
Department of Pharmacology, The University of Hong Kong, Hong Kong.
Eur J Pharmacol. 2007 Jul 30;568(1-3):75-82. doi: 10.1016/j.ejphar.2007.04.033. Epub 2007 Apr 30.
Dihydropyridine-type calcium channel antagonists, in addition to having a vasodilatory effect, are known to inhibit cellular uptake of nucleosides such as adenosine. However, the nucleoside transporter subtypes involved and the mechanism by which this occurs are not known. Therefore, we have studied the inhibitory effects of dihydropyridines on both human equilibrative nucleoside transporters, hENT-1 and hENT-2, which are the major transporters mediating nucleoside transport in most tissues. Among the dihydropyridines tested, nimodipine proved to be the most potent inhibitor of hENT-1, with an IC(50) value of 60+/-31 muM, whereas nifedipine, nicardipine, nitrendipine, and felodipine exhibited 100-fold less effective inhibitory activity. Nifedipine, nitrendipine, and nimodipine inhibited hENT-2 with IC(50) values in the micromolar range; however, nicardipine and felodipine had no significant effect on hENT-2. Removal of the 4-aryl ring or changing the nitro group at the 4-aryl ring proved not to be detrimental to the inhibitory effects of dihydropyridines on hENT-1, but resulted in a drastic decrease in their inhibitory effects on hENT-2. Kinetic studies revealed that nimodipine and nifedipine reduced V(max) of [(3)H]uridine transport without affecting K(m). The inhibitory effects of nimodipine and nifedipine could be washed out. In addition, nimodipine and nifedipine inhibited the rate of NBTGR-induced dissociation of [(3)H]NBMPR from hENT-1 cell membrane. We conclude that dihydropyridines are non-competitive inhibitors of hENT-1 and hENT-2, probably working through reversible interactions with the allosteric sites. The inhibitory potencies of dihydropyridines may be associated with the structure of the 4-aryl ring, as well as the ester groups at the C-3 and C-5 positions.
二氢吡啶类钙通道拮抗剂除具有血管舒张作用外，还已知能抑制细胞对核苷（如腺苷）的摄取。然而，所涉及的核苷转运体亚型以及发生这种情况的机制尚不清楚。因此，我们研究了二氢吡啶类对人平衡核苷转运体hENT - 1和hENT - 2的抑制作用，这两种转运体是大多数组织中介导核苷转运的主要转运体。在所测试的二氢吡啶类中，尼莫地平被证明是hENT - 1最有效的抑制剂，IC(50)值为60±31 μM，而硝苯地平、尼卡地平、尼群地平和非洛地平的抑制活性低100倍。硝苯地平、尼群地平和尼莫地平以微摩尔范围内的IC(50)值抑制hENT - 2；然而，尼卡地平和非洛地平对hENT - 2没有显著影响。去除4 - 芳基环或改变4 - 芳基环上的硝基被证明对二氢吡啶类对hENT - 1的抑制作用无害，但导致它们对hENT - 2的抑制作用急剧下降。动力学研究表明，尼莫地平和硝苯地平降低了[(3)H]尿苷转运的V(max)，而不影响K(m)。尼莫地平和硝苯地平的抑制作用可以被洗脱。此外，尼莫地平和硝苯地平抑制了NBTGR诱导的[(3)H]NBMPR从hENT - 1细胞膜上解离的速率。我们得出结论，二氢吡啶类是hENT - 1和hENT - 2的非竞争性抑制剂，可能通过与变构位点的可逆相互作用起作用。二氢吡啶类的抑制效力可能与4 - 芳基环的结构以及C - 3和C - 5位的酯基有关。
