Characterization of nucleoside transport into JVM-2 cells.

(A) Time course of uridine uptake into JVM-2 cells. Cells were incubated with 1 μM uridine either in a NaCl (▪) or a choline chloride (▴) medium. Na⁺-dependent transport (○) was calculated by subtracting those rates measured in choline medium from those measured in Na⁺ medium. Transport of the purine-nucleoside guanosine (B-C) and the pyrimidine nucleoside cytidine (D-E) was similarly measured under initial velocity conditions (2 minutes). Cross-inhibitions of Na⁺-dependent uptake were also monitored to further elucidate which nucleoside transporters were responsible for concentrative uptake activity (CNT-related). Transport of 1 μM guanosine was inhibited with 100 μM cytidine (C) and transport of 1 μM cytidine with 100 μM guanosine (E). To determine the contribution of equilibrative transport activity (ENT), 1 μM NBTI was used to discriminate between NBTI-sensitive (ENT1) and NBTI-insensitive (ENT2) transport rates. Results are the mean ± SE of 3 to 6 experiments measured in triplicate.