Nucleoside transport in human colonic epithelial cell lines: Evidence for two Na⁺-independent transport systems in T84 and Caco-2 cells¹

RT-PCR of RNA isolated from monolayers of the human colonic epithelial cell lines T84 and Caco-2 demonstrated the presence of mRNA for the two cloned Na⁺-independent equilibrative nucleoside transporters, ENT1 and ENT2, but not for the cloned Na⁺-dependent concentrative nucleoside transporters, CNT1 and CNT2. Uptake of [³H]uridine by cell monolayers in balanced Na⁺-containing and Na⁺-free media confirmed the presence of only Na⁺-independent nucleoside transport mechanisms. This uptake was decreased by 70-75% in the presence of 1 μM nitrobenzylthioinosine, a concentration that completely inhibits ENT1, and was completely blocked by the addition of 10 μM dipyridamole, a concentration that inhibits both ENT1 and ENT2. These findings indicate the presence in T84 and Caco-2 cells of two functional Na⁺-independent equilibrative nucleoside transporters, ENT1 and ENT2. Copyright (C) 1999 Elsevier Science B.V.