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

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 n ot for the cloned Na+-dependent concentrative nucleoside transporters, CNT1 and CNT2. Uptake of [H-3]uridine by cell monolayers in balanced Na+-contai ning and Na+-free media confirmed the presence of only Na+-independent nucl eoside transport mechanisms. This uptake was decreased by 70-75% in the pre sence of 1 mu M nitrobenzylthioinosine, a concentration that completely inh ibits ENT1, and was completely blocked by the addition of 10 mu M dipyridam ole, a concentration that inhibits both ENT1 and ENT2,. These findings indi cate the presence in T84 and Caco-2 cells of two functional Na+-independent equilibrative nucleoside transporters, ENT1 and ENT2. (C) 1999 Elsevier Sc ience B.V. All rights reserved.