TY - JOUR
T1 - Inhibition of human equilibrative nucleoside transporters by dihydropyridine-type calcium channel antagonists
AU - Li, Rachel W.S.
AU - Tse, Chung Ming
AU - Man, Ricky Y.K.
AU - Vanhoutte, Paul M.
AU - Leung, George P.H.
N1 - Funding Information:
This work was support by the Seed Funding for Basic Research Program of the University of Hong Kong.
PY - 2007/7/30
Y1 - 2007/7/30
N2 - 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 IC50 value of 60 ± 31 μM, whereas nifedipine, nicardipine, nitrendipine, and felodipine exhibited 100-fold less effective inhibitory activity. Nifedipine, nitrendipine, and nimodipine inhibited hENT-2 with IC50 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 Vmax of [3H]uridine transport without affecting Km. The inhibitory effects of nimodipine and nifedipine could be washed out. In addition, nimodipine and nifedipine inhibited the rate of NBTGR-induced dissociation of [3H]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.
AB - 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 IC50 value of 60 ± 31 μM, whereas nifedipine, nicardipine, nitrendipine, and felodipine exhibited 100-fold less effective inhibitory activity. Nifedipine, nitrendipine, and nimodipine inhibited hENT-2 with IC50 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 Vmax of [3H]uridine transport without affecting Km. The inhibitory effects of nimodipine and nifedipine could be washed out. In addition, nimodipine and nifedipine inhibited the rate of NBTGR-induced dissociation of [3H]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.
KW - Adenosine
KW - Dihydropyridine
KW - Nucleoside
KW - Transporter
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U2 - 10.1016/j.ejphar.2007.04.033
DO - 10.1016/j.ejphar.2007.04.033
M3 - Article
C2 - 17512522
AN - SCOPUS:34250858008
SN - 0014-2999
VL - 568
SP - 75
EP - 82
JO - European Journal of Pharmacology
JF - European Journal of Pharmacology
IS - 1-3
ER -