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

Abstract

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.