Table 1.

Kinetic analysis for hCNT1-mediated uptake of labeled nucleosides

SubstrateKm (μmol/L)Vmax (nmol/mg protein/min)Vmax/Km (μL/mg protein/min)
5-azaCyd63 ± 6*15 ± 1*238
Cytidine123 ± 6*62 ± 2*504
Uridine467 ± 50*83 ± 31*178
5-F-5′-dUrd403 ± 35*175 ± 43*434
  • NOTE: Rates of Na+-dependent intracellular accumulation of [14C]5-azaCyd, [14C]cytidine, [3H]uridine, and [3H]5-F-5′-dUrd were determined in hCNT1-transfected MDCK cells at six different substrate concentrations (0.075, 0.1, 0.15, 0.25, 0.5, and 1 mmol/L) and after an incubation time of 20 s. The Km values were calculated from double-reciprocal plots of rate versus concentration. The statistical significance was calculated by fitting the linear regression of the double-reciprocal plots, with P values < 0.001 (indicated by asterisks). Mean ± SD from triplicate experiments.